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Sample records for arsenide gallium nitride

  1. (Gallium arsenide solar cells)

    SciTech Connect

    Not Available

    1985-01-01

    A transient liquid phase epitaxial growth system is described, including the growth procedure. Also discussed are the antireflection coating of a gallium arsenide solar cell, the metal contact pattern, and current-voltage characteristics. (LEW)

  2. Properties of gallium arsenide

    SciTech Connect

    Not Available

    1985-01-01

    Properties of Gallium Arsenide' is a handbook of evaluated numeric data and reviewed knowledge distilled by those working at the frontiers of gallium arsenide research. In addition to providing numeric data on basic physical, electronic and optical properties, the book covers many device-related aspects of gallium arsenide. Carrier attributes (ionisation coefficients, concentration, mobility, diffusion etc), deep levels and defects are surveyed and related to the various growth techniques such as MBE, VPE, and MOCVD. Sections on surface structure, oxidation, interfaces and etching are of particular relevance to integrated circuit research. Especially important in the race to achieve commercially usable samples is a state-of-the-art survey on the infra-red imaging of defects in semi-insulating gallium arsenide produced by the liquid-encapsulated Czochralski process.

  3. Toxicity of indium arsenide, gallium arsenide, and aluminium gallium arsenide.

    PubMed

    Tanaka, Akiyo

    2004-08-01

    Gallium arsenide (GaAs), indium arsenide (InAs), and aluminium gallium arsenide (AlGaAs) are semiconductor applications. Although the increased use of these materials has raised concerns about occupational exposure to them, there is little information regarding the adverse health effects to workers arising from exposure to these particles. However, available data indicate these semiconductor materials can be toxic in animals. Although acute and chronic toxicity of the lung, reproductive organs, and kidney are associated with exposure to these semiconductor materials, in particular, chronic toxicity should pay much attention owing to low solubility of these materials. Between InAs, GaAs, and AlGaAs, InAs was the most toxic material to the lung followed by GaAs and AlGaAs when given intratracheally. This was probably due to difference in the toxicity of the counter-element of arsenic in semiconductor materials, such as indium, gallium, or aluminium, and not arsenic itself. It appeared that indium, gallium, or aluminium was toxic when released from the particles, though the physical character of the particles also contributes to toxic effect. Although there is no evidence of the carcinogenicity of InAs or AlGaAs, GaAs and InP, which are semiconductor materials, showed the clear evidence of carcinogenic potential. It is necessary to pay much greater attention to the human exposure of semiconductor materials.

  4. Gallium Arsenide Domino Circuit

    NASA Technical Reports Server (NTRS)

    Yang, Long; Long, Stephen I.

    1990-01-01

    Advantages include reduced power and high speed. Experimental gallium arsenide field-effect-transistor (FET) domino circuit replicated in large numbers for use in dynamic-logic systems. Name of circuit denotes mode of operation, which logic signals propagate from each stage to next when successive stages operated at slightly staggered clock cycles, in manner reminiscent of dominoes falling in a row. Building block of domino circuit includes input, inverter, and level-shifting substages. Combinational logic executed in input substage. During low half of clock cycle, result of logic operation transmitted to following stage.

  5. A FETISH for gallium arsenide

    SciTech Connect

    Barron, A.R.

    1996-12-31

    An overview of the development of a new dielectric material, cubic-GaS, from the synthesis of new organometallic compounds to the fabrication of a new class of gallium arsenide based transistor is presented as a representative example of the possibility that inorganic chemistry can directly effect the development of new semiconductor devices. The gallium sulfido compound [({sup t}Bu)GaS]{sub 4}, readily prepared from tri-tert-butyl gallium, may be used as a precursor for the growth of GaS thin films by metal organic chemical vapor deposition (MOCVD). Photoluminescence and electronic measurements indicate that this material provides a passivation coating for GaAs. Furthermore, the insulating properties of cubic-GaS make it suitable as the insulating gate layer in a new class of GaAs transistor: a field effect transistor with a sulfide heterojunction (FETISH).

  6. Thermal oxidation of gallium arsenide

    SciTech Connect

    Monteiro, O.R.; Evans, J.W.

    1989-01-01

    Here we present some results of transmission electron microscopy and secondary ion mass spectroscopy of thermally oxidized gallium arsenide with different types of dopants. At temperatures below 400 /sup 0/C an amorphous oxide is formed. Oxidation at temperatures between 500 and 600 /sup 0/C initially produces an epitaxial film of ..gamma..-Ga/sub 2/O/sub 3/. As the reaction proceeds, this film becomes polycrystalline and then transforms to ..beta..-Ga/sub 2/O/sub 3/. This film contains small crystallites of As/sub 2/O/sub 5/ and As/sub 2/O/sub 3/ in the case of the chromium doped samples, whereas only the former was detected in the case of silicon and tellurium doped samples. Elemental arsenic was always found at the interface between the oxide and GaAs. Chromium doped gallium also exhibited a slower oxidation kinetics than the other materials.

  7. Wet chemical functionalization of III-V semiconductor surfaces: alkylation of gallium arsenide and gallium nitride by a Grignard reaction sequence.

    PubMed

    Peczonczyk, Sabrina L; Mukherjee, Jhindan; Carim, Azhar I; Maldonado, Stephen

    2012-03-13

    Crystalline gallium arsenide (GaAs) (111)A and gallium nitride (GaN) (0001) surfaces have been functionalized with alkyl groups via a sequential wet chemical chlorine activation, Grignard reaction process. For GaAs(111)A, etching in HCl in diethyl ether effected both oxide removal and surface-bound Cl. X-ray photoelectron (XP) spectra demonstrated selective surface chlorination after exposure to 2 M HCl in diethyl ether for freshly etched GaAs(111)A but not GaAs(111)B surfaces. GaN(0001) surfaces exposed to PCl(5) in chlorobenzene showed reproducible XP spectroscopic evidence for Cl-termination. The Cl-activated GaAs(111)A and GaN(0001) surfaces were both reactive toward alkyl Grignard reagents, with pronounced decreases in detectable Cl signal as measured by XP spectroscopy. Sessile contact angle measurements between water and GaAs(111)A interfaces after various levels of treatment showed that GaAs(111)A surfaces became significantly more hydrophobic following reaction with C(n)H(2n-1)MgCl (n = 1, 2, 4, 8, 14, 18). High-resolution As 3d XP spectra taken at various times during prolonged direct exposure to ambient lab air indicated that the resistance of GaAs(111)A to surface oxidation was greatly enhanced after reaction with Grignard reagents. GaAs(111)A surfaces terminated with C(18)H(37) groups were also used in Schottky heterojunctions with Hg. These heterojunctions exhibited better stability over repeated cycling than heterojunctions based on GaAs(111)A modified with C(18)H(37)S groups. Raman spectra were separately collected that suggested electronic passivation by surficial Ga-C bonds at GaAs(111)A. Specifically, GaAs(111)A surfaces reacted with alkyl Grignard reagents exhibited Raman signatures comparable to those of samples treated with 10% Na(2)S in tert-butanol. For GaN(0001), high-resolution C 1s spectra exhibited the characteristic low binding energy shoulder demonstrative of surface Ga-C bonds following reaction with CH(3)MgCl. In addition, 4

  8. Development of gallium arsenide solar cells

    NASA Technical Reports Server (NTRS)

    1973-01-01

    The potential of ion implantation as a means of developing gallium arsenide solar cells with high efficiency performance was investigated. Computer calculations on gallium arsenide cell characteristics are presented to show the effects of surface recombination, junction space-charge recombination, and built-in fields produced by nonuniform doping of the surface region. The fabrication technology is summarized. Electrical and optical measurements on samples of solar cells are included.

  9. Gallium nitride optoelectronic devices

    NASA Technical Reports Server (NTRS)

    Chu, T. L.; Chu, S. S.

    1972-01-01

    The growth of bulk gallium nitride crystals was achieved by the ammonolysis of gallium monochloride. Gallium nitride single crystals up to 2.5 x 0.5 cm in size were produced. The crystals are suitable as substrates for the epitaxial growth of gallium nitride. The epitaxial growth of gallium nitride on sapphire substrates with main faces of (0001) and (1T02) orientations was achieved by the ammonolysis of gallium monochloride in a gas flow system. The grown layers had electron concentrations in the range of 1 to 3 x 10 to the 19th power/cu cm and Hall mobilities in the range of 50 to 100 sq cm/v/sec at room temperature.

  10. Window structure for passivating solar cells based on gallium arsenide

    NASA Technical Reports Server (NTRS)

    Barnett, Allen M. (Inventor)

    1985-01-01

    Passivated gallium arsenide solar photovoltaic cells with high resistance to moisture and oxygen are provided by means of a gallium arsenide phosphide window graded through its thickness from arsenic rich to phosphorus rich.

  11. Chrome doped gallium arsenide evaluation

    SciTech Connect

    Pocha, M.D.; Morse, J.D.; Brazes, W.F.

    1987-10-10

    We received, for free, two sets of Chrome doped Gallium Arsenide (GaAs:Cr) wafers, one from Cominco Electronic Materials, Inc., and the other from Furakawa Electric Co., for the purpose of evaluation as potential material for high speed photoconductive detectors. In return for the free material we promised to give the two manufacturers feed back on our evaluation of these wafers. The primary purpose of this report is to present the results of our evaluation of these wafers and conclusions regarding the usefulness of heavily doped GaAs:Cr for photoconductive detectors. We have found that response times of less than 100 ps (FWHM) are possible with GaAs:Cr detectors, but that there are several time constants to the decay which result in very long ''tails'' to the impulse response of these detectors. These long tails are unacceptable for most detector applications, but there may be some special cases where GaAs:Cr could be used. 5 figs., 1 tab.

  12. Radiation damage of gallium arsenide production cells

    NASA Technical Reports Server (NTRS)

    Mardesich, N.; Joslin, D.; Garlick, J.; Lillington, D.; Gillanders, M.; Cavicchi, B.; Scott-Monck, J.; Kachare, R.; Anspaugh, B.

    1987-01-01

    High efficiency liquid phase epitaxy (LPE) gallium arsenide cells were irradiated with 1 Mev electrons up to fluences of 1 times 10 to the 16th power cm-2. Measurements of spectral response and dark and illuminated I-V data were made at each fluence and then, using computer codes, the experimental data was fitted to gallium arsenide cell models. In this way it was possible to determine the extent of the damage, and hence damage coefficients in both the emitter and base of the cell.

  13. Oxidative dissolution of gallium arsenide and separation of gallium from arsenic

    SciTech Connect

    Coleman, J.P.; Monzyk, B.F.

    1988-07-26

    The method of dissociating gallium arsenide into a gallium-containing component and an arsenic-containing component, is described which comprises contacting the gallium arsenide with an oxidizing agent and a liquid comprising hydroxamic acid to convert the gallium to a gallium-hydroxamic acid complex and to oxidize the arsenic to a positive valence state.

  14. Surface photovoltage spectroscopy applied to gallium arsenide surfaces

    NASA Technical Reports Server (NTRS)

    Bynik, C. E.

    1975-01-01

    The experimental and theoretical basis for surface photovoltage spectroscopy is outlined. Results of this technique applied to gallium arsenide surfaces, are reviewed and discussed. The results suggest that in gallium arsenide the surface voltage may be due to deep bulk impurity acceptor states that are pinned at the Fermi level at the surface. Establishment of the validity of this model will indicate the direction to proceed to increase the efficiency of gallium arsenide solar cells.

  15. Running droplets of gallium from evaporation of gallium arsenide.

    PubMed

    Tersoff, J; Jesson, D E; Tang, W X

    2009-04-10

    High-temperature annealing of gallium arsenide in vacuum causes excess evaporation of arsenic, with accumulation of gallium as liquid droplets on the surface. Using real-time in situ surface electron microscopy, we found that these droplets spontaneously run across the crystal surface. Running droplets have been seen in many systems, but they typically require special surface preparation or gradient forces. In contrast, we show that noncongruent evaporation automatically provides a driving force for running droplets. The motion is predicted and observed to slow and stop near a characteristic temperature, with the speed increasing both below and above this temperature. The same behavior is expected to occur during the evaporation of similar III-V semiconductors such as indium arsenide.

  16. Gallium arsenide phosphide top solar cell

    SciTech Connect

    McNeely, J.B.; Barnett, A.M.

    1986-04-15

    This patent describes a tandem solar cell having a silicon solar cell for a low energy gap bottom cell and a high energy gap top cell. The improvement which a gallium arsenide phosphide top solar cell which described here is a. a transparent gallium phosphide substrate; b. a first active semiconductor layer of GaAs/sub 1-Y/P/sub Y/ and of a first conductivity type overlying the substrate; c. a second active semiconductor layer of GaAs/sub 1-X/P/sub X/ and of a second conductivity type opposite the first conductivity type overlying and forming a photovoltaic junction therewith; d. a transparent first electrical contact in ohmic contact with the substrate; and e. a transparent second electrical contact in ohmic contact with the second active semiconductor layer.

  17. Gallium nitride nanotube lasers

    SciTech Connect

    Li, Changyi; Liu, Sheng; Hurtado, Antonio; Wright, Jeremy Benjamin; Xu, Huiwen; Luk, Ting Shan; Figiel, Jeffrey J.; Brener, Igal; Brueck, Steven R. J.; Wang, George T.

    2015-01-01

    Lasing is demonstrated from gallium nitride nanotubes fabricated using a two-step top-down technique. By optically pumping, we observed characteristics of lasing: a clear threshold, a narrow spectral, and guided emission from the nanotubes. In addition, annular lasing emission from the GaN nanotube is also observed, indicating that cross-sectional shape control can be employed to manipulate the properties of nanolasers. The nanotube lasers could be of interest for optical nanofluidic applications or application benefitting from a hollow beam shape.

  18. Gallium interstitial contributions to diffusion in gallium arsenide

    NASA Astrophysics Data System (ADS)

    Schick, Joseph T.; Morgan, Caroline G.

    2011-09-01

    encountered in fitting experimental results for heavily p-type, Ga-rich gallium arsenide by simply extending a model for gallium interstitial diffusion which has been used for less p-doped material.

  19. Electrospun Gallium Nitride Nanofibers

    SciTech Connect

    Melendez, Anamaris; Morales, Kristle; Ramos, Idalia; Campo, Eva; Santiago, Jorge J.

    2009-04-19

    The high thermal conductivity and wide bandgap of gallium nitride (GaN) are desirable characteristics in optoelectronics and sensing applications. In comparison to thin films and powders, in the nanofiber morphology the sensitivity of GaN is expected to increase as the exposed area (proportional to the length) increases. In this work we present electrospinning as a novel technique in the fabrication of GaN nanofibers. Electrospinning, invented in the 1930s, is a simple, inexpensive, and rapid technique to produce microscopically long ultrafine fibers. GaN nanofibers are produced using gallium nitrate and dimethyl-acetamide as precursors. After electrospinning, thermal decomposition under an inert atmosphere is used to pyrolyze the polymer. To complete the preparation, the nanofibers are sintered in a tube furnace under a NH{sub 3} flow. Both scanning electron microscopy and profilometry show that the process produces continuous and uniform fibers with diameters ranging from 20 to a few hundred nanometers, and lengths of up to a few centimeters. X-ray diffraction (XRD) analysis shows the development of GaN nanofibers with hexagonal wurtzite structure. Future work includes additional characterization using transmission electron microscopy and XRD to understand the role of precursors and nitridation in nanofiber synthesis, and the use of single nanofibers for the construction of optical and gas sensing devices.

  20. All-optical modulation in gallium arsenide integrated optical waveguides

    SciTech Connect

    McWright, G.; Ross, B.; Guthreau, W.; Lafaw, D.; Lowry, M.; Tindall, W.

    1988-01-27

    We have investigated all-optical modulators in gallium arsenide integrated optical waveguides; these modulators use electron-hole pair generation to alter the propagation characteristics of a guided light beam. 6 refs., 6 figs.

  1. Computer simulation of radiation damage in gallium arsenide

    NASA Technical Reports Server (NTRS)

    Stith, John J.; Davenport, James C.; Copeland, Randolph L.

    1989-01-01

    A version of the binary-collision simulation code MARLOWE was used to study the spatial characteristics of radiation damage in proton and electron irradiated gallium arsenide. Comparisons made with the experimental results proved to be encouraging.

  2. Contact formation in gallium arsenide solar cells

    NASA Technical Reports Server (NTRS)

    Weizer, Victor G.; Fatemi, Navid S.

    1988-01-01

    Gold and gold-based alloys, commonly used as solar cell contact materials, are known to react readily with gallium arsenide. Experiments were performed to identify the mechanisms involved in these GaAs-metal interactions. It is shown that the reaction of GaAs with gold takes place via a dissociative diffusion process. It is shown further that the GaAs-metal reaction rate is controlled to a very great extent by the condition of the free surface of the contact metal, an interesting example of which is the previously unexplained increase in the reaction rate that has been observed for samples annealed in a vacuum environment as compared to those annealed in a gaseous ambient. A number of other hard-to-explain observations, such as the low-temperature formation of voids in the gold lattice and crystallite growth on the gold surface, are explained by invoking this mechanism.

  3. Radiation damage of gallium arsenide production cells

    NASA Technical Reports Server (NTRS)

    Mardesich, N.; Garlick, G. F. J.

    1987-01-01

    High-efficiency gallium arsenide cells, made by the liquid epitaxy method (LPE), have been irradiated with 1-MeV electrons up to fluences of 10 to the 16th e/sq cm. Measurements have been made of cell spectral response and dark and light-excited current-voltage characteristics and analyzed using computer-based models to determine underlying parameters such as damage coefficients. It is possible to use spectral response to sort out damage effects in the different cell component layers. Damage coefficients are similar to other reported in the literature for the emitter and buffer (base). However, there is also a damage effect in the window layer and possibly at the window emitter interface similar to that found for proton-irradiated liquid-phase epitaxy-grown cells. Depletion layer recombination is found to be less than theoretically expected at high fluence.

  4. The interaction of gold with gallium arsenide

    NASA Technical Reports Server (NTRS)

    Weizer, Victor G.; Fatemi, Navid S.

    1988-01-01

    Gold and gold-based alloys, commonly used as solar-cell contact materials, are known to react readily with gallium arsenide. Experiments designed to identify the mechanisms involved in these GaAs-metal interactions have yielded several interesting results. It is shown that the reaction of GaAs with gold takes place via a dissociative diffusion process. It is shown further that the GaAs-metal reaction rate is controlled to a very great extent by the condition of the free surface of the contact metal, an interesting example of which is the previously unexplained increase in the reaction rate that has been observed for samples annealed in a vacuum environment as compared to those annealed in a gaseous ambient. A number of other hard-to-explain observations, such as the low-temperature formation of voids in the gold lattice and crystallite growth on the gold surface, are also explained by invoking this mechanism.

  5. Producing gallium arsenide crystals in space

    NASA Technical Reports Server (NTRS)

    Randolph, R. L.

    1984-01-01

    The production of high quality crystals in space is a promising near-term application of microgravity processing. Gallium arsenide is the selected material for initial commercial production because of its inherent superior electronic properties, wide range of market applications, and broad base of on-going device development effort. Plausible product prices can absorb the high cost of space transportation for the initial flights provided by the Space Transportation System. The next step for bulk crystal growth, beyond the STS, is planned to come later with the use of free flyers or a space station, where real benefits are foreseen. The use of these vehicles, together with refinement and increasing automation of space-based crystal growth factories, will bring down costs and will support growing demands for high quality GaAs and other specialty electronic and electro-optical crystals grown in space.

  6. Gallium Arsenide solar cell radiation damage experiment

    NASA Technical Reports Server (NTRS)

    Maurer, R. H.; Kinnison, J. D.; Herbert, G. A.; Meulenberg, A.

    1991-01-01

    Gallium arsenide (GaAs) solar cells for space applications from three different manufactures were irradiated with 10 MeV protons or 1 MeV electrons. The electrical performance of the cells was measured at several fluence levels and compared. Silicon cells were included for reference and comparison. All the GaAs cell types performed similarly throughout the testing and showed a 36 to 56 percent power areal density advantage over the silicon cells. Thinner (8-mil versus 12-mil) GaAs cells provide a significant weight reduction. The use of germanium (Ge) substrates to improve mechanical integrity can be implemented with little impact on end of life performance in a radiation environment.

  7. Gallium arsenide solar array subsystem study

    NASA Technical Reports Server (NTRS)

    Miller, F. Q.

    1982-01-01

    The effects on life cycle costs of a number of technology areas are examined for a gallium arsenide space solar array. Four specific configurations were addressed: (1) a 250 KWe LEO mission - planer array; (2) a 250 KWe LEO mission - with concentration; (3) a 50 KWe GEO mission planer array; (4) a 50 KWe GEO mission - with concentration. For each configuration, a baseline system conceptual design was developed and the life cycle costs estimated in detail. The baseline system requirements and design technologies were then varied and their relationships to life cycle costs quantified. For example, the thermal characteristics of the baseline design are determined by the array materials and masses. The thermal characteristics in turn determine configuration, performance, and hence life cycle costs.

  8. Method of fabricating germanium and gallium arsenide devices

    NASA Technical Reports Server (NTRS)

    Jhabvala, Murzban (Inventor)

    1990-01-01

    A method of semiconductor diode fabrication is disclosed which relies on the epitaxial growth of a precisely doped thickness layer of gallium arsenide or germanium on a semi-insulating or intrinsic substrate, respectively, of gallium arsenide or germanium by either molecular beam epitaxy (MBE) or by metal-organic chemical vapor deposition (MOCVD). The method involves: depositing a layer of doped or undoped silicon dioxide on a germanium or gallium arsenide wafer or substrate, selectively removing the silicon dioxide layer to define one or more surface regions for a device to be fabricated thereon, growing a matched epitaxial layer of doped germanium or gallium arsenide of an appropriate thickness using MBE or MOCVD techniques on both the silicon dioxide layer and the defined one or more regions; and etching the silicon dioxide and the epitaxial material on top of the silicon dioxide to leave a matched epitaxial layer of germanium or gallium arsenide on the germanium or gallium arsenide substrate, respectively, and upon which a field effect device can thereafter be formed.

  9. Gallium nitride electronics

    NASA Astrophysics Data System (ADS)

    Rajan, Siddharth; Jena, Debdeep

    2013-07-01

    In the past two decades, there has been increasing research and industrial activity in the area of gallium nitride (GaN) electronics, stimulated first by the successful demonstration of GaN LEDs. While the promise of wide band gap semiconductors for power electronics was recognized many years before this by one of the contributors to this issue (J Baliga), the success in the area of LEDs acted as a catalyst. It set the field of GaN electronics in motion, and today the technology is improving the performance of several applications including RF cell phone base stations and military radar. GaN could also play a very important role in reducing worldwide energy consumption by enabling high efficiency compact power converters operating at high voltages and lower frequencies. While GaN electronics is a rapidly evolving area with active research worldwide, this special issue provides an opportunity to capture some of the great advances that have been made in the last 15 years. The issue begins with a section on epitaxy and processing, followed by an overview of high-frequency HEMTs, which have been the most commercially successful application of III-nitride electronics to date. This is followed by review and research articles on power-switching transistors, which are currently of great interest to the III-nitride community. A section of this issue is devoted to the reliability of III-nitride devices, an area that is of increasing significance as the research focus has moved from not just high performance but also production-worthiness and long-term usage of these devices. Finally, a group of papers on new and relatively less studied ideas for III-nitride electronics, such as interband tunneling, heterojunction bipolar transistors, and high-temperature electronics is included. These areas point to new areas of research and technological innovation going beyond the state of the art into the future. We hope that the breadth and quality of articles in this issue will make it

  10. Inhalation developmental toxicology studies: Gallium arsenide in mice and rats

    SciTech Connect

    Mast, T.J.; Greenspan, B.J.; Dill, J.A.; Stoney, K.H.; Evanoff, J.J.; Rommereim, R.L.

    1990-12-01

    Gallium arsenide is a crystalline compound used extensively in the semiconductor industry. Workers preparing solar cells and gallium arsenide ingots and wafers are potentially at risk from the inhalation of gallium arsenide dust. The potential for gallium arsenide to cause developmental toxicity was assessed in Sprague- Dawley rats and CD-1 (Swiss) mice exposed to 0, 10, 37, or 75 mg/m{sup 3} gallium arsenide, 6 h/day, 7 days/week. Each of the four treatment groups consisted of 10 virgin females (for comparison), and {approx}30 positively mated rats or {approx}24 positively mated mice. Mice were exposed on 4--17 days of gestation (dg), and rats on 4--19 dg. The day of plug or sperm detection was designated as 0 dg. Body weights were obtained throughout the study period, and uterine and fetal body weights were obtained at sacrifice (rats, 20 dg; mice, 18 dg). Implants were enumerated and their status recorded. Live fetuses were sexed and examined for gross, visceral, skeletal, and soft-tissue craniofacial defects. Gallium and arsenic concentrations were determined in the maternal blood and uterine contents of the rats (3/group) at 7, 14, and 20 dg. 37 refs., 11 figs., 30 tabs.

  11. Process for forming pure silver ohmic contacts to N- and P-type gallium arsenide materials

    DOEpatents

    Hogan, S.J.

    1983-03-13

    Disclosed is an improved process for manufacturing gallium arsenide semiconductor devices having as its components a n-type gallium arsenide substrate layer and a p-type gallium arsenide diffused layer. The improved process comprises forming a pure silver ohmic contact to both the diffuse layer and the substrate layer wherein the n-type layer comprises a substantially low doping carrier concentration.

  12. Pure silver ohmic contacts to N- and P- type gallium arsenide materials

    DOEpatents

    Hogan, Stephen J.

    1986-01-01

    Disclosed is an improved process for manufacturing gallium arsenide semiconductor devices having as its components an n-type gallium arsenide substrate layer and a p-type gallium arsenide diffused layer. The improved process comprises forming a pure silver ohmic contact to both the diffused layer and the substrate layer, wherein the n-type layer comprises a substantially low doping carrier concentration.

  13. Characterization of semi-insulating gallium arsenide

    NASA Astrophysics Data System (ADS)

    Blakemore, John S.

    1993-11-01

    The project was established 18 Nov. 1992 to continue for 12 months. Its purpose has been electrical and optical characterization of samples from semi-insulating (SI) melt-grown crystals of gallium arsenide (GaAs). As a further definition of the project's purpose, the primary goal has been to assist NRL in assessing the properties of SI GaAs crystals grown at NRL by the vertical zone melt (VZM) method. A second aspect of this characterization work has involved samples from SI GaAs crystals grown by various commercial vendors including samples of pre-synthesized GaAs evaluated for its suitability as starting 'feedstock' for VZM growth. Measurements made at Western Washington University (WWU) under the terms of this project accord with a Statement of Work provided at the outset. These have included the following: (1) low-field dc electrical transport data for SI GaAs samples, as functions of temperature; (2) near-infrared (NIR) transmittance/absorption spectra of polished slabs, with data concerning the well-known EL2 defect determined from NIR absorption strength and spectral form; and (3) mid-IR data on absorption caused by carbon acceptors in SI GaAs.

  14. Evaluation of the carcinogenicity of gallium arsenide.

    PubMed

    Bomhard, Ernst M; Gelbke, Heinz-Peter; Schenk, Hermann; Williams, Gary M; Cohen, Samuel M

    2013-05-01

    Gallium arsenide (GaAs) is an important semiconductor material. In 2-year inhalation studies, GaAs increased the incidence of lung tumors in female rats, but not in male rats or male and female mice. Alveolar proteinosis followed by chronic active inflammation was the predominant non-neoplastic pulmonary findings. IARC classified GaAs as carcinogenic to humans (group 1) based on the assumption that As and Ga ions are bioavailable. The European Chemical Agency Risk Assessment Committee concluded that GaAs should be classified into Carcinogenicity Category 1B (presumed to have carcinogenic potential for humans; ECHA). We evaluate whether these classifications are justified. Physico-chemical properties of GaAs particles and the degree of mechanical treatment are critical in this evaluation. The available data on mode of action (MOA), genotoxicity and bioavailability do not support the contribution of As or Ga ions to the lung tumors in female rats. Most toxicological studies utilized small particles produced by strong mechanical treatment, destroying the crystalline structure. The resulting amorphous GaAs is not relevant to crystalline GaAs at production and processing sites. The likely tumorigenic MOA is lung toxicity related to particulate-induced inflammation and increased proliferation. It is concluded that there is no evidence for a primary carcinogenic effect of GaAs.

  15. Gallium arsenide processing for gate array logic

    NASA Technical Reports Server (NTRS)

    Cole, Eric D.

    1989-01-01

    The development of a reliable and reproducible GaAs process was initiated for applications in gate array logic. Gallium Arsenide is an extremely important material for high speed electronic applications in both digital and analog circuits since its electron mobility is 3 to 5 times that of silicon, this allows for faster switching times for devices fabricated with it. Unfortunately GaAs is an extremely difficult material to process with respect to silicon and since it includes the arsenic component GaAs can be quite dangerous (toxic) especially during some heating steps. The first stage of the research was directed at developing a simple process to produce GaAs MESFETs. The MESFET (MEtal Semiconductor Field Effect Transistor) is the most useful, practical and simple active device which can be fabricated in GaAs. It utilizes an ohmic source and drain contact separated by a Schottky gate. The gate width is typically a few microns. Several process steps were required to produce a good working device including ion implantation, photolithography, thermal annealing, and metal deposition. A process was designed to reduce the total number of steps to a minimum so as to reduce possible errors. The first run produced no good devices. The problem occurred during an aluminum etch step while defining the gate contacts. It was found that the chemical etchant attacked the GaAs causing trenching and subsequent severing of the active gate region from the rest of the device. Thus all devices appeared as open circuits. This problem is being corrected and since it was the last step in the process correction should be successful. The second planned stage involves the circuit assembly of the discrete MESFETs into logic gates for test and analysis. Finally the third stage is to incorporate the designed process with the tested circuit in a layout that would produce the gate array as a GaAs integrated circuit.

  16. Method for improving the growth of cadmium telluride on a gallium arsenide substrate

    SciTech Connect

    Reno, J.L.

    1990-12-31

    A method for preparing a gallium arsenide substrate, prior to growing a layer of cadmium telluride on a support surface thereof. The preparation includes the steps of cleaning the gallium arsenide substrate and thereafter forming prepatterned shapes on the support surface of the gallium arsenide substrate. The layer of cadmium telluride then grown on the prepared substrate results in dislocation densities of approximately 1{times}10{sup 6}/cm{sup 2} or less. The prepatterned shapes on the support surface of the gallium arsenide substrate are formed by reactive ion etching an original outer surface of the gallium arsenide substrate and into the body of the gallium arsenide substrate to a depth of at least two microns. The prepatterned shapes have the appearance of cylindrical mesas each having a diameter of at lease twelve microns. After the mesas are formed on the support surface of the gallium arsenide substrate, the substrate is again cleaned.

  17. P-type gallium nitride

    DOEpatents

    Rubin, M.; Newman, N.; Fu, T.; Ross, J.; Chan, J.

    1997-08-12

    Several methods have been found to make p-type gallium nitride. P-type gallium nitride has long been sought for electronic devices. N-type gallium nitride is readily available. Discovery of p-type gallium nitride and the methods for making it will enable its use in ultraviolet and blue light-emitting diodes and lasers. pGaN will further enable blue photocathode elements to be made. Molecular beam epitaxy on substrates held at the proper temperatures, assisted by a nitrogen beam of the proper energy produced several types of p-type GaN with hole concentrations of about 5{times}10{sup 11} /cm{sup 3} and hole mobilities of about 500 cm{sup 2} /V-sec, measured at 250 K. P-type GaN can be formed of unintentionally-doped material or can be doped with magnesium by diffusion, ion implantation, or co-evaporation. When applicable, the nitrogen can be substituted with other group III elements such as Al. 9 figs.

  18. P-type gallium nitride

    DOEpatents

    Rubin, Michael; Newman, Nathan; Fu, Tracy; Ross, Jennifer; Chan, James

    1997-01-01

    Several methods have been found to make p-type gallium nitride. P-type gallium nitride has long been sought for electronic devices. N-type gallium nitride is readily available. Discovery of p-type gallium nitride and the methods for making it will enable its use in ultraviolet and blue light-emitting diodes and lasers. pGaN will further enable blue photocathode elements to be made. Molecular beam epitaxy on substrates held at the proper temperatures, assisted by a nitrogen beam of the proper energy produced several types of p-type GaN with hole concentrations of about 5.times.10.sup.11 /cm.sup.3 and hole mobilities of about 500 cm.sup.2 /V-sec, measured at 250.degree. K. P-type GaN can be formed of unintentionally-doped material or can be doped with magnesium by diffusion, ion implantation, or co-evaporation. When applicable, the nitrogen can be substituted with other group III elements such as Al.

  19. Electrooptic Waveguide Directional Coupler Modulator in Aluminum Gallium Arsenide-Gallium Arsenide.

    NASA Astrophysics Data System (ADS)

    Khan, Mujibun Nisa

    A novel optical waveguide intensity modulator in aluminum gallium arsenide and gallium arsenide material system is modeled, designed, and experimentally demonstrated at 0.83 μm wavelength. The modulator utilizes the linear electrooptic effect in a coupled waveguide structure to achieve high extinction ratio at low drive voltage. The device structure consists of a differentially -etched ridge directional coupler, where the ridge height in the gap is smaller that that of the outer sides. The effective index and semivectorial finite difference modeling techniques are developed to analyze the single ridge guides and directional coupler structures. The mode structure results from the two models are compared and the limitations of the effective index method are determined. The differential -etch design is employed to reduce the length as well as the drive voltage of the modulator. A modulation voltage of 2 volts for a 3.5-mm-long device is achieved, which is the lowest reported in literature. These results are compared with those obtained from the simplified analytical expressions for conventional couplers, and higher performance expected from the differential-etch design is verified. The modulator extinction ratio is measured to be 13 dB at 2 volts. The measured optical propagation loss of approximately 3.4 dB/cm for the modulator is speculated to be primarily due to the surface morphology of the epitaxially-grown material, and the light scattering from rough ridge walls produced during the anisotropic dry etching process. The high microwave loss of 15 dB/cm calculated for the modulator electrode design suggests a trade-off between the modulation voltage and the bandwidth, which is expected to be limited to 500 MHz. The measurement of the modulator frequency response up to 100 KHz is presented, because of the test limitations at higher frequencies due to the weak modulated intensity signals.

  20. Metal Insulator Semiconductor Structures on Gallium Arsenide.

    NASA Astrophysics Data System (ADS)

    Connor, Sean Denis

    Available from UMI in association with The British Library. The compound semiconductor gallium arsenide and its associated aluminium alloys have been the subject of intensive research in recent years. These materials offer the advantage of high electron mobilities coupled with the ability to be 'barrier engineered' leading to high injection efficiencies in bipolar devices. From a technological viewpoint however these materials are difficult to work with and device realisation is a major problem. Both thermal and anodic oxidation of these materials fail to produce a dielectric of sufficient quality for device applications and as a result devices tend to be complex non planar, mesa structures. A technique is proposed whereby the electrical interface is separated from the dielectric by means of a thin layer of AlGaAs, carrier confinement in the active GaAs region being maintained by the potential barriers to holes and electrons formed by the GaAs-AlGaAs junction. The integrity of these barriers is maintained by the provision of a suitable 'capping' dielectric. The electrical characteristics of various dielectric systems on GaAs have been investigated by means of current -voltage, capacitance-voltage and electronic breakdown measurements. Transport mechanisms for leakage current through these systems are identified and the interface properties (viz Fermi level pinning etc.) assessed by means of a direct comparison between experimental capacitance-voltage curves and theoretical data obtained from classical theory. As a technique for producing a convenient, in house 'capping' dielectric with good electrical and mechanical properties, the plasma anodisation of deposited aluminium films has been investigated. The anodisation parameters have been optimised for oxidation of these films in a microwave sustained oxygen plasma to give alumina films of around 500 A. A qualitative model for the anodisation process, involving linear and parabolic growth kinetics is proposed and

  1. The Construction and Characterization of Native Insulators on Gallium-Arsenide and Germanium

    NASA Astrophysics Data System (ADS)

    Crisman, Everett Earle

    Because of the excellent electrical properties that are obtained at the interfaces between silicon and thermally grown "native" oxides and nitrides, metal-insulator -semiconductor field effect transistors (MISFET's) have become the basic elements in fast high density computer memories as well as a primary structure for probing semiconductor surface charge transport phenomena. As silicon surface mobilities approach the bulk mobility a physical constraint is also being approached with respect to speed and density. Other semiconductors with higher bulk mobilities have, therefore, been suggested as replacements for silicon: gallium arsenide because of its very high room temperature electron mobility and germanium because it is one of the few well studied semiconductors with electron and hole mobilities of nearly the same magnitude. Unlike silicon, Ge and GaAs do not react readily wit oxygen or nitrogen to form uniform layers of interface passivating "native" insulators. In this study, techniques are reported for making native insulators on gallium arsenide and germanium. On gallium arsenide, the insulator is an oxide formed by a plasma oxidation technique (POX). On germanium, oxides have been formed by a high pressure oxidation technique (HPO) and these subsequently have been converted to nitrides (or oxynitride) by reaction with ammonia gas. Details of the formation techniques and basic characterization of the insulators and insulator/semiconductor interface electrical properties are present. Surface mobilities of about 20% of the bulk values were measured for MISFET's constructed on both GaAs and Ge using native oxides as the insulator. Fixed interface charge density in the low to mid 10('11)/cm('2) and midgap densities of states in the high 10('11)/cm('2)-eV range were also measured on similar MIS capacitors. On germanium nitride structures fixed surface charge density and interface density of states were both measured to be on the order of 10('10). Characterization

  2. III-V arsenide-nitride semiconductor

    NASA Technical Reports Server (NTRS)

    Major, Jo S. (Inventor); Welch, David F. (Inventor); Scifres, Donald R. (Inventor)

    2000-01-01

    III-V arsenide-nitride semiconductor are disclosed. Group III elements are combined with group V elements, including at least nitrogen and arsenic, in concentrations chosen to lattice match commercially available crystalline substrates. Epitaxial growth of these III-V crystals results in direct bandgap materials, which can be used in applications such as light emitting diodes and lasers. Varying the concentrations of the elements in the III-V materials varies the bandgaps, such that materials emitting light spanning the visible spectra, as well as mid-IR and near-UV emitters, can be created. Conversely, such material can be used to create devices that acquire light and convert the light to electricity, for applications such as full color photodetectors and solar energy collectors. The growth of the III-V material can be accomplished by growing thin layers of elements or compounds in sequences that result in the overall lattice match and bandgap desired.

  3. Two-photon photovoltaic effect in gallium arsenide.

    PubMed

    Ma, Jichi; Chiles, Jeff; Sharma, Yagya D; Krishna, Sanjay; Fathpour, Sasan

    2014-09-15

    The two-photon photovoltaic effect is demonstrated in gallium arsenide at 976 and 1550 nm wavelengths. A waveguide-photodiode biased in its fourth quadrant harvests electrical power from the optical energy lost to two-photon absorption. The experimental results are in good agreement with simulations based on nonlinear wave propagation in waveguides and the drift-diffusion model of carrier transport in semiconductors. Power efficiency of up to 8% is theoretically predicted in optimized devices.

  4. Trap influence on the performance of gallium arsenide radiation detectors

    SciTech Connect

    Castaldini, A.; Cavallini, A.; Polenta, L.; Canali, C.; Nava, F.; Papa, C. del

    1996-12-31

    Ohmic contacts play an important role in the performance of LEC gallium arsenide particle detectors since they possibly control the injection of charge carriers. Contact characteristics have been compared and related to electrically active defects induced during contact preparation and to the detector efficiency. The electric field distribution has also been analyzed. Spectroscopic investigations have put into evidence that the contact fabrication process significantly influences the trap density whilst it does not change their signatures.

  5. Two-photon photovoltaic effect in gallium arsenide.

    PubMed

    Ma, Jichi; Chiles, Jeff; Sharma, Yagya D; Krishna, Sanjay; Fathpour, Sasan

    2014-09-15

    The two-photon photovoltaic effect is demonstrated in gallium arsenide at 976 and 1550 nm wavelengths. A waveguide-photodiode biased in its fourth quadrant harvests electrical power from the optical energy lost to two-photon absorption. The experimental results are in good agreement with simulations based on nonlinear wave propagation in waveguides and the drift-diffusion model of carrier transport in semiconductors. Power efficiency of up to 8% is theoretically predicted in optimized devices. PMID:26466255

  6. Low temperature recombination and trapping analysis in high purity gallium arsenide by microwave photodielectric techniques

    NASA Technical Reports Server (NTRS)

    Khambaty, M. B.; Hartwig, W. H.

    1972-01-01

    Some physical theories pertinent to the measurement properties of gallium arsenide are presented and experimental data are analyzed. A model for explaining recombination and trapping high purity gallium arsenide, valid below 77 K is assembled from points made at various places and an appraisal is given of photodielectric techniques for material property studies.

  7. Gallium arsenide differentially affects processing of phagolysosomal targeted antigen by macrophages.

    PubMed

    Lewis, T A; Hartmann, C B; McCoy, K L

    1998-03-01

    Gallium arsenide, a semiconductor utilized in the electronics industry, causes immunosuppression in animals. The chemical's effect on macrophages to process antigen for activating pigeon cytochrome-specific helper T cell hybridoma was investigated. Mice were administered 200 mg/kg gallium arsenide or vehicle intraperitoneally. Five-day exposure suppressed processing by splenic macrophages but augmented processing by thioglycollate-elicited and resident peritoneal macrophages. Cytochrome coupled to latex beads was targeted to phagolysosomes to examine processing in lysosomes. Cytochrome beads required phagocytosis for processing and were located in phagolysosomes. Gallium arsenide did not alter the phagocytic ability of macrophages. Peritoneal macrophages normally processed the targeted antigen, indicating that gallium arsenide influenced compartment(s) preceding lysosomes. However, the processing efficiency of exposed splenic macrophages depended on the size of particulate cytochrome, suggesting that processing varied in phagolysosomes of different sizes. Gallium arsenide impacted different intracellular compartments in these macrophages, perhaps contributing to systemic immunotoxicity and local inflammation caused by exposure.

  8. Evaluation of the male reproductive toxicity of gallium arsenide.

    PubMed

    Bomhard, Ernst M; Cohen, Samuel M; Gelbke, Heinz-Peter; Williams, Gary M

    2012-10-01

    Gallium arsenide is an important semiconductor material marketed in the shape of wafers and thus is not hazardous to the end user. Exposure to GaAs particles may, however, occur during manufacture and processing. Potential hazards require evaluation. In 14-week inhalation studies with small GaAs particles, testicular effects have been reported in rats and mice. These effects occurred only in animals whose lungs showed marked inflammation and also had hematologic changes indicating anemia and hemolysis. The time- and concentration-dependent progressive nature of the lung and blood effects together with bioavailability data on gallium and arsenic lead us to conclude that the testicular/sperm effects are secondary to hypoxemia resulting from lung damage rather than due to a direct chemical effect of gallium or arsenide. Conditions leading to such primary effects are not expected to occur in humans at production and processing sites. This has to be taken into consideration for any classification decision for reproductive toxicity; especially a category 1 according to the EU CLP system is not warranted.

  9. Testing of gallium arsenide solar cells on the CRRES vehicle

    NASA Technical Reports Server (NTRS)

    Trumble, T. M.

    1985-01-01

    A flight experiment was designed to determine the optimum design for gallium arsenide (GaAs) solar cell panels in a radiation environment. Elements of the experiment design include, different coverglass material and thicknesses, welded and soldered interconnects, different solar cell efficiencies, different solar cell types, and measurement of annealing properties. This experiment is scheduled to fly on the Combined Release and Radiation Effects Satellite (CRRES). This satellite will simultaneously measure the radiation environment and provide engineering data on solar cell degradation that can be directly related to radiation damage.

  10. Improved performance design of gallium arsenide solar cells for space

    NASA Technical Reports Server (NTRS)

    Parekh, R. H.; Barnett, A. M.

    1984-01-01

    An improved design, shallow junction heteroface, n-p, gallium arsenide solar cell for space applications is reported, with a predicted AM0 efficiency in the 21.9 to 23.0 percent range. The optimized n-p structure, while slightly more efficient, has the added advantage of being less susceptible to radiation-induced degradation by virtue of this thin top junction layer. Detailed spectral response curves and an analysis of the loss mechanisms are reported. The details of the design are readily measurable. The optimized designs were reached by quantifying the dominant loss mechanisms and then minimizing them by using computer simulations.

  11. Microwave dielectric constants of silicon, gallium arsenide, and quartz

    SciTech Connect

    Seeger, K.

    1988-06-01

    For a determination of the dielectric constants epsilon of semiconductors, a microwave transmission interference method has been applied. For the first time, a calculation is presented which yields the full interference spectrum, not only the position of the extremal points. A comparison of the theoretical and experimental spectra results in a higher precision than previously obtained. A metal evaporation of the sample faces which are in contact with the waveguide walls turns out to be very important. Relative dielectric constants of 11.6 for silicon, 12.8 for gallium arsenide, and 4.6 for crystalline quartz, all +- 0.05, have been obtained.

  12. Anomalous tensoelectric effects in gallium arsenide tunnel diodes

    SciTech Connect

    Alekseeva, Z.M.; Vyatkin, A.P.; Krivorotov, N.P.; Shchegol', A.A.

    1988-02-01

    Anomalous tensoelectric phenomena induced in a tunnel p-n junction by a concentrated load and by hydrostatic compression were studied. The anomalous tensoelectric effects are caused by the action of concentrators of mechanical stresses in the vicinity of the p-n junction, giving rise to local microplastic strain. Under the conditions of hydrostatic compression prolate inclusions approx.100-200 A long play the role of concentrators. Analysis of irreversible changes in the current-voltage characteristics of tunnel p-n junctions made it possible to separate the energy levels of the defects produced with plastic strain of gallium arsenide.

  13. Overlapping-Gate Ccd Imagers On Gallium Arsenide

    NASA Astrophysics Data System (ADS)

    Kosel, P. B.; Katzer, D. S.; Poore, R. E...

    1987-01-01

    Charge-coupled device (CCD) imagers have been fabricated on gallium arsenide (GaAs) with very closely spaced (<100nm) Schottky-barrier metal electrodes. The short interelectrode spacing was achieved by using anodic oxidation in an ethylene glycol based electrolyte. All the active device regions of the CCD imagers were formed by silicon implantation into semi-insulating GaAs substrates followed by rapid thermal activation. The photodetectors were Schottky barrier diodes formed with thin aluminum metal anodes over silicon-implanted active regions in the semi-insulating substrate. The detectors formed a linear array along one side of the CCD channel and a three-phase transfer electrode structure was used. The imagers have been tested with front side illumination at clocking speeds up to 25 MHz.

  14. Temperature dependence of carrier capture by defects in gallium arsenide

    SciTech Connect

    Wampler, William R.; Modine, Normand A.

    2015-08-01

    This report examines the temperature dependence of the capture rate of carriers by defects in gallium arsenide and compares two previously published theoretical treatments of this based on multi phonon emission (MPE). The objective is to reduce uncertainty in atomistic simulations of gain degradation in III-V HBTs from neutron irradiation. A major source of uncertainty in those simulations is poor knowledge of carrier capture rates, whose values can differ by several orders of magnitude between various defect types. Most of this variation is due to different dependence on temperature, which is closely related to the relaxation of the defect structure that occurs as a result of the change in charge state of the defect. The uncertainty in capture rate can therefore be greatly reduced by better knowledge of the defect relaxation.

  15. Bit-systolic arithmetic arrays using dynamic differential gallium arsenide circuits

    NASA Technical Reports Server (NTRS)

    Beagles, Grant; Winters, Kel; Eldin, A. G.

    1992-01-01

    A new family of gallium arsenide circuits for fine grained bit-systolic arithmetic arrays is introduced. This scheme combines features of two recent techniques of dynamic gallium arsenide FET logic and differential dynamic single-clock CMOS logic. The resulting circuits are fast and compact, with tightly constrained series FET propagation paths, low fanout, no dc power dissipation, and depletion FET implementation without level shifting diodes.

  16. Gallium nitride junction field-effect transistor

    DOEpatents

    Zolper, John C.; Shul, Randy J.

    1999-01-01

    An all-ion implanted gallium-nitride (GaN) junction field-effect transistor (JFET) and method of making the same. Also disclosed are various ion implants, both n- and p-type, together with or without phosphorous co-implantation, in selected III-V semiconductor materials.

  17. Gallium nitride junction field-effect transistor

    DOEpatents

    Zolper, J.C.; Shul, R.J.

    1999-02-02

    An ion implanted gallium-nitride (GaN) junction field-effect transistor (JFET) and method of making the same are disclosed. Also disclosed are various ion implants, both n- and p-type, together with or without phosphorus co-implantation, in selected III-V semiconductor materials. 19 figs.

  18. Solar cell with a gallium nitride electrode

    DOEpatents

    Pankove, Jacques I.

    1979-01-01

    A solar cell which comprises a body of silicon having a P-N junction therein with a transparent conducting N-type gallium nitride layer as an ohmic contact on the N-type side of the semiconductor exposed to solar radiation.

  19. Gallium Nitride Crystals: Novel Supercapacitor Electrode Materials.

    PubMed

    Wang, Shouzhi; Zhang, Lei; Sun, Changlong; Shao, Yongliang; Wu, Yongzhong; Lv, Jiaxin; Hao, Xiaopeng

    2016-05-01

    A type of single-crystal gallium nitride mesoporous membrane is fabricated and its supercapacitor properties are demonstrated for the first time. The supercapacitors exhibit high-rate capability, stable cycling life at high rates, and ultrahigh power density. This study may expand the range of crystals as high-performance electrode materials in the field of energy storage.

  20. Preliminary survey report: control technology for gallium arsenide processing at Hewlett Packard, San Jose, California

    SciTech Connect

    Lenihan, K.L.

    1987-04-01

    A walk-through survey of the Hewlett Packard Company facility in San Jose, California, was prompted by an interest in the use of gallium arsenide as an alternative to silicon for the semiconductor industry. This facility produced gallium-arsenide and gallium phosphide Potential hazards existed from solvents, acids, and gases employed in wafer production. Some of the solvents included fluorocarbon compounds, xylene, and 1,1,1-trichloroethane Arsine, phosphine, hydrogen, and silane gases were used in the production processes. Worker exposures to gallium arsenide or arsenic dust were lower during the cleaning operation than they had been in other similar facilities, perhaps due to the small size of the crystal pullers used at this particular facility. According to the author, this facility is a possible candidate for an in-depth industry survey, but may not be representative of the entire industry.

  1. Native gallium adatoms discovered on atomically-smooth gallium nitride surfaces at low temperature.

    PubMed

    Alam, Khan; Foley, Andrew; Smith, Arthur R

    2015-03-11

    In advanced compound semiconductor devices, such as in quantum dot and quantum well systems, detailed atomic configurations at the growth surfaces are vital in determining the structural and electronic properties. Therefore, it is important to investigate the surface reconstructions in order to make further technological advancements. Usually, conventional semiconductor surfaces (e.g., arsenides, phosphides, and antimonides) are highly reactive due to the existence of a high density of group V (anion) surface dangling bonds. However, in the case of nitrides, group III rich growth conditions in molecular beam epitaxy are usually preferred leading to group III (Ga)-rich surfaces. Here, we use low-temperature scanning tunneling microscopy to reveal a uniform distribution of native gallium adatoms with a density of 0.3%-0.5% of a monolayer on the clean, as-grown surface of nitrogen polar GaN(0001̅) having the centered 6 × 12 reconstruction. Unseen at room temperature, these Ga adatoms are strongly bound to the surface but move with an extremely low surface diffusion barrier and a high density saturation coverage in thermodynamic equilibrium with Ga droplets. Furthermore, the Ga adatoms reveal an intrinsic surface chirality and an asymmetric site occupation. These observations can have important impacts in the understanding of gallium nitride surfaces.

  2. Impact of in vitro gallium arsenide exposure on macrophages.

    PubMed

    Harrison, M Travis; Hartmann, Constance B; McCoy, Kathleen L

    2003-01-01

    The semiconductor gallium arsenide (GaAs) is classified as an immunotoxicant and a carcinogen. We previously showed that GaAs in vivo induces several phenotypic changes in macrophages located at the exposure site, indicative of an activated state. These physiological alterations may be a primary or secondary consequence of chemical exposure. To discern primary influences, our current study examined the in vitro effects of the chemical on macrophage cell lines and murine peritoneal macrophages. GaAs augmented cathepsins L and B proteolytic activities in all three sources of macrophages. Expression of the two mature isoforms of invariant chain and its cleavage fragment was also significantly increased, indicating that the chemical directly affects macrophages. However, GaAs did not alter the overall cell surface expression of major histocompatibility complex class II molecules on macrophages nor influence their ability to stimulate antigen-specific helper T cell hybridomas to respond to intact antigens that require processing. These findings raise the possibility that the chemical's complete in vivo impact may involve cytokines. Further, GaAs in vitro enhanced steady-state cathepsin L protein, and cathepsins L and B mRNA expression in macrophages, indicating that GaAs may alter gene expression, which may contribute to the chemical's adverse biological effects.

  3. Gallium arsenide exposure impairs splenic B cell accessory function.

    PubMed

    Gondre-Lewis, Timothy A; Hartmann, Constance B; Caffrey, Rebecca E; McCoy, Kathleen L

    2003-03-01

    Gallium arsenide (GaAs) is utilized in industries for its semiconductor and optical properties. Chemical exposure of animals systemically suppresses several immune functions. The ability of splenic B cells to activate antigen-specific helper CD4(+) T cell hybridomas was assessed, and various aspects of antigen-presenting cell function were examined. GaAs-exposed murine B cells were impaired in processing intact soluble protein antigens, and the defect was antigen dependent. In contrast, B cells after exposure competently presented peptides to the T cells, which do not require processing. Cell surface expression of major histocompatibility complex (MHC) class II molecules and several costimulatory molecules on splenic B cells, which are critical for helper T cell activation, was not affected by chemical exposure. GaAs exposure also did not influence the stability of MHC class II heterodimers, suggesting that the defect may precede peptide exchange. GaAs-exposed B cells contained a normal level of aspartyl cathepsin activity; however, proteolytic activities of thiol cathepsins B and L were approximately half the control levels. Furthermore, two cleavage fragments of invariant chain, a molecular chaperone of MHC class II molecules, were increased in GaAs-exposed B cells, indicative of defective degradation. Thus, diminished thiol proteolytic activity in B cells may be responsible for their impaired antigen processing and invariant chain degradation, which may contribute to systemic immunosuppression caused by GaAs exposure.

  4. Deprotecting thioacetyl-terminated terphenyldithiol for assembly on gallium arsenide.

    PubMed

    Krapchetov, Dmitry A; Ma, Hong; Jen, Alex K Y; Fischer, Daniel A; Loo, Yueh-Lin

    2008-02-01

    We characterize the assembly of terphenyldithiol (TPDT) on gallium arsenide (GaAs) from ethanol (EtOH) and tetrahydrofuran (THF) as a function of ammonium hydroxide (NH4OH) concentration. NH4OH facilitates the conversion of thioacetyl end groups of the TPDT precursor to thiolates in the assembly solution. The final structure of TPDT assembled on GaAs is sensitive not only to the assembly solvent but also to NH4OH concentration. In the presence of low concentrations of NH4OH (1 mM), TPDT assemblies from EtOH are oriented upright. The same assemblies are less upright when adsorption is carried out at higher NH4OH concentrations. In THF, TPDT does not adsorb significantly on GaAs at low NH4OH concentrations. The surface coverage and structural organization of these assemblies improve with increasing NH4OH concentrations, although these assemblies are never as organized as those from EtOH. The difference in the final structure of TPDT assemblies is attributed to differences in the thiolate fraction in the assembly solution at the point of substrate immersion.

  5. Gate modulation of anodically etched gallium arsenide nanowire random network

    NASA Astrophysics Data System (ADS)

    Aikawa, Shinya; Yamada, Kohei; Asoh, Hidetaka; Ono, Sachiko

    2016-06-01

    Gallium arsenide nanowires (GaAs NWs) formed by anodic etching show an electrically semi-insulating behavior because of charge carrier depletion caused by high interface state density. Here, we demonstrate the gate modulation of an anodically etched GaAs NW random network. By applying a reverse bias voltage after anodic etching of bulk GaAs, hydrogen ion exposure of the depleted NW region occurs, and then the interface state density is possibly decreased owing to the reduction in the amount of excess As generated at the interface between the amorphous Ga2O3 and GaAs layers. Consequently, the drain current of the thin-film transistor (TFT) with the GaAs NW random network was increased and was changed by the gate voltage. In contrast, the random network film remained in the insulator in the absence of reverse electrolysis treatment. The TFT performance is still insufficient but may be improved by optimizing the hydrogen ion exposure conditions.

  6. Gallium arsenide pilot line for high performance components

    NASA Astrophysics Data System (ADS)

    1990-01-01

    The Gallium Arsenide Pilot Line for High Performance Components (Pilot Line III) is to develop a facility for the fabrication of GaAs logic and memory chips. The first thirty months of this contract are now complete, and this report covers the period from March 27 through September 24, 1989. Similar to the PT-2M SRAM function for memories, the six logic circuits of PT-2L and PT-2M have served their functions as stepping stones toward the custom, standard cell, and cell array logic circuits. All but one of these circuits was right first time; the remaining circuit had a layout error due to a bug in the design rule checker that has since been fixed. The working devices all function over the full temperature range from -55 to 125 C. They all comfortably meet the 200 MHz requirement. They do not solidly conform to the required input and output voltage levels, particularly Vih. It is known that these circuits were designed with the older design models and that they came from an era where the DFET thresholds were often not on target.

  7. Enhanced photothermal conversion in vertically oriented gallium arsenide nanowire arrays.

    PubMed

    Walia, Jaspreet; Dhindsa, Navneet; Flannery, Jeremy; Khodabad, Iman; Forrest, James; LaPierre, Ray; Saini, Simarjeet S

    2014-10-01

    The photothermal properties of vertically etched gallium arsenide nanowire arrays are examined using Raman spectroscopy. The nanowires are arranged in square lattices with a constant pitch of 400 nm and diameters ranging from 50 to 155 nm. The arrays were illuminated using a 532 nm laser with an incident energy density of 10 W/mm(2). Nanowire temperatures were highly dependent on the nanowire diameter and were determined by measuring the spectral red-shift for both TO and LO phonons. The highest temperatures were observed for 95 nm diameter nanowires, whose top facets and sidewalls heated up to 600 and 440 K, respectively, and decreased significantly for the smaller or larger diameters studied. The diameter-dependent heating is explained by resonant coupling of the incident laser light into optical modes of the nanowires, resulting in increased absorption. Photothermal activity in a given nanowire diameter can be optimized by proper wavelength selection, as confirmed using computer simulations. This demonstrates that the photothermal properties of GaAs nanowires can be enhanced and tuned by using a photonic lattice structure and that smaller nanowire diameters are not necessarily better to achieve efficient photothermal conversion. The diameter and wavelength dependence of the optical coupling could allow for localized temperature gradients by creating arrays which consist of different diameters.

  8. Gallium arsenide deep-level optical emitter for fibre optics.

    PubMed

    Pan, Janet L; McManis, Joseph E; Osadchy, Thomas; Grober, Louise; Woodall, Jerry M; Kindlmann, Peter J

    2003-06-01

    Fibre-optic components fabricated on the same substrate as integrated circuits are important for future high-speed communications. One industry response has been the costly push to develop indium phosphide (InP) electronics. However, for fabrication simplicity, reliability and cost, gallium arsenide (GaAs) remains the established technology for integrated optoelectronics. Unfortunately, the GaAs bandgap wavelength (0.85 microm) is far too short for fibre optics at 1.3-1.5 microm. This has led to work on materials that have a large lattice mismatch on GaAs. Here we demonstrate the first light-emitting diode (LED) that emits at 1.5 microm fibre-optic wavelengths in GaAs using optical transitions from arsenic antisite (As(Ga)) deep levels. This is an enabling technology for fibre-optic components that are lattice-matched to GaAs integrated circuits. We present experimental results showing significant internal optical power (24 mW) and speed (in terahertz) from GaAs optical emitters using deep-level transitions. Finally, we present theory showing the ultimate limit to the efficiency-bandwidth product of semiconductor deep-level optical emitters.

  9. Epitaxial growth of gallium arsenide from elemental arsenic

    NASA Astrophysics Data System (ADS)

    Chu, Ting L.; Chu, Shirley S.; Green, Richard F.; Cerny, C. L. A.

    1991-03-01

    Epitaxial gallium arsenide (GaAs) films of controlled electrical properties are essential for the fabrication of high performance devices. Metalorganic vapor phase epitaxy (MOVPE) utilizing the reaction of trimethylgallium (TMGa) or triethylgallium (TEGa) and arsine (AsH3) is commonly used for the epitaxial growth of GaAs. The use of highly toxic AsH3 however is a serious hazard in research and manufacturing operations. In this work the MOVPE of device quality GaAs from elemental arsenic has been demonstrated for the first time thus minimizing a major safety concern. The reaction of TEGa and As on the substrate surface at 450-550C in a H2 flow was used. The parameter of the growth process and the electrical and photoluminescent properties of epitaxial GaAs are discussed. Further TMGa TEGa and arsenic show strong absorption in far ultraviolet. The epitaxial growth of GaAs films can be achieved at low substrate temperatures by irradiating the gaseous reactant with a UV laser. Epitaxial GaAs films have been grown at 425C or higher by using ArF laser enhanced reaction of TEG and As. The electrical and photoluminescent properties of these films have also beencharacterized. Epitaxial GaAs films grown by the laser enhanced process have been found to contain considerably higher carbon concentration than films grown by the thermal process. This is due presumably to the photodissociation of carbon-hydrogen bonds in TEGa.

  10. Greyscale proton beam writing in p-type Gallium Arsenide

    NASA Astrophysics Data System (ADS)

    Diering, D.; Spemann, D.; Lenzner, J.; Müller, St.; Böntgen, T.; von Wenckstern, H.

    2013-07-01

    Proton beam writing (PBW) is a well known method for micromachining, e.g. of semiconductors. Up to now, only few indication is given on how the resulting structure height in micromachined semiconductors can be controlled by means of fluence variation. This approach for 3D-microstructuring, called Greyscale PBW, was already successfully demonstrated for negative photoresists. In this study (1 0 0) p-type Gallium Arsenide (GaAs) was irradiated with 2.28 MeV protons and fluences in the range from 1.2×1014 H+ cm-2 to 1.0×1018 H+ cm-2 at the ion beam laboratory LIPSION and subsequently electrochemically etched with 10%-KOH. A linear dependency of structure height on ion fluence was established. In this way, pyramid-like structures as well as concave-shaped structures could be created. GaAs showed a lateral anisotropic etch behaviour during the development step with preferential etching along the [0 1 1] directions. On some structures the surface roughness and the change of conductivity were investigated by atomic force and scanning capacitance microscopy, respectively. The rms roughness of the surface of the structures was 5.4 nm and 10.6 nm for a fluence of 7.8×1015 H+ cm-2 and 1.2×1017 H+ cm-2, respectively. We observed an increasing etching rate for fluences larger than 1016 H+ cm-2.

  11. Solvent-dependent assembly of terphenyl- and quaterphenyldithiol on gold and gallium arsenide.

    PubMed

    Krapchetov, Dmitry A; Ma, Hong; Jen, Alex K Y; Fischer, Daniel A; Loo, Yueh-Lin

    2005-06-21

    The assembly of terphenyldithiol (TPDT) and quaterphenyldithiol (QPDT) on gold and gallium arsenide from ethanol (EtOH), tetrahydrofuran (THF), and solutions consisting of both solvents has been characterized by near-edge X-ray absorption fine structure spectroscopy. The surface coverage and the average orientation of both TPDT and QPDT on gold are solvent-independent. These molecules readily form monolayers on gold with an ensemble-average backbone tilt of 30 degrees +/- 3 degrees from the substrate normal. In sharp contrast, the assembly of TPDT and QPDT on gallium arsenide is extremely solvent-sensitive. At high ethanol fractions, both molecules form monolayers with an ensemble-average orientation that is indistinguishable from those on gold substrates. At low ethanol fractions and in pure THF, however, these molecules are disordered on gallium arsenide and the surface coverage is poor.

  12. A study of the applicability of gallium arsenide and silicon carbide as aerospace sensor materials

    NASA Technical Reports Server (NTRS)

    Hurley, John S.

    1990-01-01

    Most of the piezoresistive sensors, to date, are made of silicon and germanium. Unfortunately, such materials are severly restricted in high temperature environments. By comparing the effects of temperature on the impurity concentrations and piezoresistive coefficients of silicon, gallium arsenide, and silicon carbide, it is being determined if gallium arsenide and silicon carbide are better suited materials for piezoresistive sensors in high temperature environments. The results show that the melting point for gallium arsenide prevents it from solely being used in high temperature situations, however, when used in the alloy Al(x)Ga(1-x)As, not only the advantage of the wider energy band gas is obtained, but also the higher desire melting temperature. Silicon carbide, with its wide energy band gap and higher melting temperature suggests promise as a high temperature piezoresistive sensor.

  13. The comparison between gallium arsenide and indium gallium arsenide as materials for solar cell performance using Silvaco application

    SciTech Connect

    Zahari, Suhaila Mohd; Norizan, Mohd Natashah; Mohamad, Ili Salwani; Osman, Rozana Aina Maulat; Taking, Sanna

    2015-05-15

    The work presented in this paper is about the development of single and multilayer solar cells using GaAs and InGaAs in AM1.5 condition. The study includes the modeling structure and simulation of the device using Silvaco applications. The performance in term of efficiency of Indium Gallium Arsenide (InGaAs) and GaAs material was studied by modification of the doping concentration and thickness of material in solar cells. The efficiency of the GaAs solar cell was higher than InGaAs solar cell for single layer solar cell. Single layer GaAs achieved an efficiency about 25% compared to InGaAs which is only 2.65% of efficiency. For multilayer which includes both GaAs and InGaAs, the output power, P{sub max} was 8.91nW/cm² with the efficiency only 8.51%. GaAs is one of the best materials to be used in solar cell as a based compared to InGaAs.

  14. Measurement of arsenic and gallium content of gallium arsenide semiconductor waste streams by ICP-MS.

    PubMed

    Torrance, Keith W; Keenan, Helen E; Hursthouse, Andrew S; Stirling, David

    2010-01-01

    The chemistry of semiconductor wafer processing liquid waste, contaminated by heavy metals, was investigated to determine arsenic content. Arsenic and gallium concentrations were determined for waste slurries collected from gallium arsenide (GaAs) wafer processing at three industrial sources and compared to slurries prepared under laboratory conditions. The arsenic and gallium content of waste slurries was analyzed using inductively coupled plasma mass-spectrometry (ICP-MS) and it is reported that the arsenic content of the waste streams was related to the wafer thinning process, with slurries from wafer polishing having the highest dissolved arsenic content at over 1,900 mgL(-1). Lapping slurries had much lower dissolved arsenic (< 90 mgL(-1)) content, but higher particulate contents. It is demonstrated that significant percentage of GaAs becomes soluble during wafer lapping. Grinding slurries had the lowest dissolved arsenic content at 15 mgL(-1). All three waste streams are classified as hazardous waste, based on their solids content and dissolved arsenic levels and treatment is required before discharge or disposal. It is calculated that as much as 93% of material is discarded through the entire GaAs device manufacturing process, with limited recycling. Although gallium can be economically recovered from waste slurries, there is little incentive to recover arsenic, which is mostly landfilled. Options for treating GaAs processing waste streams are reviewed and some recommendations made for handling the waste. Therefore, although the quantities of hazardous waste generated are miniscule in comparison to other industries, sustainable manufacturing practices are needed to minimize the environmental impact of GaAs semiconductor device fabrication.

  15. Combined Silicon and Gallium Arsenide Solar Cell UV Testing

    NASA Technical Reports Server (NTRS)

    Willowby, Douglas

    2005-01-01

    The near and long-term effect of UV on silicon solar cells is relatively understood. In an effort to learn more about the effects of UV radiation on the performance of GaAs/Ge solar cells, silicon and gallium arsenide on germanium (GaAs/Ge) solar cells were placed in a vacuum chamber and irradiated with ultraviolet light by a Spectrolab XT 10 solar simulator. Seventeen GaAs/Ge and 8 silicon solar cells were mounted on an 8 inch copper block. By having all the cells on the same test plate we were able to do direct comparison of silicon and GaAs/Ge solar cell degradation. The test article was attached to a cold plate in the vacuum chamber to maintain the cells at 25 degrees Celsius. A silicon solar cell standard was used to measure beam uniformity and any degradation of the ST-10 beam. The solar cell coverings tested included cells with AR-0213 coverglass, fused silica coverglass, BRR-0213 coverglass and cells without coverglass. Of interest in the test is the BRR-0213 coverglass material manufactured by OCLI. It has an added Infrared rejection coating to help reduce the solar cell operating temperature. This coverglass is relatively new and of interest to several current and future programs at Marshall. Due to moves of the laboratory equipment and location only 350 hours of UV degradation have been completed. During this testing a significant leveling off in the rate of degradation was reached. Data from the test and comparisons of the UV effect of the bare cells and cells with coverglass material will be presented.

  16. Indium Phosphide Window Layers for Indium Gallium Arsenide Solar Cells

    NASA Technical Reports Server (NTRS)

    Jain, Raj K.

    2005-01-01

    Window layers help in reducing the surface recombination at the emitter surface of the solar cells resulting in significant improvement in energy conversion efficiency. Indium gallium arsenide (In(x)Ga(1-x)As) and related materials based solar cells are quite promising for photovoltaic and thermophotovoltaic applications. The flexibility of the change in the bandgap energy and the growth of InGaAs on different substrates make this material very attractive for multi-bandgap energy, multi-junction solar cell approaches. The high efficiency and better radiation performance of the solar cell structures based on InGaAs make them suitable for space power applications. This work investigates the suitability of indium phosphide (InP) window layers for lattice-matched In(0.53)Ga(0.47)As (bandgap energy 0.74 eV) solar cells. We present the first data on the effects of the p-type InP window layer on p-on-n lattice-matched InGaAs solar cells. The modeled quantum efficiency results show a significant improvement in the blue region with the InP window. The bare InGaAs solar cell performance suffers due to high surface recombination velocity (10(exp 7) cm/s). The large band discontinuity at the InP/InGaAs heterojunction offers a great potential barrier to minority carriers. The calculated results demonstrate that the InP window layer effectively passivates the solar cell front surface, hence resulting in reduced surface recombination and therefore, significantly improving the performance of the InGaAs solar cell.

  17. Ultralow wear of gallium nitride

    NASA Astrophysics Data System (ADS)

    Zeng, Guosong; Tan, Chee-Keong; Tansu, Nelson; Krick, Brandon A.

    2016-08-01

    Here, we reveal a remarkable (and surprising) physical property of GaN: it is extremely wear resistant. In fact, we measured the wear rate of GaN is approaching wear rates reported for diamond. Not only does GaN have an ultralow wear rate but also there are quite a few experimental factors that control the magnitude of its wear rate, further contributing to the rich and complex physics of wear of GaN. Here, we discovered several primary controlling factors that will affect the wear rate of III-Nitride materials: crystallographic orientation, sliding environment, and coating composition (GaN, InN and InGaN). Sliding in the ⟨ 1 2 ¯ 10 ⟩ is significantly lower wear than ⟨ 1 1 ¯ 00 ⟩ . Wear increases by 2 orders of magnitude with increasing humidity (from ˜0% to 50% RH). III-Nitride coatings are promising as multifunctional material systems for device design and sliding wear applications.

  18. Spontaneous atomic ordering in MOVPE grown gallium arsenide antimonide

    NASA Astrophysics Data System (ADS)

    Jiang, Weiyang

    process. It is unlikely that the ordering mechanism is similar to the dimer-induced strain models that have been successfully used to explain CuPt ordering in InGaP. We propose a simple model based on alternating incorporation of group V adatoms at step edges. Keywords. GaAsSb; MOVPE; Bi surfactant; TEM; CuAu ordering. Subject. Gallium Arsenide Antimonide; Metalorganic Vapor-phase Epitaxy; Bismuth Surfactant; Transmission Electron Microscopy; CuAu Ordering.

  19. Testicular toxicity evaluation of arsenic-containing binary compound semiconductors, gallium arsenide and indium arsenide, in hamsters.

    PubMed

    Omura, M; Hirata, M; Tanaka, A; Zhao, M; Makita, Y; Inoue, N; Gotoh, K; Ishinishi, N

    1996-12-16

    The testicular toxicities of gallium arsenide (GaAs), indium arsenide (InAs) and arsenic trioxide (As2O3) were examined by repetitive intratracheal instillation using hamsters. GaAs (7.7 mg/kg) and As2O3 (1.3 mg/kg) were instilled twice a week a total of 16 times and InAs (7.7 mg/kg) was instilled a total of 14 times. GaAs caused testicular spermatid retention and epididymal sperm reduction, though the degrees were less severe than those in rats shown in our previous experiment. InAs and As2O3 did not show any testicular toxicities. Serum arsenic concentration in GaAs-treated hamsters was less than half of that in As2O3-treated hamsters in which no testicular toxicities were found. Serum molar concentration of gallium was 32-times higher than that of arsenic in GaAs-treated hamsters. Therefore gallium may play a main role in the testicular toxicity of GaAs in hamsters.

  20. Methods for forming group III-arsenide-nitride semiconductor materials

    NASA Technical Reports Server (NTRS)

    Major, Jo S. (Inventor); Welch, David F. (Inventor); Scifres, Donald R. (Inventor)

    2002-01-01

    Methods are disclosed for forming Group III-arsenide-nitride semiconductor materials. Group III elements are combined with group V elements, including at least nitrogen and arsenic, in concentrations chosen to lattice match commercially available crystalline substrates. Epitaxial growth of these III-V crystals results in direct bandgap materials, which can be used in applications such as light emitting diodes and lasers. Varying the concentrations of the elements in the III-V crystals varies the bandgaps, such that materials emitting light spanning the visible spectra, as well as mid-IR and near-UV emitters, can be created. Conversely, such material can be used to create devices that acquire light and convert the light to electricity, for applications such as full color photodetectors and solar energy collectors. The growth of the III-V crystals can be accomplished by growing thin layers of elements or compounds in sequences that result in the overall lattice match and bandgap desired.

  1. Thin-film gallium arsenide solar-cell research. Annual project report, March 1, 1980-February 28, 1981

    SciTech Connect

    Chu, S.S.

    1981-03-01

    The optimization of the deposition of gallium arsenide films of 10 ..mu..m thickness or less has been carried out with the objective of obtaining gallium arsenide films with uniform microstructure and good electrical properties. Gallium arsenide films of 10 ..mu..m or less thickness deposited on tungsten/graphite substrates exhibit, in most cases, pronounced shunting effects in large area MOS solar cells due to grain boundaries. The effective passivation of grain boundaries is necessary to produce solar cells with good conversion efficiency. Different grain boundary passivation techniques have been investigated to determine their effectiveness for large area solar cells from the deposited gallium arsenide films. The combination of ruthenium treatment and thermal oxidation has been shown to be the most effective passivation technique for large area MOS solar cells. MOS solar cells have been fabricated from gallium arsenide films of 10 ..mu..m thickness. The gallium arsenide films were treated with ruthenium ion and followed by thermal oxidation. The solar cells are of the configuration TiO/sub 2//Ag(grid contact)/Au/oxide/n-GaAs/n/sup +/-GaAs/W/graphite. MOS solar cells of 9 cm/sup 2/ area with an AM1 efficiency of up to 8.5% have been prepared reproducibly. The fabrication and characterization of thin film gallium arsenide homojunction solar cells have been initiated. The p/sup +/-n junction was formed in-situ by depositing the Zn-doped p/sup +/-layer immediately after the deposition of n/n/sup +/-layers. Without any surface passivation treatment, solar cells of 8 cm/sup 2/ area with an AM1 efficiency of about 7% have been prepared. With proper optimization in the fabrication processes, the conversion efficiency should be greatly improved. Therefore homojunction structure is a promising approach for the fabrication of thin film gallium arsenide solar cells.

  2. Gallium arsenide-gallium nitride wafer fusion and the n-aluminum gallium arsenide/p-gallium arsenide/n-gallium nitride double heterojunction bipolar transistor

    NASA Astrophysics Data System (ADS)

    Estrada, Sarah M.

    This dissertation describes the n-AlGaAs/p-GaAs/n-GaN heterojunction bipolar transistor (HBT), the first transistor formed via wafer fusion. The fusion process was developed as a way to combine lattice-mismatched materials for high-performance electronic devices, not obtainable via conventional all-epitaxial formation methods. Despite the many challenges of wafer fusion, successful transistors were demonstrated and improved, via the optimization of material structure and fusion process conditions. Thus, this project demonstrated the integration of disparate device materials, chosen for their optimal electronic properties, unrestricted by the conventional (and very limiting) requirement of lattice-matching. By combining an AlGaAs-GaAs emitter-base with a GaN collector, the HBT benefited from the high breakdown voltage of GaN, and from the high emitter injection efficiency and low base transit time of AlGaAs-GaAs. Because the GaAs-GaN lattice mismatch precluded an all-epitaxial formation of the HBT, the GaAs-GaN heterostructure was formed via fusion. This project began with the development of a fusion process that formed mechanically robust and electrically active GaAs-GaN heterojunctions. During the correlation of device electrical performance with a systematic variation of fusion conditions over a wide range (500--750°C, 0.5--2hours), a mid-range fusion temperature was found to induce optimal HBT electrical performance. Transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) were used to assess possible reasons for the variations observed in device electrical performance. Fusion process conditions were correlated with electrical (I-V), structural (TEM), and chemical (SIMS) analyses of the resulting heterojunctions, in order to investigate the trade-off between increased interfacial disorder (TEM) with low fusion temperature and increased diffusion (SIMS) with high fusion temperature. The best do device results (IC ˜ 2.9 kA/cm2 and beta ˜ 3.5, at VCE = 20V and IB = 10mA) were obtained with an HBT formed via fusion at 600°C for 1 hour, with an optimized base-collector design. This was quite an improvement, as compared to an HBT with a simpler base-collector structure, also fused at 600°C for 1 hour (IC ˜ 0.83 kA/cm2 and beta ˜ 0.89, at VCE = 20V and IB = 10mA). Fused AlGaAs-GaAs-GaAs HBTs were compared to fused AlGaAs-GaAs-GaN HBTs, demonstrating that the use of a wider bandgap collector (Eg,GaN > Eg,GaAs) did indeed improve HBT performance at high applied voltages, as desired for high-power applications.

  3. Fabrication of Aluminum Gallium Nitride/Gallium Nitride MESFET And It's Applications in Biosensing

    NASA Astrophysics Data System (ADS)

    Alur, Siddharth

    Gallium Nitride has been researched extensively for the past three decades for its application in Light Emitting Diodes (LED's), power devices and UV photodetectors. With the recent developments in crystal growth technology and the ability to control the doping there has been an increased interest in heterostructures formed between Gallium nitride and it's alloy Aluminium Gallium Nitride. These heterostructures due to the combined effect of spontaneous and piezoelectric effect can form a high density and a high mobility electron gas channel without any intentional doping. This high density electron gas makes these heterostructures ideal to be used as sensors. Gallium Nitride is also chemically very stable. Detection of biomolecules in a fast and reliable manner is very important in the areas of food safety and medical research. For biomolecular detection it is paramount to have a robust binding of the probes on the sensor surface. Therefore, in this dissertation, the fabrication and application of the AlGaN/GaN heterostructures as biological sensors for the detection of DNA and Organophosphate hydrolase enzyme is discussed. In order to use these AlGaN/GaN heterostructures as biological sensors capable of working in a liquid environment photodefinable polydimethyl-siloxane is used as an encapsulant. The immobilization conditions for a robust binding of thiolated DNA and the catalytic receptor enzyme organophosphate hydrolase on gold surfaces is developed with the help of X-ray photoelectron spectroscopy. DNA and OPH are detected by measuring the change in the drain current of the device as a function of time.

  4. Gallium nitride based logpile photonic crystals.

    PubMed

    Subramania, Ganapathi; Li, Qiming; Lee, Yun-Ju; Figiel, Jeffrey J; Wang, George T; Fischer, Arthur J

    2011-11-01

    We demonstrate a nine-layer logpile three-dimensional photonic crystal (3DPC) composed of single crystalline gallium nitride (GaN) nanorods, ∼100 nm in size with lattice constants of 260, 280, and 300 nm with photonic band gap in the visible region. This unique GaN structure is created through a combined approach of a layer-by-layer template fabrication technique and selective metal organic chemical vapor deposition (MOCVD). These GaN 3DPC exhibit a stacking direction band gap characterized by strong optical reflectance between 380 and 500 nm. By introducing a "line-defect" cavity in the fifth (middle) layer of the 3DPC, a localized transmission mode with a quality factor of 25-30 is also observed within the photonic band gap. The realization of a group III nitride 3DPC with uniform features and a band gap at wavelengths in the visible region is an important step toward realizing complete control of the electromagnetic environment for group III nitride based optoelectronic devices.

  5. Selenium effects on gallium arsenide induced biochemical and immunotoxicological changes in rats.

    PubMed

    Flora, S J; Kannan, G M; Kumar, P

    1999-08-30

    The influence of selenium (6.3 and 12.6 micromol/kg, intraperitoneally) on the disposition of gallium and arsenic and a few gallium arsenide (GaAs) sensitive biochemical variables was studied in male rats. Concomitant administration of Se and GaAs (70 micromol/kg, orally, 5 days a week for 4 weeks) significantly prevented the accumulation of arsenic while, the gallium concentration reduced moderately in the soft organs. The biochemical (haematopoietic and liver) and immunological variables however, responded less favorably to selenium administration. Most of the protection was however observed with the dose of 12.6 micromol rather than at 6.3 micromol. The results thus suggest a few beneficial effects of selenium in preventing the appearance of signs of GaAs toxicity like preventing inhibition of blood delta-aminolevulinic acid dehydratase (ALAD), hepatic malondialdehyde (MDA) formation and the accumulation of gallium and arsenic concentration.

  6. Cathodoluminescence spectra of gallium nitride nanorods

    PubMed Central

    2011-01-01

    Gallium nitride [GaN] nanorods grown on a Si(111) substrate at 720°C via plasma-assisted molecular beam epitaxy were studied by field-emission electron microscopy and cathodoluminescence [CL]. The surface topography and optical properties of the GaN nanorod cluster and single GaN nanorod were measured and discussed. The defect-related CL spectra of GaN nanorods and their dependence on temperature were investigated. The CL spectra along the length of the individual GaN nanorod were also studied. The results reveal that the 3.2-eV peak comes from the structural defect at the interface between the GaN nanorod and Si substrate. The surface state emission of the single GaN nanorod is stronger as the diameter of the GaN nanorod becomes smaller due to an increased surface-to-volume ratio. PMID:22168896

  7. An advanced space photovoltaic concentrator array using Fresnel lenses, gallium arsenide cells, and prismatic cell covers

    NASA Technical Reports Server (NTRS)

    O'Neill, Mark J.; Piszczor, Michael F.

    1988-01-01

    The current status of a space concentrator array which uses refractive optics, gallium arsenide cells, and prismatic cell covers to achieve excellent performance at a very low array mass is documented. The prismatically covered cells have established records for space cell performance (24.2 percent efficient at 100 AM0 suns and 25 C) and terrestrial single-junction cell performance (29.3 percent efficient at 200 AM1.5 suns and 25 C).

  8. Influence of fast neutrons on the recombination and electrical properties of neutron transmutation doped gallium arsenide

    SciTech Connect

    Bykovsky, V.A.; Karas, V.I.; Shoh, V.F.; Strzelecka, S.; Hruban, A.; Gladysz, M.

    1996-12-31

    The electrical properties, photoluminescence and DLTS spectra of LEC gallium arsenide crystals after neutron transmutation doping (NTD) has been investigated as function of starting material properties, irradiation dose and thermal to fast neutron fluences-ratio. The residual carbon acceptors interact with radiation induced defects (RD) in neutron irradiated GaAs crystals and formed nonradiative recombination centers, which are stable up to 700 C temperature.

  9. Epitaxial lift-off process for gallium arsenide substrate reuse and flexible electronics.

    PubMed

    Cheng, Cheng-Wei; Shiu, Kuen-Ting; Li, Ning; Han, Shu-Jen; Shi, Leathen; Sadana, Devendra K

    2013-01-01

    Epitaxial lift-off process enables the separation of III-V device layers from gallium arsenide substrates and has been extensively explored to avoid the high cost of III-V devices by reusing the substrates. Conventional epitaxial lift-off processes require several post-processing steps to restore the substrate to an epi-ready condition. Here we present an epitaxial lift-off scheme that minimizes the amount of post-etching residues and keeps the surface smooth, leading to direct reuse of the gallium arsenide substrate. The successful direct substrate reuse is confirmed by the performance comparison of solar cells grown on the original and the reused substrates. Following the features of our epitaxial lift-off process, a high-throughput technique called surface tension-assisted epitaxial lift-off was developed. In addition to showing full wafer gallium arsenide thin film transfer onto both rigid and flexible substrates, we also demonstrate devices, including light-emitting diode and metal-oxide-semiconductor capacitor, first built on thin active layers and then transferred to secondary substrates.

  10. Two years of on-orbit gallium arsenide performance from the LIPS solar cell panel experiment

    NASA Technical Reports Server (NTRS)

    Francis, R. W.; Betz, F. E.

    1985-01-01

    The LIPS on-orbit performance of the gallium arsenide panel experiment was analyzed from flight operation telemetry data. Algorithms were developed to calculate the daily maximum power and associated solar array parameters by two independent methods. The first technique utilizes a least mean square polynomial fit to the power curve obtained with intensity and temperature corrected currents and voltages; whereas, the second incorporates an empirical expression for fill factor based on an open circuit voltage and the calculated series resistance. Maximum power, fill factor, open circuit voltage, short circuit current and series resistance of the solar cell array are examined as a function of flight time. Trends are analyzed with respect to possible mechanisms which may affect successive periods of output power during 2 years of flight operation. Degradation factors responsible for the on-orbit performance characteristics of gallium arsenide are discussed in relation to the calculated solar cell parameters. Performance trends and the potential degradation mechanisms are correlated with existing laboratory and flight data on both gallium arsenide and silicon solar cells for similar environments.

  11. Performance of a Medipix3RX spectroscopic pixel detector with a high resistivity gallium arsenide sensor.

    PubMed

    Hamann, Elias; Koenig, Thomas; Zuber, Marcus; Cecilia, Angelica; Tyazhev, Anton; Tolbanov, Oleg; Procz, Simon; Fauler, Alex; Baumbach, Tilo; Fiederle, Michael

    2015-03-01

    High resistivity gallium arsenide is considered a suitable sensor material for spectroscopic X-ray imaging detectors. These sensors typically have thicknesses between a few hundred μm and 1 mm to ensure a high photon detection efficiency. However, for small pixel sizes down to several tens of μm, an effect called charge sharing reduces a detector's spectroscopic performance. The recently developed Medipix3RX readout chip overcomes this limitation by implementing a charge summing circuit, which allows the reconstruction of the full energy information of a photon interaction in a single pixel. In this work, we present the characterization of the first Medipix3RX detector assembly with a 500 μm thick high resistivity, chromium compensated gallium arsenide sensor. We analyze its properties and demonstrate the functionality of the charge summing mode by means of energy response functions recorded at a synchrotron. Furthermore, the imaging properties of the detector, in terms of its modulation transfer functions and signal-to-noise ratios, are investigated. After more than one decade of attempts to establish gallium arsenide as a sensor material for photon counting detectors, our results represent a breakthrough in obtaining detector-grade material. The sensor we introduce is therefore suitable for high resolution X-ray imaging applications.

  12. Hepatic and renal metallothionein induction following single oral administration of gallium arsenide in rats.

    PubMed

    Flora, S J; Tripathi, N

    1998-09-01

    Metallothionein genes (MT) are inducible by a variety of agents, including heavy metals. We report the induction of MT expression by gallium arsenide (GaAs), a superior intermetallic semiconductor material at two time intervals following single oral exposure in rats. The data is also supplemented with two additional groups exposed to gallium (III) as gallium oxide and arsenic (III) as sodium arsenite to determine which of the two moieties in GaAs is responsible for any such possible effects. The results indicate that GaAs administration does significantly induces MT in hepatic tissues accompanied by an increase in cytosolic glutathione, arsenic, zinc and copper concentration. It thus proves that arsenic moiety is chiefly responsible for such an effect.

  13. Ambient temperature deposition of gallium nitride/gallium oxynitride from a deep eutectic electrolyte, under potential control.

    PubMed

    Sarkar, Sujoy; Sampath, S

    2016-05-11

    A ternary, ionically conducting, deep eutectic solvent based on acetamide, urea and gallium nitrate is reported for the electrodeposition of gallium nitride/gallium indium nitride under ambient conditions; blue and white light emitting photoluminescent deposits are obtained under potential control. PMID:27074315

  14. Effect of barrier height on friction behavior of the semiconductors silicon and gallium arsenide in contact with pure metals

    NASA Technical Reports Server (NTRS)

    Mishina, H.; Buckley, D. H.

    1984-01-01

    Friction experiments were conducted for the semiconductors silicon and gallium arsenide in contact with pure metals. Polycrystalline titanium, tantalum, nickel, palladium, and platinum were made to contact a single crystal silicon (111) surface. Indium, nickel, copper, and silver were made to contact a single crystal gallium arsenide (100) surface. Sliding was conducted both in room air and in a vacuum of 10 to the minus 9th power torr. The friction of semiconductors in contact with metals depended on a Schottky barrier height formed at the metal semiconductor interface. Metals with a higher barrier height on semiconductors gave lower friction. The effect of the barrier height on friction behavior for argon sputtered cleaned surfaces in vacuum was more specific than that for the surfaces containing films in room air. With a silicon surface sliding on titanium, many silicon particles back transferred. In contrast, a large quantity of indium transferred to the gallium arsenide surface.

  15. Effect of gallium-arsenide laser, gallium-aluminum-arsenide laser and healing ointment on cutaneous wound healing in Wistar rats.

    PubMed

    Gonçalves, R V; Mezêncio, J M S; Benevides, G P; Matta, S L P; Neves, C A; Sarandy, M M; Vilela, E F

    2010-04-01

    This study determined the effects of gallium-aluminum-arsenide laser (GaAlAs), gallium-arsenide laser (GaAs) and Dersani healing ointment on skin wounds in Wistar rats. The parameters analyzed were: type I and III collagen fiber concentrations as well as the rate of wound closure. Five wounds, 12 mm in diameter, were made on the animals' backs. The depth of the surgical incision was controlled by removing the epithelial tissue until the dorsal muscular fascia was exposed. The animals were anesthetized with ketamine and xylazine via intraperitoneal injection. The rats were randomly divided into five groups of 6 animals each, according to the treatment received. Group 1 (L4): GaAs laser (4 J/cm(2)); group 2 (L30): GaAlAs laser (30 J/cm(2)); group 3 (L60): GaAlAs laser (60 J/cm(2)); group 4 (D): Dersani ointment; group 5 (control): 0.9% saline. The applications were made daily over a period of 20 days. Tissue fragments were stained with picrosirius to distinguish type I collagen from type III collagen. The collagen fibers were photo-documented and analyzed using the Quantum software based on the primary color spectrum (red, yellow and blue). Significant results for wound closing rate were obtained for group 1 (L4), 7.37 mm/day. The highest concentration of type III collagen fibers was observed in group 2 (L30; 37.80 + or - 7.10%), which differed from control (29.86 + or - 5.15%) on the 20th day of treatment. The type I collagen fibers of group 1 (L4; 2.67 + or - 2.23%) and group 2 (L30; 2.87 + or - 2.40%) differed significantly from control (1.77 + or - 2.97%) on the 20th day of the experiment.

  16. Thin film gallium arsenide solar cell research. Third quarterly project report, September 1, 1980-November 30, 1980. [Antireflection coating

    SciTech Connect

    Chu, S. S.

    1980-12-01

    The major objective of this contract is to produce gallium arsenide solar cells of 10% conversion efficiency in films of less than 10 micrometers thick which have been deposited by chemical vapor deposition on graphite or tungsten coated graphite substrates. Major efforts during this quarter were directed to: (1) the optimization of the deposition of gallium arsenide films of 10 ..mu..m thickness or less on tungsten/graphic substrates, (2) the investigation of the effectiveness of various grain boundary passivation techniques, (3) the deposition of tantalum pentoxide by ion beam sputtering as an antireflection coating, (4) the deposition of gallium aluminium arsenide by the organometallic process, and (5) the fabrication and characterization of large area Schottky barrier type solar cells from gallium arsenide films of about 10 ..mu..m thickness. Various grain boundary passivation techniques, such as the anodic oxidation, thermal oxidation, and ruthenium treatment, have been investigated. The combination of thermal oxidation and ruthenium treatment has been used to fabricate Schottky barrier type solar cells. Large area MOS solar cells of 9 cm/sup 2/ area with AMl efficiency of 8.5% have been fabricated from ruthenium treated gallium arsenide films of 10 ..mu..m thickness. The construction of the apparatus for the deposition of gallium aluminum arsenide by the organometallic process has been completed. The deposition of good quality tantalum pentoxide film as an antireflection coating has been carried out by the ion beam sputtering technique. The short-circuit current density and AMl efficiency of the solar cells are increased by approximately 60%, with a slight increase in the open-circuit voltage. Details are presented. (WHK)

  17. Terahertz emission from collapsing field domains during switching of a gallium arsenide bipolar transistor.

    PubMed

    Vainshtein, Sergey; Kostamovaara, Juha; Yuferev, Valentin; Knap, Wojciech; Fatimy, Abdel; Diakonova, Nina

    2007-10-26

    Broadband pulsed THz emission with peak power in the sub-mW range has been observed experimentally during avalanche switching in a gallium arsenide bipolar junction transistor at room temperature, while significantly higher total generated power is predicted in simulations. The emission is attributed to very fast oscillations in the conductivity current across the switching channels, which appear as a result of temporal evolution of the field domains generated in highly dense electron-hole plasma. This plasma is formed in turn by powerful impact ionization in multiple field domains of ultrahigh amplitude.

  18. Ultra-low power fiber-coupled gallium arsenide photonic crystal cavity electro-optic modulator.

    PubMed

    Shambat, Gary; Ellis, Bryan; Mayer, Marie A; Majumdar, Arka; Haller, Eugene E; Vučković, Jelena

    2011-04-11

    We demonstrate a gallium arsenide photonic crystal cavity injection-based electro-optic modulator coupled to a fiber taper waveguide. The fiber taper serves as a convenient and tunable waveguide for cavity coupling with minimal loss. Localized electrical injection of carriers into the cavity region via a laterally doped p-i-n diode combined with the small mode volume of the cavity enable ultra-low energy modulation at sub-fJ/bit levels. Speeds of up to 1 GHz are demonstrated with photoluminescence lifetime measurements revealing that the ultimate limit goes well into the tens of GHz.

  19. Gallium Arsenide Layers Grown by Molecular Beam Epitaxy on Single Crystalline Germanium Islands on Insulator

    NASA Astrophysics Data System (ADS)

    Takai, Mikio; Tanigawa, Takaho; Minamisono, Tadanori; Gamo, Kenji; Namba, Susumu

    1984-05-01

    Gallium arsenide (GaAs) layers have successfully been grown by molecular beam epitaxy on single crystalline germanium (Ge) islands, recrystallized by zone melting with SiO2 capping layers, on thermally-oxidized Si-wafers. The GaAs layers, grown on the single crystalline Ge islands, show smooth surfaces without any grain-boundaries, while those, grown on the Ge islands with grain-boundaries and on the SiO2, have grain-boundaries. The GaAs layers on the single crystalline Ge islands emit photoluminescence, the intensity of which is almost comparable to that of GaAs layers on bulk Ge crystals.

  20. On-orbit performance of LIPS gallium arsenide solar cell experiment

    NASA Technical Reports Server (NTRS)

    Bavaro, T.; Francis, R.; Pennell, M.

    1984-01-01

    Telemetry from the Living Plume Shield's gallium arsenide solar panel experiment was evaluated to determine degradation. The data were culled to preclude spurious results from possible shadowing or inaccurate measurements on a cold array. Two independent methods were then used to obtain the maximum power points and the various characteristics of the solar array. Fill factor, open circuit voltage, short circuit current, and series and shunt resistances were examined. The data analysis concluded that, to date, nearly all of the solar array degradation is due to the reduction in the short circuit current.

  1. Analytical and experimental procedures for determining propagation characteristics of millimeter-wave gallium arsenide microstrip lines

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R.

    1989-01-01

    In this report, a thorough analytical procedure is developed for evaluating the frequency-dependent loss characteristics and effective permittivity of microstrip lines. The technique is based on the measured reflection coefficient of microstrip resonator pairs. Experimental data, including quality factor Q, effective relative permittivity, and fringing for 50-omega lines on gallium arsenide (GaAs) from 26.5 to 40.0 GHz are presented. The effects of an imperfect open circuit, coupling losses, and loading of the resonant frequency are considered. A cosine-tapered ridge-guide text fixture is described. It was found to be well suited to the device characterization.

  2. DNA detection using plasmonic enhanced near-infrared photoluminescence of gallium arsenide.

    PubMed

    Tang, Longhua; Chun, Ik Su; Wang, Zidong; Li, Jinghong; Li, Xiuling; Lu, Yi

    2013-10-15

    Efficient near-infrared detection of specific DNA with single nucleotide polymorphism selectivity is important for diagnostics and biomedical research. Herein, we report the use of gallium arsenide (GaAs) as a sensing platform for probing DNA immobilization and targeting DNA hybridization, resulting in ∼8-fold enhanced GaAs photoluminescence (PL) at ∼875 nm. The new signal amplification strategy, further coupled with the plasmonic effect of Au nanoparticles, is capable of detecting DNA molecules with a detection limit of 0.8 pM and selectivity against single base mismatches. Such an ultrasensitive near-infrared sensor can find a wide range of biochemical and biomedical applications.

  3. Development of gallium arsenide high-speed, low-power serial parallel interface modules: Executive summary

    NASA Technical Reports Server (NTRS)

    1988-01-01

    Final report to NASA LeRC on the development of gallium arsenide (GaAS) high-speed, low power serial/parallel interface modules. The report discusses the development and test of a family of 16, 32 and 64 bit parallel to serial and serial to parallel integrated circuits using a self aligned gate MESFET technology developed at the Honeywell Sensors and Signal Processing Laboratory. Lab testing demonstrated 1.3 GHz clock rates at a power of 300 mW. This work was accomplished under contract number NAS3-24676.

  4. Formation of gallium arsenide nanostructures in Pyrex glass.

    PubMed

    Howlader, Matiar M R; Zhang, Fangfang; Deen, M Jamal

    2013-08-01

    In this paper, we report on a simple, low-cost process to grow GaAs nanostructures of a few nm diameter and ∼50 nm height in Pyrex glass wafers. These nanostructures were grown by sequential plasma activation of GaAs and Pyrex glass surfaces using a low-temperature hybrid plasma bonding technology in air. Raman analyses of the activated surfaces show gallium oxide and arsenic oxide, as well as suppressed non-bridging oxygen with aluminate and boroxol chains in glass. The flow of alkaline ions toward the cathode and the replacement of alkaline ions by Ga and As ions in glass result in the growth of GaAs nanostructures in nanopores/nanoscratches in glass. These nanopores/nanoscratches are believed to be the origin of the growth of the nanostructures. It was found that the length of the GaAs nanostructures may be controlled by an electrostatic force. Cross-sectional observation of the bonded interface using high-resolution transmission electron microscopy confirms the existence of the nanostructures. A possible application of the nanostructures in glass is a filtration system for biomolecules.

  5. Synthesis of gallium nitride nanostructures by nitridation of electrochemically deposited gallium oxide on silicon substrate

    PubMed Central

    2014-01-01

    Gallium nitride (GaN) nanostructures were successfully synthesized by the nitridation of the electrochemically deposited gallium oxide (Ga2O3) through the utilization of a so-called ammoniating process. Ga2O3 nanostructures were firstly deposited on Si substrate by a simple two-terminal electrochemical technique at a constant current density of 0.15 A/cm2 using a mixture of Ga2O3, HCl, NH4OH and H2O for 2 h. Then, the deposited Ga2O3 sample was ammoniated in a horizontal quartz tube single zone furnace at various ammoniating times and temperatures. The complete nitridation of Ga2O3 nanostructures at temperatures of 850°C and below was not observed even the ammoniating time was kept up to 45 min. After the ammoniating process at temperature of 900°C for 15 min, several prominent diffraction peaks correspond to hexagonal GaN (h-GaN) planes were detected, while no diffraction peak of Ga2O3 structure was detected, suggesting a complete transformation of Ga2O3 to GaN. Thus, temperature seems to be a key parameter in a nitridation process where the deoxidization rate of Ga2O3 to generate gaseous Ga2O increase with temperature. The growth mechanism for the transformation of Ga2O3 to GaN was proposed and discussed. It was found that a complete transformation can not be realized without a complete deoxidization of Ga2O3. A significant change of morphological structures takes place after a complete transformation of Ga2O3 to GaN where the original nanorod structures of Ga2O3 diminish, and a new nanowire-like GaN structures appear. These results show that the presented method seems to be promising in producing high-quality h-GaN nanostructures on Si. PMID:25593562

  6. Optimal power settings of aluminum gallium arsenide lasers in caries inhibition — An in vitro study

    PubMed Central

    Sharma, Sonali; Hegde, Mithra N; Sadananda, Vandana; Mathews, Blessen

    2016-01-01

    Context: Incipient carious lesions are characterized by subsurface dissolution due to more fluoride ions in the 50-100 microns of the tooth's outer surface. Aims: To determine an optimal power setting for 810 nm aluminum gallium arsenide laser for caries inhibition. Materials and Methods: Fifty-four caries-free extracted teeth were sectioned mesiodistally. The samples were divided into 18 groups for each power setting being evaluated. Each group had six samples. The laser used is 810 nm aluminum gallium arsenide laser with power setting from 0.1 watts to 5 watts. Laser fluorescence based device was used to evaluate the effect of irradiation. Statistical Analysis Used: Paired “t” test, one-way analysis of variance (ANOVA), Tukey's post hoc test, and the Pearson's correlation test. Results: The paired t-test showed that there is minimum divergence from the control for 3.5 watts. Tukey's post hoc test also showed statistically significantly results for 3.5 watts. The Pearson's correlation test showed that there was negative correlation between the watts and irradiation. Conclusions: The power setting that gave statistically significant results was 3.5 watts. PMID:27099427

  7. The metabolism of inorganic arsenic oxides, gallium arsenide, and arsine: a toxicochemical review.

    PubMed

    Carter, Dean E; Aposhian, H Vasken; Gandolfi, A Jay

    2003-12-15

    The aim of this review is to compare the metabolism, chemistry, and biological effects to determine if either of the industrial arsenicals (arsine and gallium arsenide) act like the environmental arsenic oxides (arsenite and arsenate). The metabolism of the arsenic oxides has been extensively investigated in the past 4 years and the differences between the arsenic metabolites in the oxidation states +III versus +V and with one or two methyl groups added have shown increased importance. The arsenic oxide metabolism has been compared with arsine (oxidation state -III) and arsenide (oxidation state between 0 to -III). The different metabolites appear to have different strengths of reaction for binding arsenic (III) to thiol groups, their oxidation-reduction reactions and their forming an arsenic-carbon bond. It is unclear if the differences in parameters such as the presence or absence of methyl metabolites, the rates of AsV reduction compared to the rates of AsIII oxidation, or the competition of phosphate and arsenate for cellular uptake are large enough to change biological effects. The arsine rate of decomposition, products of metabolism, target organ of toxic action, and protein binding appeared to support an oxidized arsenic metabolite. This arsine metabolite was very different from anything made by the arsenic oxides. The gallium arsenide had a lower solubility than any other arsenic compound and it had a disproportionate intensity of lung damage to suggest that the GaAs had a site of contact interaction and that oxidation reactions were important in its toxicity. The urinary metabolites after GaAs exposure were the same as excreted by arsenic oxides but the chemical compounds responsible for the toxic effects of GaAs are different from the arsenic oxides. The review concludes that there is insufficient evidence to equate the different arsenic compounds. There are several differences in the toxicity of the arsenic compounds that will require substantial

  8. The metabolism of inorganic arsenic oxides, gallium arsenide, and arsine: a toxicochemical review.

    PubMed

    Carter, Dean E; Aposhian, H Vasken; Gandolfi, A Jay

    2003-12-15

    The aim of this review is to compare the metabolism, chemistry, and biological effects to determine if either of the industrial arsenicals (arsine and gallium arsenide) act like the environmental arsenic oxides (arsenite and arsenate). The metabolism of the arsenic oxides has been extensively investigated in the past 4 years and the differences between the arsenic metabolites in the oxidation states +III versus +V and with one or two methyl groups added have shown increased importance. The arsenic oxide metabolism has been compared with arsine (oxidation state -III) and arsenide (oxidation state between 0 to -III). The different metabolites appear to have different strengths of reaction for binding arsenic (III) to thiol groups, their oxidation-reduction reactions and their forming an arsenic-carbon bond. It is unclear if the differences in parameters such as the presence or absence of methyl metabolites, the rates of AsV reduction compared to the rates of AsIII oxidation, or the competition of phosphate and arsenate for cellular uptake are large enough to change biological effects. The arsine rate of decomposition, products of metabolism, target organ of toxic action, and protein binding appeared to support an oxidized arsenic metabolite. This arsine metabolite was very different from anything made by the arsenic oxides. The gallium arsenide had a lower solubility than any other arsenic compound and it had a disproportionate intensity of lung damage to suggest that the GaAs had a site of contact interaction and that oxidation reactions were important in its toxicity. The urinary metabolites after GaAs exposure were the same as excreted by arsenic oxides but the chemical compounds responsible for the toxic effects of GaAs are different from the arsenic oxides. The review concludes that there is insufficient evidence to equate the different arsenic compounds. There are several differences in the toxicity of the arsenic compounds that will require substantial

  9. Molecular beam epitaxy growth and characterization of dysprosium phosphide and dysprosium arsenide in gallium arsenide and gallium phosphide

    NASA Astrophysics Data System (ADS)

    Lee, Paul Piyawong

    The ability to grow thermally stable Schottky/ohmic contacts and buried, epitaxial metallic or semimetallic layers on semiconductors has many potential applications in novel device structures. Many rare earth group-V compounds with the sodium chloride structure possess the properties that make them potential candidates for stable contacts, buried layers, and other applications. In this work, two novel rare earth compounds, namely dysprosium phosphide (DyP) and dysprosium arsenide (DyAs) have been studied for high temperature ohmic/Schottky contacts to III-V semiconductors as well as for buried metal layers in semiconductor/metal/semiconductor structures. DyP and DyAs have been grown by molecular beam epitaxy on GaAs and GaP substrates. Both DyP and DyAs display metallic behavior and have room temperature resistivities of 8 x 10--5 and 1 x 10--4 Ocm, respectively. The electron concentrations for DyP and DyAs are about 4 x 1020 and 1 x 1021 cm--3, respectively. High quality DyP films as determined by XRD, AFM, and TEM can be achieved at a wide range of substrate temperatures (500°C to 600°C) with excess phosphorus pressure. Unlike most rare earth-group V compounds, DyP films are stable in air with no sign of oxidation. DyP films deposited on n-type GaAs and GaP exhibit Schottky behavior with room temperature barrier heights of 0.83 and 0.90 eV, respectively, with ideality factors close to unity and low reverse bias leakage current densities. These contacts are stable up to 250°C and 350°C for GaAs and GaP, respectively. DyAs films on the other hand, oxidize in air and display weak Schottky behavior on n-type GaAs. DyP has been grown as buried layers in both GaAs/DyP/GaAs and GaAs/DyP/GaP structures. Although high quality DyP layers have been achieved, the GaAs overlayers contain defects such as twins. The poor wetting of GaAs on DyP and the crystal symmetry between the two materials are responsible for the three-dimensional growth and the defects found in the Ga

  10. Initial oxidation of gallium arsenide (001)-β2(2 x 4) surface using density functional theory.

    PubMed

    Kim, Dae-Hee; Kim, Dae-Hyun; Kim, Yeong-Cheol

    2014-10-01

    The initial oxidation of a gallium arsenide (001)-β2(2 x 4) surface with an oxygen molecule was investigated using density functional theory. The oxygen molecule was adsorbed on the surface without any energy barrier. The dissociation of the oxygen molecule on the first arsenic layer had two dissociation paths; the inter-dimer and intra-dimer. The inter-dimer dissociation was the dominant dissociation path based on the energy barriers. The two dissociated oxygen atoms preferred breaking the arsenic-gallium back-bond to form arsenic-oxygen-gallium bonds. Our results are in good agreement with literature of the scanning tunneling microscope study.

  11. Diffusion of ion-implanted group 4 n-type dopants in gallium arsenide and gallium/arsenide-based superlattices

    NASA Astrophysics Data System (ADS)

    Allen, Emily Lin

    1992-09-01

    As semiconductor device dimensions shrink, understanding and controlling dopant diffusion becomes increasingly important. For submicron FET's made in GaAs, dopant diffusion during post-implant anneal is undesirable. In addition, impurity induced intermixing of III-V heterostructures for optoelectronic devices requires a series of carefully controlled diffusion steps. A more complete understanding of the diffusion mechanisms of dopants and point defects in both GaAs and Al(x)Ga(1-x)As is thus required for several advanced technologies. Most of the published parameters for diffusion of dopants in III-V compound semiconductors are from thin film or vapor source diffusions. The effect of implant damage and extended defects on diffusion of implanted dopants in GaAs and Al(x)Ga(1-x)As has not been extensively studied. In this work we measure the carrier concentrations and diffusivities of the ion-implanted Group IV dopants Sn, Ge and Si in GaAs and Al(x)Ga(1-x)As, using SIMS, polaron and SUPREM 3.5 simulations. In the substrate, diffusion is modeled by an effective diffusivity which depends on the square of the electron concentration (n), due to enhancement of the negatively charged Ga vacancy concentration by the n-type doping. In the near-surface implanted region diffusion is suppressed for doses greater than 1 x 10(exp 14)/sq cm. The carrier concentrations for Sn implants are anomalously high in this region, and anomalously low for Ge and Si. Transmission electron microscopy shows that precipitates and dislocations form in the implanted region during annealing for doses greater than 1 x 10(exp 14)/sq cm. These extended defects may influence dopant diffusion by controlling the generation and recombination of point defects. The carrier concentration-dependent diffusion model is applied to interdiffusion of Al and Ga in AlAs/Al(x)Ga(1-x)As superlattice structures. We show that interdiffusion is enhanced more under an oxide film than under a nitride film, while a tungsten

  12. Gold/niobium thin film metallizations for gallium arsenide devices and circuits

    NASA Astrophysics Data System (ADS)

    Esser, Robert Henry

    As the information age opens, the demand for high performance electronics is increasing exponentially. High-speed communications devices and equipment are at the heart of this expansion. Gallium arsenide field effect transistors are the building blocks for those devices. GaAs FETs provide operation at speeds more than six times that of conventional silicon devices. There is a need to develop and expand the materials knowledge base in all aspects to the fabrication of III/V semiconductors. Of particular interest is developing a metallization for gallium arsenide circuits and devices that will provide a high quality diffusion barrier. The metallization must provide adhesion to the GaAs surface. It must be thermally and chemically stable. It must be compatible with the other materials encountered in semiconductor processing and packaging. A niobium/gold thin film system for first level metallization on GaAs is proposed and examined. Niobium displays good adhesion to other semiconductor substrates such as Si, SiO2, and diamond. It is corrosion resistant. Niobium has the third lowest resistance of the refractory metals. Finally, the melting point of TM = 2467°C suggests that niobium will have high temperature stability and low interdiffusion coefficients. The kinetics of Nb/Au thin films was examined using sheet resistance measurements, X-Ray diffraction and Auger Electron Spectroscopy depth profiling techniques. The data is analyzed using the Matano method and a technique proposed by Zhang and Wong to take into account the fort-nation of an intermediate intermetallic phase. The relevant diffusion coefficients for two kinetics regimes are presented. Finally, niobium/gold was used as a Schottky contact on GaAs and subjected to an anneal study. It was found that the series resistance of Schottky diodes decreased with a 1 hour anneal at 250°C to 12.5O, and remained stable for temperatures of 250°C for 672 hours. It was found that the series resistance degraded

  13. Cost Trade Between Multi-Junction, Gallium Arsenide, and Silicon Solar Cells

    NASA Technical Reports Server (NTRS)

    Gaddy, Edward M.

    1995-01-01

    Multi-junction (MJ), gallium arsenide (GaAs), and silicon (Si) solar cells have respective test efficiencies of approximately 24%, 18.5% and 14.8%. Multi-junction and gallium arsenide solar cells weigh more than silicon solar 2 cells and cost approximately five times as much per unit power at the cell level. A trade is performed for the TRMM spacecraft to determine which of these cell types would have offered an overall performance and price advantage to the spacecraft. A trade is also performed for the multi-junction cells under the assumption that they will cost over ten times that of silicon cells at the cell level. The trade shows that the TRMM project, less the cost of the instrument, ground systems and mission operations, would spend approximately $552,000 dollars per kilogram to launch and suppon3science in the case of the spacecraft equipped with silicon solar cells. If these cells are changed out for gallium arsenide solar cells, an additional 31 kilograms of science can be launched and serviced at a price of approximately $90 thousand per kilogram. The weight reduction is shown to derive from the smaller area of the array and hence reductions in the weight of the array substrate and supporting structure. ff the silicon solar cells are changed out for multi-junction solar cells, an additional 45 kilograms of science above the silicon base line can be launched and supported at a price of approximately $58,000 per kilogram. The trade shows that even if the multi-junction cells are priced over ten times that of silicon cells, a price that is much higher than projected, that the additional 45 kilograms of science are launched and serviced at $180,000 per kilogram. This is still much less than the original $552,000 per kilogram to launch and service the science. Data and qualitative factors are presented to show that these figures are subject to a great deal of uncertainty. Nonetheless, the benefit of the higher efficiency solar cells for TRMM is far greater

  14. Straw man trade between multi-junction, gallium arsenide, and silicon solar cells

    NASA Technical Reports Server (NTRS)

    Gaddy, Edward M.

    1995-01-01

    Multi-junction (MJ), gallium arsenide (GaAs), and silicon (Si) solar cells have respective test efficiencies of approximately 24%, 18.5% and 14.8%. Multi-junction and gallium arsenide solar cells weigh more than silicon solar cells and cost approximately five times as much per unit power at the cell level. A straw man trade is performed for the TRMM spacecraft to determine which of these cell types would have offered an overall performance and price advantage to the spacecraft. A straw man trade is also performed for the multi-junction cells under the assumption that they will cost over ten times that of silicon cells at the cell level. The trade shows that the TRMM project, less the cost of the instrument, ground systems and mission operations, would spend approximately $552 thousand dollars per kilogram to launch and service science in the case of the spacecraft equipped with silicon solar cells. If these cells are changed out for gallium arsenide solar cells, an additional 31 kilograms of science can be launched and serviced at a price of approximately $90 thousand per kilogram. The weight reduction is shown to derive from the smaller area of the array and hence reductions in the weight of the array substrate and supporting structure. If the silicon solar cells are changed out for multi-junction solar cells, an additional 45 kilograms of science above the silicon base line can be launched and serviced at a price of approximately $58 thousand per kilogram. The trade shows that even if the multi-junction arrays are priced over ten times that of silicon cells, a price that is much higher than projected, that the additional 45 kilograms of science are launched and serviced at $182 thousand per kilogram. This is still much less than original $552 thousand per kilogram to launch and service the science. Data and qualitative factors are presented to show that these figures are subject to a great deal of uncertainty. Nonetheless, the benefit of the higher efficiency

  15. Straw man trade between multi-junction, gallium arsenide, and silicon solar cells

    SciTech Connect

    Gaddy, E.M.

    1995-10-01

    Multi-junction (MJ), gallium arsenide (GaAs), and silicon (Si) solar cells have respective test efficiencies of approximately 24%, 18.5% and 14.8%. Multi-junction and gallium arsenide solar cells weigh more than silicon solar cells and cost approximately five times as much per unit power at the cell level. A straw man trade is performed for the TRMM spacecraft to determine which of these cell types would have offered an overall performance and price advantage to the spacecraft. A straw man trade is also performed for the multi-junction cells under the assumption that they will cost over ten times that of silicon cells at the cell level. The trade shows that the TRMM project, less the cost of the instrument, ground systems and mission operations, would spend approximately $552 thousand dollars per kilogram to launch and service science in the case of the spacecraft equipped with silicon solar cells. If these cells are changed out for gallium arsenide solar cells, an additional 31 kilograms of science can be launched and serviced at a price of approximately $90 thousand per kilogram. The weight reduction is shown to derive from the smaller area of the array and hence reductions in the weight of the array substrate and supporting structure. If the silicon solar cells are changed out for multi-junction solar cells, an additional 45 kilograms of science above the silicon base line can be launched and serviced at a price of approximately $58 thousand per kilogram. The trade shows that even if the multi-junction arrays are priced over ten times that of silicon cells, a price that is much higher than projected, that the additional 45 kilograms of science are launched and serviced at $182 thousand per kilogram. This is still much less than original $552 thousand per kilogram to launch and service the science. Data and qualitative factors are presented to show that these figures are subject to a great deal of uncertainty.

  16. Characterization of solar cells for space applications. Volume 13: Electrical characteristics of Hughes LPE gallium arsenide solar cells as a function of intensity and temperature

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.; Beckert, D. M.; Downing, R. G.; Miyahira, T. F.; Weiss, R. S.

    1980-01-01

    Electrical characteristics of Hughes Liquid phase epitaxy, P/N gallium aluminum arsenide solar cells are presented in graphical and tabular format as a function of solar illumination intensity and temperature.

  17. Gallium arsenide quantum well-based far infrared array radiometric imager

    NASA Technical Reports Server (NTRS)

    Forrest, Kathrine A.; Jhabvala, Murzy D.

    1991-01-01

    We have built an array-based camera (FIRARI) for thermal imaging (lambda = 8 to 12 microns). FIRARI uses a square format 128 by 128 element array of aluminum gallium arsenide quantum well detectors that are indium bump bonded to a high capacity silicon multiplexer. The quantum well detectors offer good responsivity along with high response and noise uniformity, resulting in excellent thermal images without compensation for variation in pixel response. A noise equivalent temperature difference of 0.02 K at a scene temperature of 290 K was achieved with the array operating at 60 K. FIRARI demonstrated that AlGaAS quantum well detector technology can provide large format arrays with performance superior to mercury cadmium telluride at far less cost.

  18. Induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures.

    PubMed

    Wan, Zhong; Kazakov, Aleksandr; Manfra, Michael J; Pfeiffer, Loren N; West, Ken W; Rokhinson, Leonid P

    2015-06-11

    Search for Majorana fermions renewed interest in semiconductor-superconductor interfaces, while a quest for higher-order non-Abelian excitations demands formation of superconducting contacts to materials with fractionalized excitations, such as a two-dimensional electron gas in a fractional quantum Hall regime. Here we report induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures and development of highly transparent semiconductor-superconductor ohmic contacts. Supercurrent with characteristic temperature dependence of a ballistic junction has been observed across 0.6 μm, a regime previously achieved only in point contacts but essential to the formation of well separated non-Abelian states. High critical fields (>16 T) in NbN contacts enables investigation of an interplay between superconductivity and strongly correlated states in a two-dimensional electron gas at high magnetic fields.

  19. Bowtie nanoantenna integrated with indium gallium arsenide antimonide for uncooled infrared detector with enhanced sensitivity.

    PubMed

    Choi, Sangjo; Sarabandi, Kamal

    2013-12-10

    A novel high-impedance nanoantenna with an embedded matching network is implemented to realize a highly sensitive infrared detector. A bowtie antenna is operated at its antiparallel resonance and loaded with a small low-bandgap (E(g)=0.52  eV) indium gallium arsenide antimonide (InGaAsSb) p-n junction. The structure is optimized for maximum power transfer and significant field enhancement at its terminals for a desired frequency band where the maximum quantum efficiency of InGaAsSb is observed. The sensitivity improvement of the proposed detector is evaluated against the traditional bulk detector and it is shown that the detectivity is improved by the field enhancement factor, which is approximately 20 for the case considered here.

  20. Development of a dome Fresnel lens/gallium arsenide photovoltaic concentrator for space applications

    NASA Technical Reports Server (NTRS)

    O'Neill, Mark J.; Piszczor, Michael F.

    1987-01-01

    A novel photovoltaic concentrator system is currently being developed. Phase I of the program, completed in late 1986, produced a conceptual design for the concentrator system, including an array weight and performance estimates based on optical, electrical, and thermal analyses. Phase II of the program, just underway, concerns the fabrication and testing of prototype concentrator panels of the design. The concentrator system uses dome Fresnel lenses for optical concentration; gallium arsenide concentrator cells for power generation; prismatic cell covers to eliminate gridline obscuration losses; a backplane radiator for heat rejection; and a honeycomb structure for the deployable panel assembly. The conceptual design of the system, its anticipated performance, and its estimated weight are reported.

  1. Alloy broadening of the emission barrier of the DX center in aluminum gallium arsenide

    NASA Astrophysics Data System (ADS)

    Subramanian, S.; Anand, S.; Chakravarty, S.; Arora, B. M.

    1989-01-01

    The effect of alloy fluctuations on the emission barrier of the DX center in aluminum gallium arsenide (AlGaAs) is studied by constant capacitance deep level transient spectroscopy using Si-doped and Sn-doped samples grown by different growth techniques. All the samples showed single broadened peaks which were analyzed by assuming a Gaussian distribution for the emission barrier. The full width at half maximum for the emission barrier spread was found to be the same (˜0.05+0.005 eV) for all the samples and is of the same order as the reported capture barrier spread for Si-doped AlGaAs, which strongly suggests that the binding energy spread of the DX center in AlGaAs is very small.

  2. Advances in gallium arsenide monolithic microwave integrated-circuit technology for space communications systems

    NASA Technical Reports Server (NTRS)

    Bhasin, K. B.; Connolly, D. J.

    1986-01-01

    Future communications satellites are likely to use gallium arsenide (GaAs) monolithic microwave integrated-circuit (MMIC) technology in most, if not all, communications payload subsystems. Multiple-scanning-beam antenna systems are expected to use GaAs MMIC's to increase functional capability, to reduce volume, weight, and cost, and to greatly improve system reliability. RF and IF matrix switch technology based on GaAs MMIC's is also being developed for these reasons. MMIC technology, including gigabit-rate GaAs digital integrated circuits, offers substantial advantages in power consumption and weight over silicon technologies for high-throughput, on-board baseband processor systems. In this paper, current developments in GaAs MMIC technology are described, and the status and prospects of the technology are assessed.

  3. A I-V analysis of irradiated Gallium Arsenide solar cells

    NASA Technical Reports Server (NTRS)

    Heulenberg, A.; Maurer, R. H.; Kinnison, J. D.

    1991-01-01

    A computer program was used to analyze the illuminated I-V characteristics of four sets of gallium arsenide (GaAs) solar cells irradiated with 1-MeV electrons and 10-MeV protons. It was concluded that junction regions (J sub r) dominate nearly all GaAs cells tested, except for irradiated Mitsubishi cells, which appear to have a different doping profile. Irradiation maintains or increases the dominance by J sub r. Proton irradiation increases J sub r more than does electron irradiation. The U.S. cells were optimized for beginning of life (BOL) and the Japanese for end of life (EOL). I-V analysis indicates ways of improving both the BOL and EOL performance of GaAs solar cells.

  4. Commercial and industrial applications of indium gallium arsenide near-infrared focal plane arrays

    NASA Astrophysics Data System (ADS)

    Cohen, Marshall J.; Ettenberg, Martin H.; Lange, Michael J.; Olsen, Gregory H.

    1999-07-01

    Sensors Unlimited, Inc. has developed focal pane arrays (FPAs) fabricated with indium gallium arsenide (InGaAs) photodiode arrays and silicon CMOS readout integrated circuits. These devices are readily available in a wide variety of formats suitable for commercial and industrial applications. InGaAs FPAs are sensitive to the near IR, operate without cooling, and come in both 2D formats and 1D formats. 1D InGaAs FPAs are used as both spectroscopic detectors and line scan imagers. Key applications include miniature spectrometers used for wavelength control and monitoring of WDM laser sources, octane determination, the sorting o plastics during recycling, and web process control. 2D InGaAs FPAs find use in applications such as laser beam profiling, visualization of 'clear' ice on aircraft and roadways, and industrial thermal imaging.

  5. Structure and electrical characterization of gallium arsenide nanowires with different V/III ratio growth parameters

    SciTech Connect

    Muhammad, R.; Ahamad, R.; Ibrahim, Z.; Othaman, Z.

    2014-03-05

    Gallium arsenide (GaAs) nanowires were grown vertically on GaAs(111)B substrate by gold-assisted using metal-organic chemical vapour deposition. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and conductivity atomic force microscopy (CAFM) analysis were carried out to investigate the effects of V/III ratio on structural properties and current-voltage changes in the wires. Results show that GaAs NWs grow preferably in the wurtzite crystal structure than zinc blende crystal structure with increasing V/III ratio. Additionally, CAFM studies have revealed that zincblende nanowires indicate ohmic characteristic compared to oscillation current occurred for wurtzite structures. The GaAs NWs with high quality structures are needed in solar cells technology for trapping energy that directly converts of sunlight into electricity with maximum capacity.

  6. Development of ultrathin silicon and gallium arsenide solar cell for space application

    SciTech Connect

    Shimodaira, M.; Matsuda, S.

    1983-10-01

    The ultrathin silicon (Si) solar cell and gallium arsenide (Ga As) solar cell for increasing radiation resistance and improving power to mass ratio and improving high energy conversion efficiency, have been developed from 1982. NASDA has almost completed fundemental evaluation of these solar cells and their prospects for space applications. The ultrathin 50..mu..m Si solar cell with maximum efficiency 13.9% (average 13.2%) at Air Mass Zero (AM0) (135.3mW/cm/sup 2/ illumination and at 28/sup 0/C) and the remaining 1sc ratio of 82% after irradiation of 1MeV electron fluences of 1 x 10/sup 15/ e/cm/sup 2/ have been demonstrated.

  7. Morphology dependence of interfacial oxidation states of gallium arsenide under near ambient conditions

    SciTech Connect

    Zhang, Xueqiang; Lamere, Edward; Ptasinska, Sylwia; Liu, Xinyu; Furdyna, Jacek K.

    2014-05-05

    The manipulation of semiconductor surfaces by tuning their electronic properties and surface chemistry is an essential ingredient for key applications in areas such as electronics, sensors, and photovoltaic devices. Here, in-situ surface reactions on gallium arsenide (GaAs) are monitored for two morphologies: a simple planar crystalline surface with (100) orientation and an ensemble of GaAs nanowires, both exposed to oxygen environment. A variety of oxide surface species, with a significant enhancement in oxidation states in the case of nanowires, are detected via near ambient pressure X-ray photoelectron spectroscopy. This enhancement in oxidation of GaAs nanowires is due to their higher surface area and the existence of more active sites for O{sub 2} dissociation.

  8. Induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures

    PubMed Central

    Wan, Zhong; Kazakov, Aleksandr; Manfra, Michael J.; Pfeiffer, Loren N.; West, Ken W.; Rokhinson, Leonid P.

    2015-01-01

    Search for Majorana fermions renewed interest in semiconductor–superconductor interfaces, while a quest for higher-order non-Abelian excitations demands formation of superconducting contacts to materials with fractionalized excitations, such as a two-dimensional electron gas in a fractional quantum Hall regime. Here we report induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures and development of highly transparent semiconductor–superconductor ohmic contacts. Supercurrent with characteristic temperature dependence of a ballistic junction has been observed across 0.6 μm, a regime previously achieved only in point contacts but essential to the formation of well separated non-Abelian states. High critical fields (>16 T) in NbN contacts enables investigation of an interplay between superconductivity and strongly correlated states in a two-dimensional electron gas at high magnetic fields. PMID:26067452

  9. Outdoor Performance of a Thin-Film Gallium-Arsenide Photovoltaic Module

    SciTech Connect

    Silverman, T. J.; Deceglie, M. G.; Marion, B.; Cowley, S.; Kayes, B.; Kurtz, S.

    2013-06-01

    We deployed a 855 cm2 thin-film, single-junction gallium arsenide (GaAs) photovoltaic (PV) module outdoors. Due to its fundamentally different cell technology compared to silicon (Si), the module responds differently to outdoor conditions. On average during the test, the GaAs module produced more power when its temperature was higher. We show that its maximum-power temperature coefficient, while actually negative, is several times smaller in magnitude than that of a Si module used for comparison. The positive correlation of power with temperature in GaAs is due to temperature-correlated changes in the incident spectrum. We show that a simple correction based on precipitable water vapor (PWV) brings the photocurrent temperature coefficient into agreement with that measured by other methods and predicted by theory. The low operating temperature and small temperature coefficient of GaAs give it an energy production advantage in warm weather.

  10. Gallium arsenide

    SciTech Connect

    Blakemore, J.S.

    1987-01-01

    The characteristics and applications of GaAs are discussed in a collection of previously published papers from the period 1961-1985. Topics addressed include mechanical and thermal properties, dielectric and optical properties, crystalline-GaAs bands and gaps, GaAs surfaces, carrier transport and energy loss, impurity and defect phenomena, and recombination processes. Diagrams, graphs, and tables of numerical data are provided.

  11. Ultra-low threshold gallium nitride photonic crystal nanobeam laser

    SciTech Connect

    Niu, Nan Woolf, Alexander; Wang, Danqing; Hu, Evelyn L.; Zhu, Tongtong; Oliver, Rachel A.; Quan, Qimin

    2015-06-08

    We report exceptionally low thresholds (9.1 μJ/cm{sup 2}) for room temperature lasing at ∼450 nm in optically pumped Gallium Nitride (GaN) nanobeam cavity structures. The nanobeam cavity geometry provides high theoretical Q (>100 000) with small modal volume, leading to a high spontaneous emission factor, β = 0.94. The active layer materials are Indium Gallium Nitride (InGaN) fragmented quantum wells (fQWs), a critical factor in achieving the low thresholds, which are an order-of-magnitude lower than obtainable with continuous QW active layers. We suggest that the extra confinement of photo-generated carriers for fQWs (compared to QWs) is responsible for the excellent performance.

  12. Neutron detection using boron gallium nitride semiconductor material

    SciTech Connect

    Atsumi, Katsuhiro; Inoue, Yoku; Nakano, Takayuki; Mimura, Hidenori; Aoki, Toru

    2014-03-01

    In this study, we developed a new neutron-detection device using a boron gallium nitride (BGaN) semiconductor in which the B atom acts as a neutron converter. BGaN and gallium nitride (GaN) samples were grown by metal organic vapor phase epitaxy, and their radiation detection properties were evaluated. GaN exhibited good sensitivity to α-rays but poor sensitivity to γ-rays. Moreover, we confirmed that electrons were generated in the depletion layer under neutron irradiation. This resulted in a neutron-detection signal after α-rays were generated by the capture of neutrons by the B atoms. These results prove that BGaN is useful as a neutron-detecting semiconductor material.

  13. Aqueous stability of Ga- and N-polar gallium nitride.

    PubMed

    Foster, Corey M; Collazo, Ramon; Sitar, Zlatko; Ivanisevic, Albena

    2013-01-01

    The stability of III-nitride semiconductors in various solutions becomes important as researchers begin to integrate them into sensing platforms. This study quantitatively compares the stability of GaN surfaces with different polarities. This type of quantification is important because it represents the first step toward designing semiconductor material interfaces compatible with solution conditions. A stability study of Ga- and N-polar GaN was conducted by immersion of the surfaces in deionized H(2)O, pH 5, pH 9, and H(2)O(2) solutions for 7 days. Inductively coupled plasma mass spectrometry of the solutions was conducted to determine the amount of gallium leached from the surface. X-ray photoelectron spectroscopy and atomic force microscopy were used to compare the treated surfaces to untreated surfaces. The results show that both gallium nitride surface types exhibit the greatest stability in acidic and neutral solutions. Gallium polar surfaces were found to exhibit superior stability to nitrogen polar surfaces in the solutions studied. Our findings highlight the need for further research on surface passivation and functionalization techniques for polar III-nitride semiconductors.

  14. In vitro toxicity of gallium arsenide in alveolar macrophages evaluated by magnetometry, cytochemistry and morphology.

    PubMed

    Okada, M; Karube, H; Niitsuya, M; Aizawa, Y; Okayasu, I; Kotani, M

    1999-12-01

    Gallium arsenide (GaAs), a chemical compound of gallium and arsenic, causes various toxic effects including pulmonary diseases in animals. Since the toxicity is not completely investigated, GaAs has been used in workplaces as the material of various semiconductor products. The present study was conducted to clarify the toxicity of GaAs particles in the alveolar macrophages of hamsters using magnetometry, enzyme release assays and morphological examinations. Alveolar macrophages obtained from hamsters by tracheobronchial lavage and adhered to the disks in the bottom of wells were exposed to ferrosoferric oxide and GaAs particles. Ferrosoferric oxide particles were magnetized externally and the remanent magnetic field was measured. Relaxation, a fast decline of the remanent magnetic fields radiated from the alveolar macrophages, was delayed and decay constants were decreased dose-dependently due to exposure to GaAs. Because the relaxation is thought to be associated with cytoskeleton, the exposure of GaAs may have impaired the motor function of them. Enzyme release assay and morphological findings indicated the damage to the macrophages. Thus the cytotoxicity causes cytostructural changes and cell death. According to DNA electrophoresis and the TUNEL method, necrotic changes occur more frequently than apoptotic changes.

  15. In vitro toxicity of gallium arsenide in alveolar macrophages evaluated by magnetometry, cytochemistry and morphology.

    PubMed

    Okada, M; Karube, H; Niitsuya, M; Aizawa, Y; Okayasu, I; Kotani, M

    1999-12-01

    Gallium arsenide (GaAs), a chemical compound of gallium and arsenic, causes various toxic effects including pulmonary diseases in animals. Since the toxicity is not completely investigated, GaAs has been used in workplaces as the material of various semiconductor products. The present study was conducted to clarify the toxicity of GaAs particles in the alveolar macrophages of hamsters using magnetometry, enzyme release assays and morphological examinations. Alveolar macrophages obtained from hamsters by tracheobronchial lavage and adhered to the disks in the bottom of wells were exposed to ferrosoferric oxide and GaAs particles. Ferrosoferric oxide particles were magnetized externally and the remanent magnetic field was measured. Relaxation, a fast decline of the remanent magnetic fields radiated from the alveolar macrophages, was delayed and decay constants were decreased dose-dependently due to exposure to GaAs. Because the relaxation is thought to be associated with cytoskeleton, the exposure of GaAs may have impaired the motor function of them. Enzyme release assay and morphological findings indicated the damage to the macrophages. Thus the cytotoxicity causes cytostructural changes and cell death. According to DNA electrophoresis and the TUNEL method, necrotic changes occur more frequently than apoptotic changes. PMID:10739163

  16. Zone recrystallization of gallium arsenide with discrete zones in a temperature gradient

    SciTech Connect

    Efremova, N.P.; Popov, V.P.

    1987-07-01

    A laboratory procedure for zone recrystallization with a temperature gradient is developed for gallium arsenide, using discrete zones, which permit linear and point zones 20-200 /sup +/m in diameter to move stably in the temperature range 820-1050/sup 0/C. The dependences of the rate of movement of the discrete zones on their thickness and temperatures are determined, which are explained by theories for systems with volatile components. The dislocation density in the recrystallized regions is not higher than in the substrate. Current-voltage characteristics of the p-n junctions, formed on the boundary of the channels with the starting materials, have high parameters. A gallium zone enables purifying the material effectively from tin (by 2-3 orders of magnitude) and to create structures which have the Gunn effect. Doping with silicon from a linear zone gives rise to the possibility of forming multilayer structures due to poorly defined dependence of the inversion temperature of the conductivity type on the crystal orientation of the growing surface.

  17. Size and environment dependence of surface phonon modes of gallium arsenide nanowires as measured by Raman spectroscopy.

    PubMed

    Spirkoska, D; Abstreiter, G; Fontcuberta I Morral, A

    2008-10-29

    Gallium arsenide nanowires were synthesized by gallium-assisted molecular beam epitaxy. By varying the growth time, nanowires with diameters ranging from 30 to 160 nm were obtained. Raman spectra of the nanowire ensembles were measured. The small linewidth of the optical phonon modes agree with an excellent crystalline quality. A surface phonon mode was also revealed, as a shoulder at lower frequencies of the longitudinal optical mode. In agreement with the theory, the surface mode shifts to lower wavenumbers when the diameter of the nanowires is decreased or the environment dielectric constant increased.

  18. Determination of the position of the. pi. -. nu. -junction in epitaxial structures of gallium arsenide doped with iron

    SciTech Connect

    Chernov, N.A.; Asanov, O.M.; Bakin, N.N.; Vilisova, M.D.

    1984-05-01

    An investigation of the distribution of the electrolyte-semiconductor capacitance barrier over the thickness of epitaxial layers of gallium arsenide doped with iron on a low-resistance substrate is described. It is shown that measurements of the barrier capacitance at low frequencies enables the position of the ..pi..-..nu..-junction, formed at the boundary of separation of the epitaxial layer and the substrate, to be accurately determined.

  19. Oral co-administration of α-lipoic acid, quercetin and captopril prevents gallium arsenide toxicity in rats.

    PubMed

    Bhatt, Kapil; Flora, S J S

    2009-07-01

    Gallium arsenide (GaAs), an inter-metallic semiconductor, known to exhibit superior optical and electronic properties compared to silicon, promotes its use in semiconductor industries. Extensive use of GaAs will inevitably lead to an increase in the exposure of workers manufacturing these products. Antioxidants are exogenous or endogenous compounds acting in several ways, including scavenging reactive oxygen species (ROS) or their precursors, inhibiting ROS formation, and binding metal ions needed for the catalysis of ROS generation. In the present study we investigated the protective efficacy of α-lipoic acid, quercetin and captopril individually against gallium arsenide exposure. Co-administration of α-lipoic acid with GaAs was most effective in reducing GaAs induced inhibition of blood δ-aminolevulinic acid dehydratase (ALAD) activity, liver, kidney and brain reduced glutathione (GSH) level and elevation of oxidized glutathione (GSSG). Captopril, on the other hand was effective in reducing thiobarbituric acid reactive substance (TBARS) levels, while quercetin reduced ROS in liver and kidney. The results suggest comparatively better preventive efficacy of concomitant α-lipoic acid administration during Gallium arsenide exposure compared to quercetin and captopril in preventing GaAs induced oxidative stress.

  20. Alternative substrates for gallium nitride epitaxy and devices: Laterally overgrown gallium nitride and silicon(111)

    NASA Astrophysics Data System (ADS)

    Marchand, Hugues

    Gallium nitride films grown on sapphire or silicon carbide using the conventional 'two-step' technique typically exhibit threading dislocations on the order of ˜109 cm-2, which are detrimental to device performance. In addition, sapphire and silicon carbide substrates are expensive and available only in limited size (2-3 inch diameter). This work addresses both issues by evaluating the properties of GaN films synthesized by lateral epitaxial overgrowth (LEO) and conventional growth on sapphire and Si(111) substrates. LEO consists of partially masking a previously-grown seed layer and performing a subsequent regrowth such that the regrown features extend over the masked areas. Under favorable conditions the threading dislocations originating from the seed material are blocked by the mask material or redirected by the growing facets. In this work dislocation densities as low as ˜106 cm-2 were observed in the laterally-overgrown areas. The overgrown features exhibited well-defined facets ((0001), {11¯01}, {112¯0}, {112¯1}, {112¯2}), the persistence of which depended on the orientation of the mask as well as on the growth conditions. The relationship between the morphology of the LEO stripes and the growth conditions (temperature, pressure, ammonia and trimethylgallium partial pressures) was characterized for LEO on GaN/sapphire substrates. A qualitative model of the growth mechanisms was presented based on the microscopic structure of the growing surfaces. Microstructural characterization revealed a crystallographic tilt between the seed and the LEO region, which resulted in the formation of dislocations above the mask edge and at the junction plane of adjacent stripes. GaN stripes laterally overgrown on AlN/Si(111) exhibited similar properties. However, chemical interactions between the substrate and the precursors caused morphological degradation, which could be avoided by using a thick (≥180 nm) AlN buffer layer. In addition, thermal expansion mismatch

  1. Visible light metasurfaces based on gallium nitride high contrast gratings

    NASA Astrophysics Data System (ADS)

    Wang, Zhenhai; He, Shumin; Liu, Qifa; Wang, Wei

    2016-05-01

    We propose visible-light metasurfaces (VLMs) capable of serving as lens and beam deflecting element based on gallium nitride (GaN) high contrast gratings (HCGs). By precisely manipulating the wavefront of the transmitted light, we theoretically demonstrate an HCG focusing lens with transmissivity of 86.3%, and a VLM with beam deflection angle of 6.09° and transmissivity as high as 91.4%. The proposed all-dielectric metasurfaces are promising for GaN-based visible light-emitting diodes (LEDs), which would be robust and versatile for controlling the output light propagation and polarization, as well as enhancing the extraction efficiency of the LEDs.

  2. Pulmonary clearance and toxicity of respirable gallium arsenide particulates intratracheally instilled into rats

    SciTech Connect

    Webb, D.R.; Wilson, S.E.; Carter, D.E.

    1987-07-01

    Gallium arsenide (GaAs) is an intermetallic compound that is recognized as a potential toxicological risk to workers occupationally exposed to its dust. Previous results have shown that rats intratracheally instilled with a fraction of GaAs particulates, characterized with a mean count diameter of 8.30 ..mu..m and a mean volume diameter of 12.67 ..mu..m, developed signs of systemic arsenic intoxication, pulmonary inflammation, and pneumocyte hyperplasia. The results of the present study confirm these findings and also show that a significantly smaller fraction of GaAs is a relatively more severe pneumotoxicant. Decreasing the particle mean count and mean volume diameter to 1.63 ..mu..m and 5.82 ..mu..m, respectively, increased in vivo dissolution rate of GaAs, increased the severity of pulmonary lesions previously associated with GaAs exposure, and resulted in unique pathological sequalae in affected lung tissue. Pulmonary fibrosis, as indicated by analysis of lung 4-hydroxyproline content, was not considered statistically significant although histological examination of lung tissue revealed a mild fibrotic response. These results provide additional evidence that pulmonary exposure to respirable GaAs particulates is a potential health hazard in the semiconductor industry.

  3. Arsenic moiety in gallium arsenide is responsible for neuronal apoptosis and behavioral alterations in rats

    SciTech Connect

    Flora, Swaran J.S. Bhatt, Kapil; Mehta, Ashish

    2009-10-15

    Gallium arsenide (GaAs), an intermetallic semiconductor finds widespread applications in high frequency microwave and millimeter wave, and ultra fast supercomputers. Extensive use of GaAs has led to increased exposure to humans working in semiconductor industry. GaAs has the ability to dissociate into its constitutive moieties at physiological pH and might be responsible for the oxidative stress. The present study was aimed at evaluating, the principle moiety (Ga or As) in GaAs to cause neurological dysfunction based on its ability to cause apoptosis, in vivo and in vitro and if this neuronal dysfunction translated to neurobehavioral changes in chronically exposed rats. Result indicated that arsenic moiety in GaAs was mainly responsible for causing oxidative stress via increased reactive oxygen species (ROS) and nitric oxide (NO) generation, both in vitro and in vivo. Increased ROS further caused apoptosis via mitochondrial driven pathway. Effects of oxidative stress were also confirmed based on alterations in antioxidant enzymes, GPx, GST and SOD in rat brain. We noted that ROS induced oxidative stress caused changes in the brain neurotransmitter levels, Acetylcholinesterase and nitric oxide synthase, leading to loss of memory and learning in rats. The study demonstrates for the first time that the slow release of arsenic moiety from GaAs is mainly responsible for oxidative stress induced apoptosis in neuronal cells causing behavioral changes.

  4. Structural anomalies in undoped Gallium Arsenide observed in high resolution diffraction imaging with monochromatic synchrotron radiation

    NASA Technical Reports Server (NTRS)

    Steiner, B.; Kuriyama, M.; Dobbyn, R. C.; Laor, U.; Larson, D.; Brown, M.

    1988-01-01

    Novel, streak-like disruption features restricted to the plane of diffraction have recently been observed in images obtained by synchrotron radiation diffraction from undoped, semi-insulating gallium arsenide crystals. These features were identified as ensembles of very thin platelets or interfaces lying in (110) planes, and a structural model consisting of antiphase domain boundaries was proposed. We report here the other principal features observed in high resolution monochromatic synchrotron radiation diffraction images: (quasi) cellular structure; linear, very low-angle subgrain boundaries in (110) directions, and surface stripes in a (110) direction. In addition, we report systematic differences in the acceptance angle for images involving various diffraction vectors. When these observations are considered together, a unifying picture emerges. The presence of ensembles of thin (110) antiphase platelet regions or boundaries is generally consistent not only with the streak-like diffraction features but with the other features reported here as well. For the formation of such regions we propose two mechanisms, operating in parallel, that appear to be consistent with the various defect features observed by a variety of techniques.

  5. Radiation effects in silicon and gallium arsenide solar cells using isotropic and normally incident radiation

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.; Downing, R. G.

    1984-01-01

    Several types of silicon and gallium arsenide solar cells were irradiated with protons with energies between 50 keV and 10 MeV at both normal and isotropic incidence. Damage coefficients for maximum power relative to 10 MeV were derived for these cells for both cases of omni-directional and normal incidence. The damage coefficients for the silicon cells were found to be somewhat lower than those quoted in the Solar Cell Radiation Handbook. These values were used to compute omni-directional damage coefficients suitable for solar cells protected by coverglasses of practical thickness, which in turn were used to compute solar cell degradation in two proton-dominated orbits. In spite of the difference in the low energy proton damage coefficients, the difference between the handbook prediction and the prediction using the newly derived values was negligible. Damage coefficients for GaAs solar cells for short circuit current, open circuit voltage, and maximum power were also computed relative to 10 MeV protons. They were used to predict cell degradation in the same two orbits and in a 5600 nmi orbit. Results show the performance of the GaAs solar cells in these orbits to be superior to that of the Si cells.

  6. Resonant photo-thermal modification of vertical gallium arsenide nanowires studied using Raman spectroscopy.

    PubMed

    Walia, Jaspreet; Boulanger, Jonathan; Dhindsa, Navneet; LaPierre, Ray; Tang, Xiaowu Shirley; Saini, Simarjeet S

    2016-06-17

    Gallium arsenide nanowires have shown considerable promise for use in applications in which the absorption of light is required. When the nanowires are oriented vertically, a considerable amount of light can be absorbed, leading to significant heating effects. Thus, it is important to understand the threshold power densities that vertical GaAs nanowires can support, and how the nanowire morphology is altered under these conditions. Here, resonant photo-thermal modification of vertical GaAs nanowires was studied using both Raman spectroscopy and electron microscopy techniques. Resonant waveguiding, and subsequent absorption of the excited optical mode reduces the irradiance vertical GaAs nanowires can support relative to horizontal ones, by three orders of magnitude before the onset of structural changes occur. A power density of only 20 W mm(-2) was sufficient to induce local heating in the nanowires, resulting in the formation of arsenic species. Upon further increasing the power, a hollow nanowire morphology was realized. These findings are pertinent to all optical applications and spectroscopic measurements involving vertically oriented GaAs nanowires. Understanding the optical absorption limitations, and the effects of exceeding these limitations will help improve the development of all III-V nanowire devices. PMID:27172276

  7. Resonant photo-thermal modification of vertical gallium arsenide nanowires studied using Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Walia, Jaspreet; Boulanger, Jonathan; Dhindsa, Navneet; LaPierre, Ray; (Shirley Tang, Xiaowu; Saini, Simarjeet S.

    2016-06-01

    Gallium arsenide nanowires have shown considerable promise for use in applications in which the absorption of light is required. When the nanowires are oriented vertically, a considerable amount of light can be absorbed, leading to significant heating effects. Thus, it is important to understand the threshold power densities that vertical GaAs nanowires can support, and how the nanowire morphology is altered under these conditions. Here, resonant photo-thermal modification of vertical GaAs nanowires was studied using both Raman spectroscopy and electron microscopy techniques. Resonant waveguiding, and subsequent absorption of the excited optical mode reduces the irradiance vertical GaAs nanowires can support relative to horizontal ones, by three orders of magnitude before the onset of structural changes occur. A power density of only 20 W mm-2 was sufficient to induce local heating in the nanowires, resulting in the formation of arsenic species. Upon further increasing the power, a hollow nanowire morphology was realized. These findings are pertinent to all optical applications and spectroscopic measurements involving vertically oriented GaAs nanowires. Understanding the optical absorption limitations, and the effects of exceeding these limitations will help improve the development of all III-V nanowire devices.

  8. Theory, design, and simulation of GASP: A block data flow architecture for gallium arsenide supercomputers

    SciTech Connect

    Fouts, D.J.

    1990-01-01

    The advantages and disadvantages of using high-speed gallium arsenide (GaAs) logic for implementing digital systems are reviewed. A set of design guidelines is presented for systems that will be constructed with high-speed technologies such as GaAs and silicon emitter coupled logic (ECL). A new class of computer and digital system architectures, known as functionally modular architectures, is defined and explained. Functionally modular architectures are ideal for implementation in GaAs because they adhere to the design guidelines. GASP, a new, functionally modular, block data flow computer architecture is then described. SPICE simulations indicate that if constructed with existing GaAs IC technology, parts of GASP could run at a clock speed of 1 GHz, with the rest of the architecture using a 500 MHz clock. The new architecture uses data flow techniques at a program block level, which allows efficient execution of parallel programs while maintaining reasonably good performance on sequential programs. A simulation study of the architecture's best case and worst case performance is presented. Simulations of GASP executing a highly parallel program indicate that an instruction execution rate of over 30,000 MIPS can be attained with a 65 processor system.

  9. Resonant photo-thermal modification of vertical gallium arsenide nanowires studied using Raman spectroscopy.

    PubMed

    Walia, Jaspreet; Boulanger, Jonathan; Dhindsa, Navneet; LaPierre, Ray; Tang, Xiaowu Shirley; Saini, Simarjeet S

    2016-06-17

    Gallium arsenide nanowires have shown considerable promise for use in applications in which the absorption of light is required. When the nanowires are oriented vertically, a considerable amount of light can be absorbed, leading to significant heating effects. Thus, it is important to understand the threshold power densities that vertical GaAs nanowires can support, and how the nanowire morphology is altered under these conditions. Here, resonant photo-thermal modification of vertical GaAs nanowires was studied using both Raman spectroscopy and electron microscopy techniques. Resonant waveguiding, and subsequent absorption of the excited optical mode reduces the irradiance vertical GaAs nanowires can support relative to horizontal ones, by three orders of magnitude before the onset of structural changes occur. A power density of only 20 W mm(-2) was sufficient to induce local heating in the nanowires, resulting in the formation of arsenic species. Upon further increasing the power, a hollow nanowire morphology was realized. These findings are pertinent to all optical applications and spectroscopic measurements involving vertically oriented GaAs nanowires. Understanding the optical absorption limitations, and the effects of exceeding these limitations will help improve the development of all III-V nanowire devices.

  10. Arsenic moiety in gallium arsenide is responsible for neuronal apoptosis and behavioral alterations in rats.

    PubMed

    Flora, Swaran J S; Bhatt, Kapil; Mehta, Ashish

    2009-10-15

    Gallium arsenide (GaAs), an intermetallic semiconductor finds widespread applications in high frequency microwave and millimeter wave, and ultra fast supercomputers. Extensive use of GaAs has led to increased exposure to humans working in semiconductor industry. GaAs has the ability to dissociate into its constitutive moieties at physiological pH and might be responsible for the oxidative stress. The present study was aimed at evaluating, the principle moiety (Ga or As) in GaAs to cause neurological dysfunction based on its ability to cause apoptosis, in vivo and in vitro and if this neuronal dysfunction translated to neurobehavioral changes in chronically exposed rats. Result indicated that arsenic moiety in GaAs was mainly responsible for causing oxidative stress via increased reactive oxygen species (ROS) and nitric oxide (NO) generation, both in vitro and in vivo. Increased ROS further caused apoptosis via mitochondrial driven pathway. Effects of oxidative stress were also confirmed based on alterations in antioxidant enzymes, GPx, GST and SOD in rat brain. We noted that ROS induced oxidative stress caused changes in the brain neurotransmitter levels, Acetylcholinesterase and nitric oxide synthase, leading to loss of memory and learning in rats. The study demonstrates for the first time that the slow release of arsenic moiety from GaAs is mainly responsible for oxidative stress induced apoptosis in neuronal cells causing behavioral changes.

  11. Transport-reaction model for defect and carrier behavior within displacement cascades in gallium arsenide

    SciTech Connect

    Wampler, William R.; Myers, Samuel M.

    2014-02-01

    A model is presented for recombination of charge carriers at displacement damage in gallium arsenide, which includes clustering of the defects in atomic displacement cascades produced by neutron or ion irradiation. The carrier recombination model is based on an atomistic description of capture and emission of carriers by the defects with time evolution resulting from the migration and reaction of the defects. The physics and equations on which the model is based are presented, along with details of the numerical methods used for their solution. The model uses a continuum description of diffusion, field-drift and reaction of carriers and defects within a representative spherically symmetric cluster. The initial radial defect profiles within the cluster were chosen through pair-correlation-function analysis of the spatial distribution of defects obtained from the binary-collision code MARLOWE, using recoil energies for fission neutrons. Charging of the defects can produce high electric fields within the cluster which may influence transport and reaction of carriers and defects, and which may enhance carrier recombination through band-to-trap tunneling. Properties of the defects are discussed and values for their parameters are given, many of which were obtained from density functional theory. The model provides a basis for predicting the transient response of III-V heterojunction bipolar transistors to pulsed neutron irradiation.

  12. Analysis of costs of gallium arsenide and silicon solar arrays for space power applications

    NASA Technical Reports Server (NTRS)

    Jefferies, K. S.

    1981-01-01

    A parametric analysis was performed to compare the costs of silicon and gallium arsenide arrays for Earth orbital missions. The missions included electric power in low Earth orbit (LEO), electric power in geosynchronous Earth orbit (GEO), and power for electric propulsion of a LEO to GEO orbit transfer mission. Inputs to the analysis for all missions included launch and purchase costs of the array. For the orbit transfer mission, the launch and purchase costs of the electric propulsion system were added. Radiation flux as a function of altitude and rediation tolerance as a function of cell type were used to determine power degradation for each mission. Curves were generated that show the sensitivity of launch-array cost and total mission cost to a variety of input parameters for each mission. These parameters included mission duration, cover glass thickness, array specific cost, array specific mass, and solar cell efficiency. Solar concentration was considered and the sensitivities of cost to concentration ratio, concentrator costs, and concentrator mass were also evaluated. Results indicate that solar cell development should give a high priority to reducing array costs and that the development of low cost, lightweight, solar concentrators should be pursued.

  13. Forward-biased current annealing of radiation degraded indium phosphide and gallium arsenide solar cells

    NASA Technical Reports Server (NTRS)

    Michael, Sherif; Cypranowski, Corinne; Anspaugh, Bruce

    1990-01-01

    The preliminary results of a novel approach to low-temperature annealing of previously irradiated indium phosphide and gallium arsenide solar cells are reported. The technique is based on forward-biased current annealing. The two types of III-V solar cells were irradiated with 1-MeV electrons to a fluence level of (1-10) x 10 to the 14th electrons/sq cm. Several annealing attempts were made, varying all conditions. Optimum annealing was achieved when cells were injected with minority currents at a constant 90 C. The current density for each type of cell was also determined. Significant recovery of degraded parameters was achieved in both cases. However, the InP cell recovery notably exceeded the recovery in GaAs cells. The recovery is thought to be caused by current-stimulated reordering of the radiator-induced displacement damage. Both types of cell were then subjected to several cycles of irradiation and annealing. The results were also very promising. The significant recovery of degraded cell parameters at low temperature might play a major role in considerably extending the end of life of future spacecraft.

  14. Model for transport and reaction of defects and carriers within displacement cascades in gallium arsenide

    SciTech Connect

    Wampler, William R. Myers, Samuel M.

    2015-01-28

    A model is presented for recombination of charge carriers at evolving displacement damage in gallium arsenide, which includes clustering of the defects in atomic displacement cascades produced by neutron or ion irradiation. The carrier recombination model is based on an atomistic description of capture and emission of carriers by the defects with time evolution resulting from the migration and reaction of the defects. The physics and equations on which the model is based are presented, along with the details of the numerical methods used for their solution. The model uses a continuum description of diffusion, field-drift and reaction of carriers, and defects within a representative spherically symmetric cluster of defects. The initial radial defect profiles within the cluster were determined through pair-correlation-function analysis of the spatial distribution of defects obtained from the binary-collision code MARLOWE, using recoil energies for fission neutrons. Properties of the defects are discussed and values for their parameters are given, many of which were obtained from density functional theory. The model provides a basis for predicting the transient response of III-V heterojunction bipolar transistors to displacement damage from energetic particle irradiation.

  15. Model for transport and reaction of defects and carriers within displacement cascades in gallium arsenide

    NASA Astrophysics Data System (ADS)

    Wampler, William R.; Myers, Samuel M.

    2015-01-01

    A model is presented for recombination of charge carriers at evolving displacement damage in gallium arsenide, which includes clustering of the defects in atomic displacement cascades produced by neutron or ion irradiation. The carrier recombination model is based on an atomistic description of capture and emission of carriers by the defects with time evolution resulting from the migration and reaction of the defects. The physics and equations on which the model is based are presented, along with the details of the numerical methods used for their solution. The model uses a continuum description of diffusion, field-drift and reaction of carriers, and defects within a representative spherically symmetric cluster of defects. The initial radial defect profiles within the cluster were determined through pair-correlation-function analysis of the spatial distribution of defects obtained from the binary-collision code MARLOWE, using recoil energies for fission neutrons. Properties of the defects are discussed and values for their parameters are given, many of which were obtained from density functional theory. The model provides a basis for predicting the transient response of III-V heterojunction bipolar transistors to displacement damage from energetic particle irradiation.

  16. Growth of gallium nitride and indium nitride nanowires on conductive and flexible carbon cloth substrates

    NASA Astrophysics Data System (ADS)

    Yang, Yi; Ling, Yichuan; Wang, Gongming; Lu, Xihong; Tong, Yexiang; Li, Yat

    2013-02-01

    We report a general strategy for synthesis of gallium nitride (GaN) and indium nitride (InN) nanowires on conductive and flexible carbon cloth substrates. GaN and InN nanowires were prepared via a nanocluster-mediated growth method using a home built chemical vapor deposition (CVD) system with Ga and In metals as group III precursors and ammonia as a group V precursor. Electron microscopy studies reveal that the group III-nitride nanowires are single crystalline wurtzite structures. The morphology, density and growth mechanism of these nanowires are determined by the growth temperature. Importantly, a photoelectrode fabricated by contacting the GaN nanowires through a carbon cloth substrate shows pronounced photoactivity for photoelectrochemical water oxidation. The ability to synthesize group III-nitride nanowires on conductive and flexible substrates should open up new opportunities for nanoscale photonic, electronic and electrochemical devices.We report a general strategy for synthesis of gallium nitride (GaN) and indium nitride (InN) nanowires on conductive and flexible carbon cloth substrates. GaN and InN nanowires were prepared via a nanocluster-mediated growth method using a home built chemical vapor deposition (CVD) system with Ga and In metals as group III precursors and ammonia as a group V precursor. Electron microscopy studies reveal that the group III-nitride nanowires are single crystalline wurtzite structures. The morphology, density and growth mechanism of these nanowires are determined by the growth temperature. Importantly, a photoelectrode fabricated by contacting the GaN nanowires through a carbon cloth substrate shows pronounced photoactivity for photoelectrochemical water oxidation. The ability to synthesize group III-nitride nanowires on conductive and flexible substrates should open up new opportunities for nanoscale photonic, electronic and electrochemical devices. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr

  17. Smooth cubic commensurate oxides on gallium nitride

    SciTech Connect

    Paisley, Elizabeth A.; Gaddy, Benjamin E.; LeBeau, James M.; Shelton, Christopher T.; Losego, Mark D.; Mita, Seiji; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L.; Maria, Jon-Paul; Biegalski, Michael D.; Christen, Hans M.

    2014-02-14

    Smooth, commensurate alloys of 〈111〉-oriented Mg{sub 0.52}Ca{sub 0.48}O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

  18. Gallium nitride microcavities formed by photoenhanced wet oxidation

    SciTech Connect

    Peng, L.-H.; Lu, C.-Y.; Wu, W.-H.; Wang, S.-L.

    2005-10-17

    We report the formation of gallium nitride (GaN) microcavities by manipulating a photoenhanced oxidation rate difference between the polar and nonpolar crystallographic planes of GaN. When immersed in a buffered acetic (CH{sub 3}COOH) electrolyte of pH{approx}6.2 at room temperature, it is shown that the photo-oxidation can proceed at a rate that is one order of magnitude slower on the nonpolar plane of {l_brace}1100{r_brace}{sub GaN} than on the polar plane of {l_brace}0001{r_brace}{sub GaN} due to the reduced surface field action. Gallium nitride microcavities bounded by optically smooth {l_brace}1100{r_brace} and {l_brace}1103{r_brace} facets can thus be preferentially formed on the c-plane sapphire substrate after dissolving the oxide layer. The optical properties of these GaN hexagonal cavities reveal characteristic peaks of whispering gallery modes in resonance with the GaN band edge emission spectrum. A typical cavity Q factor of 10{sup 3} is observed in these GaN microcavities due to a reduced optical scattering loss in the wet chemical reaction process.

  19. Electron transport in zinc-blende wurtzite biphasic gallium nitride nanowires and GaNFETs

    DOE PAGESBeta

    Jacobs, Benjamin W.; Ayres, Virginia M.; Stallcup, Richard E.; Hartman, Alan; Tupta, Mary Ann; Baczewski, Andrew David; Crimp, Martin A.; Halpern, Joshua B.; He, Maoqi; Shaw, Harry C.

    2007-10-19

    Two-point and four-point probe electrical measurements of a biphasic gallium nitride nanowire and current–voltage characteristics of a gallium nitride nanowire based field effect transistor are reported. The biphasic gallium nitride nanowires have a crystalline homostructure consisting of wurtzite and zinc-blende phases that grow simultaneously in the longitudinal direction. There is a sharp transition of one to a few atomic layers between each phase. Here, all measurements showed high current densities. Evidence of single-phase current transport in the biphasic nanowire structure is discussed.

  20. Wurtzite Gallium Nitride as a scintillator detector for alpha particles (a Geant4 simulation)

    NASA Astrophysics Data System (ADS)

    Taheri, A.; Sheidaiy, M.

    2015-05-01

    Gallium Nitride has become a very popular material in electronics and optoelectronics. Because of its interesting properties, it is suitable for a large range of applications. This material also shows very good scintillation properties that make it a possible candidate for use as a charged particles scintillator detector. In this work, we simulated the scintillation and optical properties of the gallium nitride in the presence of alpha particles using Geant4. The results show that gallium nitride can be an appropriate choice for this purpose.

  1. Gallium arsenide (GaAs) island growth under SiO(2) nanodisks patterned on GaAs substrates.

    PubMed

    Tjahjana, Liliana; Wang, Benzhong; Tanoto, Hendrix; Chua, Soo-Jin; Yoon, Soon Fatt

    2010-05-14

    We report a growth phenomenon where uniform gallium arsenide (GaAs) islands were found to grow underneath an ordered array of SiO(2) nanodisks on a GaAs(100) substrate. Each island eventually grows into a pyramidal shape resulting in the toppling of the supported SiO(2) nanodisk. This phenomenon occurred consistently for each nanodisk across a large patterned area of approximately 50 x 50 microm(2) (with nanodisks of 210 nm diameter and 280 nm spacing). The growth mechanism is attributed to a combination of 'catalytic' growth and facet formation.

  2. Coherent detection of THz waves based on THz-induced time-resolved luminescence quenching in bulk gallium arsenide.

    PubMed

    Chu, Zheng; Liu, Jinsong; Wang, Kejia

    2012-05-01

    A kind of photoluminescence quenching, in which the time-resolved photoluminescence is modulated by a THz pulse, has been theoretically investigated by performing the ensemble Monte Carlo method in bulk gallium arsenide (GaAs) at room temperature. The quenching ratio could reach up to 50% under a strong THz field (100  kV/cm). The range in which luminescence quenching is linearly proportional to the THz field could be over 60  kV/cm. On the basis of these results, a principle for THz modulation and coherent detection is proposed.

  3. Selectivity control of photosensitive structures based on gallium arsenide phosphide solid solutions by changing the rate of surface recombination

    NASA Astrophysics Data System (ADS)

    Tarasov, S. A.; Andreev, M. Y.; Lamkin, I. A.; Solomonov, A. V.

    2016-08-01

    In this paper, we demonstrate the effect of surface recombination on spectral sensitivity of structures based on gallium arsenide phosphide solid solutions. Simulation of the effect for structures based on a p-n junction and a Schottky barrier was carried out. Photodetectors with different rates of surface recombination were fabricated by using different methods of preliminary treatment of the semiconductor surface. We experimentally demonstrated the possibility to control photodetector selectivity by altering the rate of surface recombination. The full width at half maximum was reduced by almost 4 times, while a relatively small decrease in sensitivity at the maximum was observed.

  4. Coherent near infrared photodetection with indium gallium arsenide based optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Fu, Jun-Xian

    Over the extremely broad electromagnetic spectrum, the near-infrared region (0.7--3 mum) is of great interests to physicists, chemists and biologists. Coherent photo-detection in the near-infrared as well as visible and other wavelength regions is extremely useful in identifying coherent light sources from the noisy background. It has great potential to be applied to single-molecule detection by surface-enhanced coherent anti-Stokes Raman scattering. Other applications include chemical gas detection, remote sensing and environmental monitoring, semiconductor processing control and others. Indium gallium arsenide (InGaAs) based optoelectronic devices have been extensively investigated in the wavelength range extending from 800nm for gallium-rich material to 3mum for indium-rich material. A range of InGaAs alloys with bandgap energies in the near infrared wavelength range are investigated by solid-source molecular beam epitaxy (SSMBE). They include strain-free standard In0.532Ga0.468As and In0.532Ga0.468 AsNxSby lattice-matched to InP substrates, highly strained pseudomorphic InxGa1-xAs/InyGa 1-yAs quantum structures on InP substrates and relaxed metamorphic thick Inx>0.8Ga1-xAs device layers with cyclic arsenic-assisted in-situ annealed step-graded InAlAs buffer layers on GaAs and InP substrates. An InP/InAlAs/InGaAs heterojunction bipolar phototransistor (HPT) is designed, simulated and fabricated. The electrical and optical properties, such as responsivity and spectral response, of the HPT are characterized. A compact standing-wave Fourier-transform interferometer system capable of coherent detection in the near-infrared region is demonstrated. A new technique of identifying coherent light sources using harmonic Fourier spectra analysis is developed. The system only includes a PZT-controlled gold-coated scan mirror and a partial-transparent (3.8% single-path loss) InP/InAlAs/InGaAs HPT. The close-loop scan range of PZT-controlled mirror is 32mum. With such mirror

  5. Gallium arsenide modulates proteolytic cathepsin activities and antigen processing by macrophages.

    PubMed

    Lewis, T A; Hartmann, C B; McCoy, K L

    1998-09-01

    Gallium arsenide (GaAs) is a semiconductor utilized in the electronics industry. Chemical exposure of animals causes a local inflammatory reaction, but systemic immunosuppression. Mice were administered i.p. 200 mg/kg GaAs crystals or latex beads, or vehicle. Five days after exposure, splenic macrophages were defective, whereas thioglycolate-elicited peritoneal macrophages (PEC) were more efficient in processing the Ag, pigeon cytochrome c, than vehicle control macrophages. Various aspects of the MHC class II Ag-processing pathway were examined. Both macrophage populations normally presented a peptide fragment to the CD4+ T cells. Surface MHC class II expression on the PEC was up-regulated, but splenic cells had normal MHC class II expression. PEC had elevated levels of glutathione and cysteine, major physiologic reducing thiols. However, the cysteine content of splenic macrophages was diminished. Proteolytic activities of aspartyl cathepsin D, and thiol cathepsins B and L were decreased significantly in splenic macrophages. On the other hand, thiol cathepsin activities were increased selectively in PEC. Latex bead-exposed PEC were not more potent APC, and their thiol cathepsin activities were unchanged, indicating that phagocytosis and nonspecific irritation were not responsible. The phenotype of PEC directly exposed to GaAs mirrored cytokine-activated macrophages, in contrast to splenic macrophages from a distant site. Therefore, GaAs exposure differentially modulated cathepsin activities in splenic macrophages and PEC, which correlated with their Ag-processing efficiency. Perhaps such distinct alterations may contribute to the local inflammation and systemic immunotoxicity caused by chemical exposure.

  6. Metallic behavior and metal insulator transition of two-dimensional holes in gallium arsenide

    NASA Astrophysics Data System (ADS)

    Gao, Xuan

    This thesis is an investigation of the anomalous metallic behavior and metal-insulator transition (MIT) of low density two dimensional (2D) holes in gallium arsenide (GaAs) quantum well. The prevailing one parameter scaling theory of localization for disordered 2D Fermi liquids predicts an insulating ground state at zero magnetic field for small rs---the ratio of Coulomb interaction energy over the Fermi energy. On the other hand, metallic-like temperature (T) dependent transport has been observed in various high mobility Fermionic 2D systems with high rs. Exploring the electronic transport of high mobility hole gas in 2D GaAs quantum wells down to 10mKelvin temperature range, we find that weak localization or single particle quantum interference is greatly suppressed in both the temperature dependence of the resistance and the low field magnetoresistance. We observe that a parallel magnetic field B11 applied in the 2D plane does not affect T *, the temperature/energy scale of the metallic resistance drop of the system, although it suppresses the magnitude of the resistance drop. Furthermore, the temperature dependent conductivity of 2D holes in a strong B 11 agrees with the Coulomb interaction theory of a spin polarized Fermi liquid in both the diffusive (T < h/k Btau) and ballistic (T > h/ kBtau) transport regime, with r being the momentum relaxation time. Our transport data are consistent with the phase separation scenario. Driven by the competition between kinetic energy and Coulomb potential energy, the 2D hole liquid phase separates into a mixture of the localized 2D Fermi liquid phase and a metallic phase below T*. The 2D MIT at zero magnetic field in turn could be due to the localized Fermi liquid phase percolates through the metallic phase as disorder strength increases.

  7. Gallium arsenide selectively up-regulates inflammatory cytokine expression at exposure site.

    PubMed

    Becker, Stephen M; McCoy, Kathleen L

    2003-12-01

    Gallium arsenide (GaAs), a technologically and economically important semiconductor, is widely utilized in both military and commercial applications. This chemical is a potential health hazard as a carcinogen and immunotoxicant. We previously reported that macrophages at the exposure site exhibit characteristics of activation. In vitro culture of macrophages with GaAs fails to recapitulate the in vivo phenotype, suggesting that complete GaAs-mediated activation in vivo may require other cells or components found in the body's microenvironment. Our present study examined the role of cytokines upon GaAs-mediated macrophage activation. Intraperitoneal administration of GaAs elicited rapid specific recruitment of blood monocytes to the exposure site. This recruitment occurred concomitant with up-regulation of 17 chemokine and inflammatory cytokine mRNAs, while transcripts of three inhibitory cytokines diminished. Administration of latex beads caused less cytokine induction than GaAs, indicating that changes in mRNA levels could not be attributed to phagocytosis. Four representative chemokines and cytokines were selected for further analysis. Increased cytokine mRNA expression was paralleled by similar increases in cytokine protein levels, and secreted protein products were detected in peritoneal fluid. Cytokine protein expression was constrained to myeloid cells, and to a lesser extent to B cells. Alterations in patterns of cytokine gene expression elucidate mechanisms for increased cellular activation and antigen processing, and modulation of the inflammatory response. Our findings indicate that in vivo GaAs exposure alters cytokine gene expression, which may lead to an inflammatory reaction and contribute to pathological tissue damage.

  8. Indium gallium arsenide imaging with smaller cameras, higher-resolution arrays, and greater material sensitivity

    NASA Astrophysics Data System (ADS)

    Ettenberg, Martin H.; Cohen, Marshall J.; Brubaker, Robert M.; Lange, Michael J.; O'Grady, Matthew T.; Olsen, Gregory H.

    2002-08-01

    Indium Gallium Arsenide (InGaAs) photodiode arrays have numerous commercial, industrial, and military applications. During the past 10 years, great strides have been made in the development of these devices starting with simple 256-element linear photodiode arrays and progressing to the large 640 x 512 element area arrays now readily available. Linear arrays are offered with 512 elements on a 25 micron pitch with no defective pixels, and are used in spectroscopic monitors for wavelength division multiplexing (WDM) systems as well as in machine vision applications. A 320 x 240 solid-state array operates at room temperature, which allows development of a camera which is smaller than 25 cm3 in volume, weighs less than 100 g and uses less than 750 mW of power. Two dimensional focal plane arrays and cameras have been manufactured with detectivity, D*, greater than 1014 cm-(root)Hz/W at room temperature and have demonstrated the ability to image at night. Cameras are also critical tools for the assembly and performance monitoring of optical switches and add-drop multiplexers in the telecommunications industry. These same cameras are used for the inspection of silicon wafers and fine art, laser beam profiling, and metals manufacturing. By varying the Indium content, InGaAs photodiode arrays can be tailored to cover the entire short-wave infrared spectrum from 1.0 micron to 2.5 microns. InGaAs focal plane arrays and cameras sensitive to 2.0 micron wavelength light are now available in 320 x 240 formats.

  9. Investigation on properties of ultrafast switching in a bulk gallium arsenide avalanche semiconductor switch

    SciTech Connect

    Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Yuan, Xuelin

    2014-03-07

    Properties of ultrafast switching in a bulk gallium arsenide (GaAs) avalanche semiconductor switch based on semi-insulating wafer, triggered by an optical pulse, were analyzed using physics-based numerical simulations. It has been demonstrated that when a voltage with amplitude of 5.2 kV is applied, after an exciting optical pulse with energy of 1 μJ arrival, the structure with thickness of 650 μm reaches a high conductivity state within 110 ps. Carriers are created due to photons absorption, and electrons and holes drift to anode and cathode terminals, respectively. Static ionizing domains appear both at anode and cathode terminals, and create impact-generated carriers which contribute to the formation of electron-hole plasma along entire channel. When the electric field in plasma region increases above the critical value (∼4 kV/cm) at which the electrons drift velocity peaks, a domain comes into being. An increase in carrier concentration due to avalanche multiplication in the domains reduces the domain width and results in the formation of an additional domain as soon as the field outside the domains increases above ∼4 kV/cm. The formation and evolution of multiple powerfully avalanching domains observed in the simulations are the physical reasons of ultrafast switching. The switch exhibits delayed breakdown with the characteristics affected by biased electric field, current density, and optical pulse energy. The dependence of threshold energy of the exciting optical pulse on the biased electric field is discussed.

  10. An Indium Gallium Arsenide Visible/SWIR Focal Plane Array for Low Light Level Imaging

    NASA Technical Reports Server (NTRS)

    Cohen, Marshall J.; Ettenberg, Martin H.; Lange, Michael J.; Olsen, Gregory H.

    1999-01-01

    PIN photodiodes fabricated from indium gallium arsenide lattice-matched to indium phosphide substrates (In(.53)Ga(.47)As/InP) exhibit low reverse saturation current densities (JD < 10(exp -8) A/sq cm), and high shunt resistance-area products (RoA > 10(exp 6) omega-sq cm) at T=290K. Backside-illuminated, hybrid-integrated InGaAs FPAs are sensitive from 0.9 micrometers to 1.7 micrometers. 290K detectivities, D(*), greater than 10(exp 14) cm-(square root of Hz/W) are demonstrated. This represents the highest room temperature detectivity of any infrared material. The long wavelength cutoff (1.7 micrometers) makes In(.53)Ga(.47)As an idea match to the available airglow that has major peaks at 1.3 micrometers and 1.6 micrometers. The short wavelength 'cut-on' at 0.9 micrometers is due to absorption in the InP substrate. We will report on new InGaAs FPA epitaxial structures and processing techniques. These have resulted in improved performance in the form of a 10 x increase in detectivity and visible response via removal of the InP substrate. The resulting device features visible and SWIR response with greater than 15% quantum efficiency at 0.5 micrometers while maintaining the long wavelength cutoff. Imaging has been demonstrated under overcast starlight/urban glow conditions with cooling provided by a single stage thermoelectric cooler. Details on the material structure and device fabrication, quantitative characterization of spectral response and detectivity, as well as examples of night vision imagery are presented.

  11. Localized surface phonon polariton resonances in polar gallium nitride

    SciTech Connect

    Feng, Kaijun Islam, S. M.; Verma, Jai; Hoffman, Anthony J.; Streyer, William; Wasserman, Daniel; Jena, Debdeep

    2015-08-24

    We demonstrate the excitation of localized surface phonon polaritons in an array of sub-diffraction pucks fabricated in an epitaxial layer of gallium nitride (GaN) on a silicon carbide (SiC) substrate. The array is characterized via polarization- and angle-dependent reflection spectroscopy in the mid-infrared, and coupling to several localized modes is observed in the GaN Reststrahlen band (13.4–18.0 μm). The same structure is simulated using finite element methods and the charge density of the modes are studied; transverse dipole modes are identified for the transverse electric and magnetic polarizations and a quadrupole mode is identified for the transverse magnetic polarization. The measured mid-infrared spectrum agrees well with numerically simulated spectra. This work could enable optoelectronic structures and devices that support surface modes at mid- and far-infrared wavelengths.

  12. Localized surface phonon polariton resonances in polar gallium nitride

    NASA Astrophysics Data System (ADS)

    Feng, Kaijun; Streyer, William; Islam, S. M.; Verma, Jai; Jena, Debdeep; Wasserman, Daniel; Hoffman, Anthony J.

    2015-08-01

    We demonstrate the excitation of localized surface phonon polaritons in an array of sub-diffraction pucks fabricated in an epitaxial layer of gallium nitride (GaN) on a silicon carbide (SiC) substrate. The array is characterized via polarization- and angle-dependent reflection spectroscopy in the mid-infrared, and coupling to several localized modes is observed in the GaN Reststrahlen band (13.4-18.0 μm). The same structure is simulated using finite element methods and the charge density of the modes are studied; transverse dipole modes are identified for the transverse electric and magnetic polarizations and a quadrupole mode is identified for the transverse magnetic polarization. The measured mid-infrared spectrum agrees well with numerically simulated spectra. This work could enable optoelectronic structures and devices that support surface modes at mid- and far-infrared wavelengths.

  13. Meso 2,3-dimercaptosuccinic acid (DMSA) and monoisoamyl DMSA effect on gallium arsenide induced pathological liver injury in rats.

    PubMed

    Flora, S J S; Dubey, Rupa; Kannan, G M; Chauhan, R S; Pant, B P; Jaiswal, D K

    2002-06-01

    The effect of meso 2,3-dimercaptosuccinic acid (DMSA) and monoisoamyl DMSA (MiADMSA) on gallium arsenide (GaAs) induced liver damage was studied. The oral feeding rat model was used in this study. The animals were exposed to 10 mg/kg GaAs, orally, once daily, 5 days a week for 24 weeks and treated thereafter with single oral daily dose of either 0.3 mmol/kg DMSA or MiADMSA for two course of 5 days treatment. The animals were sacrificed thereafter. Lipid peroxidation was assessed by measuring liver thiobarbituric acid reactive substance (TBARS). Liver damage was assessed by number of biochemical variables and by light microscopy. The activity of superoxide dismutase (SOD) and delta-aminolevulinic acid dehydratase (ALAD) beside reduced glutathione (GSH) concentration was measured in blood. Exposure to GaAs produced a significant reduction in GSH while, increased the oxidized glutathione (GSSG) concentration. Hepatic glutathione peroxidase (GPx) and catalase activity increased significantly while level of serum transaminase increased moderately. Gallium arsenide exposure also produced marked hepatic histopathological lesions. Overall, treatment with MiADMSA proved to be better than DMSA in the mobilization of arsenic and in the turnover of some of the above mentioned GaAs sensitive biochemical alterations. Histopathological lesions also, responded more favorably to chelation treatment with MiADMSA than DMSA.

  14. Low temperature solid-state synthesis of nanocrystalline gallium nitride

    SciTech Connect

    Wang, Liangbiao; Shi, Liang; Li, Qianwen; Si, Lulu; Zhu, Yongchun; Qian, Yitai

    2012-11-15

    Graphical abstract: Display Omitted Highlights: ► GaN nanocrystalline was prepared via a solid-state reacion at relatively low temperature. ► The sizes and crystallinities of the GaN samples obtained at the different temperatures are investigated. ► The GaN sample has oxidation resistance and good thermal stability below 1000 °C. -- Abstract: Nanocrystalline gallium nitride was synthesized by a solid-state reaction of metallic magnesium powder, gallium sesquioxide and sodium amide in a stainless steel autoclave at a relatively low temperature (400–550 °C). The structures and morphologies of the obtained products were derived from X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). XRD patterns indicated that the products were hexagonal GaN (JCPDS card no. 76-0703). The influence of reaction temperature on size of the products was studied by XRD and TEM. Furthermore, the thermal stability and oxidation resistance of the nanocrystalline GaN were also investigated. It had good thermal stability and oxidation resistance below 800 °C in air.

  15. Manganese Atom Ordered Monolayer on Wurtzite Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Chinchore, Abhijit; Wang, Kangkang; Lin, Wenzhi; Pak, Jeongihm; Liu, Yinghao; Smith, Arthur

    2009-03-01

    While transition-metal-doped gallium nitride (GaN) thin films have been explored as potential dilute magnetic semiconductor bulk layers, the structural and magnetic effects of various transition metal adatoms on GaN surfaces are not even well understood. In this work, we investigate the sub-monolayer deposition of manganese (Mn) onto the N-polar wurtzite GaN (000-1) 1x1 surface. The growth is monitored in-situ using reflection high energy electron diffraction (RHEED). A fresh GaN(000-1) 1x1 surface is prepared by rf nitrogen plasma-assisted MBE followed by annealing to remove excess gallium adatoms. The atomically flat GaN surface, held at 200^o C, is then exposed to submonolayer doses of Mn. The deposition rate is maintained at 0.007 ML per second, and a 3x pattern develops along [10-10]; whereas, only 1x is seen along [11-20]. Analysis of the RHEED pattern and subsequent modeling indicates a 3 x3 R 30^o structure consisting of 2/3 ML Mn atoms in a row-like arrangement having spacing 3a/2 along rows and 3a/2 between rows. Scanning tunneling microscopy/spectroscopy studies are currently underway to explore this surface further. This work is supported by DOE (Grant No.DE-FG02-06ER46317) and NSF (Grant No. 0730257).

  16. Experimental investigation of electron transport properties of gallium nitride nanowires

    NASA Astrophysics Data System (ADS)

    Motayed, Abhishek; Davydov, Albert V.; Mohammad, S. N.; Melngailis, John

    2008-07-01

    We report transport properties of gallium nitride (GaN) nanowires grown using direct reaction of ammonia and gallium vapor. Reliable devices, such as four-terminal resistivity measuring structures and field-effect transistors, were realized by dielectrophoretically aligning the nanowires on an oxidized silicon substrate and subsequently applying standard microfabrication techniques. Room-temperature resistivity in the range of (1.0-6.2)×10-2 Ω cm was obtained for the nanowires with diameters ranging from 200 to 90 nm. Temperature-dependent resistivity and mobility measurements indicated the possible sources for the n-type conductivity and high background charge carrier concentration in these nanowires. Specific contact resistance in the range of 5.0×10-5 Ω cm2 was extracted for Ti/Al/Ti/Au metal contacts to GaN nanowires. Significant reduction in the activation energy of the dopants at low temperatures (<200 K) was observed in the temperature-dependent resistivity measurement of these nanowires, which is linked to the onset of degeneracy. Temperature-dependent field-effect mobility measurements indicated that the ionized impurity scattering is the dominant mechanism in these nanowires at all temperatures.

  17. Methods for forming group III-V arsenide-nitride semiconductor materials

    NASA Technical Reports Server (NTRS)

    Major, Jo S. (Inventor); Welch, David F. (Inventor); Scifres, Donald R. (Inventor)

    2000-01-01

    Methods are disclosed for forming Group III--arsenide-nitride semiconductor materials. Group III elements are combined with group V elements, including at least nitrogen and arsenic, in concentrations chosen to lattice match commercially available crystalline substrates. Epitaxial growth of these III-V crystals results in direct bandgap materials, which can be used in applications such as light emitting diodes and lasers. Varying the concentrations of the elements in the III-V crystals varies the bandgaps, such that materials emitting light spanning the visible spectra, as well as mid-IR and near-UV emitters, can be created. Conversely, such material can be used to create devices that acquire light and convert the light to electricity, for applications such as full color photodetectors and solar energy collectors. The growth of the III-V crystals can be accomplished by growing thin layers of elements or compounds in sequences that result in the overall lattice match and bandgap desired.

  18. Characterization of solar cells for space applications. Volume 14: Electrical characteristics of Hughes liquid phase epitaxy gallium arsenide solar cells as a function of intensity, temperature and irradiation

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.; Downing, R. G.; Miyahira, T. F.; Weiss, R. S.

    1981-01-01

    Electrical characteristics of liquid phase epitaxy, P/N gallium aluminum arsenide solar cells are presented in graphical and tabular format as a function of solar illumination intensity and temperature. The solar cells were exposed to 1 MeV electron fluences of, respectively, 0, one hundred trillion, one quadrillion, and ten quadrillion e/sq cm.

  19. Msm Photodetectors for Two-Dimensional Meander Channel CCD Imagers on Gallium Arsenide

    NASA Astrophysics Data System (ADS)

    Bozorgebrahimi, Nercy

    This dissertation describes the design, fabrication, and performance of metal-semiconductor-metal (MSM) photodetectors on gallium arsenide (GaAs) and demonstrates their application in charge-coupled-device (CCD) imagers by integrating them with meander channel CCDs on GaAs in a two-dimensional imager device. The MSM photodetectors have a simple structure formed by interdigitated aluminum electrodes on a semi -insulating (SI) GaAs substrate. The CCD structure used in the imager is a two-phase overlapping-gate meander channel device. Potential barriers are formed by recessed electrodes along the CCD channel, using a self-aligned technique. The overlapping-gate structures are formed by anodic oxidation of the recessed metal and subsequent deposition of a second overlapping Al layer. The imager layout consists of four rows of 128 cells; two rows at each end of a large rectangular region, coupled by a 237-cell vertical CCD register. Hence, the imager imitates a 79 times 128 pixel device with the central 75 rows removed. The pixel size is 18mum times 33.5mum, with a fill-factor of ~15%. An interelectrode spacing and an electrode finger width of 2mum are used in the MSM photodetectors. From the theoretical simulations, dark current densities of 62 nA/cm^2 and 139 nA/cm^2 are obtained for the detector and the CCD, respectively, which results in a minimum dark -current-limited square-wave clock frequency of 4.5 MHz (432 frames/s) for the CCD imager. Similarly, a maximum transmission-line-limited square-wave clock frequency of 139 MHz (13329 frames/s) is obtained for the imager. A dark current of 6 pA/pixel is measured for the MSM photodetectors which is larger than the theoretical value by at least an order of magnitude. This is shown to be the result of leaky Schottky contacts. Large responsivities are measured for the MSM photodetectors in the wavelength range of 364-760nm, with a maximum responsivity of > 2100 A/W at a wavelength of 364nm and a reverse applied voltage of

  20. Comparative study of the toxic effects of gallium arsenide, indium arsenide and arsenic trioxide following intratracheal instillations to the lung of Syrian golden hamsters.

    PubMed

    Tanaka, A; Hirata, M; Omura, M; Zhao, M; Makita, Y; Yamazaki, K; Inoue, N; Gotoh, K

    2000-01-01

    Toxic effects of gallium arsenide (GaAs), indium arsenide (InAs) and arsenic trioxide (As2O3) were studied in male Syrian golden hamsters. GaAs (7.7 mg/kg) and As2O3 (1.3 mg/kg) particles were instilled intratracheally twice a week a total of 16 times, while InAs (7.7 mg/kg) was instilled a total of 14 times. As a control, hamsters were treated with the vehicle, phosphate buffer solution. During the instillation period, the cumulative body weight gain of the InAs-, but not the GaAs- or As2O3-treated hamsters was suppressed significantly, when compared with the control group. Slight to severe inflammatory responses were observed in the lung for all treatment groups. The most severe inflammatory change, characterized by an accumulation of neutrophils and macrophages, exudation, thickness of the pleura and fibrotic proliferation was found in the InAs-treated hamsters. Extensive alveolar or bronchiolar cell hyperplasia with or without keratinizing squamous cell metaplasia was observed in almost all the InAs-treated hamsters. Furthermore, squamous cell metaplasia or squamous cell hyperplasia developed in some of the InAs-treated hamsters, but not in the GaAs- or As2O3-treated hamsters. Slight to mild lesions were found in the convoluted tubules of the kidney in both the GaAs and InAs groups. From the present study, the toxic potency of these particles was provisionally estimated to be in the following order: InAs > GaAs > As2O3, at the dosage level used in this study. Furthermore, there was evidence that InAs particles could induce pulmonary, renal or systemic toxicity, and as such, InAs particles may produce pulmonary precancerous change when instilled intratracheally into hamsters.

  1. Nanoscale optical properties of indium gallium nitride/gallium nitride nanodisk-in-rod heterostructures.

    PubMed

    Zhou, Xiang; Lu, Ming-Yen; Lu, Yu-Jung; Jones, Eric J; Gwo, Shangjr; Gradečak, Silvija

    2015-03-24

    III-nitride based nanorods and nanowires offer great potential for optoelectronic applications such as light emitting diodes or nanolasers. We report nanoscale optical studies of InGaN/GaN nanodisk-in-rod heterostructures to quantify uniformity of light emission on the ensemble level, as well as the emission characteristics from individual InGaN nanodisks. Despite the high overall luminescence efficiency, spectral and intensity inhomogeneities were observed and directly correlated to the compositional variations among nanodisks and to the presence of structural defect, respectively. Observed light quenching is correlated to type I1 stacking faults in InGaN nanodisks, and the mechanisms for stacking fault induced nonradiative recombinations are discussed in the context of band structure around stacking faults and Fermi level pinning at nanorod surfaces. Our results highlight the importance of controlling III-nitride nanostructure growths to further reduce defect formation and ensure compositional homogeneity for optoelectronic devices with high efficiencies and desirable spectrum response.

  2. Measuring Nanoscale Heat Transfer for Gold-(Gallium Oxide)-Gallium Nitride Interfaces as a Function

    NASA Astrophysics Data System (ADS)

    Szwejkowski, Chester; Sun, Kai; Constantin, Costel; Giri, Ashutosh; Saltonstall, Christopher; Hopkins, Patrick; NanoSynCh Team; Exsite Team

    2014-03-01

    Gallium nitride (GaN) is considered the most important semiconductor after the discovery of Silicon. Understanding the properties of GaN is imperative in determining the utility and applicability of this class of materials to devices. We present results of time domain thermoreflectance (TDTR) measurements as a function of surface root mean square (RMS) roughness. We used commercially available 5mm x 5mm, single-side polished GaN (3-7 μm)/Sapphire (430 μm) substrates that have a Wurtzite crystal structure and are slightly n-type doped. The GaN substrates were annealed in the open atmosphere for 10 minutes (900-1000 °C). This high-temperature treatment produced RMS values from 1-60 nm and growth of gallium oxide (GaO) as measured with an atomic force microscopy and transmission electron microscopy respectively. A gold film (80nm) was deposited on the GaN surface using electron beam physical vapor deposition which was verified using ellipsometry and profilometry. The TDTR measurements suggest that the thermal conductivity decays exponentially with RMS roughness and that there is a minimum value for thermal boundary conductance at a roughness of 15nm.

  3. In vitro bio-functionality of gallium nitride sensors for radiation biophysics.

    PubMed

    Hofstetter, Markus; Howgate, John; Schmid, Martin; Schoell, Sebastian; Sachsenhauser, Matthias; Adigüzel, Denis; Stutzmann, Martin; Sharp, Ian D; Thalhammer, Stefan

    2012-07-27

    There is an increasing interest in the integration of hybrid bio-semiconductor systems for the non-invasive evaluation of physiological parameters. High quality gallium nitride and its alloys show promising characteristics to monitor cellular parameters. Nevertheless, such applications not only request appropriate sensing capabilities but also the biocompatibility and especially the biofunctionality of materials. Here we show extensive biocompatibility studies of gallium nitride and, for the first time, a biofunctionality assay using ionizing radiation. Analytical sensor devices are used in medical settings, as well as for cell- and tissue engineering. Within these fields, semiconductor devices have increasingly been applied for online biosensing on a cellular and tissue level. Integration of advanced materials such as gallium nitride into these systems has the potential to increase the range of applicability for a multitude of test devices and greatly enhance sensitivity and functionality. However, for such applications it is necessary to optimize cell-surface interactions and to verify the biocompatibility of the semiconductor. In this work, we present studies of mouse fibroblast cell activity grown on gallium nitride surfaces after applying external noxa. Cell-semiconductor hybrids were irradiated with X-rays at air kerma doses up to 250 mGy and the DNA repair dynamics, cell proliferation, and cell growth dynamics of adherent cells were compared to control samples. The impact of ionizing radiation on DNA, along with the associated cellular repair mechanisms, is well characterized and serves as a reference tool for evaluation of substrate effects. The results indicate that gallium nitride does not require specific surface treatments to ensure biocompatibility and suggest that cell signaling is not affected by micro-environmental alterations arising from gallium nitride-cell interactions. The observation that gallium nitride provides no bio-functional influence on

  4. Aluminum gallium nitride/gallium nitride high electron mobility transistor fabrication and characterization

    NASA Astrophysics Data System (ADS)

    Disanto, David W.

    In the last decade, Al1-xGaxN/GaN High Electron Mobility Transistors (HEMTs) have been intensively studied because their intrinsic electrical properties make them attractive for high power microwave device applications. Despite much progress, current slump continues to be a problem, limiting output power, reducing reliability, and complicating device modelling. In this work, a complete Al1-xGaxN/GaN HEMT fabrication procedure was developed, and electrical characteristics related to current slump, microwave modelling, and delay time analysis were explored. Low resistance ohmic contacts were achieved, enabling high channel current densities. Schottky contacts were developed with a new ion implant isolation architecture, enabling gate leakage currents 2 to 4 orders of magnitude lower than typical results from the literature. Through pulsed current-voltage measurements, the importance of bias stresses in the gate-source region was demonstrated for the first time. In contrast to the conventional "virtual gate" model, gate-source stresses were shown to be more important than gate-drain stresses when biased near threshold. Slow slump transients were studied by passivating transistor surfaces with ultra-thin layers. These results excluded dielectric strain and electron injection reduction as viable passivation mechanisms. A novel model was proposed associating slow slump behaviour with trapping of many electrons at screw dislocation sites. The effect of slump on RF properties was examined through microwave measurements by extracting the parasitic source and drain resistances without special biasing. Besides significantly improving the accuracy of small-signal modelling, we were able to show the bias dependence of parasitic resistances which confirmed the effect of source-side bias stressing. The question of channel electron velocities in nitride transistors remains controversial. We determined an effective electron velocity of ˜ 1.9 x 107 cm/s through two methods. We

  5. Photodetectors based on carbon nanotubes deposited by using a spray technique on semi-insulating gallium arsenide.

    PubMed

    Melisi, Domenico; Nitti, Maria Angela; Valentini, Marco; Valentini, Antonio; Ligonzo, Teresa; De Pascali, Giuseppe; Ambrico, Marianna

    2014-01-01

    In this paper, a spray technique is used to perform low temperature deposition of multi-wall carbon nanotubes on semi-insulating gallium arsenide in order to obtain photodectors. A dispersion of nanotube powder in non-polar 1,2-dichloroethane is used as starting material. The morphological properties of the deposited films has been analysed by means of electron microscopy, in scanning and transmission mode. Detectors with different layouts have been prepared and current-voltage characteristics have been recorded in the dark and under irradiation with light in the range from ultraviolet to near infrared. The device spectral efficiency obtained from the electrical characterization is finally reported and an improvement of the photodetector behavior due to the nanotubes is presented and discussed.

  6. An experiment to test the viability of a gallium-arsenide cathode in a SRF electron gun

    SciTech Connect

    Kewisch,J.; Ben-Zvi, I.; Rao, T.; Burrill, A.; Pate, D.; Wu, Q.; Todd, R.; Wang, E.; Bluem, H.; Holmes, D.; Schultheiss, T.

    2009-05-04

    Strained gallium arsenide cathodes are used in electron guns for the production of polarized electrons. In order to have a sufficient quantum efficiency lifetime of the cathode the vacuum in the gun must be 10{sup -11} Torr or better, so that the cathode is not destroyed by ion back bombardment or through contamination with residual gases. All successful polarized guns are DC guns, because such vacuum levels can not be obtained in normal conducting RF guns. A superconductive RF gun may provide a sufficient vacuum level due to cryo-pumping of the cavity walls. We report on the progress of our experiment to test such a gun with normal GaAs-Cs crystals.

  7. A gallium-arsenide digital phase shifter for clock and control signal distribution in high-speed digital systems

    NASA Technical Reports Server (NTRS)

    Fouts, Douglas J.

    1992-01-01

    The design, implementation, testing, and applications of a gallium-arsenide digital phase shifter and fan-out buffer are described. The integrated circuit provides a method for adjusting the phase of high-speed clock and control signals in digital systems, without the need for pruning cables, multiplexing between cables of different lengths, delay lines, or similar techniques. The phase of signals distributed with the described chip can be dynamically adjusted in eight different steps of approximately 60 ps per step. The IC also serves as a fan-out buffer and provides 12 in-phase outputs. The chip is useful for distributing high-speed clock and control signals in synchronous digital systems, especially if components are distributed over a large physical area or if there is a large number of components.

  8. Optical absorption and photocurrent enhancement in semi-insulating gallium arsenide by femtosecond laser pulse surface microstructuring.

    PubMed

    Zhao, Zhen-Yu; Song, Zhi-Qiang; Shi, Wang-Zhou; Zhao, Quan-Zhong

    2014-05-19

    We observe an enhancement of optical absorption and photocurrent from semi-insulating gallium arsenide (SI-GaAs) irradiated by femtosecond laser pulses. The SI-GaAs wafer is treated by a regeneratively amplified Ti: Sapphire laser of 120 fs laser pulse at 800 nm wavelength. The laser ablation induced 0.74 μm periodic ripples, and its optical absorption-edge is shifted to a longer wavelength. Meanwhile, the steady photocurrent of irradiated SI-GaAs is found to enhance 50%. The electrical properties of samples are calibrated by van der Pauw method. It is found that femtosecond laser ablation causes a microscale anti-reflection coating surface which enhances the absorption and photoconductivity.

  9. The electrical properties of 60 keV zinc ions implanted into semi-insulating gallium arsenide

    NASA Technical Reports Server (NTRS)

    Littlejohn, M. A.; Anikara, R.

    1972-01-01

    The electrical behavior of zinc ions implanted into chromium-doped semiinsulating gallium arsenide was investigated by measurements of the sheet resistivity and Hall effect. Room temperature implantations were performed using fluence values from 10 to the 12th to 10 to the 15th power/sq cm at 60 keV. The samples were annealed for 30 minutes in a nitrogen atmosphere up to 800 C in steps of 200 C and the effect of this annealing on the Hall effect and sheet resistivity was studied at room temperature using the Van der Pauw technique. The temperature dependence of sheet resistivity and mobility was measured from liquid nitrogen temperature to room temperature. Finally, a measurement of the implanted profile was obtained using a layer removal technique combined with the Hall effect and sheet resistivity measurements.

  10. Therapeutic potential of monoisoamyl and monomethyl esters of meso 2,3-dimercaptosuccinic acid in gallium arsenide intoxicated rats.

    PubMed

    Flora, Swaran J S; Mehta, Ashish; Rao, P V Lakshmana; Kannan, Gurusamy M; Bhaskar, A S B; Dube, Shashi N; Pant, Bhagwat P

    2004-02-15

    The dose dependent effects of monoisoamyl and monomethyl esters of meso 2,3-dimercaptosuccinic acid (DMSA) (0.1, 0.3 and 0.5 mmol kg(-1), intraperitoneally (i.p.) once daily for 5 days) to offset the characteristic biochemical, immunological, oxidative stress consequences and DNA damage (based on DNA fragmentation and comet assay) following sub-chronic administration of gallium arsenide and the mobilization of gallium and arsenic were examined. The effects of these chelators alone in normal animals too were examined on above-mentioned variables. Male Wistar rats were exposed to 10 mg kg(-1), GaAs, orally once daily for 12 weeks and were administered DMSA or two of its monoesters (monoisoamyl or monomethyl) for 5 consecutive days. DMSA was used as a positive control. DMSA and its derivatives, when given alone, generally have no adverse effects on various parameters. After 5 days of chelation therapy in GaAs pre-exposed rats, MiADMSA was most effective in the reduction of inhibited blood delta-aminolevulinic acid dehydratase (ALAD) activity and zinc protoporphyrin level while, all three chelators effectively reduced urinary ALA excretion, compared to GaAs alone exposed rats. MiADMSA was also effective, particularly at a dose of 0.3 mmol kg(-1), in enhancing the inhibited hepatic transaminase activities. Parameters indicative of oxidative stress responded less favorably to the chelation therapy, however, three chelators significantly restored the altered immunological variables. MiADMSA was relatively more effective than the other two chelators. GaAs produced significant DNA damage in the liver and kidneys and the chelation treatment had moderate but significant influence in reducing DNA damage. All three chelators significantly reduced arsenic concentration and, however, MiADMSA was more effective than the other two chelators in depleting arsenic concentration from blood and other soft tissues. A dose of 0.3 mmol kg(-1) was found to be relatively better than the

  11. Indium nitride and gallium nitride grown from the melt at subatmospheric pressures

    NASA Astrophysics Data System (ADS)

    Dyck, Jeffrey Scott

    The wide-band-gap, group III nitride semiconductors (Al,Ga,In)N are a promising system for visible/near-UV optoelectronic devices. Despite significant technological advances, improvement in material quality is required. Moreover, pure InN has received little attention due to unavailability of high quality crystals, and uncertainty on the fundamental properties of InN exist in the literature. In this work, bulk, polycrystalline gallium nitride and indium nitride were synthesized without a substrate by saturating gallium or indium metal with atomic nitrogen from both ECR and ball plasma microwave sources. The results show that atomic nitrogen is an attractive alternative to high pressure N2 for the synthesis of the bulk nitrides. The GaN and InN crystals were confirmed to be wurtzitic by x-ray and electron diffraction. Weak yellow-band photoluminescence intensity and near-band-edge linewidths of 4 meV for some GaN crystals indicated high optical quality. The high crystalline quality of the InN crystals allowed for the most precise measurement of the lattice parameters currently possible: a = 3.5366 A, c = 5.7009 A. Raman spectra of InN were taken from both randomly oriented polycrystals and groups of oriented, faceted platelets. Phonon modes were assigned as ETO1=445cm -1,ATO1 =472cm-1, E22=448 cm-1, and ALO1=558 cm-1 , and previous disagreement in the literature is explained. The E22 and ALO1 linewidths of were 2.5 and 19 cm-1 are the narrowest ever reported. The measured TO phonon frequencies and lattice parameters were compared to those calculated from first principles and excellent agreement was found. Preliminary experiments on the growth of GaN from Ga/In alloys were performed. Addition of inert, soluble third elements to the Ga/N melt depresses the liquidus temperature, which is equivalent to increasing the solubility of GaN at constant temperature. Upon introduction of an (0001) sapphire substrate into the melt, oriented thin films of the solid nitride formed

  12. Cell behavior on gallium nitride surfaces: peptide affinity attachment versus covalent functionalization.

    PubMed

    Foster, Corey M; Collazo, Ramon; Sitar, Zlatko; Ivanisevic, Albena

    2013-07-01

    Gallium nitride is a wide band gap semiconductor that demonstrates a unique set of optical and electrical properties as well as aqueous stability and biocompatibility. This combination of properties makes gallium nitride a strong candidate for use in chemical and biological applications such as sensors and neural interfaces. Molecular modification can be used to enhance the functionality and properties of the gallium nitride surface. Here, gallium nitride surfaces were functionalized with a PC12 cell adhesion promoting peptide using covalent and affinity driven attachment methods. The covalent scheme proceeded by Grignard reaction and olefin metathesis while the affinity driven scheme utilized the recognition peptide isolated through phage display. This study shows that the method of attaching the adhesion peptide influences PC12 cell adhesion and differentiation as measured by cell density and morphological analysis. Covalent attachment promoted monolayer and dispersed cell adhesion while affinity driven attachment promoted multilayer cell agglomeration. Higher cell density was observed on surfaces modified using the recognition peptide. The results suggest that the covalent and affinity driven attachment methods are both suitable for promoting PC12 cell adhesion to the gallium nitride surface, though each method may be preferentially suited for distinct applications.

  13. Probing the Surface Defect States of Gallium Nitride Nanowires

    NASA Astrophysics Data System (ADS)

    Simonsen, Lauren; Yang, Yuchen; Borys, Nicholas; Ghimire, Anil; Schuck, James; Aloni, Shaul; Gerton, Jordan

    In this work, we investigate gallium nitride nanowires (NWs) as a potential system for solar-driven water splitting. Although bulk GaN has a UV bandgap, the synthesized NWs exhibit strong absorption and fluorescence emission across the visible spectrum. Density functional theory calculations suggest that this visible fluorescence originates from mid-gap surface-defect states along the triangular facets of the NWs. The orientation of the NWs can be controlled during MOCVD growth, leading to different exposed crystallographic surface terminations with different electronic structures. High resolution microscopy techniques using AFM and confocal hyper-spectral imaging show spectral inhomogeneity across the widths of the NWs, providing evidence that various crystallographic terminations produce different surface states. These NWs also exhibit wave guiding properties, leading to Fabry-Perot fringes and high intensity spectra and the ends of the wires. Photoluminescence excitation spectroscopy reveals a non-linear dependence of the emission spectral features on excitation wavelength, indicating a complex distribution of mid-gap defect states. Time-resolved spectroscopy reveals non-exponential decay dynamics through a complicated manifold of mid-gap states.

  14. Probing the Surface Defect States of Gallium Nitride Nanowires

    NASA Astrophysics Data System (ADS)

    Simonsen, Lauren; Yang, Yuchen; Borys, Nicholas; Ghimire, Anil; Schuck, James; Aloni, Shaul; Gerton, Jordan

    2016-03-01

    In this work, we investigate gallium nitride nanowires (NWs) as a potential system for solar-driven water splitting. Although bulk GaN has a UV bandgap, the synthesized NWs exhibit strong absorption and fluorescence emission across the visible spectrum. Density functional theory calculations suggest that this visible fluorescence originates from mid-gap surface-defect states along the triangular facets of the NWs. The orientation of the NWs can be controlled during MOCVD growth, leading to different exposed crystallographic surface terminations with various electronic structures. High resolution microscopy techniques using AFM and confocal hyper-spectral imaging show spectral inhomogeneity across the widths of the NWs, providing evidence that various crystallographic terminations produce different surface states. These NWs also exhibit wave guiding properties, leading to Fabry-Perot fringes and high intensity spectra at the ends of the wires. Photoluminescence excitation spectroscopy reveals a non-linear dependence of the emission spectral features on excitation wavelength, indicating a complex distribution of mid-gap defect states. Time-resolved spectroscopy reveals non-exponential decay dynamics through a complicated manifold of mid-gap states.

  15. Lattice thermal conductivity of freestanding gallium nitride nanowires

    NASA Astrophysics Data System (ADS)

    Zou, Jie

    2010-08-01

    We report detailed calculations of the lattice thermal conductivity of freestanding gallium nitride (GaN) nanowires with diameters ranging from 20 to 140 nm. Results are compared with experimental data on GaN nanowires grown by thermal chemical vapor deposition (CVD). Calculations are based on the Boltzmann transport equation and take into account the change in the nonequilibrium phonon distribution in the case of diffuse scattering at the surfaces. Phonon dispersion relation is obtained in the elastic continuum approximation for each given nanowire. For valid comparisons with the experimental data, simulations are performed with a dopant concentration and impurity profile characteristic of thermal CVD GaN nanowires. Our results show that the room-temperature thermal conductivity of the nanowires has very low values, ranging from 6.74 W/m K at 20 nm to 16.4 W/m K at 140 nm. The obtained results are in excellent agreement with the experimental data. We have also demonstrated that in addition to impurity scattering, boundary scattering, and phonon confinement, the change in the nonequilibrium phonon distribution leads to a further reduction in the thermal conductivity of the nanowires and has to be taken into account in the calculations. Our conclusion is different from that of an earlier study which attributed the very low thermal conductivity to the unusually large mass-difference scattering in the nanowires.

  16. Size-dependent pyroelectric properties of gallium nitride nanowires

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Wang, Chengyuan

    2016-04-01

    The size scale effect on the pyroelectric properties is studied for gallium nitride (GaN) nanowires (NWs) based on molecular dynamics simulations and the theoretical analysis. Due to the significant influence of the surface thermoelasticity and piezoelectricity at the nanoscale, the pyroelectric coefficient of GaN NWs is found to depend on the cross-sectional size. This size-dependent pyroelectric coefficient of GaN NWs together with the size-dependent dielectric constant reported in our previous study is employed to study the pyroelectric potential of GaN NWs subjected to heating. The results show that the size scale effect is significant for thin NWs (cross-sectional size in nanometers) and may raise the pyroelectric potential of GaN NWs by over 10 times. Such a size scale effect on the pyroelectric properties of NWs originates from the influence of thermoelasticity, piezoelectricity, and dielectricity at the nanoscale and decreases with increasing cross-section of GaN NWs. It is expected that the present study may have strong implication in the field of energy harvesting at the nanoscale, as pyroelectricity offers a new avenue to the design of novel nanogenerators.

  17. Indium gallium nitride/gallium nitride vacuum microelectronic cold cathodes: Piezoelectric surface barrier lowering

    NASA Astrophysics Data System (ADS)

    Underwood, Robert Douglas

    Vacuum microelectronic devices are electronic devices fabricated using microelectronic processing and using vacuum as a transport medium. The electron velocity in vacuum can be larger than in solid state, which allows higher frequency operation of vacuum devices compared to solid-state devices. The effectiveness of vacuum microelectronic devices relies on the realization of an efficient source of electrons supplied to the vacuum. Cold cathodes do not rely on thermal energy for the emission of electrons into vacuum. Cold cathodes based on field emission are the most common types of vacuum microelectronic cold cathode because they have a very high efficiency and high current density electron emission. Materials used to fabricate field emitters must have the properties of high electron concentration, low surface reactivity, resistance to sputtering by ions, high thermal conductivity, and a method of fabrication of uniform arrays of field emitters. The III--V nitride semiconductors possess these material properties and uniform arrays of GaN field emitter pyramids have been produced by selective area, self-limited metalorganic chemical vapor deposition. The first GaN field emitter arrays were fabricated and measured. Emission currents as large as 82 muA at 1100 V from 245,000 pyramids have been realized using an external anode, separated by 0.25 mm, to apply voltage bias. The operation voltage was reduced by the development of an integrated anode structure. The anode-cathode separation achievable with the integrated anode was in the range of 0.5--2.4 m. The turn-on voltages of these devices were reduced to the range of 175--435 V. The operation voltage of field emitter cathodes is related to the surface energy barrier, which for n-type semiconductors is the electron affinity. A new method to reduce the effective electron affinity using a piezoelectric dipole in an InGaN/GaN heterostructure has been proposed and tested. The piezoelectric field produced in the strained In

  18. Growth and fabrication of gallium nitride and indium gallium nitride-based optoelectronic devices

    NASA Astrophysics Data System (ADS)

    Berkman, Erkan Acar

    In this study, heteroepitaxial growth of III-Nitrides was performed by metalorganic chemical vapor deposition (MOCVD) technique on (0001) Al 2O3 substrates to develop GaN and InxGa1-x N based optoelectronic devices. Comprehensive experimental studies on emission and relaxation mechanisms of InxGa1-xN quantum wells (QWs) and InxGa 1-xN single layers were performed. The grown films were characterized by x-ray diffraction (XRD), Hall Effect measurements, photoluminescence measurements (PL) and transmission electron microscopy (TEM). An investigation on the effect of number and width of QWs on PL emission properties of InxGa 1-xN single QWs and multi-quantum wells (MQW) was conducted. The experimental results were explained by the developed theoretical bandgap model. The study on the single layer InxGa1-xN films within and beyond critical layer thickness (CLT) demonstrated that thick InxGa 1-xN films display simultaneous presence of strained and (partially) relaxed layers. The In incorporation into the lattice was observed to be dependent on the strain state of the film. The findings on InxGa1-xN QWs and single layers were implemented in the development of InxGa1-xN based LEDs and photodiodes, respectively. The as-grown samples were fabricated using conventional lithography techniques into various optoelectronic devices including long wavelength LEDs, dichromatic monolithic white LEDs, and p-i-n photodiodes. Emission from InxGa1-xN/GaN MQW LEDs at wavelengths as long as 625nm was demonstrated. This is one of the longest peak emission wavelengths reported for MOCVD grown InxGa1-xN MQW structures. Dichromatic white emission in LEDs was realized by utilizing two InGaN MQW active regions emitting at complementary wavelengths. InGaN p-i-n photodiodes operating at various regions of the visible spectrum tailored by the i-layer properties were developed. This was achieved by the novel approach of employing InxGa1-xN in all layers of the p-i-n photodiodes, enabling nearly

  19. Micro and nano-structured green gallium indium nitride/gallium nitride light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Stark, Christoph J. M.

    Light-emitting diodes (LEDs) are commonly designed and studied based on bulk material properties. In this thesis different approaches based on patterns in the nano and micrometer length scale range are used to tackle low efficiency in the green spectral region, which is known as “green gap”. Since light generation and extraction are governed by microscopic processes, it is instructive to study LEDs with lateral mesa sizes scaled to the nanometer range. Besides the well-known case of the quantum size effect along the growth direction, a continuous lateral scaling could reveal the mechanisms behind the purported absence of a green gap in nanowire LEDs and the role of their extraction enhancement. Furthermore the possibility to modulate strain and piezoelectric polarization by post growth patterning is of practical interest, because the internal electric fields in conventional wurtzite GaN LEDs cause performance problems. A possible alternative is cubic phase GaN, which is free of built-in polarization fields. LEDs on cubic GaN could show the link between strong polarization fields and efficiency roll-off at high current densities, also known as droop. An additional problem for all nitride-based LEDs is efficient light extraction. For a planar GaN LED only roughly 8% of the generated light can be extracted. Novel lightextraction structures with extraction-favoring geometry can yield significant increase in light output power. To investigate the effect of scaling the mesa dimension, micro and nano-sized LED arrays of variable structure size were fabricated. The nano-LEDs were patterned by electron beam lithography and dry etching. They contained up to 100 parallel nano-stripe LEDs connected to one common contact area. The mesa width was varied over 1 μm, 200 nm, and 50 nm. These LEDs were characterized electrically and optically, and the peak emission wavelength was found to depend on the lateral structure size. An electroluminescence (EL) wavelength shift of 3 nm

  20. Thermal Cycling and High Temperature Reverse Bias Testing of Control and Irradiated Gallium Nitride Power Transistors

    NASA Technical Reports Server (NTRS)

    Patterson, Richard L.; Boomer, Kristen T.; Scheick, Leif; Lauenstein, Jean-Marie; Casey, Megan; Hammoud, Ahmad

    2014-01-01

    The power systems for use in NASA space missions must work reliably under harsh conditions including radiation, thermal cycling, and exposure to extreme temperatures. Gallium nitride semiconductors show great promise, but information pertaining to their performance is scarce. Gallium nitride N-channel enhancement-mode field effect transistors made by EPC Corporation in a 2nd generation of manufacturing were exposed to radiation followed by long-term thermal cycling and testing under high temperature reverse bias conditions in order to address their reliability for use in space missions. Result of the experimental work are presented and discussed.

  1. Growth and Characterization of Gallium Nitride (GaN) Thin Films by Pecvd

    NASA Astrophysics Data System (ADS)

    Mahmood, Hasan; Moore, S.; Zhang, D.; McIlroy, David N.

    2004-05-01

    Gallium nitride is a good candidate of nano-optical materials. Gallium nitride thin film was grown on Si (100) substrate by using plasma enhanced chemical vapor deposition (PECVD) technique in a UHV chamber with a base pressure of 9x10-10 torr. The temperature of precursor, Ga, was maintained at 800oC. The working pressure of nitrogen plasma was around 5x10-5 torr. The substrate temperature was in the range of 750-900oC. The chemical, morphological and crystal structural properties studied with XRD, XPS, SEM and ellipsometer will be presented.

  2. In vitro bio-functionality of gallium nitride sensors for radiation biophysics

    SciTech Connect

    Hofstetter, Markus; Howgate, John; Schmid, Martin; Schoell, Sebastian; Sachsenhauser, Matthias; Adiguezel, Denis; Stutzmann, Martin; Sharp, Ian D.; Thalhammer, Stefan

    2012-07-27

    Highlights: Black-Right-Pointing-Pointer Gallium nitride based sensors show promising characteristics to monitor cellular parameters. Black-Right-Pointing-Pointer Cell growth experiments reveal excellent biocompatibiltiy of the host GaN material. Black-Right-Pointing-Pointer We present a biofunctionality assay using ionizing radiation. Black-Right-Pointing-Pointer DNA repair is utilized to evaluate material induced alterations in the cellular behavior. Black-Right-Pointing-Pointer GaN shows no bio-functional influence on the cellular environment. -- Abstract: There is an increasing interest in the integration of hybrid bio-semiconductor systems for the non-invasive evaluation of physiological parameters. High quality gallium nitride and its alloys show promising characteristics to monitor cellular parameters. Nevertheless, such applications not only request appropriate sensing capabilities but also the biocompatibility and especially the biofunctionality of materials. Here we show extensive biocompatibility studies of gallium nitride and, for the first time, a biofunctionality assay using ionizing radiation. Analytical sensor devices are used in medical settings, as well as for cell- and tissue engineering. Within these fields, semiconductor devices have increasingly been applied for online biosensing on a cellular and tissue level. Integration of advanced materials such as gallium nitride into these systems has the potential to increase the range of applicability for a multitude of test devices and greatly enhance sensitivity and functionality. However, for such applications it is necessary to optimize cell-surface interactions and to verify the biocompatibility of the semiconductor. In this work, we present studies of mouse fibroblast cell activity grown on gallium nitride surfaces after applying external noxa. Cell-semiconductor hybrids were irradiated with X-rays at air kerma doses up to 250 mGy and the DNA repair dynamics, cell proliferation, and cell growth

  3. Study of the structure of a thin aluminum layer on the vicinal surface of a gallium arsenide substrate by high-resolution electron microscopy

    SciTech Connect

    Lovygin, M. V. Borgardt, N. I.; Seibt, M.; Kazakov, I. P.; Tsikunov, A. V.

    2015-12-15

    The results of electron-microscopy studies of a thin epitaxial aluminum layer deposited onto a misoriented gallium-arsenide substrate are reported. It is established that the layer consists of differently oriented grains, whose crystal lattices are coherently conjugated with the substrate with the formation of misfit dislocations, as in the case of a layer on a singular substrate. Atomic steps on the substrate surface are visualized, and their influence on the growth of aluminum crystal grains is discussed.

  4. As-Grown Gallium Nitride Nanowire Electromechanical Resonators

    NASA Astrophysics Data System (ADS)

    Montague, Joshua R.

    Technological development in recent years has led to a ubiquity of micro- and nano-scale electromechanical devices. Sensors for monitoring temperature, pressure, mass, etc., are now found in nearly all electronic devices at both the industrial and consumer levels. As has been true for integrated circuit electronics, these electromechanical devices have continued to be scaled down in size. For many nanometer-scale structures with large surface-to-volume ratio, dissipation (energy loss) becomes prohibitively large causing a decreasing sensitivity with decreasing sensor size. In this work, gallium nitride (GaN) nanowires are investigated as singly-clamped (cantilever) mechanical resonators with typical mechanical quality factors, Q (equal to the ratio of resonance frequency to peak full-width-at-half-maximum-power) and resonance frequencies, respectively, at or above 30,000, and near 1 MHz. These Q values---in vacuum at room temperature---indicate very low levels of dissipation; they are essentially the same as those for bulk quartz crystal resonators that form the basis of simple clocks and mass sensors. The GaN nanowires have lengths and diameters, respectively, of approximately 15 micrometers and hundreds of nanometers. As-grown GaN nanowire Q values are larger than other similarly-sized, bottom-up, cantilever resonators and this property makes them very attractive for use as resonant sensors. We demonstrate the capability of detecting sub-monolayer levels of atomic layer deposited (ALD) films, and the robust nature of the GaN nanowires structure that allows for their 'reuse' after removal of such layers. In addition to electron microscope-based measurement techniques, we demonstrate the successful capacitive detection of a single nanowire using microwave homodyne reflectometry. This technique is then extended to allow for simultaneous measurements of large ensembles of GaN nanowires on a single sample, providing statistical information about the distribution of

  5. Emergence of spin-orbit fields in magnetotransport of quasi-two-dimensional iron on gallium arsenide.

    PubMed

    Hupfauer, T; Matos-Abiague, A; Gmitra, M; Schiller, F; Loher, J; Bougeard, D; Back, C H; Fabian, J; Weiss, D

    2015-06-08

    The desire for higher information capacities drives the components of electronic devices to ever smaller dimensions so that device properties are determined increasingly more by interfaces than by the bulk structure of the constituent materials. Spintronic devices, especially, benefit from the presence of interfaces--the reduced structural symmetry creates emergent spin-orbit fields that offer novel possibilities to control device functionalities. But where does the bulk end, and the interface begin? Here we trace the interface-to-bulk transition, and follow the emergence of the interfacial spin-orbit fields, in the conducting states of a few monolayers of iron on top of gallium arsenide. We observe the transition from the interface- to bulk-induced lateral crystalline magnetoanisotropy, each having a characteristic symmetry pattern, as the epitaxially grown iron channel increases from four to eight monolayers. Setting the upper limit on the width of the interface-imprinted conducting channel is an important step towards an active control of interfacial spin-orbit fields.

  6. Ab initio finite field (hyper)polarizability computations on stoichiometric gallium arsenide clusters GanAsn (n=2-9).

    PubMed

    Karamanis, Panaghiotis; Bégué, Didier; Pouchan, Claude

    2007-09-01

    We report reliable ab initio finite field (hyper)polarizability values at Hartree-Fock and second order Moller-Plesset perturbation theory (MP2) levels of theory for different geometrical configurations of small gallium arsenide clusters Ga(n)As(n) with n=2-5. We relied on all-electron basis sets and pseudopotentials suitable for (hyper)polarizability calculations. In each case, we used structures that have been established in the literature after we optimized their geometries at B3LYP/cc-pVTZ-PP level of theory. Our results suggest that the first order hyperpolarizability (beta) is much more sensitive to the special geometric features than the second order hyperpolarizability (gamma). For the most stable configurations up to ten atoms the second order hyperpolarizability at MP2 level of theory varies between 15 x 10(4) and 32 x 10(4) e(4)a0 (4)Eh(-3). In addition, we examined the polarizability per atom evolution versus the cluster size for Ga(n)As(n) with n=2-9. Our work extends earlier theoretical studies which were limited to eight atoms and exposes that the polarizability/atom of the most stable stoichiometric configurations up to Ga(9)As(9) continues the monotonic downward trend with increasing size. Lastly, from the methodological point of view, our analysis shows that apart from polarizabilities, augmented pseudopotentials yield reliable first and second hyperpolarizability values as well.

  7. CO{sub 2} laser-based dispersion interferometer utilizing orientation-patterned gallium arsenide for plasma density measurements

    SciTech Connect

    Bamford, D. J.; Cummings, E. A.; Panasenko, D.; Fenner, D. B.; Hensley, J. M.; Boivin, R. L.; Carlstrom, T. N.; Van Zeeland, M. A.

    2013-09-15

    A dispersion interferometer based on the second-harmonic generation of a carbon dioxide laser in orientation-patterned gallium arsenide has been developed for measuring electron density in plasmas. The interferometer includes two nonlinear optical crystals placed on opposite sides of the plasma. This instrument has been used to measure electron line densities in a pulsed radio-frequency generated argon plasma. A simple phase-extraction technique based on combining measurements from two successive pulses of the plasma has been used. The noise-equivalent line density was measured to be 1.7 × 10{sup 17} m{sup −2} in a detection bandwidth of 950 kHz. One of the orientation-patterned crystals produced 13 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 13 W of peak power. Two crystals arranged sequentially produced 58 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 37 W of peak power.

  8. Epitaxial dysprosium phosphide grown by gas-source and solid-source MBE on gallium arsenide substrates

    NASA Astrophysics Data System (ADS)

    Sadwick, L. P.; Lee, P. P.; Patel, M.; Nikols, M.; Hwu, R. J.; Shield, J. E.; Streit, D. C.; Brehmer, D.; McCormick, K.; Allen, S. J.; Gedridge, R. W.

    1996-07-01

    We report the first known study of the growth of epitaxial dysprosium phosphide (DyP) grown on gallium arsenide (GaAs). DyP is lattice matched to GaAs, with the room-temperature mismatch being less than 0.01%. We have grown DyP on GaAs by gas-source and by solid-source molecular beam epitaxy using custom-designed group V thermal cracker cells and group III high temperature effusion cells. X-ray diffraction results show the DyP epilayer to be (001) single crystal on GaAs(001) substrate. Electrical and optical measurements performed to date are inconclusive as to whether DyP is a semi-metal or a semiconductor with a small band gap. The undoped films are n-type with measured electron concentrations on the order of 5 × 10 19-6 × 10 20cm -3 with mobilities of 1-10 cm 2/V · s. {DyP}/{GaAs} is stable in air with no apparent oxidation taking place, even after months of exposure to ambient untreated air. Material and surface science properties measured for {DyP}/{GaAs} include Hall measurements, 2ϑ and double-crystal X-ray diffraction spectra and photothermal deflection spectroscopy.

  9. Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells

    DOE PAGESBeta

    Eyderman, Sergey; John, Sajeev

    2016-06-23

    Here, we demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300-865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO2.more » Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm2 is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 103 cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%.« less

  10. A novel three-jet microreactor for localized metal-organic chemical vapour deposition of gallium arsenide: design and simulation

    NASA Astrophysics Data System (ADS)

    Konakov, S. A.; Krzhizhanovskaya, V. V.

    2016-08-01

    We present a novel three-jet microreactor design for localized deposition of gallium arsenide (GaAs) by low-pressure Metal-Organic Chemical Vapour Deposition (MOCVD) for semiconductor devices, microelectronics and solar cells. Our approach is advantageous compared to the standard lithography and etching technology, since it preserves the nanostructure of the deposited material, it is less time-consuming and less expensive. We designed two versions of reactor geometry with a 10-micron central microchannel for precursor supply and with two side jets of a dilutant to control the deposition area. To aid future experiments, we performed computational modeling of a simplified-geometry (twodimensional axisymmetric) microreactor, based on Navier-Stokes equations for a laminar flow of chemically reacting gas mixture of Ga(CH3)3-AsH3-H2. Simulation results show that we can achieve a high-rate deposition (over 0.3 μm/min) on a small area (less than 30 μm diameter). This technology can be used in material production for microelectronics, optoelectronics, photovoltaics, solar cells, etc.

  11. Structural anomalies in undoped gallium arsenide observed in high-resolution diffraction imaging with monochromatic synchrotron radiation

    NASA Technical Reports Server (NTRS)

    Steiner, B.; Kuriyama, M.; Dobbyn, R. C.; Laor, U.; Larson, D.

    1989-01-01

    Novel, streak-like disruption features restricted to the plane of diffraction have recently been observed in images obtained by synchrotron radiation diffraction from undoped, semi-insulating gallium arsenide crystals. These features were identified as ensembles of very thin platelets or interfaces lying in (110) planes, and a structural model consisting of antiphase domain boundaries was proposed. We report here the other principal features observed in high resolution monochromatic synchrotron radiation diffraction images: (quasi) cellular structure; linear, very low-angle subgrain boundaries in (110) directions, and surface stripes in a (110) direction. In addition, we report systematic differences in the acceptance angle for images involving various diffraction vectors. When these observations are considered together, a unifying picture emerges. The presence of ensembles of thin (110) antiphase platelet regions or boundaries is generally consistent not only with the streak-like diffraction features but with the other features reported here as well. For the formation of such regions we propose two mechanisms, operating in parallel, that appear to be consistent with the various defect features observed by a variety of techniques.

  12. High-performance organic/inorganic hybrid heterojunction based on Gallium Arsenide (GaAs) substrates and a conjugated polymer

    NASA Astrophysics Data System (ADS)

    Jameel, D. A.; Felix, J. F.; Aziz, M.; Al Saqri, N.; Taylor, D.; de Azevedo, W. M.; da Silva, E. F.; Albalawi, H.; Alghamdi, H.; Al Mashary, F.; Henini, M.

    2015-12-01

    In this paper, we present an extensive study of the electrical properties of organic-inorganic hybrid heterojunctions. Polyaniline (PANI) thin films were deposited by a very simple technique on (1 0 0) and (3 1 1)B n-type Gallium Arsenide (GaAs) substrates to fabricate hybrid devices with excellent electrical properties. The hybrid devices were electrically characterized using current-voltage (I-V), capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements in the temperature range 20-440 K. The analysis of I-V characteristics based on the thermionic emission mechanism has shown a decrease of the barrier height and an increase of the ideality factor at lower temperatures for both hybrid devices. The interface states were analyzed by series resistance obtained using the C-G-V methods. The interface state density (Dit) of PANI/(1 0 0) GaAs devices is approximately one order of magnitude higher than that of PANI/(3 1 1)B GaAs devices. This behaviour is attributed to the effect of crystallographic orientation of the substrates, and was confirmed by DLTS results as well. Additionally, the devices show excellent air stability, with rectification ratio values almost unaltered after two years of storage under ambient conditions, making the polyaniline an interesting conductor polymer for future devices applications.

  13. Gain and bandwidth analysis and comparison for gallium arsenide and silicon avalanche photodiodes with very thin multiplication layer

    NASA Astrophysics Data System (ADS)

    Majumder, Kanishka; Das, Nikhil Ranjan

    2013-05-01

    We describe the calculation of gain and bandwidth of an n+-i-p+ avalanche photodiode (APD) for a multiplication layer down to tens of nanometers. The computed results are used to make a comparative study of gallium arsenide (GaAs) and silicon (Si) APDs. In the analysis, the depletion region is discretized into equal energy segments to take into account the discontinuous nature of impact ionization in the multiplication layer due to dead-space effect. Also, the carrier diffusion from undepleted regions is considered to study the effect of low bias on the frequency response. Carrier distribution within the structure is obtained by a numerical solution of coupled equations and recurrence relations. The model is verified with some experimental data taken from literature. Results show that gain increases with bias more rapidly for thinner multiplication layer. The Si APD is thinner than GaAs APD for the same gain at a given bias. Diffusion causes significant reduction of bandwidth at a low gain, with the change being sharper for GaAs APD than for Si APD.

  14. Development of a unique laboratory standard: Indium gallium arsenide detector for the 500-1700 nm spectral region

    NASA Technical Reports Server (NTRS)

    1987-01-01

    A planar (5 mm diameter) indium gallium arsenide detector having a high (greater than 50 pct) quantum efficiency from the visible into the infrared spectrum (500 to 1700 nm) was fabricated. Quantum efficiencies as high as 37 pct at 510 nm, 58 pct at 820 nm and 62 pct at 1300 nm and 1550 nm were measured. A planar InP/InGaAs detector structure was also fabricated using vapor phase epitaxy to grow device structures with 0, 0.2, 0.4 and 0.6 micrometer thick InP caps. Quantum efficiency was studied as a function of cap thickness. Conventional detector structures were also used by completely etching off the InP cap after zinc diffusion. Calibrated quantum efficiencies were measured. Best results were obtained with devices whose caps were completely removed by etching. Certain problems still remain with these detectors including non-uniform shunt resistance, reproducibility, contact resistance and narrow band anti-reflection coatings.

  15. Gallium arsenide exposure impairs processing of particulate antigen by macrophages: modification of the antigen reverses the functional defect.

    PubMed

    Hartmann, Constance B; McCoy, Kathleen L

    2004-06-11

    Gallium arsenide (GaAs), a semiconductor used in the electronics industry, causes systemic immunosuppression in animals. The chemical's impact on macrophages to process the particulate antigen, sheep red blood cells (SRBC), for a T cell response in culture was examined after in vivo exposure of mice. GaAs-exposed splenic macrophages were defective in activating SRBC-primed lymph node T cells that could not be attributed to impaired phagocytosis. Modified forms of SRBC were generated to examine the compromised function of GaAs-exposed macrophages. SRBC were fixed to maintain their particulate nature and subsequently delipidated with detergent. Delipidation of intact SRBC was insufficient to restore normal antigen processing in GaAs-exposed macrophages. However, chemically exposed cells efficiently processed soluble sheep proteins. These findings suggest that the problem may lie in the release of sequestered sheep protein antigens, which then could be effectively cleaved to peptides. Furthermore, opsonization of SRBC with IgG compensated for the macrophage processing defect. The influence of signal transduction and phagocytosis via Fcgamma receptors on improved antigen processing could be dissociated. Immobilized anti-Fcgamma receptor antibody activated macrophages to secrete a chemokine, but did not enhance processing of unmodified SRBC by GaAs-exposed macrophages. Restoration of normal processing of particulate SRBC by chemically exposed macrophages involved phagocytosis through Fcgamma receptors. Hence, initial immune responses may be very sensitive to GaAs exposure, and the chemical's immunosuppression may be averted by opsonized particulate antigens.

  16. Acute electrophysiological effect of pulsed gallium-arsenide low-energy laser irradiation on isolated frog sciatic nerve.

    PubMed

    Cömelekoğlu, U; Bagiş, S; Büyükakilli, B; Sahin, G; Erdoğan, C; Kanik, A

    2002-01-01

    We evaluated the acute electrophysiological effects of low-energy pulsed laser irradiation on isolated frog sciatic nerve measured by extracellular recording technique. A pulsed gallium-arsenide (GaAs) laser (wavelength: 904 nm, pulse duration 220 ns, peak power per pulse: 27W, spot size: 0.28 cm(2), total applied energy density: 0.005-2.5J/cm(2)) was used for the experiment. Sixty isolated nerves were divided into six groups (n=10), each of which received a different laser dose. In each group, action potentials were recorded before laser irradiation which served as the control data. The extracellular action potentials were recorded for each combination of 1, 3, 5, 7, 10, 13 and 15 minutes of irradiation time and 4, 8, 16, 32, 64 and 128 repetition frequency by using a BIOPAC MP 100 Acquisition System Version 3.5.7 (Santa Barbara, USA). Action potential amplitude, area, duration and conduction velocity were measured. Statistical evaluation was performed using repeated measures variance analysis by SPSS 9.0. There were no statistically significant differences for action potential amplitude, area and conduction velocity among the laser groups and control data (p>0.05). The study showed that low-energy GaAs irradiation at 4-128 Hz repetition frequencies administered for irradiation times of 1-15 min generates no effect on action potential amplitude, area, duration and conduction velocity in isolated frog sciatic nerve.

  17. CO2 laser-based dispersion interferometer utilizing orientation-patterned gallium arsenide for plasma density measurements.

    PubMed

    Bamford, D J; Cummings, E A; Panasenko, D; Fenner, D B; Hensley, J M; Boivin, R L; Carlstrom, T N; Van Zeeland, M A

    2013-09-01

    A dispersion interferometer based on the second-harmonic generation of a carbon dioxide laser in orientation-patterned gallium arsenide has been developed for measuring electron density in plasmas. The interferometer includes two nonlinear optical crystals placed on opposite sides of the plasma. This instrument has been used to measure electron line densities in a pulsed radio-frequency generated argon plasma. A simple phase-extraction technique based on combining measurements from two successive pulses of the plasma has been used. The noise-equivalent line density was measured to be 1.7 × 10(17) m(-2) in a detection bandwidth of 950 kHz. One of the orientation-patterned crystals produced 13 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 13 W of peak power. Two crystals arranged sequentially produced 58 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 37 W of peak power.

  18. CO2 laser-based dispersion interferometer utilizing orientation-patterned gallium arsenide for plasma density measurements

    NASA Astrophysics Data System (ADS)

    Bamford, D. J.; Cummings, E. A.; Panasenko, D.; Fenner, D. B.; Hensley, J. M.; Boivin, R. L.; Carlstrom, T. N.; Van Zeeland, M. A.

    2013-09-01

    A dispersion interferometer based on the second-harmonic generation of a carbon dioxide laser in orientation-patterned gallium arsenide has been developed for measuring electron density in plasmas. The interferometer includes two nonlinear optical crystals placed on opposite sides of the plasma. This instrument has been used to measure electron line densities in a pulsed radio-frequency generated argon plasma. A simple phase-extraction technique based on combining measurements from two successive pulses of the plasma has been used. The noise-equivalent line density was measured to be 1.7 × 1017 m-2 in a detection bandwidth of 950 kHz. One of the orientation-patterned crystals produced 13 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 13 W of peak power. Two crystals arranged sequentially produced 58 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 37 W of peak power.

  19. Emergence of spin–orbit fields in magnetotransport of quasi-two-dimensional iron on gallium arsenide

    PubMed Central

    Hupfauer, T.; Matos-Abiague, A.; Gmitra, M.; Schiller, F.; Loher, J.; Bougeard, D.; Back, C. H.; Fabian, J.; Weiss, D.

    2015-01-01

    The desire for higher information capacities drives the components of electronic devices to ever smaller dimensions so that device properties are determined increasingly more by interfaces than by the bulk structure of the constituent materials. Spintronic devices, especially, benefit from the presence of interfaces—the reduced structural symmetry creates emergent spin–orbit fields that offer novel possibilities to control device functionalities. But where does the bulk end, and the interface begin? Here we trace the interface-to-bulk transition, and follow the emergence of the interfacial spin–orbit fields, in the conducting states of a few monolayers of iron on top of gallium arsenide. We observe the transition from the interface- to bulk-induced lateral crystalline magnetoanisotropy, each having a characteristic symmetry pattern, as the epitaxially grown iron channel increases from four to eight monolayers. Setting the upper limit on the width of the interface-imprinted conducting channel is an important step towards an active control of interfacial spin–orbit fields. PMID:26051594

  20. P-doping mechanisms in catalyst-free gallium arsenide nanowires.

    PubMed

    Dufouleur, Joseph; Colombo, Carlo; Garma, Tonko; Ketterer, Bernt; Uccelli, Emanuele; Nicotra, Marco; Fontcuberta i Morral, Anna

    2010-05-12

    Doped catalyst-free GaAs nanowires have been grown by molecular beam epitaxy with the gallium-assisted method. The spatial dependence of the dopant concentration and resistivity have been measured by Raman spectroscopy and four point electrical measurements. Along with theoretical considerations, the doping mechanisms have been revealed. Two competing mechanisms have been revealed: dopant incorporation from the side facets and from the gallium droplet. In the latter incorporation path, doping compensation seems to play an important role in the effective dopant concentration. Hole concentrations of at least 2.4 x 10(18) cm(-3) have been achieved, which to our knowledge is the largest p doping range obtained up to date. This work opens the avenue for the use of doped GaAs nanowires in advanced applications and in mesoscopic physics experiments.

  1. Ohmic contact formation process on low n-type gallium arsenide (GaAs) using indium gallium zinc oxide (IGZO)

    SciTech Connect

    Yang, Seong-Uk; Jung, Woo-Shik; Lee, In-Yeal; Jung, Hyun-Wook; Kim, Gil-Ho; Park, Jin-Hong

    2014-02-01

    Highlights: • We propose a method to fabricate non-gold Ohmic contact on low n-type GaAs with IGZO. • 0.15 A/cm{sup 2} on-current and 1.5 on/off-current ratio are achieved in the junction. • InAs and InGaAs formed by this process decrease an electron barrier height. • Traps generated by diffused O atoms also induce a trap-assisted tunneling phenomenon. - Abstract: Here, an excellent non-gold Ohmic contact on low n-type GaAs is demonstrated by using indium gallium zinc oxide and investigating through time of flight-secondary ion mass spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy, J–V measurement, and H [enthalpy], S [entropy], Cp [heat capacity] chemistry simulation. In is diffused through GaAs during annealing and reacts with As, forming InAs and InGaAs phases with lower energy bandgap. As a result, it decreases the electron barrier height, eventually increasing the reverse current. In addition, traps generated by diffused O atoms induce a trap-assisted tunneling phenomenon, increasing generation current and subsequently the reverse current. Therefore, an excellent Ohmic contact with 0.15 A/cm{sup 2} on-current density and 1.5 on/off-current ratio is achieved on n-type GaAs.

  2. Measurement of Impact Ionization Coefficients in Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Ozbek, Ayse Merve

    2011-12-01

    of the electric field has been accurately measured for both GaN epitaxial layers grown on bulk GaN substrates and GaN epitaxial layers grown on Sapphire substrates. The impact ionization coefficients for both electrons and holes are observed to decrease with increasing temperature. This is consistent with the measured increase in the breakdown voltage with temperature for high voltage Schottky barrier diodes. This is an important observation demonstrating that stable power devices can be fabricated from Gallium Nitride. Electron Beam Induced Current (EBIC) technique was employed in order to understand the role of defects on the breakdown characteristics of GaN. The impact ionization coefficients for electrons and holes measured at the defective site were found to be higher than those measured at a non-defective site. These results indicate that the breakdown voltage of GaN devices can be reduced due to the presence of defects.

  3. Sub-Half Micrometer Gate Lift-Off By Three Layer Resist Process Via Electron Beam Lithography For Gallium Arsenide Monolithic Microwave Integrated Circuits (MIMICs)

    NASA Astrophysics Data System (ADS)

    Nagarajan, Rao M.; Rask, Steven D.; King, Michael R.; Yard, Thomas K.

    1988-06-01

    A three layer resist process for gate lift-oft on Gallium Arsenide MIMICs by electron Dean and optical lithographies are described. The electron beam lithography process consists of Poly (Dimethyl Glutarimide) PMGI as tne planarizing layer, a Plasma Enhanced Chemical Vapour Deposition silicon nitride (SiN) as an intermediate barrier layer and Poly (Methyl methacrylate), PMMA, as the top imaging layer. The PivimA is exposed by Cambridge Electron beam system EBMF 6.4 at 20kev and developed in Methyl Ethyl Ketone/Iso Propyl Alcohol. The pattern is then transferred to the SiN layer by cF4/o2 plasma etcning. The SiN layer is then used as the mask to transfer the pattern to the PMGI layer by 02 kteactive Ion Etching until tne GaAS is exposed. The various processing parameters are optimized to obtain lip or overnang suitable for lift-off with 0.20μm gate dimension. After the GaAS has been recessed (to reduce the parasitic source resistance), a thick 9000Å Ti/Pt/Au gate metal is evaporated and the unwanted gate metal is lifted oft using PMGI stripper. To use the three layer resist process in optical litnograpny, the MG.'. planarizing layer and PECVD SiN layer is used along with optical pnotoresist AZ1450J as a top imaging layer. inc sofcbake, uV exposure dose (436 nm) and development time for AZ145UJ are optimized to obtain 0.5μm to 1.0μm gate dimensions. The etch parameters for the pattern transfer to SiN and tnen to PMGI layers are same as in tne above process. The process levels such as mesa, source/drain, contact and metal levels for GaAs mlivilt,s are defined by UV lithography (Karl Suss contact aligner) using single layer pnotoresist. A nign overlay accuracy is obtained by use of gold metal Dumps as registration marks for aligning tne electron Dean exposed gate to optically exposed source/drain channel. Thus a higher tnrougnput and better linewidtn control are obtained using electron beam/optical lithography tecnniques. This approach is currently used to

  4. A novel in-situ method for inhibiting surface roughening during the thermal oxide desorption etching of silicon and gallium arsenide

    NASA Astrophysics Data System (ADS)

    Pun, Arthur Fong-Yuen

    A method inhibiting surface roughening of silicon and gallium arsenide wafers during the thermal desorption of their native oxide layers is proposed and tested experimentally, with silicon results indicating a 75% reduction in surface roughness from an averaged value of 2.20 nm to 0.56 nm, and gallium arsenide results indicating a 76% reduction from an averaged surface roughness of 1.6 nm to 0.4 nm. This method does not significantly alter the semiconductor crystalline surface, thus retaining suitability for subsequent epitaxial growth, as demonstrated experimentally. The method is readily implementable in currently utilized deposition systems, subject to the requirements of material growth, substrate heating, and producing a non-oxidizing environment, either inert atmosphere or reduced pressures. The technique involves depositing a thin sacrificial film directly onto the native oxide surface at lower temperatures, of which the thickness is dependent on both the native oxide thickness and the oxide stochiometry initially present within the oxide layer, but has been found experimentally to be on the order of 0.5 nm -- 4 nm for a 2 nm to 4 nm air-formed native oxide layer. Upon heating this structure to high temperatures, the native oxide preferentially reacts with the sacrificial deposited film instead of the bulk wafer, resulting in the chemical reduction to volatile components, which are evaporated at these temperatures. This method is developed for silicon and gallium arsenide and examined experimentally utilizing atomic force microscopy and reflection high-energy electron diffraction. Different native oxide preparation techniques are theorized to yield varying chemical stochiometries, with experimental results elucidating information regarding these differences. Further, a modified tri-layer implementation, in which the deposited film is re-oxidized, is tested for applicability as a novel wafer pacification technique.

  5. Resonant second harmonic generation in a gallium nitride two-dimensional photonic crystal on silicon

    NASA Astrophysics Data System (ADS)

    Zeng, Y.; Roland, I.; Checoury, X.; Han, Z.; El Kurdi, M.; Sauvage, S.; Gayral, B.; Brimont, C.; Guillet, T.; Mexis, M.; Semond, F.; Boucaud, P.

    2015-02-01

    We demonstrate second harmonic generation in a gallium nitride photonic crystal cavity embedded in a two-dimensional free-standing photonic crystal platform on silicon. The photonic crystal nanocavity is optically pumped with a continuous-wave laser at telecom wavelengths in the transparency window of the nitride material. The harmonic generation is evidenced by the spectral range of the emitted signal, the quadratic power dependence vs. input power, and the spectral dependence of second harmonic signal. The harmonic emission pattern is correlated to the harmonic polarization generated by the second-order nonlinear susceptibilities χzxx (2 ), χzyy (2 ) and the electric fields of the fundamental cavity mode.

  6. Near-infrared gallium nitride two-dimensional photonic crystal platform on silicon

    SciTech Connect

    Roland, I.; Zeng, Y.; Han, Z.; Checoury, X.; Blin, C.; El Kurdi, M.; Ghrib, A.; Sauvage, S.; Boucaud, P.; Gayral, B.; Brimont, C.; Guillet, T.; Semond, F.

    2014-07-07

    We demonstrate a two-dimensional free-standing gallium nitride photonic crystal platform operating around 1550 nm and fabricated on a silicon substrate. Width-modulated waveguide cavities are integrated and exhibit loaded quality factors up to 34 000 at 1575 nm. We show the resonance tunability by varying the ratio of air hole radius to periodicity, and cavity hole displacement. We deduce a ∼7.9 dB/cm linear absorption loss for the suspended nitride structure from the power dependence of the cavity in-plane transmission.

  7. Near-infrared gallium nitride two-dimensional photonic crystal platform on silicon

    NASA Astrophysics Data System (ADS)

    Roland, I.; Zeng, Y.; Han, Z.; Checoury, X.; Blin, C.; El Kurdi, M.; Ghrib, A.; Sauvage, S.; Gayral, B.; Brimont, C.; Guillet, T.; Semond, F.; Boucaud, P.

    2014-07-01

    We demonstrate a two-dimensional free-standing gallium nitride photonic crystal platform operating around 1550 nm and fabricated on a silicon substrate. Width-modulated waveguide cavities are integrated and exhibit loaded quality factors up to 34 000 at 1575 nm. We show the resonance tunability by varying the ratio of air hole radius to periodicity, and cavity hole displacement. We deduce a ˜7.9 dB/cm linear absorption loss for the suspended nitride structure from the power dependence of the cavity in-plane transmission.

  8. Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells

    NASA Astrophysics Data System (ADS)

    Eyderman, Sergey; John, Sajeev

    2016-06-01

    We demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300–865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO2. Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm2 is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 103 cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%.

  9. Determination of boron in silicon-doped gallium arsenide by electrothermal atomic absorption spectrometry and ultraviolet-visible spectrophotometry.

    PubMed

    Taddia, Marco; Cerroni, Maria Grazia; Morelli, Elio; Musiani, Andrea

    2002-01-01

    Two methods have been developed for the determination of boron impurities in silicon-doped gallium arsenide (GaAs) for electronics. The first method employs the electrothermal atomic absorption spectrometry (ETAAS), the second, the UV-Vis molecular absorption spectrophotomety. In both cases the GaAs sample is decomposed with aqua regia (1+1). To prevent Ga(III) interference on the ETAAS determination of boron, a double extraction of the chlorogallic acid (HGaCl4) in diethyl ether is performed. To improve the overall ETAAS performance, the graphite tubes were pre-treated with iridium(III) and tungsten(IV). A mixed chemical modifier containing Ni(II), Sr(II) and citric acid was also used. The characteristic mass (m0) is 301 +/- 47 pg and the detection limit (3sB) is 2.4 microg g(-1). The classic UV-Vis spectrophotometric procedure using curcumin was also extended to the determination of boron in GaAs. By masking Ga(III) with EDTA and a preliminary extraction of boron with 2-ethyl-hexane 1,3-diol, performed on a semi-micro scale, a detection limit of 0.6 microg g(-1) was achieved. Both methods were applied to the analysis of two Si-doped GaAs samples which were suspected of being boron-contaminated. Results are compared with those obtained by direct analysis of the decomposed sample solution using the inductively coupled plasma atomic emission spectrometry (ICP-AES).

  10. Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells

    PubMed Central

    Eyderman, Sergey; John, Sajeev

    2016-01-01

    We demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300–865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO2. Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm2 is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 103 cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%. PMID:27334045

  11. Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells.

    PubMed

    Eyderman, Sergey; John, Sajeev

    2016-01-01

    We demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300-865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO2. Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm(2) is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 10(3) cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%. PMID:27334045

  12. Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells.

    PubMed

    Eyderman, Sergey; John, Sajeev

    2016-06-23

    We demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300-865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO2. Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm(2) is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 10(3) cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%.

  13. Effects of a low-level semiconductor gallium arsenide laser on local pathological alterations induced by Bothrops moojeni snake venom.

    PubMed

    Aranha de Sousa, Elziliam; Bittencourt, José Adolfo Homobono Machado; Seabra de Oliveira, Nayana Keyla; Correia Henriques, Shayanne Vanessa; dos Santos Picanço, Leide Caroline; Lobato, Camila Pena; Ribeiro, José Renato; Pereira, Washington Luiz Assunção; Carvalho, José Carlos Tavares; da Silva, Jocivânia Oliveira

    2013-10-01

    Antivenom therapy has been ineffective in neutralizing the tissue damage caused by snakebites. Among therapeutic strategies to minimize effects after envenoming, it was hypothesized that a low level laser would reduce complications and reduce the severity of local snake venom effects. In the current study, the effect of a low-level semiconductor gallium arsenide (GaAs) laser on the local pathological alterations induced by B. moojeni snake venom was investigated. The experimental groups consisted of five male mice, each administered either B. moojeni venom (VB), B. moojeni venom + antivenom (VAV), B. moojeni venom + laser (VL), B. moojeni venom + antivenom + laser (VAVL), or sterile saline solution (SSS) alone. Paw oedema was induced by intradermal administration of 0.05 mg kg(-1) of B. moojeni venom and was expressed in mm of directly induced oedema. Mice received by subcutaneous route 0.20 mg kg(-1) of venom for evaluating nociceptive activity and the time (in seconds) spent in licking and biting the injected paw was taken as an indicator of pain response. Inflammatory infiltration was determined by counting the number of leukocytes present in the gastrocnemius muscle after venom injection (0.10 mg kg(-1)). For histological examination of myonecrosis, venom (0.10 mg kg(-1)) was administered intramuscularly. The site of venom injection was irradiated by the GaAs laser and some animals received antivenom intraperitoneally. The results indicated that GaAs laser irradiation can help in reducing some local effects produced by the B. moojeni venom in mice, stimulating phagocytosis, proliferation of myoblasts and the regeneration of muscle fibers.

  14. Novel approach for n-type doping of HVPE gallium nitride with germanium

    NASA Astrophysics Data System (ADS)

    Hofmann, Patrick; Krupinski, Martin; Habel, Frank; Leibiger, Gunnar; Weinert, Berndt; Eichler, Stefan; Mikolajick, Thomas

    2016-09-01

    We present a novel method for germanium doping of gallium nitride by in-situ chlorination of solid germanium during the hydride vapour phase epitaxy (HVPE) process. Solid germanium pieces were placed in the doping line with a hydrogen chloride flow directed over them. We deduce a chlorination reaction taking place at 800 ° C , which leads to germanium chloroform (GeHCl3) or germanium tetrachloride (GeCl4). The reactor shows a germanium rich residue after in-situ chlorination experiments, which can be removed by hydrogen chloride etching. All gallium nitride crystals exhibit n-type conductivity, which shows the validity of the in-situ chlorination of germanium for doping. A complex doping profile is found for each crystal, which was assigned to a combination of localised supply of the dopant and sample rotation during growth and switch-off effects of the HVPE reactor.

  15. Photocurrent enhancement of an individual gallium nitride nanowire decorated with gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Sundararajan, Jency Pricilla; Sargent, Meredith; McIlroy, David N.

    2011-03-01

    Variation in electron transport properties of individual n-type gallium nitride (GaN) nanowire and gold decorated gallium nitride (Au-GaN) nanowire were studied with respect to laser exposure of different wavelength and intensity. Single nanowire devices were manufactured by photolithography process in nanotechnology cleanroom, were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). A drop in electrical conductivity of Au-GaN nanowire was observed relative to bare GaN nanowire. Under laser illumination, we noticed an enhancement in photocurrent in Au-GaN nanowire, which increased with increase in excitation power at ambient conditions. We present a comparative study of the opto-electrical behavior of bare GaN nanowire vs Au-GaN nanowire and explain the IV characteristics and FET characteristics with respect to the length and diameter of nanowire. USDA, UI-BANTech.

  16. The Effects of Thermal Cycling on Gallium Nitride and Silicon Carbide Semiconductor Devices for Aerospace Use

    NASA Technical Reports Server (NTRS)

    Patterson, Richard L.; Hammoud, Ahmad

    2012-01-01

    Electronics designed for use in NASA space missions are required to work efficiently and reliably under harsh environment conditions. These Include radiation, extreme temperatures, thermal cycling, to name a few. Preliminary data obtained on new Gallium Nitride and Silicon Carbide power devices under exposure to radiation followed by long term thermal cycling are presented. This work was done in collaboration with GSFC and JPL in support of the NASA Electronic Parts and Packaging (NEPP) Program

  17. Gas source molecular beam epitaxy of scandium nitride on silicon carbide and gallium nitride surfaces

    SciTech Connect

    King, Sean W. Davis, Robert F.; Nemanich, Robert J.

    2014-11-01

    Scandium nitride (ScN) is a group IIIB transition metal nitride semiconductor with numerous potential applications in electronic and optoelectronic devices due to close lattice matching with gallium nitride (GaN). However, prior investigations of ScN have focused primarily on heteroepitaxial growth on substrates with a high lattice mismatch of 7%–20%. In this study, the authors have investigated ammonia (NH{sub 3}) gas source molecular beam epitaxy (NH{sub 3}-GSMBE) of ScN on more closely lattice matched silicon carbide (SiC) and GaN surfaces (<3% mismatch). Based on a thermodynamic analysis of the ScN phase stability window, NH{sub 3}-GSMBE conditions of 10{sup −5}–10{sup −4} Torr NH{sub 3} and 800–1050 °C where selected for initial investigation. In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Rutherford backscattering measurements showed all ScN films grown using these conditions were stoichiometric. For ScN growth on 3C-SiC (111)-(√3 × √3)R30° carbon rich surfaces, the observed attenuation of the XPS Si 2p and C 1s substrate core levels with increasing ScN thickness indicated growth initiated in a layer-by-layer fashion. This was consistent with scanning electron microscopy (SEM) images of 100–200 nm thick films that revealed featureless surfaces. In contrast, ScN films grown on 3C-SiC (111)-(3 × 3) and 3C-SiC (100)-(3 × 2) silicon rich surfaces were found to exhibit extremely rough surfaces in SEM. ScN films grown on both 3C-SiC (111)-(√3 × √3)R30° and 2H-GaN (0001)-(1 × 1) epilayer surfaces exhibited hexagonal (1 × 1) low energy electron diffraction patterns indicative of (111) oriented ScN. X-ray diffraction ω-2θ rocking curve scans for these same films showed a large full width half maximum of 0.29° (1047 arc sec) consistent with transmission electron microscopy images that revealed the films to be poly-crystalline with columnar grains oriented at ≈15° to the [0001] direction of the

  18. Transport studies on very high purity gallium arsenide grown by organometallic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Tsang, Cheung Fat

    1997-12-01

    Very high purity GaAs layers have been grown in a modified organometallic vapor phase epitaxy (OMVPE) system using trimethyl gallium (TMGa) and arsine including the purest layer ever reported from these chemical sources with purity approaching the very best reported by the chloride-VPE technique. Several of these high purity GaAs samples were chemically etched into Kelvin and Greek cross structures which were fabricated with PdGe ohmic contacts for the specific contact resistivity, Hall effect, and persistent photo-Hall measurements performed in the full temperature range (4.2 K to 305 K). Resonant excitation photoluminescence technique operated at zero magnetic field was used to discriminate the impurity species in the very high purity layer where Ge and C were detected as the principle impurities. The consistency of growing GaAs layers with very low donor impurity concentration was found to be limited by the variability of arsine quality from bottle to bottle. Peak mobilities of the high purity GaAs layers are shown to be linearly dependent on the donor concentration while the low temperature mobilities are limited by the acceptor impurity level and the degree of carrier compensation. The acoustic deformation potential is generally conceived as a material constant but is demonstrated in the analysis as a variable parameter that has a linear relationship with the total impurity concentration. As for the contact resistivity of PdGe contacts on high purity GaAs layers, a room temperature Nsb{D}sp{-1/2} dependence was confirmed. Inhomogeneities in several samples were detected by the persistent photo-Hall measurements and the impurity band formation-like characteristics were observed at the very low temperatures. This technique was also used to facilitate the measurement of a carrier-depleted, high purity GaAs layer that has a relatively high carrier compensation. Finally, chemical etching techniques for the fabrication of the measurement samples including the micro

  19. A final report for: Gallium arsenide P-I-N detectors for high-sensitivity imaging of thermal neutrons

    SciTech Connect

    Vernon, Stanley M.

    1999-04-01

    This SBIR Phase I developed neutron detectors made from gallium arsenide (GaAs) p-type/ intrinsic/n-type (P-I-N) diodes grown by metalorganic chemical vapor deposition (MOCVD) onto semi-insulating (S1) bulk GaAs wafers. A layer of isotonically enriched boron-10 evaporated onto the front surface serves to convert incoming neutrons into lithium ions and a 1.47 MeV alpha particle which creates electron-hole pairs that are detected by the GaAs diode. Various thicknesses of ''intrinsic'' (I) undoped GaAs were tested, as was use of a back-surface field (BSF) formed from a layer of Al{sub x}Ga{sub 1-x}As. Schottky-barrier diodes formed from the same structures without the p+ GaAs top layer were tested as a comparison. After mesa etching and application of contacts, devices were tested in visible light before application of the boron coating. Internal quantum efficiency (IQE) of the best diode near the GaAs bandedge is over 90%. The lowest dark current measured is 1 x 10{sup -12} amps at -1 V on a 3mm x 3mm diode, or a density of 1.1 x 10{sup -11} amps cm{sup -2}, with many of the diode structures tested having nearly similar results. The PIN diodes were significantly better than the Schottky barrier device, which had six orders of magnitude higher dark current. Diodes were characterized in terms of their current-mode response to 5.5 MeV alpha particles from 241-Americium. These radiation-induced currents were as high as 9.78 x 10{sup -7} A cm{sup -1} on a PIN device with an Al{sub x}Ga{sub 1-x}As BSF. Simple PIN diodes had currents as high as 2.44 x 10{sup -7} A cm{sup -2}, with thicker undoped layers showing better sensitivity. Boron coatings were applied, and response to neutrons tested at University of Michigan by Dr. Doug McGregor. Devices with PIN and Schottky barrier designs showed neutron detection efficiencies as high as 2% on 5 {micro}m thick devices, with no need for external bias voltages. PIN diodes showed higher breakdown voltages and lower noise

  20. Sapphire surface preparation and gallium nitride nucleation by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Dwikusuma, Fransiska

    The nucleation and initial growth of gallium nitride (GaN) films on sapphire substrates using hydride vapor phase epitaxy (HVPE) technique depends on many factors including the chemical treatment of sapphire surface, nitridation, and the specific growth conditions. Liquid and gas phase treatments of the sapphire surface were systematically studied as a function of temperature and time. Phosphoric acid (H3PO4) etches sapphire preferentially at defect sites and resulted in pits formation on the surface, while etching in sulfuric acid (H2SO4) can produce a smooth, pit-free surface. Air-annealing the sapphire at 1400°C produces an atomically smooth surface consisting of a terrace-and-step structure. The mechanism of sapphire nitridation within the HVPE environment was elucidated. During nitridation, nitrogen is incorporated into the sapphire surface. The sapphire nitridation mechanism can be modeled as a diffusion couple of aluminum nitride (AlN) and aluminum oxide (Al2O 3), where N3- and O2- inter-diffuse in the 'rigid' Al3+ framework. Nitrogen diffuses into sapphire and substitutes for oxygen to bond with aluminum. The replaced oxygen diffuses out to the surface. The overall nitridation rate is controlled by the diffusion of oxygen. Sapphire surface treatments of air-annealing and liquid-based etchings have different effects on nitridation and HVPE GaN nucleation. Upon nitridation, the air-annealed sapphire has ˜1.5 times higher nitrogen content compared to liquid-based etchings. Nevertheless, the air-annealed sapphire yields the lowest density of GaN islands. Sapphire nitridation, which yields a thin AlN layer, results in the growth of higher GaN island densities with a smaller mosaic spread. Sapphire surface, which is etched in H2SO4 and then nitridated, produces a high density GaN islands resulting in improved-quality of thick GaN films. The nucleation and initial growth kinetics of GaN on sapphire grown by HVPE were investigated. As the growth temperature

  1. Charge accumulation at a threading edge dislocation in gallium nitride

    SciTech Connect

    Leung, K.; Wright, A.F.; Stechel, E.B.

    1999-04-01

    We have performed Monte Carlo calculations to determine the charge accumulation on threading edge dislocations in GaN as a function of the dislocation density and background dopant density. Four possible core structures have been examined, each of which produces defect levels in the gap and may therefore act as electron or hole traps. Our results indicate that charge accumulation, and the resulting electrostatic interactions, can change the relative stabilities of the different core structures. Structures having Ga and N vacancies at the dislocation core are predicted to be stable under nitrogen-rich and gallium-rich growth conditions, respectively. Due to dopant depletion at high dislocation density and the multitude of charge states, the line charge exhibits complex crossover behavior as the dopant and dislocation densities vary. {copyright} {ital 1999 American Institute of Physics.}

  2. Process for growing epitaxial gallium nitride and composite wafers

    DOEpatents

    Weber, Eicke R.; Subramanya, Sudhir G.; Kim, Yihwan; Kruger, Joachim

    2003-05-13

    A novel growth procedure to grow epitaxial Group III metal nitride thin films on lattice-mismatched substrates is proposed. Demonstrated are the quality improvement of epitaxial GaN layers using a pure metallic Ga buffer layer on c-plane sapphire substrate. X-ray rocking curve results indicate that the layers had excellent structural properties. The electron Hall mobility increases to an outstandingly high value of .mu.>400 cm.sup.2 /Vs for an electron background concentration of 4.times.10.sup.17 cm.sup.-3.

  3. The challenge of decomposition and melting of gallium nitride under high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Porowski, S.; Sadovyi, B.; Gierlotka, S.; Rzoska, S. J.; Grzegory, I.; Petrusha, I.; Turkevich, V.; Stratiichuk, D.

    2015-10-01

    Gallium nitride (GaN) is considered to be one of the most important semiconductors nowadays. In this report a solution of the long standing puzzle regarding GaN decomposition and melting under high pressure and high temperature is presented. This includes the discussion of results obtained so far. The possibility of a consistent parameterisation of pressure (P) evolution of the melting temperature (Tm) in basic semiconductors (GaN, germanium, silicon…), independently from signs of dTm / dP is also presented.

  4. Effects of Radiation and Long-Term Thermal Cycling on EPC 1001 Gallium Nitride Transistors

    NASA Technical Reports Server (NTRS)

    Patterson, Richard L.; Scheick, Leif; Lauenstein, Jean-Marie; Casey, Megan; Hammoud, Ahmad

    2012-01-01

    Electronics designed for use in NASA space missions are required to work efficiently and reliably under harsh environment conditions. These include radiation, extreme temperatures, and thermal cycling, to name a few. Data obtained on long-term thermal cycling of new un-irradiated and irradiated samples of EPC1001 gallium nitride enhancement-mode transistors are presented. This work was done by a collaborative effort including GRC, GSFC, and support the NASA www.nasa.gov 1 JPL in of Electronic Parts and Packaging (NEPP) Program

  5. Free-standing gallium nitride membrane-based sensor for the impedimetric detection of alcohols

    NASA Astrophysics Data System (ADS)

    Alifragis, Y.; Roussos, G.; Pantazis, A. K.; Konstantinidis, G.; Chaniotakis, N.

    2016-02-01

    We report on the fabrication and characterization of single-crystal Gallium Nitride (GaN) membrane organic gas sensor. The sensing device is based on the highly stable free-standing III-nitride membrane, and it is probed using non-destructive impedance spectroscopy. Monitoring the effect of a series of polar organic molecules on the electrochemical impedance spectrum of the sensing membrane in the frequency range of 1 mHz to 0.1 MHz at room temperature, we concluded that the sensor is highly sensitive to alcohols, in the gas phase, with selectivity that depends on the molecular weight and vapor pressure of the molecules. The highly robust and stable GaN crystalline membrane and the ability to test these sensors using impedance spectroscopy and electrochemical probing techniques suggest that single crystal GaN-based sensors can find a wide range of applications in harsh and extreme environments.

  6. Resonant second harmonic generation in a gallium nitride two-dimensional photonic crystal on silicon

    SciTech Connect

    Zeng, Y.; Roland, I.; Checoury, X.; Han, Z.; El Kurdi, M.; Sauvage, S.; Boucaud, P.; Gayral, B.; Brimont, C.; Guillet, T.; Mexis, M.; Semond, F.

    2015-02-23

    We demonstrate second harmonic generation in a gallium nitride photonic crystal cavity embedded in a two-dimensional free-standing photonic crystal platform on silicon. The photonic crystal nanocavity is optically pumped with a continuous-wave laser at telecom wavelengths in the transparency window of the nitride material. The harmonic generation is evidenced by the spectral range of the emitted signal, the quadratic power dependence vs. input power, and the spectral dependence of second harmonic signal. The harmonic emission pattern is correlated to the harmonic polarization generated by the second-order nonlinear susceptibilities χ{sub zxx}{sup (2)}, χ{sub zyy}{sup (2)} and the electric fields of the fundamental cavity mode.

  7. Advanced Epi Tools for Gallium Nitride Light Emitting Diode Devices

    SciTech Connect

    Patibandla, Nag; Agrawal, Vivek

    2012-12-01

    Over the course of this program, Applied Materials, Inc., with generous support from the United States Department of Energy, developed a world-class three chamber III-Nitride epi cluster tool for low-cost, high volume GaN growth for the solid state lighting industry. One of the major achievements of the program was to design, build, and demonstrate the world’s largest wafer capacity HVPE chamber suitable for repeatable high volume III-Nitride template and device manufacturing. Applied Materials’ experience in developing deposition chambers for the silicon chip industry over many decades resulted in many orders of magnitude reductions in the price of transistors. That experience and understanding was used in developing this GaN epi deposition tool. The multi-chamber approach, which continues to be unique in the ability of the each chamber to deposit a section of the full device structure, unlike other cluster tools, allows for extreme flexibility in the manufacturing process. This robust architecture is suitable for not just the LED industry, but GaN power devices as well, both horizontal and vertical designs. The new HVPE technology developed allows GaN to be grown at a rate unheard of with MOCVD, up to 20x the typical MOCVD rates of 3{micro}m per hour, with bulk crystal quality better than the highest-quality commercial GaN films grown by MOCVD at a much cheaper overall cost. This is a unique development as the HVPE process has been known for decades, but never successfully commercially developed for high volume manufacturing. This research shows the potential of the first commercial-grade HVPE chamber, an elusive goal for III-V researchers and those wanting to capitalize on the promise of HVPE. Additionally, in the course of this program, Applied Materials built two MOCVD chambers, in addition to the HVPE chamber, and a robot that moves wafers between them. The MOCVD chambers demonstrated industry-leading wavelength yield for GaN based LED wafers and industry

  8. Novel approach to realizing quasi-phase-matched gallium arsenide optical parametric oscillators for use in mid-IR laser systems

    NASA Astrophysics Data System (ADS)

    Mason, Paul D.; McBrearty, Euan J.; Orchard, David A.; Harris, Michael R.; Lewis, Keith L.

    2004-06-01

    Most of the applications that require frequency agile solid state laser systems for use in the mid-infrared are centred on the development of optical parametric oscillators. These exploit the non-linear optical characteristics of non-centrosymmetric materials, in particular the chalcopyrite class of materials that includes AgGaSe2 and ZnGeP2. Whilst such materials are generally difficult to produce, major strides have been made in recent years to optimise crystal growth processes which have enabled the generation of moderate laser output powers. Other approaches have been centred on the use of periodically poled lithium niobate and diffusion bonded gallium arsenide. The latter system is particularly attractive because it exploits a readily available crystalline material, but its implementation is difficult because of the need for an ultra-clean processing environment and relatively high bonding temperatures. This paper describes progress in the development of a new, low-temperature approach for achieving quasi-phase matched gallium arsenide by bonding with an index-matched chalcogenide glass. A major advantage of this approach is the tolerance to GaAs wafer thickness variations and to defects at the surface of the GaAs wafers. Several glass compositions in the germanium-arsenic-selenium-tellurium system have the desired refractive indices, but only some provide the characteristics necessary to ensure the formation of stable low-loss bonds. The glass bonding process begins by RF sputtering films of the glass from pre-manufactured targets onto each side of individual GaAs substrates. These coated substrates are then assembled in a vacuum oven and uniaxially pressed under carefully controlled conditions until a single composite assembly is formed. Issues such as glass purity, the integrity of the sputtering process and choice of pressing conditions are important in ensuring that a high quality non-linear crystal is produced.

  9. Study of manganese doped gallium nitride for spintronic applications

    NASA Astrophysics Data System (ADS)

    Arkun, Fevzi Erdem

    Spintronics is an emerging field in which the spin of carriers in addition to the charge of carriers can be used to achieve new functionalities in electronic devices. The availability of materials exhibiting ferromagnetism above room temperature is prerequisite for realizing such devices. Materials suitable for spintronic applications are desired to be compatible with conventional growth and fabrication techniques in addition to exhibiting above room temperature ferromagnetic properties. In this research the growth of GaMnN has been achieved on (0001) sapphire substrates by metal organic chemical vapor deposition using TMGa and (EtCp 2)Mn as organometallic precursors. Magnetic characterization of the grown films was performed by a Superconducting Quantum Interference Device (SQUID) at room temperature. Ferromagnetic properties were observed above room temperature for this material. Co-doping of ferromagnetic GaMnN by silicon and magnesium was performed and ferromagnetic properties of GaMnN have been found to depend on the Fermi level in the crystal itself. The mechanism of ferromagnetism in this material was proposed to be carrier mediated. The magnetic properties were also altered by carrier transfer at a heterointerface indicating that the electronic band structure of the crystal affects the magnetic properties of this material. Growth of GaN based blue light emitting diode structures were achieved by MOCVD using conventional organometallic sources. Fabrication of grown structures was performed in a clean room using standard fabrication techniques for III-Nitrides. Two spin-LEDs containing GaMnN injector layers were also grown to determine the polarization state of the emission from these spin-LEDs.

  10. An electron beam induced current study of gallium nitride and diamond materials

    SciTech Connect

    Cropper, A.D.; Moore, D.J.; Scott, C.S.; Green, R.

    1995-12-31

    The continual need for microelectronic devices that operate under severe electronic and environmental conditions (high temperature, high frequency, high power, and radiation tolerance) has sustained research in wide bandgap semiconductor materials. The properties suggest these wide-bandgap semiconductor materials have tremendous potential for military and commercial applications. High frequency bipolar transistors and field effect transistors, diodes, and short wavelength optical devices have been proposed using these materials. Although research efforts involving the study of transport properties in Gallium Nitride (GaN) and Diamond have made significant advances, much work is still needed to improve the material quality so that the electrophysical behavior of device structures can be further understood and exploited. Electron beam induced current (EBIC) measurements can provide a method of understanding the transport properties in Gallium Nitride (GaN) and Diamond. This technique basically consists of measuring the current or voltage transient response to the drift and diffusion of carriers created by a short-duration pulse of radiation. This method differs from other experimental techniques because it is based on a fast transient electron beam probe created from a high speed, laser pulsed photoemission system.

  11. Vapor-phase epitaxy of gallium nitride by gallium arc discharge evaporation

    NASA Astrophysics Data System (ADS)

    Heikman, S.; Keller, S.; Mishra, U. K.

    2006-08-01

    Vapor-phase epitaxy of GaN was performed by combining ammonia with gallium evaporated into an inert gas stream by a DC arc discharge, and letting the mixture pass through a pair of heated graphite susceptors. Growth rates as high as 30 μm/h were achieved. The growth on the top sample was specular in a large area, and was of high quality as characterized by atomic force microscopy and photoluminescence spectroscopy. The bottom sample had a high density of macroscopic defects, presumably caused by Ga droplets in the gas phase resulting from the arc evaporation process. The experimental growth rate was found to be less than {1}/{3} of values predicted in a computer flow dynamic model of the growth system, and Ga-NH 3 pre-reactions were implicated as the likely cause of the discrepancy. The growth efficiency, calculated to 2%, could arguably be improved by reducing the reactor growth pressure, and by changing the reactor geometry to avoid Ga condensation on walls. Potential advantages of the described growth technique are cheap source materials of high purity and low equipment costs. Furthermore, since no corrosive gasses were used, hardware corrosion and gas-phase impurities can be reduced.

  12. Acute oral gallium arsenide exposure and changes in certain hematological, hepatic, renal and immunological indices at different time intervals in male Wistar rats.

    PubMed

    Flora, S J; Kumar, P; Kannan, G M; Rai, G P

    1998-01-31

    Male albino rats were given a single oral dose of gallium arsenide (GaAs) (100, 200 or 500 mg/kg). Erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity was inhibited in all the three GaAs-exposed groups accompanied by elevated urinary excretion of ALA. A significant increase in serum aspartate aminotransferase (AST) activity, and gamma-glutamyltranspeptidase (gamma-GT) was observed. A significant increase in hepatic malondialdehyde (MDA) and a decrease in hepatic glutathione contents were also noted. Renal alkaline phosphatase activity, urinary ALA and protein excretion increased significantly on GaAs exposure. These changes were accompanied by significant alterations in almost all the immunological variables, with an increase in gallium and arsenic concentration in blood and soft tissues. While most of the above biochemical alterations were prominent at day 7 following single exposure to 200 and 500 mg/kg GaAs, most of the immunological indices altered with all the three doses and remained high even at day 21. The results suggest only a moderate effect of GaAs on renal and hepatic tissues. By contrast, immunological and haematological systems are the most vulnerable to the toxic effects of GaAs.

  13. Co-administration of meso 2,3-dimercaptosuccinic acid monoesters reduces arsenic concentration and oxidative stress in gallium arsenide exposed rats.

    PubMed

    Flora, Swaran J S; Bhatt, Kapil; Dwivedi, Nidhi; Pachauri, Vidhu; Kushwah, Pramod K

    2011-07-01

    1. Gallium arsenide (GaAs), a semiconductor, exerts toxicity as a result of its constitutive moieties; that is, gallium and arsenic that becomes dissociated after exposure. The present study focuses on reducing arsenic concentration from the target organs using monoesters of meso 2,3-dimercaptosuccinic acid (DMSA) either individually or in combination. 2. Animals were exposed to GaAs (0.0014 mol/kg, orally for 8 weeks) and then treated with monoisoamyl DMSA (MiADMSA), monocyclohexyl DMSA (MchDMSA) or monomethyl DMSA (MmDMSA) either individually (0.3 mmol/kg, orally) or in combination (0.15 mmol/kg each, orally) for five consecutive days. 3. GaAs exposure significantly inhibited blood δ-aminolevulinic acid dehydrogenase (ALAD), suggesting alterations in the heme synthesis pathway. Whereas a significant increase in blood, liver and kidney reactive oxygen species accompanied by an increase in lipid peroxidation points to the involvement of oxidative stress in GaAs toxicity. 4. GaAs also significantly disturbed glutathione metabolism. Hepatic and renal catalase activity decreased significantly, whereas hepatic and renal superoxide dismutase activity, as well as serum transaminases activity, showed marginal increase. Treatment with MiADMSA in combination with MchDMSA showed better therapeutic efficacy compared with other treatments in the aforementioned variables. 5. Co-administration of MiADMSA with MchDMSA provided better therapeutic effects, including reduction of arsenic burden, compared with all other treatments.

  14. Metalorganic chemical vapor deposition of gallium nitride on sacrificial substrates

    NASA Astrophysics Data System (ADS)

    Fenwick, William Edward

    GaN-based light emitting diodes (LEDs) face several challenges if the technology is to continue to make a significant impact in general illumination, and on technology that has become known as solid state lighting (SSL). Two of the most pressing challenges for the continued penetration of SSL into traditional lighting applications are efficacy and total lumens from the device, and their related cost. The development of alternative substrate technologies is a promising avenue toward addressing both of these challenges, as both GaN-based device technology and the associated metalorganic chemical vapor deposition (MOCVD) technology are already relatively mature technologies with a well-understood cost base. Zinc oxide (ZnO) and silicon (Si) are among the most promising alternative substrates for GaN epitaxy. These substrates offer the ability to access both higher efficacy and lumen devices (ZnO) at a much reduced cost. This work focuses on the development of MOCVD growth processes to yield high quality GaN-based materials and devices on both ZnO and Si. ZnO is a promising substrate for growth of low defect-density GaN because of its similar lattice constant and thermal expansion coefficient. The major hurdles for GaN growth on ZnO are the instability of the substrate in a hydrogen atmosphere, which is typical of nitride growth conditions, and the inter-diffusion of zinc and oxygen from the substrate into the GaN-based epitaxial layer. A process was developed for the MOCVD growth of GaN and InxGa 1-xN on ZnO that attempted to address these issues. The structural and optical properties of these films were studied using various techniques. X-ray diffraction (XRD) showed the growth of wurtzite GaN on ZnO, and room-temperature photoluminescence (RT-PL) showed near band-edge luminescence from the GaN and InxGa1-xN layers. However, high zinc and oxygen concentrations due to interdiffusion near the ZnO substrate remained an issue; therefore, the diffusion of zinc and oxygen

  15. Microstructure and micro-Raman studies of nitridation and structure transition of gallium oxide nanowires

    SciTech Connect

    Ning, J.Q.; Xu, S.J.; Wang, P.W.; Song, Y.P.; Yu, D.P.; Shan, Y.Y.; Lee, S.T.; Yang, H.

    2012-11-15

    Here we present a detailed study on nitridation and structure transition in monoclinic gallium oxide ({beta}-Ga{sub 2}O{sub 3}) nanowires grown on Si substrates with chemical vapor phase epitaxy. The nanowires were systematically nitridated at different temperatures. Their morphologies and microstructures were precisely characterized using field-emission scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and confocal micro-Raman spectroscopy. It is found that heat treatment of Ga{sub 2}O{sub 3} nanowires in the gas of ammonia results in rich substructures including the Ga{sub 2}O{sub 3} phase, the crystalline GaN phase, and other meta structures. The identification of these structures helps to understand some interesting phenomena observed in nanostructures, such as the microstructural origin of the unknown Raman lines in GaN nanowires. - Highlights: Black-Right-Pointing-Pointer Nitridation and structure transition of Ga{sub 2}O{sub 3} significantly depend on temperature. Black-Right-Pointing-Pointer G-N bonds form at lower temperatures but the Ga{sub 2}O{sub 3} lattice is still dominant. Black-Right-Pointing-Pointer Amorphous GaN coexists with crystalline Ga{sub 2}O{sub 3} at higher temperatures. Black-Right-Pointing-Pointer Crystalline GaN with distinct morphology is obtained at much higher temperatures.

  16. Gallium

    SciTech Connect

    1996-01-01

    Discovered in 1875 through a study of its spectral properties, gallium was the first element to be uncovered following the publication of Mendeleev`s Periodic Table. French chemist, P.E. Lecoq de Boisbaudran, named his element discovery in honor of his native country; gallium is derived from the Latin word for France-{open_quotes}Gallia.{close_quotes}. This paper describes the properties, sources, and market for gallium.

  17. Two-dimensional dopant profiling of gallium nitride p-n junctions by scanning capacitance microscopy

    NASA Astrophysics Data System (ADS)

    Lamhamdi, M.; Cayrel, F.; Frayssinet, E.; Bazin, A. E.; Yvon, A.; Collard, E.; Cordier, Y.; Alquier, D.

    2016-04-01

    Two-dimensional imaging of dopant profiles for n and p-type regions are relevant for the development of new power semiconductors, especially for gallium nitride (GaN) for which classical profiling techniques are not adapted. This is a challenging task since it needs a technique with simultaneously good sensitivity, high spatial resolution and high dopant gradient resolution. To face these challenges, scanning capacitance microscopy combined with Atomic Force Microscopy is a good candidate, presenting reproducible results, as demonstrated in literature. In this work, we attempt to distinguish reliably and qualitatively the various doping concentrations and type at p-n and unipolar junctions. For both p-n and unipolar junctions three kinds of samples were prepared and measured separately. The space-charge region of the p-n metallurgical junction, giving rise to different contrasts under SCM imaging, is clearly observed, enlightening the interest of the SCM technique.

  18. Radiation and Thermal Cycling Effects on EPC1001 Gallium Nitride Power Transistors

    NASA Technical Reports Server (NTRS)

    Patterson, Richard L.; Scheick, Leif Z.; Lauenstein, Jean M.; Casey, Megan C.; Hammoud, Ahmad

    2012-01-01

    Electronics designed for use in NASA space missions are required to work efficiently and reliably under harsh environment conditions. These include radiation, extreme temperatures, and thermal cycling, to name a few. Information pertaining to performance of electronic parts and systems under hostile environments is very scarce, especially for new devices. Such data is very critical so that proper design is implemented in order to ensure mission success and to mitigate risks associated with exposure of on-board systems to the operational environment. In this work, newly-developed enhancement-mode field effect transistors (FET) based on gallium nitride (GaN) technology were exposed to various particles of ionizing radiation and to long-term thermal cycling over a wide temperature range. Data obtained on control (un-irradiated) and irradiated samples of these power transistors are presented and the results are discussed.

  19. Positive focal shift of gallium nitride high contrast grating focusing reflectors

    NASA Astrophysics Data System (ADS)

    He, Shumin; Wang, Zhenhai; Liu, Qifa

    2016-09-01

    We design a type of metasurfaces capable of serving as a visible-light focusing reflector based on gallium nitride (GaN) high contrast gratings (HCGs). The wavefront of the reflected light is precisely manipulated by spatial variation of the grating periods along the subwavelength ridge array to achieve light focusing. Different from conventional negative focal shift effect, a positive focal shift is observed in such focusing reflectors. Detailed investigations of the influence of device size on the focusing performance, especially the focal length, are preformed via a finite element method . The results show that all performance parameters are greatly affected by the reflector size. A more concentrated focal point, or a better focusing capability, can be achieved by larger size. With increasing reflector size, the achieved focal length decreases and gradually approaches to the design, thus the corresponding positive focal shift decreases. Our results are helpful for understanding the visible-light control of the planar HCG-based focusing reflectors.

  20. Gallium Nitride Nanowires and Heterostructures: Toward Color-Tunable and White-Light Sources.

    PubMed

    Kuykendall, Tevye R; Schwartzberg, Adam M; Aloni, Shaul

    2015-10-14

    Gallium-nitride-based light-emitting diodes have enabled the commercialization of efficient solid-state lighting devices. Nonplanar nanomaterial architectures, such as nanowires and nanowire-based heterostructures, have the potential to significantly improve the performance of light-emitting devices through defect reduction, strain relaxation, and increased junction area. In addition, relaxation of internal strain caused by indium incorporation will facilitate pushing the emission wavelength into the red. This could eliminate inefficient phosphor conversion and enable color-tunable emission or white-light emission by combining blue, green, and red sources. Utilizing the waveguiding modes of the individual nanowires will further enhance light emission, and the properties of photonic structures formed by nanowire arrays can be implemented to improve light extraction. Recent advances in synthetic methods leading to better control over GaN and InGaN nanowire synthesis are described along with new concept devices leading to efficient white-light emission. PMID:26032973

  1. Gallium nitride is biocompatible and non-toxic before and after functionalization with peptides.

    PubMed

    Jewett, Scott A; Makowski, Matthew S; Andrews, Benjamin; Manfra, Michael J; Ivanisevic, Albena

    2012-02-01

    The toxicity of semiconductor materials can significantly hinder their use for in vitro and in vivo applications. Gallium nitride (GaN) is a material with remarkable properties, including excellent chemical stability. This work demonstrated that functionalized and etched GaN surfaces were stable in aqueous environments and leached a negligible amount of Ga in solution even in the presence of hydrogen peroxide. Also, GaN surfaces in cell culture did not interfere with nearby cell growth, and etched GaN promoted the adhesion of cells compared to etched silicon surfaces. A model peptide, "IKVAV", covalently attached to GaN and silicon surfaces increased the adhesion of PC12 cells. Peptide terminated GaN promoted greater cell spreading and extension of neurites. The results suggest that peptide modified GaN is a biocompatible and non-toxic material that can be used to probe chemical and electrical stimuli associated with neural interfaces.

  2. Gallium Nitride Nanowires and Heterostructures: Toward Color-Tunable and White-Light Sources.

    PubMed

    Kuykendall, Tevye R; Schwartzberg, Adam M; Aloni, Shaul

    2015-10-14

    Gallium-nitride-based light-emitting diodes have enabled the commercialization of efficient solid-state lighting devices. Nonplanar nanomaterial architectures, such as nanowires and nanowire-based heterostructures, have the potential to significantly improve the performance of light-emitting devices through defect reduction, strain relaxation, and increased junction area. In addition, relaxation of internal strain caused by indium incorporation will facilitate pushing the emission wavelength into the red. This could eliminate inefficient phosphor conversion and enable color-tunable emission or white-light emission by combining blue, green, and red sources. Utilizing the waveguiding modes of the individual nanowires will further enhance light emission, and the properties of photonic structures formed by nanowire arrays can be implemented to improve light extraction. Recent advances in synthetic methods leading to better control over GaN and InGaN nanowire synthesis are described along with new concept devices leading to efficient white-light emission.

  3. Imaging the p-n junction in a gallium nitride nanowire with a scanning microwave microscope

    SciTech Connect

    Imtiaz, Atif; Wallis, Thomas M.; Brubaker, Matt D.; Blanchard, Paul T.; Bertness, Kris A.; Sanford, Norman A.; Kabos, Pavel; Weber, Joel C.; Coakley, Kevin J.

    2014-06-30

    We used a broadband, atomic-force-microscope-based, scanning microwave microscope (SMM) to probe the axial dependence of the charge depletion in a p-n junction within a gallium nitride nanowire (NW). SMM enables the visualization of the p-n junction location without the need to make patterned electrical contacts to the NW. Spatially resolved measurements of S{sub 11}{sup ′}, which is the derivative of the RF reflection coefficient S{sub 11} with respect to voltage, varied strongly when probing axially along the NW and across the p-n junction. The axial variation in S{sub 11}{sup ′}  effectively mapped the asymmetric depletion arising from the doping concentrations on either side of the junction. Furthermore, variation of the probe tip voltage altered the apparent extent of features associated with the p-n junction in S{sub 11}{sup ′} images.

  4. On the effect of vacancy defect on the mechanical properties of gallium nitride nanosheets

    NASA Astrophysics Data System (ADS)

    Rouhi, Saeed

    2016-08-01

    Using molecular dynamics (MD) simulations, the influence of the vacancy defects on the mechanical properties of gallium nitride (GaN) nanosheets is investigated. Two types of defective nanosheets are studied. In one of them, only one atom is removed at the vacancies and in the other, the number of removed atoms is not limited. It is shown that GaN nanosheets with multiple vacancies have larger in-plane elastic modulus than nanosheets with single vacancies. Besides, the ultimate stress and strain of GaN nanosheets are computed. Compared to perfect nanosheet, a significant decrease is observed in the ultimate stress of GaN nanosheet with only 2% defect. By plotting the fracture evolution of nanosheets under uni-directional tensile loading, three different patterns are observed. Moreover, by using bi-directional tensile tests on the nanosheets, the bulk moduli of perfect and defective GaN nanosheets are computed.

  5. Fundamental studies of the metallurgical, electrical, and optical properties of gallium phosphide and gallium phosphide alloys

    NASA Technical Reports Server (NTRS)

    1972-01-01

    Abstracts, bibliographic data, oral presentations, and published papers on (1) Diffusion of Sulfur in Gallium Phosphide and Gallium Arsenide, and (2) Properties of Gallium Phosphide Schottky Barrier Rectifiers for Use at High Temperature are presented.

  6. Gallium nitride surface protection during RTA annealing with a GaOxNy cap-layer

    NASA Astrophysics Data System (ADS)

    Khalfaoui, Wahid; Oheix, T.; Cayrel, F.; Benoit, R.; Yvon, A.; Collard, E.; Alquier, D.

    2016-04-01

    Gallium nitride (GaN) is generally considered a good candidate for power electronic devices such as Schottky barrier diodes (SBDs). Nevertheless, GaN has a strong sensitivity to high temperature treatments and a cap-layer is mandatory to protect the material surface during annealing at high temperature such as post-implantation treatments. In this work, an oxidized gallium nitride layer (GaOxNy) was generated with Oxford PECVD equipment using a N2O plasma treatment to protect the GaN surface during a rapid thermal annealing (RTA), in the range of 1000 °C-1150 °C for a few minutes. Before annealing, c-TLM patterns were processed on the GaOxNy/GaN sample to characterize its sheet resistance. After the N2O plasma treatment, the sample exhibited lower sheet resistance, indicating a better n-type conduction of the GaOxNy layer due to an excess of free carriers, compared to the as-grown GaN layer. The GaOxNy/GaN surface was then annealed at 1150 °C for 3 min and observed through AFM imaging. The surface exhibited a good quality with a low roughness, nevertheless, a low density of small hexagonal pits appeared after annealing. Finally, studies to determine an efficient etching process of the GaOxNy cap-layer were conducted using both chemical and physical approaches. We observed that efficient etching of the layer was achieved using a heated hydrofluoridric acid (HF 25%) solution. To conclude, GaOxNy has proved to be an efficient cap-layer for GaN protection at high temperature.

  7. Chemical vapor deposition of metal nitrides, phosphides and arsenides. Final report

    SciTech Connect

    Hoffman, D.M.

    1994-03-01

    The author recently reported that dialkylamido complexes are promising precursors to nitride thin films. On this basis it was reasoned that transition metal and main group disilazide complexes in which the silicon has dialkylamido substituents are potential precursors to ternary silicon nitride films. Bulky disilazide ligands are known to stabilize main group and transition metal complexes with low coordination numbers. Reaction of dimethylamine with Cl{sub 3}SiN(H)SiMe{sub 3} in hexane solution at 25{degrees}C gave the bulky disilazane [(Me{sub 2}N){sub 3}Si]N(h)SiMe{sub 3} (1) in 73% yield. Reaction of (1) with n-butyl lithium in benzene at 0{degrees}C produced [(Me{sub 2}N){sub 3}Si]N(Li)SiMe{sub 3} in 82% yield. LiN[Si(NMe{sub 2}){sub 3}]{sub 2} was chemically prepared in 92% yield and was converted to the amine with 83% yield. The author examined the use of amido precursors for main group oxide thin films. Sn(NMe{sub 2}){sub 4} and Si(NMe{sub 2}){sub 4} react with oxygen in an atmospheric pressure chemical vapor deposition reactor to give SnO{sub 2} and SiO{sub 2} films, respectively. The films were deposited on quartz, silicon, and glass at substrate temperatures of 250--400 {degrees}C. The results of the characterizations of the films and compounds are presented in this report.

  8. ANALYSIS OF THE WATER-SPLITTING CAPABILITIES OF GALLIUM INDIUM PHOSPHIDE NITRIDE (GaInPN)

    SciTech Connect

    Head, J.; Turner, J.

    2007-01-01

    With increasing demand for oil, the fossil fuels used to power society’s vehicles and homes are becoming harder to obtain, creating pollution problems and posing hazard’s to people’s health. Hydrogen, a clean and effi cient energy carrier, is one alternative to fossil fuels. Certain semiconductors are able to harness the energy of solar photons and direct it into water electrolysis in a process known as photoelectrochemical water-splitting. P-type gallium indium phosphide (p-GaInP2) in tandem with GaAs is a semiconductor system that exhibits water-splitting capabilities with a solar-tohydrogen effi ciency of 12.4%. Although this material is effi cient at producing hydrogen through photoelectrolysis it has been shown to be unstable in solution. By introducing nitrogen into this material, there is great potential for enhanced stability. In this study, gallium indium phosphide nitride Ga1-yInyP1-xNx samples were grown using metal-organic chemical vapor deposition in an atmospheric-pressure vertical reactor. Photocurrent spectroscopy determined these materials to have a direct band gap around 2.0eV. Mott-Schottky analysis indicated p-type behavior with variation in fl atband potentials with varied frequencies and pH’s of solutions. Photocurrent onset and illuminated open circuit potential measurements correlated to fl atband potentials determined from previous studies. Durability analysis suggested improved stability over the GaInP2 system.

  9. A hybrid density functional view of native vacancies in gallium nitride.

    PubMed

    Gillen, Roland; Robertson, John

    2013-10-01

    We investigated the transition energy levels of the vacancy defects in gallium nitride by means of a hybrid density functional theory approach (DFT). We show that, in contrast to predictions from a recent study on the level of purely local DFT, the inclusion of screened exchange stabilizes the triply positive charge state of the nitrogen vacancy for Fermi energies close to the valence band. On the other hand, the defect levels associated with the negative charge states of the nitrogen vacancy hybridize with the conduction band and turn out to be energetically unfavorable, except for high n-doping. For the gallium vacancy, the increased magnetic splitting between up-spin and down-spin bands due to stronger exchange interactions in sX-LDA pushes the defect levels deeper into the band gap and significantly increases the associated charge transition levels. Based on these results, we propose the ϵ(0| - 1) transition level as an alternative candidate for the yellow luminescence in GaN.

  10. Chemical exfoliation and optical characterization of threading-dislocation-free gallium-nitride ultrathin nanomembranes

    NASA Astrophysics Data System (ADS)

    ElAfandy, Rami T.; Majid, Mohammed A.; Ng, Tien Khee; Zhao, Lan; Cha, Dongkyu; Ooi, Boon S.

    2014-11-01

    Semiconductor nanostructures have generated tremendous scientific interests as well as practical applications stemming from the engineering of low dimensional physics phenomena. Unlike 0D and 1D nanostructures, such as quantum dots and nanowires, respectively, 2D structures, such as nanomembranes, are unrivalled in their scalability for high yield manufacture and are less challenging in handling with the current transfer techniques. Furthermore, due to their planar geometry, nanomembranes are compatible with the current complementary metal oxide semiconductor (CMOS) technology. Due to these superior characteristics, there are currently different techniques in exfoliating nanomembranes with different crystallinities, thicknesses and compositions. In this work we demonstrate a new facile technique of exfoliating gallium nitride (GaN) nanomembranes with novel features, namely with the non-radiative cores of their threading-dislocations (TDs) being etched away. The exfoliation process is based on engineering the gallium vacancy (VGa) density during the GaN epitaxial growth with subsequent preferential etching. Based on scanning and transmission electron microscopies, as well as micro-photoluminescence measurements, a model is proposed to uncover the physical processes underlying the formation of the nanomembranes. Raman measurements are also performed to reveal the internal strain within the nanomembranes. After transferring these freely suspended 25 nm thin GaN nanomembranes to other substrates, we demonstrate the temperature dependence of their bandgap by photoluminescence technique, in order to shed light on the internal carrier dynamics.

  11. Surface studies of gallium nitride quantum dots grown using droplet epitaxy on bulk, native substrates

    NASA Astrophysics Data System (ADS)

    Jones, Christina; Jeon, Sunyeol; Goldman, Rachel; Yacoby, Yizhak; Clarke, Roy

    Gallium nitride (GaN) and its applications in light-emitting diodes play an integral part in efficient, solid-state lighting, as evidenced by its recognition in the 2014 Nobel prize in physics. In order to push this technology towards higher efficiency and reliability and lower cost, we must understand device growth on bulk GaN substrates, which have lower defect densities and strain than template GaN substrates grown on sapphire. In this work, we present our findings on the surface properties of GaN quantum dots (QDs) grown on commercial bulk GaN. QDs are grown using the droplet epitaxy method and analyzed using a surface X-ray diffraction technique called Coherent Bragg Rod Analysis (COBRA), which uses phase retrieval to reconstruct atomic positions near the substrate surface. While several QD growth conditions in our study produce dense QDs, COBRA reveals that only low nitridation temperatures result in GaN QDs that are coherent with the bulk GaN substrate. Results are supported with atomic force microscopy and high-resolution transmission electron microscopy.

  12. Thermo-piezo-electro-mechanical simulation of AlGaN (aluminum gallium nitride) / GaN (gallium nitride) High Electron Mobility Transistors

    NASA Astrophysics Data System (ADS)

    Stevens, Lorin E.

    Due to the current public demand of faster, more powerful, and more reliable electronic devices, research is prolific these days in the area of high electron mobility transistor (HEMT) devices. This is because of their usefulness in RF (radio frequency) and microwave power amplifier applications including microwave vacuum tubes, cellular and personal communications services, and widespread broadband access. Although electrical transistor research has been ongoing since its inception in 1947, the transistor itself continues to evolve and improve much in part because of the many driven researchers and scientists throughout the world who are pushing the limits of what modern electronic devices can do. The purpose of the research outlined in this paper was to better understand the mechanical stresses and strains that are present in a hybrid AlGaN (Aluminum Gallium Nitride) / GaN (Gallium Nitride) HEMT, while under electrically-active conditions. One of the main issues currently being researched in these devices is their reliability, or their consistent ability to function properly, when subjected to high-power conditions. The researchers of this mechanical study have performed a static (i.e. frequency-independent) reliability analysis using powerful multiphysics computer modeling/simulation to get a better idea of what can cause failure in these devices. Because HEMT transistors are so small (micro/nano-sized), obtaining experimental measurements of stresses and strains during the active operation of these devices is extremely challenging. Physical mechanisms that cause stress/strain in these structures include thermo-structural phenomena due to mismatch in both coefficient of thermal expansion (CTE) and mechanical stiffness between different materials, as well as stress/strain caused by "piezoelectric" effects (i.e. mechanical deformation caused by an electric field, and conversely voltage induced by mechanical stress) in the AlGaN and GaN device portions (both

  13. Process Development of Gallium Nitride Phosphide Core-Shell Nanowire Array Solar Cell

    NASA Astrophysics Data System (ADS)

    Chuang, Chen

    Dilute Nitride GaNP is a promising materials for opto-electronic applications due to its band gap tunability. The efficiency of GaNxP1-x /GaNyP1-y core-shell nanowire solar cell (NWSC) is expected to reach as high as 44% by 1% N and 9% N in the core and shell, respectively. By developing such high efficiency NWSCs on silicon substrate, a further reduction of the cost of solar photovoltaic can be further reduced to 61$/MWh, which is competitive to levelized cost of electricity (LCOE) of fossil fuels. Therefore, a suitable NWSC structure and fabrication process need to be developed to achieve this promising NWSC. This thesis is devoted to the study on the development of fabrication process of GaNxP 1-x/GaNyP1-y core-shell Nanowire solar cell. The thesis is divided into two major parts. In the first parts, previously grown GaP/GaNyP1-y core-shell nanowire samples are used to develop the fabrication process of Gallium Nitride Phosphide nanowire solar cell. The design for nanowire arrays, passivation layer, polymeric filler spacer, transparent col- lecting layer and metal contact are discussed and fabricated. The property of these NWSCs are also characterized to point out the future development of Gal- lium Nitride Phosphide NWSC. In the second part, a nano-hole template made by nanosphere lithography is studied for selective area growth of nanowires to improve the structure of core-shell NWSC. The fabrication process of nano-hole templates and the results are presented. To have a consistent features of nano-hole tem- plate, the Taguchi Method is used to optimize the fabrication process of nano-hole templates.

  14. Low-level (gallium-aluminum-arsenide) laser irradiation of Par-C10 cells and acinar cells of rat parotid gland.

    PubMed

    Onizawa, Katsuhiro; Muramatsu, Takashi; Matsuki, Miwako; Ohta, Kazumasa; Matsuzaka, Kenichi; Oda, Yutaka; Shimono, Masaki

    2009-03-01

    We investigated cell response, including cell proliferation and expression of heat stress protein and bcl-2, to clarify the influence of low-level [gallium-aluminum-arsenide (Ga-Al-As) diode] laser irradiation on Par-C10 cells derived from the acinar cells of rat parotid glands. Furthermore, we also investigated amylase release and cell death from irradiation in acinar cells from rat parotid glands. The number of Par-C10 cells in the laser-irradiated groups was higher than that in the non-irradiated group at days 5 and 7, and the difference was statistically significant (P < 0.01). Greater expression of heat shock protein (HSP)25 and bcl-2 was seen on days 1 and 3 in the irradiated group. Assay of the released amylase showed no significant difference statistically between the irradiated group and the non-irradiated group. Trypan blue exclusion assay revealed that there was no difference in the ratio of dead to live cells between the irradiated and the non-irradiated groups. These results suggest that low-level laser irradiation promotes cell proliferation and expression of anti-apoptosis proteins in Par-C10 cells, but it does not significantly affect amylase secretion and does not induce rapid cell death in isolated acinar cells from rat parotid glands.

  15. Application of low-cost Gallium Arsenide light-emitting-diodes as kerma dosemeter and fluence monitor for high-energy neutrons.

    PubMed

    Mukherjee, B; Simrock, S; Khachan, J; Rybka, D; Romaniuk, R

    2007-01-01

    Displacement damage (DD) caused by fast neutrons in unbiased Gallium Arsenide (GaAs) light emitting diodes (LED) resulted in a reduction of the light output. On the other hand, a similar type of LED irradiated with gamma rays from a (60)Co source up to a dose level in excess of 1.0 kGy (1.0 x 10(5) rad) was found to show no significant drop of the light emission. This phenomenon was used to develop a low cost passive fluence monitor and kinetic energy released per unit mass dosemeter for accelerator-produced neutrons. These LED-dosemeters were used to assess the integrated fluence of photoneutrons, which were contaminated with a strong bremsstrahlung gamma-background generated by the 730 MeV superconducting electron linac driving the free electron laser in Hamburg (FLASH) at Deutsches Elektronen-Synchrotron. The applications of GaAs LED as a routine neutron fluence monitor and DD precursor for the electronic components located in high-energy accelerator environment are highlighted.

  16. Note: All solid-state high repetitive sub-nanosecond risetime pulse generator based on bulk gallium arsenide avalanche semiconductor switches.

    PubMed

    Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Fan, Yajun; Liu, Chunliang

    2016-08-01

    An all solid-state high repetitive sub-nanosecond risetime pulse generator featuring low-energy-triggered bulk gallium arsenide (GaAs) avalanche semiconductor switches and a step-type transmission line is presented. The step-type transmission line with two stages is charged to a potential of 5.0 kV also biasing at the switches. The bulk GaAs avalanche semiconductor switch closes within sub-nanosecond range when illuminated with approximately 87 nJ of laser energy at 905 nm in a single pulse. An asymmetric dipolar pulse with peak-to-peak amplitude of 9.6 kV and risetime of 0.65 ns is produced on a resistive load of 50 Ω. A technique that allows for repetition-rate multiplication of pulse trains experimentally demonstrated that the parallel-connected bulk GaAs avalanche semiconductor switches are triggered in sequence. The highest repetition rate is decided by recovery time of the bulk GaAs avalanche semiconductor switch, and the operating result of 100 kHz of the generator is discussed. PMID:27587178

  17. Note: All solid-state high repetitive sub-nanosecond risetime pulse generator based on bulk gallium arsenide avalanche semiconductor switches.

    PubMed

    Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Fan, Yajun; Liu, Chunliang

    2016-08-01

    An all solid-state high repetitive sub-nanosecond risetime pulse generator featuring low-energy-triggered bulk gallium arsenide (GaAs) avalanche semiconductor switches and a step-type transmission line is presented. The step-type transmission line with two stages is charged to a potential of 5.0 kV also biasing at the switches. The bulk GaAs avalanche semiconductor switch closes within sub-nanosecond range when illuminated with approximately 87 nJ of laser energy at 905 nm in a single pulse. An asymmetric dipolar pulse with peak-to-peak amplitude of 9.6 kV and risetime of 0.65 ns is produced on a resistive load of 50 Ω. A technique that allows for repetition-rate multiplication of pulse trains experimentally demonstrated that the parallel-connected bulk GaAs avalanche semiconductor switches are triggered in sequence. The highest repetition rate is decided by recovery time of the bulk GaAs avalanche semiconductor switch, and the operating result of 100 kHz of the generator is discussed.

  18. Note: All solid-state high repetitive sub-nanosecond risetime pulse generator based on bulk gallium arsenide avalanche semiconductor switches

    NASA Astrophysics Data System (ADS)

    Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Fan, Yajun; Liu, Chunliang

    2016-08-01

    An all solid-state high repetitive sub-nanosecond risetime pulse generator featuring low-energy-triggered bulk gallium arsenide (GaAs) avalanche semiconductor switches and a step-type transmission line is presented. The step-type transmission line with two stages is charged to a potential of 5.0 kV also biasing at the switches. The bulk GaAs avalanche semiconductor switch closes within sub-nanosecond range when illuminated with approximately 87 nJ of laser energy at 905 nm in a single pulse. An asymmetric dipolar pulse with peak-to-peak amplitude of 9.6 kV and risetime of 0.65 ns is produced on a resistive load of 50 Ω. A technique that allows for repetition-rate multiplication of pulse trains experimentally demonstrated that the parallel-connected bulk GaAs avalanche semiconductor switches are triggered in sequence. The highest repetition rate is decided by recovery time of the bulk GaAs avalanche semiconductor switch, and the operating result of 100 kHz of the generator is discussed.

  19. Synthesis and characterization of visible emission from rare-earth doped aluminum nitride, gallium nitride and gallium aluminum nitride powders and thin films

    NASA Astrophysics Data System (ADS)

    Tao, Jonathan Huai-Tse

    A three-step solution-based process had been used synthesize powders of GaN, AlN and their alloys. The complete solid solubility and tunable nature of these nitride band gaps in the visible spectrum were the motivation of these studies due to their application in solid state lighting. Energy dispersive X-ray spectroscopy confirmed the reduction in oxygen content for the GaN powders to as low as 4 atom % with an 8 % oxygen to nitrogen ratio. Relative to commercial GaN powders, the bandedge of the powders synthesized by such approach also shifted to higher energy, which indicated fewer defects, as observed from reflectance measurements. Inspired by the use of rare-earth elements as color emitters in fluorescent lamp phosphors, these elements were also used as activators in our nitride material. Visible emission was demonstrated through photoluminescence measurements in AlN powders activated with rare-earth elements Eu3+, Tb3+, Tm3+. These ions showed emission in the red, green and blue regions of the visible spectrum, respectively. Eu3+ and Tb3+ co-activation was also observed in an AlN sample that indicated successful energy transfer from the host to sensitizer, and subsequently to another activator. Tb3+ emission was observed under cathodoluminescence in GaN powders synthesized by the same method, and a concentration study showed no effect of concentration quenching up to 8 atom %. Using the same source powder, a pulsed-laser deposited thin film was fabricated that showed both band gap emission and activator-related emission, suggesting a reduction of defects when the powders were deposited as thin films. Additionally, GaN:Tb3+ films were also fabricated using metallorganic vapor phase epitaxy using precursors with and without oxygen ligands. Tb3+ emission was only observed in the sample fabricated from the precursor with oxygen ligand, suggestion that oxygen may be required for effective rare earth luminescence. Finally, Ga1-xAl xN alloy powders (x=0.5) and Ga1-x

  20. Combined administration of oxalic acid, succimer and its analogue for the reversal of gallium arsenide-induced oxidative stress in rats.

    PubMed

    Flora, Swaran J S; Kannan, Gurusamy M; Pant, Bhagwat P; Jaiswal, Devendra K

    2002-06-01

    Gallium arsenide (GaAs), a group III-VA intermetallic semiconductor, possesses superior electronic and optical properties and has a wide application in the electronics industry. Exposure to GaAs in the semiconductor industry is a potential occupational hazard because cleaning and slicing GaAs ingots to yield the desired wafer could generate GaAs particles. The ability of GaAs to induce oxidative stress has not yet been reported. The present study reports the role of oxidative stress in GaAs-induced haematological and liver disorders and its possible reversal overturn by administration of meso-2,3-dimercaptosuccinic acid (DMSA) and one of its analogue, monoisoamyl DMSA (MiADMSA), either individually or in combination with oxalic acid. While DMSA and MiADMSA are potential arsenic chelators, oxalic acid is reported to be an effective gallium chelator. Male rats were exposed to 10 mg/kg GaAs orally, 5 days a week for 8 weeks. GaAs exposure was then stopped and rats were given a 0.5 mmol/kg dose of succimers (DMSA or MiADMSA), oxalic acid or a combination of the two, intraperitoneally once daily for 5 consecutive days. We found a significant fall in blood delta-aminolevulinic acid dehydratase (ALAD) activity and blood glutathione (GSH) level, and an increased urinary excretion of delta-aminolevulinic acid (ALA) and an increased malondialdehyde (MDA) level in erythrocytes of rats exposed to GaAs. Hepatic GSH levels decreased, whereas there was an increase in GSSG and MDA levels. The results suggest a role of oxidative stress in GaAs-induced haematological and hepatic damage. Administration of DMSA and MiADMSA produced effective recovery in most of the above variables. However, a greater effectiveness of the chelation treatment (i.e. removal of both gallium and arsenic from body organs) could be achieved by combined administration of succimer (DMSA) with oxalic acid since, after MiADMSA administration, a marked loss of essential metals (copper and zinc) is of concern.

  1. Homoepitaxial growth of gallium nitride and aluminum nitride and its effects on device properties

    NASA Astrophysics Data System (ADS)

    Grandusky, James R.

    Lattice and thermal mismatch between epitaxial layers and substrates have long been the major challenge in obtaining high quality devices in the III-Nitride material system due to the lack of availability of native substrates. Recently methods for obtaining high quality free standing native substrates have been achieved and these products are beginning to enter the commercial market. However the quality of these substrates is significantly lower than those in traditional substrates such as Si and GaAs and the high cost and low availability makes it difficult to study the homoepitaxial growth. In order to use these substrates for epitaxial growth, one first must understand what features are needed for the substrates to be epi ready. In addition, one must understand what features in the substrates impact optoelectronic device performances most significantly. Initial homoepitaxial growth was carried out on both AIN and GaN substrates. On AIN substrates it was found that annealing the sample prior to growth was very important to obtain improved surface morphologies for the homoepitaxial layers. Similar annealing steps were attempted on GaN substrates, however annealing under hydrogen left large Ga droplets on the surface. For homoepitaxy on HVPE GaN substrates, the substrate characteristics, such as bowing, surface morphology, structural properties, and optical properties were found to have a large influence on growth and device performance. Even with a reduced dislocation density, substrates with poor characteristics performed worse than devices on GaN/sapphire. The effect of polishing process on the substrates was found to be very important and substrates with subsurface damage led to poor growth, even though the starting surface was very smooth. Optimization of a thin GaN layer and a multiple quantum well structure revealed very different optimum growth conditions for the HVPE substrates and the GaN/sapphire templates. Theoretical modeling using density functional

  2. In situ chemical functionalization of gallium nitride with phosphonic acid derivatives during etching.

    PubMed

    Wilkins, Stewart J; Greenough, Michelle; Arellano, Consuelo; Paskova, Tania; Ivanisevic, Albena

    2014-03-01

    In situ functionalization of polar (c plane) and nonpolar (a plane) gallium nitride (GaN) was performed by adding (3-bromopropyl) phosphonic acid or propyl phosphonic acid to a phosphoric acid etch. The target was to modulate the emission properties and oxide formation of GaN, which was explored through surface characterization with atomic force microscopy, X-ray photoelectron spectroscopy, photoluminescence (PL), inductively coupled plasma-mass spectrometry, and water contact angle. The use of (3-bromopropyl) phosphonic acid and propyl phosphonic acid in phosphoric acid demonstrated lower amounts of gallium oxide formation and greater hydrophobicity for both sample sets, while also improving PL emission of polar GaN samples. In addition to crystal orientation, growth-related factors such as defect density in bulk GaN versus thin GaN films residing on sapphire substrates were investigated as well as their responses to in situ functionalization. Thin nonpolar GaN layers were the most sensitive to etching treatments due in part to higher defect densities (stacking faults and threading dislocations), which accounts for large surface depressions. High-quality GaN (both free-standing bulk polar and bulk nonpolar) demonstrated increased sensitivity to oxide formation. Room-temperature PL stands out as an excellent technique to identify nonradiative recombination as observed in the spectra of heteroepitaxially grown GaN samples. The chemical methods applied to tune optical and physical properties of GaN provide a quantitative framework for future novel chemical and biochemical sensor development.

  3. Study of gallium nitride-based materials for light-emitting applications

    NASA Astrophysics Data System (ADS)

    Barletta, Philip

    The purpose of this study was to explore the possibility of fabricating phosphor-free white-emitting LED's based in the gallium nitride material system. The structures were to be grown using metal-organic chemical vapor deposition (MOCVD). Toward this end, a Thomas Swan Scientific close-coupled showerhead reactor was installed. The first experimental step in this project was the optimization of nominally undoped GaN. This was achieved successfully, as smooth, non-compensated, optically-active films were demonstrated. Additionally, a full on- and off-axis x-ray diffraction study showed that the crystal quality of this material compared favorably to that of published standards. Successful n- and p-type doping of GaN were also demonstrated. Device-worthy mobility and carrier concentration values were demonstrated. Atomic force microscopy of n-type material verified that the films was sufficiently smooth as to serve as a layer upon which active-layer quantum wells could be grown. Photoluminescence of both n- and p-type material was examined as well. An extensive indium gallium nitride growth study was carried out. The effects of several growth parameters on emission characteristics were presented. PL emission wavelengths as high as 561 nm were demonstrated. The issues of uniformity and indium platelet formation were also addressed. This InGaN experimental work was complemented with a series of calculations which gave the expected emission wavelength of an InGaN/GaN quantum well structure based on In content and well width. Strain, the quantum size effect, and the quantum-confined Stark effect were all factored into these calculations in order to study their individual contributions to emission wavelength values. This work concluded with an examination of white device structure and fabrication. Both two- and three-color devices were considered. Monochromtic devices emitting in the green and yellow were fabricated. The yellow device, emitting at 575nm, yielded the

  4. Novel approach to the growth and characterization of aligned epitaxial gallium nitride nanowires

    NASA Astrophysics Data System (ADS)

    Henry, Tania Alicia

    Nanowire devices are potential building blocks for complex electronic circuitry, however, challenges such as in-place alignment, precise positioning and nanowire device integration need to be addressed. In this work selective area grown (SAG), micron sized gallium nitride (GaN) mesas were used as growth substrates for lateral epitaxial GaN nanowire arrays. The thermodynamically stable mesa facets provide a crystallographic match for directed nanowire synthesis by minimizing the surface energy at the interface between the nanowire and substrate Nanowires grow from the sidewalls of GaN mesas forming parallel and hexagonal networks. Alignment occurs in the nonpolar m-axis <10l0> and semipolar <10ll> directions respectively. Gallium nitride nanowires are interconnected between thermodynamically stable and smooth pyramidal (10ll) , and (1l22) surfaces of adjacent GaN mesas, and they also grow from a single mesa to form free-standing nanowire cantilevers. The synthesis of lateral free-standing nanowires has led to exciting studies of their structural, electrical, and optical properties. Characterization of the electrical properties is carried out by in situ probing of single nanowires on the growth substrate inside a scanning electron microscope (SEM). The current transport is found to be largely dominated by thermionic field emission and Fowler-Nordheim tunneling, and is significantly limited by a large contact resistance at the probe-nanowire interface. The carrier concentration and mobilities of the probed nanowires are extracted and are in agreement with standard field effects transistors (FETs) fabricated from nanowires grown using similar growth conditions. These results reveal that electrical probing of lateral GaN nanowires is a reliable means of characterizing their electrical properties once the interface resistance between the probe and nanowire is considered. The optical properties of the nanowires were investigated. Photon emission at 3.26 eV dominated the

  5. Electrophysical properties of gallium arsenide in combination with impurity-doped germanium and isovalent indium and antimony impurities

    SciTech Connect

    Krivov, M.A.; Malisova, E.V.; Nikiforova, M.P.; Starikov, A.N.; Khludkov, S.S.; Grigor'ev, Yu.A.; Egorova, O.L.; Osvenskii, V.B.

    1988-03-01

    The temperature dependence of the charge carrier concentration and mobility in n-type GaAs monocrystals doped jointly by Ge and isovalent In and Sb impurities is investigated. The observable charge carrier concentration and mobility changes in the GaAs:Ge:In and GaAs:Ge:Sb are compared with the corresponding characteristics in GaAs:Ge, and the change in properties along the ingots can be explained by the Ge impurity redistribution in the gallium and arsenic sublattices in the presence of an isovalent impurity.

  6. Basic Equations for the Modeling of Gallium Nitride (gan) High Electron Mobility Transistors (hemts)

    NASA Technical Reports Server (NTRS)

    Freeman, Jon C.

    2003-01-01

    Gallium nitride (GaN) is a most promising wide band-gap semiconductor for use in high-power microwave devices. It has functioned at 320 C, and higher values are well within theoretical limits. By combining four devices, 20 W has been developed at X-band. GaN High Electron Mobility Transistors (HEMTs) are unique in that the two-dimensional electron gas (2DEG) is supported not by intentional doping, but instead by polarization charge developed at the interface between the bulk GaN region and the AlGaN epitaxial layer. The polarization charge is composed of two parts: spontaneous and piezoelectric. This behavior is unlike other semiconductors, and for that reason, no commercially available modeling software exists. The theme of this document is to develop a self-consistent approach to developing the pertinent equations to be solved. A Space Act Agreement, "Effects in AlGaN/GaN HEMT Semiconductors" with Silvaco Data Systems to implement this approach into their existing software for III-V semiconductors, is in place (summer of 2002).

  7. Giant piezoelectric size effects in zinc oxide and gallium nitride nanowires. A first principles investigation.

    PubMed

    Agrawal, Ravi; Espinosa, Horacio D

    2011-02-01

    Nanowires made of materials with noncentrosymmetric crystal structure are under investigation for their piezoelectric properties and suitability as building blocks for next-generation self-powered nanodevices. In this work, we investigate the size dependence of piezoelectric coefficients in nanowires of two such materials - zinc oxide and gallium nitride. Nanowires, oriented along their polar axis, ranging from 0.6 to 2.4 nm in diameter were modeled quantum mechanically. A giant piezoelectric size effect is identified for both GaN and ZnO nanowires. However, GaN exhibits a larger and more extended size dependence than ZnO. The observed size effect is discussed in the context of charge redistribution near the free surfaces leading to changes in local polarization. The study reveals that local changes in polarization and reduction of unit cell volume with respect to bulk values lead to the observed size effect. These results have strong implication in the field of energy harvesting, as piezoelectric voltage output scales with the piezoelectric coefficient.

  8. Near-infrared electroluminescence at room temperature from neodymium-doped gallium nitride thin films

    SciTech Connect

    Kim, Joo Han; Holloway, Paul H.

    2004-09-06

    Strong near-infrared (NIR) electroluminescence (EL) at room temperature from neodymium (Nd)-doped gallium nitride (GaN) thin films is reported. The Nd-doped GaN films were grown by radio-frequency planar magnetron cosputtering of separate GaN and metallic Nd targets in a pure nitrogen ambient. X-ray diffraction data did not identify the presence of any secondary phases and revealed that the Nd-doped GaN films had a highly textured wurtzite crystal structure with the c-axis normal to the surface of the film. The EL devices were fabricated with a thin-film multilayered structure of Al/Nd-doped GaN/Al{sub 2}O{sub 3}-TiO{sub 2}/indium-tin oxide and tested at room temperate. Three distinct NIR EL emission peaks were observed from the devices at 905, 1082, and 1364 nm, arising from the radiative relaxation of the {sup 4}F{sub 3sol2} excited-state energy level to the {sup 4}I{sub 9sol2}, {sup 4}I{sub 11sol2}, and {sup 4}I{sub 13sol2} levels of the Nd{sup 3+} ion, respectively. The threshold voltage for all the three emission peaks was {approx}150 V. The external power efficiency of the fabricated EL devices was {approx}1x10{sup -5} measured at 40 V above the threshold voltage.

  9. Unusual strategies for using indium gallium nitride grown on silicon (111) for solid-state lighting

    PubMed Central

    Kim, Hoon-sik; Brueckner, Eric; Song, Jizhou; Li, Yuhang; Kim, Seok; Lu, Chaofeng; Sulkin, Joshua; Choquette, Kent; Huang, Yonggang; Nuzzo, Ralph G.; Rogers, John A.

    2011-01-01

    Properties that can now be achieved with advanced, blue indium gallium nitride light emitting diodes (LEDs) lead to their potential as replacements for existing infrastructure in general illumination, with important implications for efficient use of energy. Further advances in this technology will benefit from reexamination of the modes for incorporating this materials technology into lighting modules that manage light conversion, extraction, and distribution, in ways that minimize adverse thermal effects associated with operation, with packages that exploit the unique aspects of these light sources. We present here ideas in anisotropic etching, microscale device assembly/integration, and module configuration that address these challenges in unconventional ways. Various device demonstrations provide examples of the capabilities, including thin, flexible lighting “tapes” based on patterned phosphors and large collections of small light emitters on plastic substrates. Quantitative modeling and experimental evaluation of heat flow in such structures illustrates one particular, important aspect of their operation: small, distributed LEDs can be passively cooled simply by direct thermal transport through thin-film metallization used for electrical interconnect, providing an enhanced and scalable means to integrate these devices in modules for white light generation. PMID:21666096

  10. Unusual strategies for using indium gallium nitride grown on silicon (111) for solid-state lighting.

    PubMed

    Kim, Hoon-sik; Brueckner, Eric; Song, Jizhou; Li, Yuhang; Kim, Seok; Lu, Chaofeng; Sulkin, Joshua; Choquette, Kent; Huang, Yonggang; Nuzzo, Ralph G; Rogers, John A

    2011-06-21

    Properties that can now be achieved with advanced, blue indium gallium nitride light emitting diodes (LEDs) lead to their potential as replacements for existing infrastructure in general illumination, with important implications for efficient use of energy. Further advances in this technology will benefit from reexamination of the modes for incorporating this materials technology into lighting modules that manage light conversion, extraction, and distribution, in ways that minimize adverse thermal effects associated with operation, with packages that exploit the unique aspects of these light sources. We present here ideas in anisotropic etching, microscale device assembly/integration, and module configuration that address these challenges in unconventional ways. Various device demonstrations provide examples of the capabilities, including thin, flexible lighting "tapes" based on patterned phosphors and large collections of small light emitters on plastic substrates. Quantitative modeling and experimental evaluation of heat flow in such structures illustrates one particular, important aspect of their operation: small, distributed LEDs can be passively cooled simply by direct thermal transport through thin-film metallization used for electrical interconnect, providing an enhanced and scalable means to integrate these devices in modules for white light generation.

  11. Electron mobility limited by scattering from threading dislocation lines within gallium nitride

    NASA Astrophysics Data System (ADS)

    Mohammad Alavi, Seyed; Bagani, Erfan

    2016-03-01

    Theoretical as well as experimental studies in the literature suggest that defect sites associated with the threading dislocation lines within n-type gallium nitride (GaN) act to trap free electrons from the bulk of this semiconductor material. As a result, the core of the threading dislocation lines become negatively charged. The charge accumulated along the core of a threading dislocation line should be screened by a charge of opposite polarity and equal in absolute value per unit length along the dislocation line. In the present work, we model this screened charge buildup along the threading dislocation lines by two concentric space-charge cylinders. Quantum mechanical theory of scattering in cylindrical coordinates is then employed in order to numerically compute the electron mobility limited by scattering from the charged threading dislocation lines. The dependence of the computed electron mobility on the dislocation line density and on the amount of charge accumulated per unit length along the core of the dislocation lines is also investigated in this work. Our computed electron mobility results are compared with results from existing calculations of the GaN dislocation scattering limited electron mobility in the literature.

  12. In-situ multi-information measurement system for preparing gallium nitride photocathode

    NASA Astrophysics Data System (ADS)

    Fu, Xiao-Qian; Chang, Ben-Kang; Qian, Yun-Sheng; Zhang, Jun-Ju

    2012-03-01

    We introduce the first domestic in-situ multi-information measurement system for a gallium nitride (GaN) photocathode. This system can successfully fulfill heat cleaning and activation for GaN in an ultrahigh vacuum environment and produce a GaN photocathode with a negative electron affinity (NEA) status. Information including the heat cleaning temperature, vacuum degree, photocurrent, electric current of cesium source, oxygen source, and the most important information about the spectral response, or equivalently, the quantum efficiency (QE) can be obtained during preparation. The preparation of a GaN photocathode with this system indicates that the optimal heating temperature in a vacuum is about 700 °C. We also develop a method of quickly evaluating the atomically clean surface with the vacuum degree versus wavelength curve to prevent possible secondary contamination when the atomic level cleaning surface is tested with X-ray photoelectron spectroscopy. The photocurrent shows a quick enhancement when the current ratio between the cesium source and oxygen source is 1.025. The spectral response of the GaN photocathode is flat in a wavelength range from 240 nm to 365 nm, and an abrupt decline is observed at 365 nm, which demonstrates that with the in-situ multi-information measurement system the NEA GaN photocathode can be successfully prepared.

  13. Investigation of phonon modes in gallium nitride nanowires deposited by thermal CVD

    NASA Astrophysics Data System (ADS)

    Rizal, Umesh; Swain, Bhabani. S.; Swain, Bibhu. P.

    2016-04-01

    Gallium nitride nanowires (GaN-NWs) of diameters ranging from 20 to 80 nm were grown on the p-type Si substrate by Thermal Chemical Vapor Deposition (TCVD) using Iron (Fe) catalyst via VLS mechanism. Raman and FTIR spectra reveal the presence of broad transverse optic (TO) and longitudinal optic (LO) phonon peak spreads over 500-600 cm-1 and 720 cm-1 respectively. The detail deconvolution of integrated transverse and longitudinal phonon analysis reveals phonon confinement brought out by incorporation of hydrogen atom. The red shifts of TO and LO phonon peak position indicates nanosized effect. IA1(LO)/IA1(TO) increases from 0.073 to 1.0 and their respective fwhmA1(LO)/fwhmA1(TO) also increases from 0.71 to 1.31 with increasing H2 flow rate. E1(LO) - E1(TO) and A1(LO) - A1(TO) increases from 173.83 to 190.73 and 184.89 to 193.22 respectively. Apart from this usual TO and LO phonon, we have found Surface Optic (SO) phonon at 671 cm-1 in FTIR spectra. The intensity of PL peak increases with increasing H2 dilution reveals efficient passivation of defect centre at surface of GaN-NWs.

  14. Gas phase interactions with bare and gold nanoparticle decorated gallium nitride nanowires by ultraviolet photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Niraula, Ishwar; Kengne, Blaise-Alexis; McIlroy, David

    2012-02-01

    Ultraviolet photoelectron spectroscopy (UPS) has been used to characterize the interaction of CO and H2O with the surface of bare and gold nanoparticle (Au NP) decorated gallium nitride nanowires at 298 K, 77 K and 20 K. The average diameter of the Au NPs is 4.5 ± 0.5 nm and the average nanowire diameter is 105 ± 75 nm. CO and H2O do not bond to the surface of the bare GaN nanowires at 298K, 77K, or 20K. Temperature dependent UPS analysis reveals that CO and H2O weakly physisorbed to the Au NP decorated GaN nanowires with heats of adsorption of 4.37 ± 0.03 meV and 1.25 ± 0.04 meV , respectively. The adsorption at 298K of 50 Langmuir of CO followed by 50 Langmuir of H2O showed that CO adsorption promotes H2O adsorption, while 50 Langmuir of H2O followed by 50 Langmuir of CO showed that H2O inhibits CO adsorption. The findings of this study that the adsorption of H2O inhibits CO adsorption onto the Au NP-GaN nanowires explains previous studies of the gas sensing properties of mats of Au NP- GaN nanowires.

  15. Optical waveguiding properties into porous gallium nitride structures investigated by prism coupling technique

    SciTech Connect

    Alshehri, Bandar; Dogheche, Elhadj; Lee, Seung-Min; Kang, Jin-Ho; Ryu, Sang-Wan; Gong, Su-Hyun; Cho, Yong-Hoon

    2014-08-04

    In order to modulate the refractive index and the birefringence of Gallium Nitride (GaN), we have developed a chemical etching method to perform porous structures. The aim of this research is to demonstrate that optical properties of GaN can be tuned by controlling the pores density. GaN films are prepared on sapphire by metal organic chemical vapor deposition and the microstructure is characterized by transmission electron microscopy, and scanning electron microscope analysis. Optical waveguide experiment is demonstrated here to determine the key properties as the ordinary (n{sub 0}) and extraordinary (n{sub e}) refractive indices of etched structures. We report here the dispersion of refractive index for porous GaN and compare it to the bulk material. We observe that the refractive index decreases when the porous density p is increased: results obtained at 0.975 μm have shown that the ordinary index n{sub 0} is 2.293 for a bulk layer and n{sub 0} is 2.285 for a pores density of 20%. This value corresponds to GaN layer with a pore size of 30 nm and inter-distance of 100 nm. The control of the refractive index into GaN is therefore fundamental for the design of active and passive optical devices.

  16. Nonpolar m-plane gallium Nitride-based Laser Diodes in the Blue Spectrum

    NASA Astrophysics Data System (ADS)

    Kelchner, Kathryn M.

    Gallium nitride (GaN), together with its alloys with aluminum and indium, have revolutionized the solid-state optoelectronics market for their ability to emit a large portion of the visible electromagnetic spectrum from deep ultraviolet and into the infrared. GaN-based semiconductor laser diodes (LDs) with emission wavelengths in the violet, blue and green are already seeing widespread implementation in applications ranging from energy storage, lighting and displays. However, commercial GaN-based LDs use the basal c-plane orientation of the wurtzite crystal, which can suffer from large internal electric fields due to discontinuities in spontaneous and piezoelectric polarizations, limiting device performance. The nonpolar orientation of GaN benefits from the lack of polarization-induced electric field as well as enhanced gain. This dissertation discusses some of the benefits and limitations of m-plane oriented nonpolar GaN for LD applications in the true blue spectrum (450 nm). Topics include an overview of material growth by metal-organic chemical vapor deposition (MOCVD), waveguide design and processing techniques for improving device performance for multiple lateral mode and single lateral mode ridge waveguides.

  17. Defect Reduction in Semi-Polar (11bar 22) Gallium Nitride Grown Using Epitaxial Lateral Overgrowth

    NASA Astrophysics Data System (ADS)

    Zhu, Tongtong; Sutherland, Danny; Badcock, Tom J.; Hao, Rui; Moram, Michelle A.; Dawson, Philip; Kappers, Menno J.; Oliver, Rachel A.

    2013-08-01

    We report on the characterization of semi-polar (11bar 22) gallium nitride (GaN) films grown on m-plane (1bar 100) sapphire by an asymmetric epitaxial lateral overgrowth (ELOG) process first reported by de Mierry et al. [Appl. Phys. Lett. 94 (2009) 191903]. The overgrowth conditions were engineered to greatly enhance the growth rate along the [0001] direction, which combined with the inclination of the [0001] axis from the film surface at ˜32°, allowing a low defect density wing to overgrow the highly defective window region and thus eliminating basal plane stacking faults (BSFs). By correlating cross-sectional transmission electron microscopy and cathodoluminescence data, we confirm that BSFs and dislocations are terminated by the coalescence boundary formed as a result of the overgrowth anisotropy. Low temperature photoluminescence spectra reveal a strong GaN emission at 3.485 eV associated with donor-bound exciton recombination and very small BSF-related emission at 3.425 eV. The intensity ratio between the GaN bound exciton and the BSF emission is ˜220, which is four orders of magnitude greater than that of the semi-polar seed layer. Scanning capacitance microscopy data showed that almost the entire film is unintentionally n-type. The impurity incorporation rate is strongly dependent on which crystallographic planes are present during different stages of the ELOG process.

  18. More Efficient Power Conversion for EVs: Gallium-Nitride Advanced Power Semiconductor and Packaging

    SciTech Connect

    2010-02-01

    Broad Funding Opportunity Announcement Project: Delphi is developing power converters that are smaller and more energy efficient, reliable, and cost-effective than current power converters. Power converters rely on power transistors which act like a very precisely controlled on-off switch, controlling the electrical energy flowing through an electrical circuit. Most power transistors today use silicon (Si) semiconductors. However, Delphi is using semiconductors made with a thin layer of gallium-nitride (GaN) applied on top of the more conventional Si material. The GaN layer increases the energy efficiency of the power transistor and also enables the transistor to operate at much higher temperatures, voltages, and power-density levels compared to its Si counterpart. Delphi is packaging these high-performance GaN semiconductors with advanced electrical connections and a cooling system that extracts waste heat from both sides of the device to further increase the device’s efficiency and allow more electrical current to flow through it. When combined with other electronic components on a circuit board, Delphi’s GaN power transistor package will help improve the overall performance and cost-effectiveness of HEVs and EVs.

  19. The effect of gallium arsenide aluminum laser therapy in the management of cervical myofascial pain syndrome: a double blind, placebo-controlled study.

    PubMed

    Dundar, U; Evcik, D; Samli, F; Pusak, H; Kavuncu, V

    2007-06-01

    The efficacy of low-level laser therapy (LLLT) in myofascial pain syndrome (MPS) seems controversial. A prospective, double-blind, randomized controlled trial was conducted in patients with chronic MPS in the neck to evaluate the effects of low-level 830-nm gallium arsenide aluminum (Ga-As-Al) laser therapy. The study group consisted of 64 MPS patients. The patients were randomly assigned into two groups. In group 1 (n = 32), Ga-As-Al laser treatment was applied over three trigger points bilaterally for 2 min over each point once a day for 15 days during a period of 3 weeks. In group 2 (n = 32), the same treatment protocol was given, but the laser instrument was switched off during applications. All patients in both groups performed daily isometric exercise and stretching exercises for cervical region. Parameters were measured at baseline and after 4 weeks. All patients were evaluated with respect to pain (at rest, movement, and night) and assessed by visual analog scale, measurement of active range of motion using an inclinometer and a goniometer, and the neck disability index. In both groups, statistically significant improvements were detected in all outcome measures compared with baseline (p < 0.05). However, no significant differences were obtained between the two groups (p > 0.05). In conclusion, although the laser therapy has no superiority over placebo groups in this study, we cannot exclude the possibility of effectivity with another treatment regimen including different laser wavelengths and dosages (different intensity and density and/or treatment interval).

  20. High Final Energy of Low-Level Gallium Arsenide Laser Therapy Enhances Skeletal Muscle Recovery without a Positive Effect on Collagen Remodeling.

    PubMed

    de Freitas, Carlos Eduardo Assumpção; Bertaglia, Raquel Santilone; Vechetti Júnior, Ivan José; Mareco, Edson Assunção; Salomão, Rondinelle Artur Simões; de Paula, Tassiana Gutierrez; Nai, Gisele Alborghetti; Carvalho, Robson Francisco; Pacagnelli, Francis Lopes; Dal-Pai-Silva, Maeli

    2015-01-01

    The aim of this study was to evaluate the effects of a Gallium Arsenide (GaAs) laser, using a high final energy of 4.8 J, during muscle regeneration after cryoinjury. Thirty Wistar rats were divided into three groups: Control (C, n = 10); Injured (I, n = 10) and Injured and laser treated (Injured/LLLT, n = 10). The cryoinjury was induced in the central region of the tibialis anterior muscle (TA). The applications of the laser (904 nm, 50 mW average power) were initiated 24 h after injury, at energy density of 69 J cm(-1) for 48 s, for 5 days, to two points of the lesion. Twenty-four hours after the final application, the TA muscle was removed and frozen in liquid nitrogen to assess the general muscle morphology and the gene expression of TNF-α, TGF-β, MyoD, and Myogenin. The Injured/LLLT group presented a higher number of regenerating fibers and fewer degenerating fibers (P < 0.05) without changes in the collagen remodeling. In addition, the Injured/LLLT group presented a significant decrease in the expression of TNF-α and myogenin compared to the injured group (P < 0.05). The results suggest that the GaAs laser, using a high final energy after cryoinjury, promotes muscle recovery without changing the collagen remodeling in the muscle extracellular matrix.

  1. Schottky junctions on semi-insulating LEC gallium arsenide for X- and {gamma}-ray spectrometers operated at and below room temperature

    SciTech Connect

    Bertuccio, G.; Pullia, A. |; Canali, C. |; Nava, F. |; Lanzieri

    1997-04-01

    This work deals with the study of a Schottky junction used as an X- and {gamma}-ray detector in a spectrometer operated in the temperature range from {minus}30 C to +22 C. The device, fabricated on liquid encapsulated Czochralski (LEC) semi-insulating Gallium Arsenide, is designed with a noninjecting ohmic contact which allows biasing voltages up to 550 V. At room temperature (22 C) the energy resolution is found to be relatively poor (15.5-keV full-width at half-maximum (FWHM) at 59.5 keV) due to the large junction reverse current, whose density is within the typical values for Schottky junctions on SI LEC GaAs. By cooling of the detector to {minus}30 C, the noise of the reverse current is drastically lowered, thus achieving electronic noise levels around 160--180 rms electrons. At 500-V bias, the {sup 241}Am spectrum has been resolved down to an energy of 4 keV with charge collection efficiency of cce = 97% and a resolution of about 2-keV FWHM for the Np L lines and 2.4-keV FWHM for the 59.5-keV {gamma} photons. The linearity of the detector has been measured to be better than {+-}0.6% within the explored energy range (14--59 keV). From the experimental spectra, it has been analyzed how either the electronic noise or the trapping of the signal charge contribute to the energy resolution of the spectrometer. The result is that despite the high measured cce, the trapping gives a contribution higher than 1.5 keV FWHM for the 59.5-keV spectral line. A comparison between the experimental results and Monte Carlo simulations, based on the Hecht model of charge trapping in detectors, is shown to give a satisfactory justification of the observed phenomena.

  2. Synergic phototoxic effect of visible light or Gallium-Arsenide laser in the presence of different photo-sensitizers on Porphyromonas gingivalis and Fusobacterium nucleatum

    PubMed Central

    Ghanbari, Habibollah; Mousavi, Seyed Amir; Forouzanfar, Ali; Zakeri, Mahdi; Shafaee, Hooman; Shahnaseri, Shirin

    2015-01-01

    Background: According to the development of resistant strains of pathogenic bacteria following treatment with antimicrobial chemotherapeutic agents, alternative approaches such as lethal photosensitization are being used. The aim of this study was to evaluate the effect of visible light and laser beam radiation in conjugation with three different photosensitizers on the survival of two main periodontopathogenic bacteria including Porphyromonas gingivalis and Fusobacterium nucleatum in different exposure periods. Materials and Methods: In this in vitro prospective study, strains of P. gingivalis and F. nucleatum. were exposed to visible light at wavelengths of 440 nm and diode laser light, Gallium-Arsenide, at wavelength of 830 nm in the presence of a photosensitizer (erythrosine, curcuma, or hydrogen peroxide). They were exposed 1-5 min to each light. Each experiment was repeated 3 times for each strain of bacteria. Data were analyzed by two-ways ANOVA and least significant difference post-hoc tests. P < 0.05 was considered as significant. After 4 days the colonies were counted. Results: Viability of P. gingivalis was reduced 10% and 20% subsequent to exposure to visible light and diode laser, respectively. The values were 65% and 75% for F. nucleatum in a period of 5-min, respectively. Exposure to visible light or laser beam in conjugation with the photosensitizers suspension caused significant reduction in the number of P. gingivalis in duration of 5-min, suggesting a synergic phototoxic effect. However, the survival rate of F. nucleatum following the exposure to laser with hydrogen peroxide, erythrosine and rhizome of Curcuma longa (curcumin) after 5-min was 10%, 20% and 90% respectively. Conclusion: Within the limitations of this study, the synergic phototoxic effect of visible light in combination with each of the photosensitizers on P. gingivalis and F. nucleatum. However, the synergic phototoxic effect of laser exposure and hydrogen peroxide and curcumin as

  3. Surface characterization of gallium nitride modified with peptides before and after exposure to ionizing radiation in solution.

    PubMed

    Berg, Nora G; Nolan, Michael W; Paskova, Tania; Ivanisevic, Albena

    2014-12-30

    An aqueous surface modification of gallium nitride was employed to attach biomolecules to the surface. The modification was a simple two-step process using a single linker molecule and mild temperatures. The presence of the peptide on the surface was confirmed with X-ray photoelectron spectroscopy. Subsequently, the samples were placed in water baths and exposed to ionizing radiation to examine the effects of the radiation on the material in an environment similar to the body. Surface analysis confirmed degradation of the surface of GaN after radiation exposure in water; however, the peptide molecules successfully remained on the surface following exposure to ionizing radiation. We hypothesize that during radiation exposure of the samples, the radiolysis of water produces peroxide and other reactive species on the sample surface. Peroxide exposure promotes the formation of a more stable layer of gallium oxyhydroxide which passivates the surface better than other oxide species.

  4. A Monolithically Integrated Gallium Nitride Nanowire/Silicon Solar Cell Photocathode for Selective Carbon Dioxide Reduction to Methane.

    PubMed

    Wang, Yichen; Fan, Shizhao; AlOtaibi, Bandar; Wang, Yongjie; Li, Lu; Mi, Zetian

    2016-06-20

    A gallium nitride nanowire/silicon solar cell photocathode for the photoreduction of carbon dioxide (CO2 ) is demonstrated. Such a monolithically integrated nanowire/solar cell photocathode offers several unique advantages, including the absorption of a large part of the solar spectrum and highly efficient carrier extraction. With the incorporation of copper as the co-catalyst, the devices exhibit a Faradaic efficiency of about 19 % for the 8e(-) photoreduction to CH4 at -1.4 V vs Ag/AgCl, a value that is more than thirty times higher than that for the 2e(-) reduced CO (ca. 0.6 %). PMID:27128407

  5. A Monolithically Integrated Gallium Nitride Nanowire/Silicon Solar Cell Photocathode for Selective Carbon Dioxide Reduction to Methane.

    PubMed

    Wang, Yichen; Fan, Shizhao; AlOtaibi, Bandar; Wang, Yongjie; Li, Lu; Mi, Zetian

    2016-06-20

    A gallium nitride nanowire/silicon solar cell photocathode for the photoreduction of carbon dioxide (CO2 ) is demonstrated. Such a monolithically integrated nanowire/solar cell photocathode offers several unique advantages, including the absorption of a large part of the solar spectrum and highly efficient carrier extraction. With the incorporation of copper as the co-catalyst, the devices exhibit a Faradaic efficiency of about 19 % for the 8e(-) photoreduction to CH4 at -1.4 V vs Ag/AgCl, a value that is more than thirty times higher than that for the 2e(-) reduced CO (ca. 0.6 %).

  6. Adsorption and adhesion of common serum proteins to nanotextured gallium nitride

    NASA Astrophysics Data System (ADS)

    Bain, Lauren E.; Hoffmann, Marc P.; Bryan, Isaac; Collazo, Ramón; Ivanisevic, Albena

    2015-01-01

    As the broader effort towards device and material miniaturization progresses in all fields, it becomes increasingly important to understand the implications of working with functional structures that approach the size scale of molecules, particularly when considering biological systems. It is well known that thin films and nanostructures feature different optical, electrical, and mechanical properties from their bulk composites; however, interactions taking place at the interface between nanomaterials and their surroundings are less understood. Here, we explore interactions between common serum proteins - serum albumin, fibrinogen, and immunoglobulin G - and a nanotextured gallium nitride surface. Atomic force microscopy with a carboxyl-terminated colloid tip is used to probe the `activity' of proteins adsorbed onto the surface, including both the accessibility of the terminal amine to the tip as well as the potential for protein extension. By evaluating the frequency of tip-protein interactions, we can establish differences in protein behaviour on the basis of both the surface roughness as well as morphology, providing an assessment of the role of surface texture in dictating protein-surface interactions. Unidirectional surface features - either the half-unit cell steppes of as-grown GaN or those produced by mechanical polishing - appear to promote protein accessibility, with a higher frequency of protein extension events taking place on these surfaces when compared with less ordered surface features. Development of a full understanding of the factors influencing surface-biomolecule interactions can pave the way for specific surface modification to tailor the bio-material interface, offering a new path for device optimization.As the broader effort towards device and material miniaturization progresses in all fields, it becomes increasingly important to understand the implications of working with functional structures that approach the size scale of molecules

  7. Study of Nitrogen Incorporation in Indium Antimonide on Gallium Arsenide by Molecular Beam Epitaxy for Long Wavelength Infrared Devices

    NASA Astrophysics Data System (ADS)

    Patra, Nimai Chand

    The distinguishing features of dilute nitride III-V semiconductors lie in the large simultaneous reduction in the band gap and lattice parameter when N is incorporated in small amounts in an otherwise wide band gap III-V material. In particular, N incorporation in InSb is attracting great attention due to its potential applications in the long wavelength infrared (LWIR) applications. However, the relatively small atomic size of N with respect to Sb makes the growth of good quality InSbN layers challenging with effective N incorporation. In this dissertation we present a correlation of the molecular beam epitaxial growth parameters on the type of N-bonding in the InSbN epilayers. Lower growth temperatures of ~290 °C were observed to favor formation of more substitutional N (In-N) and less interstitial N (Sb-N, N-N and In-N-Sb) in the InSbN epilayers. The types of N-bonding were observed to have dominant effect on the structural, vibrational, electrical and optical properties of these dilute nitride epilayers grown on GaAs substrates. As-grown epilayers with high N incorporation of 2.6 % were observed to exhibit a blue shift in the absorption edge to 0.132 eV due to Moss-Burstein effect. Both ex-situ and in-situ annealing at 430 °C improved the quality of the layers as attested to by the micro-Raman spectra, reduced the carrier concentration to ~10 16 cm-3, increased the mobility (micro) to ~13,000 cm2/V-s and red shift the absorption edge to ~10 microm at room temperature (RT). Amongst the heterostructures examined, consisting of different combination of thickness of InSb and InSbN layers, the growth of a relatively thick (~1.4 microm) InSb buffer layer was found to prevent the propagation of rotational and threading dislocations into the subsequent InSbN epilayers. Thus, high RT micro exceeding 40,000 cm2/Vs and an optical absorption edge at ~12 microm in the LWIR range have been achieved for 450 °C ex-situ annealed 0.4 microm InSbN/ 1.4 microm InSb/ Ga

  8. Characterization of irradiated and temperature-compensated gallium nitride surface acoustic wave resonators

    NASA Astrophysics Data System (ADS)

    Shankar, Ashwin; Angadi, Chetan; Bhattacharya, Sharmila; Lin, Chih-Ming; Senesky, Debbie G.

    2014-06-01

    Conventional electronic components are prone to failure and drift when exposed to space environments, which contain harsh conditions, such as extreme variation in temperature and radiation exposure. As a result, electronic components are often shielded with heavy and complex packaging. New material platforms that leverage the radiation and temperature tolerance of wide bandgap materials can be used to develop robust electronic components without complex packaging. One such component that is vital for communication, navigation and signal processing on space exploration systems is the on-board timing reference, which is conventionally provided by a quartz crystal resonator and is prone to damage from radiation and temperature fluctuations. As a possible alternative, this paper presents the characterization of microfabricated and wide bandgap gallium nitride (GaN) surface acoustic wave (SAW) resonators in radiation environments. Ultimately, in combination with the two-dimensional gas (2DEG) layer at the AlGaN/GaN interface, high electron mobility transistor (HEMT) structures can provide a monolithic solution for timing electronics on board space systems. One-port SAW resonators are microfabricated on a GaN-on-sapphire substrate are used to explore the impact of irradiation on the device performance. The GaN-based SAW resonator was subjected to extreme temperature conditions to study the change in resonance frequency. Thermal characterization of the resonator has revealed a self-compensating property at cryogenic temperatures. In addition, GaN-on-sapphire samples were irradiated using a Cs-137 source up to 55 krads of total ionizing dose (TID). The measured frequency response and Raman spectroscopy of the GaN/sapphire SAW resonators microfabricated from the irradiated samples are presented.

  9. Electron-phonon relaxation and excited electron distribution in gallium nitride

    NASA Astrophysics Data System (ADS)

    Zhukov, V. P.; Tyuterev, V. G.; Chulkov, E. V.; Echenique, P. M.

    2016-08-01

    We develop a theory of energy relaxation in semiconductors and insulators highly excited by the long-acting external irradiation. We derive the equation for the non-equilibrium distribution function of excited electrons. The solution for this function breaks up into the sum of two contributions. The low-energy contribution is concentrated in a narrow range near the bottom of the conduction band. It has the typical form of a Fermi distribution with an effective temperature and chemical potential. The effective temperature and chemical potential in this low-energy term are determined by the intensity of carriers' generation, the speed of electron-phonon relaxation, rates of inter-band recombination, and electron capture on the defects. In addition, there is a substantial high-energy correction. This high-energy "tail" largely covers the conduction band. The shape of the high-energy "tail" strongly depends on the rate of electron-phonon relaxation but does not depend on the rates of recombination and trapping. We apply the theory to the calculation of a non-equilibrium distribution of electrons in an irradiated GaN. Probabilities of optical excitations from the valence to conduction band and electron-phonon coupling probabilities in GaN were calculated by the density functional perturbation theory. Our calculation of both parts of distribution function in gallium nitride shows that when the speed of the electron-phonon scattering is comparable with the rate of recombination and trapping then the contribution of the non-Fermi "tail" is comparable with that of the low-energy Fermi-like component. So the high-energy contribution can essentially affect the charge transport in the irradiated and highly doped semiconductors.

  10. Adsorption and adhesion of common serum proteins to nanotextured gallium nitride.

    PubMed

    Bain, Lauren E; Hoffmann, Marc P; Bryan, Isaac; Collazo, Ramón; Ivanisevic, Albena

    2015-02-14

    As the broader effort towards device and material miniaturization progresses in all fields, it becomes increasingly important to understand the implications of working with functional structures that approach the size scale of molecules, particularly when considering biological systems. It is well known that thin films and nanostructures feature different optical, electrical, and mechanical properties from their bulk composites; however, interactions taking place at the interface between nanomaterials and their surroundings are less understood. Here, we explore interactions between common serum proteins - serum albumin, fibrinogen, and immunoglobulin G - and a nanotextured gallium nitride surface. Atomic force microscopy with a carboxyl-terminated colloid tip is used to probe the 'activity' of proteins adsorbed onto the surface, including both the accessibility of the terminal amine to the tip as well as the potential for protein extension. By evaluating the frequency of tip-protein interactions, we can establish differences in protein behaviour on the basis of both the surface roughness as well as morphology, providing an assessment of the role of surface texture in dictating protein-surface interactions. Unidirectional surface features - either the half-unit cell steppes of as-grown GaN or those produced by mechanical polishing - appear to promote protein accessibility, with a higher frequency of protein extension events taking place on these surfaces when compared with less ordered surface features. Development of a full understanding of the factors influencing surface-biomolecule interactions can pave the way for specific surface modification to tailor the bio-material interface, offering a new path for device optimization.

  11. Vertical 2D/3D Semiconductor Heterostructures Based on Epitaxial Molybdenum Disulfide and Gallium Nitride.

    PubMed

    Ruzmetov, Dmitry; Zhang, Kehao; Stan, Gheorghe; Kalanyan, Berc; Bhimanapati, Ganesh R; Eichfeld, Sarah M; Burke, Robert A; Shah, Pankaj B; O'Regan, Terrance P; Crowne, Frank J; Birdwell, A Glen; Robinson, Joshua A; Davydov, Albert V; Ivanov, Tony G

    2016-03-22

    When designing semiconductor heterostructures, it is expected that epitaxial alignment will facilitate low-defect interfaces and efficient vertical transport. Here, we report lattice-matched epitaxial growth of molybdenum disulfide (MoS2) directly on gallium nitride (GaN), resulting in high-quality, unstrained, single-layer MoS2 with strict registry to the GaN lattice. These results present a promising path toward the implementation of high-performance electronic devices based on 2D/3D vertical heterostructures, where each of the 3D and 2D semiconductors is both a template for subsequent epitaxial growth and an active component of the device. The MoS2 monolayer triangles average 1 μm along each side, with monolayer blankets (merged triangles) exhibiting properties similar to that of single-crystal MoS2 sheets. Photoluminescence, Raman, atomic force microscopy, and X-ray photoelectron spectroscopy analyses identified monolayer MoS2 with a prominent 20-fold enhancement of photoluminescence in the center regions of larger triangles. The MoS2/GaN structures are shown to electrically conduct in the out-of-plane direction, confirming the potential of directly synthesized 2D/3D semiconductor heterostructures for vertical current flow. Finally, we estimate a MoS2/GaN contact resistivity to be less than 4 Ω·cm(2) and current spreading in the MoS2 monolayer of approximately 1 μm in diameter. PMID:26866442

  12. Vertical 2D/3D Semiconductor Heterostructures Based on Epitaxial Molybdenum Disulfide and Gallium Nitride.

    PubMed

    Ruzmetov, Dmitry; Zhang, Kehao; Stan, Gheorghe; Kalanyan, Berc; Bhimanapati, Ganesh R; Eichfeld, Sarah M; Burke, Robert A; Shah, Pankaj B; O'Regan, Terrance P; Crowne, Frank J; Birdwell, A Glen; Robinson, Joshua A; Davydov, Albert V; Ivanov, Tony G

    2016-03-22

    When designing semiconductor heterostructures, it is expected that epitaxial alignment will facilitate low-defect interfaces and efficient vertical transport. Here, we report lattice-matched epitaxial growth of molybdenum disulfide (MoS2) directly on gallium nitride (GaN), resulting in high-quality, unstrained, single-layer MoS2 with strict registry to the GaN lattice. These results present a promising path toward the implementation of high-performance electronic devices based on 2D/3D vertical heterostructures, where each of the 3D and 2D semiconductors is both a template for subsequent epitaxial growth and an active component of the device. The MoS2 monolayer triangles average 1 μm along each side, with monolayer blankets (merged triangles) exhibiting properties similar to that of single-crystal MoS2 sheets. Photoluminescence, Raman, atomic force microscopy, and X-ray photoelectron spectroscopy analyses identified monolayer MoS2 with a prominent 20-fold enhancement of photoluminescence in the center regions of larger triangles. The MoS2/GaN structures are shown to electrically conduct in the out-of-plane direction, confirming the potential of directly synthesized 2D/3D semiconductor heterostructures for vertical current flow. Finally, we estimate a MoS2/GaN contact resistivity to be less than 4 Ω·cm(2) and current spreading in the MoS2 monolayer of approximately 1 μm in diameter.

  13. Synthesis, characterization, growth mechanism, photoluminescence and field emission properties of novel dandelion-like gallium nitride

    NASA Astrophysics Data System (ADS)

    Nabi, Ghulam; Cao, Chuanbao; Khan, Waheed S.; Hussain, Sajad; Usman, Zahid; Safdar, Muhammad; Shah, Sajjad Hussain; Khattak, Noor Abass Din

    2011-09-01

    Dandelion-like gallium nitride (GaN) microstructures were successfully synthesized via Ni catalyst assisted chemical vapor deposition method at 1200 °C under NH3 atmosphere by pre-treating precursors with aqueous ammonia. The as-synthesized product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). X-ray diffraction analysis revealed that as-synthesized dandelion-like GaN was pure and has hexagonal wurtzite structure. SEM results showed that the size of the dandelion-like GaN structure was in the range of 30-60 μm. Dandelion-like GaN microstructures exhibited reasonable field emission properties with the turn-on field of 9.65 V μm-1 (0.01 mA cm-2) and threshold field of 11.35 V μm-1 (1 mA cm-2) which is sufficient for applications of electron emission devices, field emission displays and vacuum micro electronic devices. Optical properties were studied at room temperature by using fluorescence spectrophotometer. Photoluminescence (PL) measurements of dandelion-like GaN showed a strong near-band-edge emission at 370.2 nm (3.35 eV) with blue band emission at 450.4 nm (2.75 eV) and 465.2 nm (2.66 eV) but with out yellow band emission. The room-temperature photoluminescence properties showed that it has also potential application in light-emitting devices. The tentative growth mechanism for the growth of dandelion-like GaN was also described.

  14. Self-Consistent Calculation of the correct Band-Gap and Low Energy Conduction Bands in Gallium-Nitride

    NASA Astrophysics Data System (ADS)

    Zhao, G. L.; Bagayoko, D.; Fan, J. D.

    1998-03-01

    The III-V nitrides are viewed as new semiconductors for optoelectronic applications in the blue and UV wavelengths and, more recently, as high-power, high-temperature electronic devices. However, a reliable prediction of the band gap and the low energy conduction bands had, until now, remained a problem in ab initio computations. A spurious effect of the variational procedure and of basis sets is shown to be a source of this problem. We present first principle computational steps that avoid this effect. We applied our new approach to calculate the electronic structure of III-V gallium-nitride using a local density approximation (LDA) for the exchange-correlation potential. Our calculated electronic structure and band gap, for an optimum basis set, agree qualitatively and quantitatively with experiment. *Work supported in part by funding from the Department of the Navy, Office of Naval Research (ONR), and from the Physics Graduate Program at Southern University and A & M College.

  15. NTP Toxicology and Carcinogenesis Studies of Gallium Arsenide (CAS No. 1303-00-0) in F344/N Rats and B6C3F1 Mice (Inhalation Studies).

    PubMed

    2000-09-01

    Gallium arsenide is used primarily to make light- emitting diodes, lasers, laser windows, and photodetectors and in the photoelectronic transmission of data through optical fibers. Gallium arsenide was nominated for study because of its widespread use in the microelectronics industry, the potential for worker exposure, and the absence of chronic toxicity data. Male and female F344/N rats and B6C3F1 mice were exposed to gallium arsenide particles (greater than 98% pure; mass median aerodynamic diameter = 0.8 to 1.0 &mgr;m) by inhalation for 16 days, 14 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, and the frequency of micronuclei was determined in the peripheral blood of mice exposed to gallium arsenide for 14 weeks. 16-DAY STUDY IN RATS: Groups of five male and five female rats were exposed to particulate aerosols of gallium arsenide with a mass median aerodynamic diameter of approximately 1 &mgr;m at concentrations of 0, 1, 10, 37, 75, or 150 mg/m(3) by inhalation, 6 hours per day, 5 days per week, for 16 days. All rats survived to the end of the study. The final mean body weights of all exposed groups of males and females were similar to those of the chamber controls. Compared to chamber controls, the liver and lung weights of males exposed to 1 mg/m(3) or greater and females exposed to 10 mg/m(3) or greater were increased; the thymus weights of all exposed groups of males were decreased. Gallium arsenide particles were visible in the alveolar spaces and, to a lesser extent, within alveolar macrophages of exposed rats. Moderate proteinosis (surfactant mixed with small amounts of fibrin) and minimal histiocytic cellular infiltrate were observed in the alveoli of exposed males and females. Epithelial hyperplasia and squamous metaplasia of the larynx were observed primarily in males exposed to 150 mg/m(3). 16-DAY STUDY IN MICE: Groups of five male and four or five female mice were exposed to particulate aerosols of gallium

  16. Niobium and niobium nitride contacts on semiconducting material

    SciTech Connect

    Cukauskas, E.; Carter, W.; Pond, J.; Newman, H.

    1989-06-30

    This invention related generally to a metallization layer of niobium or niobium nitride on a semiconductor in an integrated-circuit structure, which can function from the superconducting-temperature regime to above room temperature. Niobium or niobium nitride is deposited onto a heated gallium arsenide substrate. This metallization will maintain chemical stability after high-temperature post processing. These materials provide a low-resistivity metallization suitable for Schottky contacts used over a wide operating temperature range and are superconducting at low temperatures.

  17. Tuning the surface Fermi level on p-type gallium nitride nanowires for efficient overall water splitting.

    PubMed

    Kibria, M G; Zhao, S; Chowdhury, F A; Wang, Q; Nguyen, H P T; Trudeau, M L; Guo, H; Mi, Z

    2014-04-30

    Solar water splitting is one of the key steps in artificial photosynthesis for future carbon-neutral, storable and sustainable source of energy. Here we show that one of the major obstacles for achieving efficient and stable overall water splitting over the emerging nanostructured photocatalyst is directly related to the uncontrolled surface charge properties. By tuning the Fermi level on the nonpolar surfaces of gallium nitride nanowire arrays, we demonstrate that the quantum efficiency can be enhanced by more than two orders of magnitude. The internal quantum efficiency and activity on p-type gallium nitride nanowires can reach ~51% and ~4.0 mol hydrogen h(-1) g(-1), respectively. The nanowires remain virtually unchanged after over 50,000 μmol gas (hydrogen and oxygen) is produced, which is more than 10,000 times the amount of photocatalyst itself (~4.6 μmol). The essential role of Fermi-level tuning in balancing redox reactions and in enhancing the efficiency and stability is also elucidated.

  18. Design and Characterization of p-i-n Devices for Betavoltaic Microbatteries on Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Khan, Muhammad Raziuddin A.

    Betavoltaic microbatteries convert nuclear energy released as beta particles directly into electrical energy. These batteries are well suited for electrical applications such as micro-electro-mechanical systems (MEMS), implantable medical devices and sensors. Such devices are often located in hard to access places where long life, micro-size and lightweight are required. The working principle of a betavoltaic device is similar to a photovoltaic device; they differ only in that the electron hole pairs (EHPs) are generated in the device by electrons instead of photons. In this study, the performance of a betavoltaic device fabricated from gallium nitride (GaN) is investigated for beta particle energies equivalent to Tritium (3H) and Nickel-63 (N63) beta sources. GaN is an attractive choice for fabricating betavoltaic devices due to its wide band gap and radiation resistance. Another advantage GaN has is that it can be alloyed with aluminum (Al) to further increase the bandgap, resulting in a higher output power and increased efficiency. Betavoltaic devices were fabricated on p-i-n GaN structures grown by metalorganic chemical vapor deposition (MOCVD). The devices were characterized using current - voltage (IV) measurements without illumination (light or beta), using a laser driven light source, and under an electron beam. Dark IV measurements showed a turn on-voltage of ~ 3.4 V, specific-on-resistance of 15.1 m O-cm2, and a leakage current of 0.5 mA at -- 10 V. A clear photo-response was observed when IV curves were measured for these devices under a light source at a wavelength of 310 nm (4.0 eV). These devices were tested under an electron beam in order to evaluate their behavior as betavoltaic microbatteries without using radioactive materials. Output power of 70 nW and 640 nW with overall efficiencies of 1.2% and 4.0% were determined at the average energy emission of 3H (5.6 keV) and 63N (17 keV) respectively.

  19. Magnesium-doped gallium nitride for electronic and optoelectronic device applications

    NASA Astrophysics Data System (ADS)

    Kozodoy, Peter

    1999-11-01

    Magnesium doping of gallium nitride (GaN) for p-type conductivity is a crucial technology for a host of optoelectronic and electronic device applications. The performance of many of these devices is presently limited by the various difficulties associated with Mg doping, both fundamental (such as the deep nature of the Mg acceptor) and technological (such as the problems in forming ohmic contacts). Both types of issues are addressed in this work. Heavy doping effects have been investigated in order to understand the consequences of the high dopant concentration typically employed; increased compensation and a reduction in the acceptor binding energy are among the effects observed. The compensation level is believed to limit the hole mobility in these films, and is found to depend on the choice of growth conditions; the results point to nitrogen vacancies as a likely candidate for one of the compensating donor species. The optimization of various processing procedures has also been addressed. These include the annealing procedure used to remove the hydrogen passivation as well as ohmic contact recipes. In addition, the electrical effects of plasma-induced damage to the p-type GaN surface are investigated; these effects are particularly important for bipolar transistor applications where a plasma etch is needed in order to reveal the base layer. The electrical characteristics of GaN p-n junctions formed both with and without dislocations are compared using the lateral epitaxial overgrowth technique; the dislocations are found to be the dominant leakage path in reverse-bias operation. The electrical consequences of the deep Mg acceptor are also addressed. These include the unusual nature of the low-frequency depletion region, and dispersion in the high-frequency depletion region due to the finite response time of the Mg acceptor. Finally, a novel scheme is presented that uses the strong polarization fields present in AlGaN/GaN superlattices to enhance the doping

  20. White light-emitting diodes based on nonpolar and semipolar gallium nitride orientations

    NASA Astrophysics Data System (ADS)

    Demille, Natalie Fellows

    Gallium nitride has become one of the key components when fabricating white light-emitting diodes. Its use as the blue source in conjunction with a wavelength converter such as the yellow emitting phosphor YAG:Ce 3+ is a technology that is commercially available and usable for solid state lighting applications. Currently available white phosphor-based LEDs (pcLEDs) use the basal plane of wurtzite GaN as their source. Although research over the past couple decades has developed this technology into devices with good photometric performance and high reliability, the introduction of nonbasal plane wurtzite GaN orientations have benefits over basal plane GaN that can be incorporated into the white LED. The focus of this research deals with exploring white illumination on nonpolar and semipolar planes of GaN. Light extraction techniques will be described that allowed for high output powers and efficiencies on the c-plane as well as the (1100), (10 11), and (1122) planes of GaN. With higher performing devices, white pcLEDs were fabricated on c-plane, m-plane, and the (1011) semipolar plane. The novelty in the present research is producing white LEDs with nonbasal plane diodes which exhibit optical polarization anisotropy. This feature, absent on the basal plane, allows for tuning photometric quantities both electrically and optically. This is demonstrated on pcLEDs as well as dichromatic LEDs comprised solely of InGaN diodes. As a consequence of these measurements, an apparent optical polarization was seen to be occurring in the luminescence of the YAG:Ce3+ when the system absorbed linearly polarized light. Polarized emission in YAG:Ce3+ was explored by obtaining single crystals of YAG:Ce3+ with different planar orientations. The experiments led to the conclusion that crystal orientation plays no part in the optical polarization. It is suggested that the cause is a result of electric dipole transitions given by various selection rules between the Ce 3+ ion's 4f and 5d

  1. Physical mechanisms affecting hot carrier-induced degradation in gallium nitride HEMTs

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shubhajit

    Gallium Nitride or GaN-based high electron mobility transistors (HEMTs) is currently the most promising device technology in several key military and civilian applications due to excellent high-power as well as high-frequency performance. Even though the performance figures are outstanding, GaN-based HEMTs are not as mature as some competing technologies, which means that establishing the reliability of the technology is important to enable use in critical applications. The objective of this research is to understand the physical mechanisms affecting the reliability of GaN HEMTs at moderate drain biases (typically VDS < 30 V in the devices considered here). The degradation in device performance is believed to be due to the formation or modification of charged defects near the interface by hydrogen depassivation processes (due to electron-activated hydrogen removal) from energetic carriers. A rate-equation describing the defect generation process is formulated based on this assumption. A combination of ensemble Monte-Carlo (EMC) simulation statistics, ab-initio density functional theory (DFT) calculations, and accelerated stress experiments is used to relate the candidate defects to the overall degradation behavior (VT and gm). The focus of this work is on the 'semi-ON' mode of transistor operation in which the degradation is usually observed to be at its highest. This semi-ON state is reasonably close to the biasing region of class-AB high power amplifiers, which are popular because of the combination of high efficiency and low distortion that is associated with this configuration. The carrier-energy distributions are obtained using an EMC simulator that was developed specifically for III-V HFETs. The rate equation is used to model the degradation at different operating conditions as well as longer stress times from the result of one short duration stress test, by utilizing the carrier-energy distribution obtained from EMC simulations for one baseline condition

  2. Size effects in the thermal conductivity of gallium oxide (β-Ga2O3) films grown via open-atmosphere annealing of gallium nitride

    NASA Astrophysics Data System (ADS)

    Szwejkowski, Chester J.; Creange, Nicole C.; Sun, Kai; Giri, Ashutosh; Donovan, Brian F.; Constantin, Costel; Hopkins, Patrick E.

    2015-02-01

    Gallium nitride (GaN) is a widely used semiconductor for high frequency and high power devices due to of its unique electrical properties: a wide band gap, high breakdown field, and high electron mobility. However, thermal management has become a limiting factor regarding efficiency, lifetime, and advancement of GaN devices and GaN-based applications. In this work, we study the thermal conductivity of beta-phase gallium oxide (β-Ga2O3) thin films, a component of typical gate oxides used in such devices. We use time domain thermoreflectance to measure the thermal conductivity of a variety of polycrystalline β-Ga2O3 films of different thicknesses grown via open atmosphere annealing of the surfaces of GaN films on sapphire substrates. We show that the measured effective thermal conductivity of these β-Ga2O3 films can span 1.5 orders of magnitude, increasing with an increased film thickness, which is indicative of the relatively large intrinsic thermal conductivity of the β-Ga2O3 grown via this technique (8.8 ± 3.4 W m-1 K-1) and large mean free paths compared to typical gate dielectrics commonly used in GaN device contacts. By conducting time domain thermoreflectance (TDTR) measurements with different metal transducers (Al, Au, and Au with a Ti wetting layer), we attribute this variation in effective thermal conductivity to a combination of size effects in the β-Ga2O3 film resulting from phonon scattering at the β-Ga2O3/GaN interface and thermal transport across the β-Ga2O3/GaN interface. The measured thermal properties of open atmosphere-grown β-Ga2O3 and its interface with GaN set the stage for thermal engineering of gate contacts in high frequency GaN-based devices.

  3. Effects of Hydrogen on Tantalum Nitride Resistors

    NASA Technical Reports Server (NTRS)

    Weiler, James

    2000-01-01

    In this paper we report on observations of degradation of thin film Tantalum Nitride chip resistors in a hermetically sealed hybrid. The observations have been attributed to the reaction of residual Palladium with desorbed Hydrogen on the surface of the resistor film. Hydrogen gas has been observed to desorb from various sources within the sealed hybrid as a result of temperature elevation. The hydrogen gas has been reported to undergo a reaction with elements such as Platinum and Palladium causing device degradation in Gallium Arsenide Field Effect Transistors. The experimental procedures and data relating to this observation along with a discussion of available risk mitigation techniques will be presented.

  4. Quantificaion of ion diffusion in gallium arsenide-based spintronic Light-Emitting Diode devices using time-of-flight secondary ion mass spectrometry

    NASA Astrophysics Data System (ADS)

    Cogswell, Jeffrey Ryan

    Depth profiling using Secondary Ion Mass Spectrometry (SIMS) is a direct method to measure diffusion of atomic or molecular species that have migrated distances of nanometers/micrometers in a specific material. For this research, the diffusion of Mn, sequentially Ga ions, in Gallium Arsenide (GaAs)-based spin Light Emitting Diode (LED) devices is studied by quantitative Time-of-Flight (ToF) SIMS. The goal is to prove conclusively the driving force and mechanism behind Mn diffusion in GaAs by quantifying the diffusion of these ions in each device. Previous work has identified two competing processes for the movement of Mn in GaAs: diffusion and phase separation. The process is dependent on the temperature the sample is exposed to, either by post-annealing, or during the molecular beam epitaxy (MBE) growth process. The hypothesis is that Manganese Arsenide (MnAs) is thermodynamically more stable than randomly distributed Mn ions in GaAs, and that by annealing at a certain temperature, a pure MnAs layer can be produced from a GaMnAs layer in a working spin LED device. Secondly, the spin efficiencies will be measured and the difference will be related to the formation of a pure MnAs layer. The first chapter of this dissertation discusses the history of spintronic devices, including details on the established methods for characterization, the importance for potential application to the semiconductor industry, and the requirements for the full implementation of spintronic devices in modern-day computers. MnAs and GaMnAs devices are studied, their preparation and properties are described, and the study's experimental design is covered in the latter part of Chapter 1. Chapter 2 includes a review of diffusion in semiconductors, including the types of diffusion, mechanisms they follow, and the different established experimental methods for studying diffusion. The later sections include summaries of Mn diffusion and previous studies investigating Mn diffusion in different

  5. Growing Gallium Arsenide On Silicon

    NASA Technical Reports Server (NTRS)

    Radhakrishnan, Gouri

    1989-01-01

    Epitaxial layers of high quality formed on <111> crystal plane. Present work reports successful growth of 1- and 2-micrometer thick layers of n-type, 7-ohms per cm, 2-inch diameter, Si<111> substrate. Growth conducted in Riber-2300(R) MBE system. Both doped and undoped layers of GaAs grown. Chamber equipped with electron gun and camera for in-situ reflection high-energy-electron diffraction measurements. RHEED patterns of surface monitored continuously during slow growth stage.

  6. Effects of radiation and temperature on gallium nitride (GaN) metal-semiconductor-metal ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Chiamori, Heather C.; Angadi, Chetan; Suria, Ateeq; Shankar, Ashwin; Hou, Minmin; Bhattacharya, Sharmila; Senesky, Debbie G.

    2014-06-01

    The development of radiation-hardened, temperature-tolerant materials, sensors and electronics will enable lightweight space sub-systems (reduced packaging requirements) with increased operation lifetimes in extreme harsh environments such as those encountered during space exploration. Gallium nitride (GaN) is a ceramic, semiconductor material stable within high-radiation, high-temperature and chemically corrosive environments due to its wide bandgap (3.4 eV). These material properties can be leveraged for ultraviolet (UV) wavelength photodetection. In this paper, current results of GaN metal-semiconductor-metal (MSM) UV photodetectors behavior after irradiation up to 50 krad and temperatures of 15°C to 150°C is presented. These initial results indicate that GaN-based sensors can provide robust operation within extreme harsh environments. Future directions for GaN-based photodetector technology for down-hole, automotive and space exploration applications are also discussed.

  7. Compact, Interactive Electric Vehicle Charger: Gallium-Nitride Switch Technology for Bi-directional Battery-to-Grid Charger Applications

    SciTech Connect

    2010-10-01

    ADEPT Project: HRL Laboratories is using gallium nitride (GaN) semiconductors to create battery chargers for electric vehicles (EVs) that are more compact and efficient than traditional EV chargers. Reducing the size and weight of the battery charger is important because it would help improve the overall performance of the EV. GaN semiconductors process electricity faster than the silicon semiconductors used in most conventional EV battery chargers. These high-speed semiconductors can be paired with lighter-weight electrical circuit components, which helps decrease the overall weight of the EV battery charger. HRL Laboratories is combining the performance advantages of GaN semiconductors with an innovative, interactive battery-to-grid energy distribution design. This design would support 2-way power flow, enabling EV battery chargers to not only draw energy from the power grid, but also store and feed energy back into it.

  8. Studies of metal/gallium nitride gas sensors: Sensing response, morphology and sensing applications

    NASA Astrophysics Data System (ADS)

    Duan, Barrett Kai-Bong

    Reliable gas sensors with excellent sensitivity and robustness are important for the development of advanced technological applications while ensuring a safe environment in both industrial and household security. The chemically and mechanically robust gallium nitride (GaN) is a promising semiconductor for these important applications, especially for use at high temperatures and in extreme environments. When a metal is in contact with a semiconductor surface, a space charge region and Schottky barrier are formed on the semiconductor side. In this thesis, the sensing response of Pt and GaN to gaseous H2 and CO and the dependence of the response on Pt and GaN surface morphologies are explored. The sensing opportunities are expanded when GaN is decorated with Ag and the structure is used for small molecule analysis using surface enhanced Raman scattering (SERS). Combining the high surface area of nanoporous GaN with Pt nanoparticles deposited by electroless chemical deposition, the sensing performance of the well-known H-mediated Schottky barrier based on the Pt/GaN sensor is studied. The H2 sensing performance of, as defined by the limit of detection (LOD), Pt-decorated porous GaN measured by AC four-point probe resistance measurements is more than an order of magnitude better than planar GaN sensors based on the same Pt/GaN Schottky barrier height concept. The potential utility of high surface area porous GaN was realized by decorating the confined nanopores with metal (Pt), thus increasing the surface area available for sensing and lowering the LOD. Pt/GaN structures can also be used to detect CO at high temperature. The CO sensing response is also dependent on the Pt morphology. For continuous films, CO signal increases as the thickness of the metal film decreases. In discontinuous Pt films, increasing Pt surface area also increases the CO signal when the Pt/GaN interfacial area remains constant. A model is proposed, in which the influence of the adsorbed CO on Pt

  9. Understanding the Impact of Point Defects on the Optoelectronic Properties of Gallium Nitride from First-Principles

    NASA Astrophysics Data System (ADS)

    Lewis, Kirk; Matsubara, Masahiko; Bellotti, Enrico; Sharifzadeh, Sahar

    Gallium nitride (GaN) and related alloys form a class of wide bandgap semiconductors that have broad applications as components in optoelectronic devices; in particular, power electronics and blue and ultraviolet optical devices. Nitride films grow with high defect densities, and understanding the relationship between structural defects and optoelectronic function will be central to the design of new high-performance materials. Here, we take a first-principles density functional theory (DFT) and many-body perturbation theory (MBPT) approach to quantify the influence of defects on the electronic and optical properties of GaN. We predict, as expected, that introduction of a N or Ga vacancy results in several energetically favorable charged states within bulk GaN; these energetically favorable defects result in a significant modification of the quasiparticle and excitonic properties of GaN. We will discuss the implications of defect-induced-states for the electron transport and absorption properties of GaN. This work was partially supported by the Army Research Office (ARO) within the Collaborative Research Alliance (CRA-MSME).

  10. Size effects in the thermal conductivity of gallium oxide (β-Ga{sub 2}O{sub 3}) films grown via open-atmosphere annealing of gallium nitride

    SciTech Connect

    Szwejkowski, Chester J.; Giri, Ashutosh; Donovan, Brian F.; Hopkins, Patrick E.; Creange, Nicole C.; Constantin, Costel; Sun, Kai

    2015-02-28

    Gallium nitride (GaN) is a widely used semiconductor for high frequency and high power devices due to of its unique electrical properties: a wide band gap, high breakdown field, and high electron mobility. However, thermal management has become a limiting factor regarding efficiency, lifetime, and advancement of GaN devices and GaN-based applications. In this work, we study the thermal conductivity of beta-phase gallium oxide (β-Ga{sub 2}O{sub 3}) thin films, a component of typical gate oxides used in such devices. We use time domain thermoreflectance to measure the thermal conductivity of a variety of polycrystalline β-Ga{sub 2}O{sub 3} films of different thicknesses grown via open atmosphere annealing of the surfaces of GaN films on sapphire substrates. We show that the measured effective thermal conductivity of these β-Ga{sub 2}O{sub 3} films can span 1.5 orders of magnitude, increasing with an increased film thickness, which is indicative of the relatively large intrinsic thermal conductivity of the β-Ga{sub 2}O{sub 3} grown via this technique (8.8 ± 3.4 W m{sup −1} K{sup −1}) and large mean free paths compared to typical gate dielectrics commonly used in GaN device contacts. By conducting time domain thermoreflectance (TDTR) measurements with different metal transducers (Al, Au, and Au with a Ti wetting layer), we attribute this variation in effective thermal conductivity to a combination of size effects in the β-Ga{sub 2}O{sub 3} film resulting from phonon scattering at the β-Ga{sub 2}O{sub 3}/GaN interface and thermal transport across the β-Ga{sub 2}O{sub 3}/GaN interface. The measured thermal properties of open atmosphere-grown β-Ga{sub 2}O{sub 3} and its interface with GaN set the stage for thermal engineering of gate contacts in high frequency GaN-based devices.

  11. Non-Ideal Properties of Gallium Nitride Based Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Shan, Qifeng

    The spectacular development of gallium nitride (GaN) based light-emitting diodes (LEDs) in recent years foreshadows a new era for lighting. There are still several non-ideal properties of GaN based LEDs that hinder their widespread applications. This dissertation studies these non-ideal properties including the large reverse leakage current, large subthreshold forward leakage current, an undesired parasitic cyan luminescence and high-concentration deep levels in GaInN blue LEDs. This dissertation also studies the thermal properties of GaInN LEDs. Chapter 1 gives a brief introduction of non-ideal properties of GaN based LEDs. The leakage current of GaN based LEDs, defects in epitaxially grown GaN devices, and doping problems of p-type GaN materials are discussed. The transient junction temperature measurement technique for GaN based LEDs is introduced. The leakage current of an LED includes the subthreshold forward leakage current and the reverse leakage current. The leakage current of GaN based LEDs affects the reliability, electrostatic discharge resilience, and sub-threshold power consumption. In Chapter 2, the reverse leakage current of a GaInN LED is analyzed by temperaturedependent current-voltage measurements. At low temperature, the reverse leakage current is attributed to the variable-range-hopping conduction. At high temperature, the reverse leakage current is attributed to a thermally-assisted multi-step tunneling. The thermal activation energies (95 meV ~ 162 meV), extracted from the Arrhenius plot for the reverse current in the high-temperature range, indicate a thermally activated tunneling process. Additional room-temperature capacitance-voltage (C-V) measurements are performed to obtain information on the depletion width and doping concentration of the LED. The average internal electric field is estimated by the C-V measurements. The strong internal electric field enhances the thermal emission of electrons in the

  12. Non-Ideal Properties of Gallium Nitride Based Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Shan, Qifeng

    The spectacular development of gallium nitride (GaN) based light-emitting diodes (LEDs) in recent years foreshadows a new era for lighting. There are still several non-ideal properties of GaN based LEDs that hinder their widespread applications. This dissertation studies these non-ideal properties including the large reverse leakage current, large subthreshold forward leakage current, an undesired parasitic cyan luminescence and high-concentration deep levels in GaInN blue LEDs. This dissertation also studies the thermal properties of GaInN LEDs. Chapter 1 gives a brief introduction of non-ideal properties of GaN based LEDs. The leakage current of GaN based LEDs, defects in epitaxially grown GaN devices, and doping problems of p-type GaN materials are discussed. The transient junction temperature measurement technique for GaN based LEDs is introduced. The leakage current of an LED includes the subthreshold forward leakage current and the reverse leakage current. The leakage current of GaN based LEDs affects the reliability, electrostatic discharge resilience, and sub-threshold power consumption. In Chapter 2, the reverse leakage current of a GaInN LED is analyzed by temperaturedependent current-voltage measurements. At low temperature, the reverse leakage current is attributed to the variable-range-hopping conduction. At high temperature, the reverse leakage current is attributed to a thermally-assisted multi-step tunneling. The thermal activation energies (95 meV ~ 162 meV), extracted from the Arrhenius plot for the reverse current in the high-temperature range, indicate a thermally activated tunneling process. Additional room-temperature capacitance-voltage (C-V) measurements are performed to obtain information on the depletion width and doping concentration of the LED. The average internal electric field is estimated by the C-V measurements. The strong internal electric field enhances the thermal emission of electrons in the

  13. Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide

    SciTech Connect

    Kerr, A. J.; Chagarov, E.; Kaufman-Osborn, T.; Kummel, A. C.; Gu, S.; Wu, J.; Asbeck, P. M.; Madisetti, S.; Oktyabrsky, S.

    2014-09-14

    A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al{sub 2}O{sub 3} gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001)

  14. Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide.

    PubMed

    Kerr, A J; Chagarov, E; Gu, S; Kaufman-Osborn, T; Madisetti, S; Wu, J; Asbeck, P M; Oktyabrsky, S; Kummel, A C

    2014-09-14

    A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al2O3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001).

  15. Epitaxial growth of III-V nitrides and phase separation and ordering in indium gallium nitride alloys

    NASA Astrophysics Data System (ADS)

    Doppalapudi, Dharanipal

    The family of III-V nitrides are wide band-gap semiconductors with a broad range of opto-electronic applications in LEDs, laser diodes, UV detectors as well as high temperature/high frequency devices. Due to the lack of good quality native substrates, GaN is grown on foreign substrates that have a lattice and thermal mismatch with GaN. This results in a material with a high density of defects, which in turn adversely affects the opto-electronic properties of the epilayer. In this study, GaN films were epitaxially grown on various substrates (C-plane sapphire, A-plane sapphire, SiC and ZnO) by molecular beam epitaxy. Additionally, GaN homoepitaxy onto laterally overgrown thick GaN substrates was investigated. It was demonstrated that the polarity of the GaN film plays a major role in determining the properties of the films. The growth parameters were optimized to eliminate inversion domain boundaries, which result in domains of opposite polarity in the GaN lattice. For growth on A-plane sapphire, it was found that substrate nitridation and low temperature buffer deposition are critical in order to obtain good epitaxial growth, in spite of the relatively small mismatch between the film and substrate. A crystallographic model was developed to explain this observation. By optimizing growth parameters, GaN films with excellent structural, transport, optical and device properties were grown. The second part of this research involves growth of ternary alloys and superlattice structures, which are essential in the fabrication of many devices. It was found that the InN-GaN pseudo-binary system is not homogeneous over the entire composition range. Due to the mismatch between the tetrahedral radii of GaN and InN, InGaN alloys exhibited phase separation and long-range atomic ordering. Investigations of InxGa1-xN films grown over a wide range of compositions by XRD and TEM showed that the predominant strain relieving mechanism was phase separation in films with x > 0.2, and

  16. Current status and scope of gallium nitride-based vertical transistors for high-power electronics application

    NASA Astrophysics Data System (ADS)

    Chowdhury, Srabanti; Swenson, Brian L.; Hoi Wong, Man; Mishra, Umesh K.

    2013-07-01

    Gallium nitride (GaN) is becoming the material of choice for power electronics to enable the roadmap of increasing power density by simultaneously enabling high-power conversion efficiency and reduced form factor. This is because the low switching losses of GaN enable high-frequency operation which reduces bulky passive components with negligible change in efficiency. Commercialization of GaN-on-Si materials for power electronics has led to the entry of GaN devices into the medium-power market since the performance-over-cost of even first-generation products looks very attractive compared to today's mature Si-based solutions. On the other hand, the high-power market still remains unaddressed by lateral GaN devices. The current and voltage demand for high-power conversion application makes the chip area in a lateral topology so large that it becomes difficult to manufacture. Vertical GaN devices would play a big role alongside silicon carbide (SiC) to address the high-power conversion needs. In this paper vertical GaN devices are discussed with emphasis on current aperture vertical electron transistors (CAVETs) which have shown promising performance. The fabrication-related challenges and the future possibilities enabled by the availability of good-quality, cost-competitive bulk GaN material are also evaluated for CAVETs. This work was done at Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, USA.

  17. Optimized Spiral Metal-Gallium-Nitride Nanowire Cavity for Ultra-High Circular Dichroism Ultraviolet Lasing at Room Temperature.

    PubMed

    Liao, Wei-Chun; Liao, Shu-Wei; Chen, Kuo-Ju; Hsiao, Yu-Hao; Chang, Shu-Wei; Kuo, Hao-Chung; Shih, Min-Hsiung

    2016-01-01

    Circularly polarized laser sources with small footprints and high efficiencies can possess advanced functionalities in optical communication and biophotonic integrated systems. However, the conventional lasers with additional circular-polarization converters are bulky and hardly compatible with nanophotonic circuits, and most active chiral plasmonic nanostructures nowadays exhibit broadband emission and low circular dichroism. In this work, with spirals of gallium nitride (GaN) nanowires (NWRs) covered by a metal layer, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and -1.6 (±2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with the high degrees of circular polarizations. PMID:27220650

  18. Optimized Spiral Metal-Gallium-Nitride Nanowire Cavity for Ultra-High Circular Dichroism Ultraviolet Lasing at Room Temperature

    PubMed Central

    Liao, Wei-Chun; Liao, Shu-Wei; Chen, Kuo-Ju; Hsiao, Yu-Hao; Chang, Shu-Wei; Kuo, Hao-Chung; Shih, Min-Hsiung

    2016-01-01

    Circularly polarized laser sources with small footprints and high efficiencies can possess advanced functionalities in optical communication and biophotonic integrated systems. However, the conventional lasers with additional circular-polarization converters are bulky and hardly compatible with nanophotonic circuits, and most active chiral plasmonic nanostructures nowadays exhibit broadband emission and low circular dichroism. In this work, with spirals of gallium nitride (GaN) nanowires (NWRs) covered by a metal layer, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and −1.6 (±2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with the high degrees of circular polarizations. PMID:27220650

  19. Low-temperature growth of gallium nitride films by inductively coupled-plasma-enhanced reactive magnetron sputtering

    SciTech Connect

    Ni, Chih-Jui; Chau-Nan Hong, Franklin

    2014-05-15

    Gallium nitride (GaN) films were grown on sapphire substrate by reactive magnetron sputtering. Inductively coupled-plasma (ICP) source was installed between the substrate holder and the sputtering target to increase the plasma density and the degree of ionization of nitrogen gas. Liquid Ga and Ar/N{sub 2} were used as the sputtering target and sputtering gases, respectively. X-ray diffraction measurements confirmed that the authors could grow high quality GaN crystallites at 500 °C. However, the crystalline GaN (0002) peak remained even by lowering the growth temperature down to 300 °C. The N:Ga ratio of the film grown at 500 °C was almost 1:1, and the nitrogen composition became higher toward the 1:1 N:Ga ratio with increasing the growth temperature. The high degree of ionization induced by ICP source was essential to the growth of high crystalline quality GaN films.

  20. The effect of hydrogen-based, high density plasma etching on the electronic properties of gallium nitride

    SciTech Connect

    Eddy, C.R. Jr.; Molnar, B.

    1996-11-01

    Development of devices based on the wide gap semiconductor gallium nitride (GaN) requires the realization of reliable, high fidelity, low damage pattern transfer processes. In this work, GaN thin films grown by OMVPE have been subjected to both chlorine- and methane/hydrogen-based etch chemistries in an electron cyclotron resonance microwave plasma reactive ion etching system. Both n-type and semi-insulating thin films have been utilized to examine the effect of these etch processes on the electronic properties of the materials. The methane/hydrogen-based etch system (CH{sub 4}/H{sub 2}/Ar) induced considerable changes in the electrical properties of both n-type and semi-insulating films, causing the former to become more insulating and the latter to become conducting. In both cases, the original electrical properties were recoverable after a short, high temperature anneal. In the chlorine-based etching system (Cl{sub 2}), no changes in the electrical properties were observed and etch rates five times greater than in the methane/hydrogen-based system were achieved. Proposed mechanism responsible for the observed behavior will be discussed. These results show that pattern transfer processes based in chlorine etch chemistries are more suitable for the generation of high performance GaN devices.

  1. Mechanical Resonance and Damping Properties of Gallium Nitride Nanowires in Selected-Area Growth Arrays Measured via Optical Bragg Scattering

    NASA Astrophysics Data System (ADS)

    Houlton, John; Brubaker, M. D.; Bertness, K. A.; Rogers, C. T.

    We report the use of optical Bragg scattering to measure the mechanical resonance frequencies and quality factors (Q) of gallium nitride (GaN) nanowires (NWs) in selected-area growth arrays. The GaN NWs are grown by catalyst-free molecular beam epitaxy on silicon (111) wafers. Hexagonal arrays of approximately 100 GaN NWs with pitch spacings of 400 - 1000 nm have been prepared. The NWs contained in such arrays have diameters ranging from 100-300 nm and lengths from 3 - 10 μm. A diode laser operating at 640 nm and 2 mW of optical power is used to perform Bragg scattering homodyne detection to passively read out the thermally induced Brownian mechanical motion of the NWs. The first order cantilever-mode mechanical resonance frequencies of these NWs have been measured to be between 2 - 12 MHz. We find that the optical readout via Bragg scattered light allows the simultaneous detection of all lowest order mechanical resonances in a given array. Q factors ranging from 1,000 - 12,000 have been seen at room temperature and 10-5 Torr pressures. Qs as high as 25,000 have been seen at temperatures of 80 K. These results show that the narrow mechanical resonances observed in freely-grown GaN NWs can also be seen in NWs prepared via selected-area growth. We gratefully acknowledge funding via NIST MSE Grant # 1553451.

  2. The study of influence of the gas flow rate to etched layer thickness, and roughness of the anisotropy field of gallium arsenide is etched in the plasma chemical etching process

    NASA Astrophysics Data System (ADS)

    Ageev, O. A.; Klimin, V. S.; Solodovnik, M. S.; Eskov, A. V.; Krasnoborodko, S. Y.

    2016-08-01

    In the experiments on the etched surface of gallium arsenide were performed. We studied the effect of BCl3 gas flow rate on the thickness of the etched layer. GaAs etching rate was: 537,4 nm/min 28,7 nm/min 2,6 nm/min, the values of the flow rate of BCl3 NBCl3 - 15, 10, 5 cc/min, respectively. The effect of BCl3 gas flow rate to the mean-square roughness of the etched surface. The influence of the anisotropy of the process on the geometry of the etched area. Revealed that the deflection angle for the samples treated with the working gas flow rate NBCl3 - 15 cc/min in the [110] direction was α [110] = 65,5° in direction [111] was α [111] = 45,58°. For samples treated with the working gas flow rate NBCl3 - 10 cc/min in the [110] direction was α [110] = 20,94° in direction [111] was α [111] = 11,37°. For samples treated with the working gas flow rate NBCl3 - 5 cc/min in the [110] was α [110] = 0,32° in direction [111] was α [111] = 0,21°. The results can be used to produce discrete diodes, heterojunction devices, and other results.

  3. Simultaneous specimen current and time-dependent cathodoluminescence measurements on gallium nitride

    NASA Astrophysics Data System (ADS)

    Campo, E. M.; Hopkins, L.; Pophristic, M.; Ferguson, I. T.

    2016-06-01

    Time-dependent cathodoluminescence (CL) and specimen current (SC) are monitored to evaluate trapping behavior and evolution of charge storage. Examination of CL and SC suggests that the near band edge emission in GaN is reduced primarily by the activation of traps upon irradiation, and Gallium vacancies are prime candidates. At the steady state, measurement of the stored charge by empiric-analytical methods suggests that all available traps within the interaction volume have been filled, and that additional charge is being stored interstitially, necessarily beyond the interaction volume. Once established, the space charge region is responsible for the steady state CL emission and, prior to build up, it is responsible for the generation of diffusion currents. Since the non-recombination effects resulting from diffusion currents that develop early on are analogous to those leading to device failure upon aging, this study is fundamental toward a holistic insight into optical properties in GaN.

  4. Electrical properties of TiN on gallium nitride grown using different deposition conditions and annealing

    SciTech Connect

    Li, Liuan; Kishi, Akinori; Shiraishi, Takayuki; Jiang, Ying; Wang, Qingpeng; Ao, Jin-Ping

    2014-03-15

    This study evaluates the thermal stability of different refractory metal nitrides used as Schottky electrodes on GaN. The results demonstrate that TiN, MoSiN, and MoN possess good rectification and adhesion strength, with barrier heights of 0.56, 0.54, and 0.36 eV, respectively. After thermal treatment at 850 °C for 1 min, the TiN and MoN electrodes still exhibit rectifying characteristics, while the MoSiN degrades to an ohmic-like contact. For further study, several TiN films are deposited using different N{sub 2}/Ar reactive/inert sputtering gas ratios, thereby varying the nitrogen content present in the sputtering gas. Ohmic-like contact is observed with the pure Ti contact film, and Schottky characteristics are observed with the samples possessing nitrogen in the film. The average Schottky barrier height is about 0.5 eV and remains virtually constant with varying nitrogen deposition content. After examining Raman spectra and x-ray photoelectron spectroscopy results, the increase in the film resistivity after thermal treatment is attributed to oxidation and/or nitridation. Films deposited with a medium (40% and 60%) nitrogen content show the best film quality and thermal stability.

  5. Novel gallium nitride based microwave noise and power heterostructure field effect transistors

    NASA Astrophysics Data System (ADS)

    Chumbes, Eduardo Martin

    With the pioneering efforts of Isamu Akasaki of Meiji University and Shuji Nakamura of Nichia Chemical Industries in the late 1980's and early 1990's, the first long-lived candela-class blue and ultraviolet light emitting devices have finally come to fruition. Their success in conquering this Holy Grail in opto-electronics is due to their development of a new technology based remarkably on a class of semiconductor materials that has been practically ignored and overlooked by almost everyone for the past twenty years---the nitrides of Al, Ga and In and their alloys. The breakthroughs made from this new technology in the last decade of the 20th century has revolutionized and revitalized worldwide research and development efforts to the point where it is feasible for other important technologies such as high-density information storage, high-resolution full-color displays and efficient white light lamps and UV sensors to come much closer to realization. Equally important is the potential that this new technology can bring toward the development of efficient ultra-high power and high-temperature electronics that will revolutionize the aerospace and high-speed communication industries. Specifically, the large bandgap and strong polar properties of the group III-nitrides has at present allowed for the realization of simple doped and remarkably undoped AlGaN/GaN transistor structures on sapphire and SiC substrates with two-dimensional electron gas sheet densities significantly greater than that of conventional transistor structures based on GaAs and InP. This dissertation will look specifically at extending undoped AlGaN/GaN heterostructure field-effect transistors or HFETs towards more advanced system applications involving the integration of these devices onto a more advanced Si technology and looking at the feasibility of this integration. It will also address important issues similar devices on semi-insulating SiC substrates have in robust microwave low noise and

  6. Irradiation effects of graphene-enhanced gallium nitride (GaN) metal-semiconductor-metal (MSM) ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Chiamori, Heather C.; Miller, Ruth; Suria, Ateeq; Broad, Nicholas; Senesky, Debbie G.

    2015-05-01

    Ultraviolet (UV) photodetectors are used for applications such as flame detection, space navigation, biomedical and environmental monitoring. Robust operation within large ranges of temperatures, radiation, salinity and/or corrosive chemicals require sensor materials with the ability to withstand and function reliably within these extreme harsh environments. For example, spacecraft can utilize a sun sensor (light-based sensor) to assist with determination of orientation and may be exposed to both ionizing radiation and extreme temperature swings during operation. Gallium nitride (GaN), a wide bandgap semiconductor material, has material properties enabling visible-blindness, tunable cutoff wavelength selection based on ternary alloy mole fraction, high current density, thermal/chemical stability and high radiation tolerance due to the strength of the chemical bond. Graphene, with outstanding electrical, optical and mechanical properties and a flat absorption spectrum from 300 to 2,500 nm, has potential use as a transparent conductor for GaN-based metal-semiconductor-metal (MSM) photodetectors. Here, graphene-enhanced MSM UV photodetectors are fabricated with transparent and conductive graphene interdigitated electrodes on thin film GaN-on-sapphire substrates serving as back-to-back Schottky contacts. We report on the irradiation response of graphene/GaN-based MSM UV photodetectors up to 750 krad total ionizing dose (TID) then tested under dark and UV light (365 nm) conditions. In addition, based on current-voltage measurements from 75 krad to 750 krad TID, calculated photodetector responsivity values change slightly by 25% and 11% at -5 V and -2 V, respectively. These initial findings suggest that graphene/GaN MSM UV photodetectors could potentially be engineered to reliably operate within radiation environments.

  7. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics--a Comparative Study with Gallium Nitride.

    PubMed

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L; Roy, Ajit K; Luo, Tengfei

    2016-01-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN)--another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics. PMID:26928396

  8. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics – a Comparative Study with Gallium Nitride

    PubMed Central

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L.; Roy, Ajit K.; Luo, Tengfei

    2016-01-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN) – another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics. PMID:26928396

  9. The effect of gallium nitride on long-term culture induced aging of neuritic function in cerebellar granule cells.

    PubMed

    Chen, Chi-Ruei; Young, Tai-Horng

    2008-04-01

    Gallium nitride (GaN) has been developed for a variety of microelectronic and optical applications due to its unique electric property and chemical stability. In the present study, n-type and p-type GaN were used as substrates to culture cerebellar granule neurons to examine the effect of GaN on cell response for a long-term culture period. It was found that GaN could rapidly induce cultured neurons to exhibit a high phosphorylated Akt level after 20h of incubation. It was assumed that the anti-apoptotic effect of Akt phosphorylation could be correlated with cell survival, neurite growth and neuronal function for up to 35 days of incubation. Morphological studies showed GaN induced larger neuronal aggregates and neurite fasciculation to exhibit a dense fiber network after 8 days of incubation. Western blot analysis and immunocytochemical characterization showed that GaN still exhibited the expression of neurite growth and function, such as high levels of GAP-43, synapsin I and synaptophysin even after 35 days of incubation. In addition, survival of cerebellar granule neurons on GaN was improved by the analysis of lactate dehydrogenase (LDH) release from damaged cells. These results indicated that neuronal connections were formed on GaN by a gradual process from Akt activation and cell aggregation to develop neurite growth, fasciculation and function. Therefore, GaN offers a good model system to identify a well-characterized pattern of neuronal behavior for a long-term culture period, consistent with the development of a neurochip requiring the integration of biological system and semiconductor material.

  10. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics--a Comparative Study with Gallium Nitride.

    PubMed

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L; Roy, Ajit K; Luo, Tengfei

    2016-03-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN)--another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics.

  11. Gas phase interactions at the surface of bare and gold nanoparticle decorated gallium nitride nanowires by ultraviolet photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Niraula, Ishwar B.; Kengne, Blaise-Alexis F.; McIlroy, David N.

    2012-10-01

    Ultraviolet photoelectron spectroscopy (UPS) has been used to characterize the interactions of CO and H2O with the surface of bare and gold nanoparticle decorated gallium nitride (Au-GaN) nanowires (NWs) at 20, 77, and 298 K at three different dosing pressures: 9×10-8, 9×10-7, and 9×10-6 Torr. The average diameter of the Au NPs is 4.5±0.5 nm and the average NW diameter is 105±75 nm. CO and H2O do not bond to the surface of the bare GaN NWs at 20, 77, or 298 K, even at the highest dosing pressure. Temperature and pressure dependent UPS analysis reveals that CO and H2O weakly physisorbed to the Au NP decorated GaN NWs. For the exposure up to 200 L (Langmuir), the activation energy of adsorption of CO and H2O has been found to range from 9.0±1.0 to 45.6±4.3 kJ/mol and 2.0±0.1 to 5.0±0.1 kJ/mol, respectively. The adsorption at 298 K of 100 L of CO at all the three dosing pressures, followed by 100 L of H2O, showed that CO adsorption promotes H2O adsorption, while 100 L of H2O followed by 100 L of CO showed that H2O inhibits CO adsorption. The findings of this study that the adsorption of H2O inhibits CO adsorption onto the Au-GaN NWs explain previous studies of the gas sensing properties of mats of Au-GaN NWs.

  12. Analysis of Gain and Absorption Spectra of Gallium Nitride-based Laser Diodes

    NASA Astrophysics Data System (ADS)

    Melo, Thiago

    Laser diodes (LDs) based on the III-Nitride material system, (Al,In,Ga)N, stand to satisfy a number of application needs, and their huge market segment has been further growing with the use of LDs for full color laser projection. All commercially available GaN-based devices are based on the conventional c-plane (polar) orientation of this material. However, strong polarization fields caused by strained quantum-well (QW) layers on c-plane induce the quantum-confined Stark effect (QCSE), which leads to reduced radiative recombination rate and are aggravated when more indium is added into the QW(s) in order to achieve longer wavelengths. A promising solution for this is the use of nonpolar and semipolar crystal growth orientations. Elimination or mitigation of polarization-related fields within the QWs grown along these novel orientations is observed and one expects increased radiative recombination rate and stabilization of the wavelength emission with respect to the injection current. In order to have more insights on the advantages of using the novel crystal orientations of the III-Nitride material system, we compare the gain of LD structures fabricated from c-plane, nonpolar and semipolar GaN substrates. Using thesegmented contact method, single-pass gain spectra of LD epitaxial structures at wafer level are compared for the different crystal orientations as well as the single-pass absorption coefficient spectrum of the active region material and its dependence on reversed bias. Experimental gain spectra under continuous-wave (CW) operation of actual industry LDs fabricated from c-plane and nonpolar/semipolar GaN-based materials emitting wavelengths in the visible are then presented, using the Hakki-Paoli technique at high resolution. Measurements of the transparency current density, total losses and differential modal gain curves up to threshold are analyzed and compared between nonpolar/semipolar and c-plane LDs in violet and blue spectral regions regions. In a

  13. Opaque gallium nitride photocathodes in UV imaging detectors with microchannel plates

    NASA Astrophysics Data System (ADS)

    Tremsin, Anton S.; Hull, Jeffrey S.; Siegmund, Oswald H. W.; McPhate, Jason B.; Vallerga, John V.; Dabiran, Amir M.; Mane, Anil; Elam, Jeff

    2013-09-01

    The optimization and performance of opaque Galium Nitride (GaN) photocathodes deposited directly on novel Microchannel Plates (MCPs) are presented in this paper. The novel borosilicate glass MCPs, which are manufactured with the help of Atomic Layer Deposition, can withstand higher temperatures enabling direct deposition of GaN films on their surfaces. The quantum efficiency of MBE-grown GaN photocathodes of various thickness and buffer layers was studied in the spectral range of ~200-400 nm for the films grown on different surface layers (such as Al2O3 or buffer AlN layer) in order to determine the optimal opaque photocathode configuration. The MCPs with the GaN photocathodes were activated with surface cesiation in order to achieve the negative Electron Affinity for the efficient photon detection. The opaque photocathodes enable substantial broadening of the spectral sensitivity range compared to the semitransparent configuration when the photocathodes are deposited on the input window. The design of currently processed sealed tube event counting detector with an opaque GaN photocathode are also described in this paper. Our experiments demonstrate that although there is still development work required the detection quantum efficiencies exceeding 20% level should be achievable in 200-400 nm range and <50% in 100-200 nm range for the event counting MCP detectors with high spatial resolution (better than 50 μm) and timing resolution of <100 ps and very low background levels of only few events cm-2 s-1.

  14. Characterization of Defects on MOCVD Grown Gallium Nitride Using Transient Analysis Techniques

    NASA Astrophysics Data System (ADS)

    Kasani, Sujan Phani Kumar

    Since the invention of the first visible spectrum (red) LED by Holonyak in 1962, there has been a need for more efficient, more reliable and less expensive LEDs. The III-nitrides revolutionized semiconductor technology with their applications in the blue LED's. However the internal quantum efficiency of LED's are limited by the deep level traps in GaN substrate. Traps are defects in the crystal lattice, which depends on growth parameters. These traps act as non-radiative centers where non-radiative recombination occurs without conversion of available energy into light. Characterization of these traps in a material is necessary for better understanding of the material growth quality and resulting device performance. In this work Capacitance-Voltage (C-V) and Deep Level Transient Spectroscopy (DLTS) are conducted which provide electronic properties of trap centers like activation energy, doping concentration and capture cross-section. In n-GaN grown by Metalorganic Chemical Vapor Deposition (MOCVD) on Sapphire two defects types are detected and are characterized by Capacitance-Voltage and Deep Level Transient Spectroscopy. Two deep levels E1 and E2 are typically observed in n-GaN with the activation energies of 0.21eV and 0.53eV at 125°K and 325°K, respectively. The deep level E1 is caused by linear line defects along dislocation cores while deep level E2 is related to point defects. The characterization techniques, experimental systems and preliminary characterization results are discussed in detail.

  15. Effect of strain on indium incorporation in heteroepitaxial (indium, gallium) nitride nanomaterials

    NASA Astrophysics Data System (ADS)

    Ewoldt, David A.

    2011-12-01

    One of the challenges facing LED lighting today is the achievement of low-cost true white lighting. Ideally, multiple LEDs of different colors, blue, red and green, would be utilized in order to achieve white light. Currently, the quality of green LEDs is low when compared to the red and blue counterparts. Green emission from LEDs is difficult to achieve due to phase segregation that occurs during growth of the (In,Ga)N LED structure, which separates into compositions of high and low InN concentration and prevents the moderate composition required for green emission. On the nanoscale, strain effects in the (In,Ga)N material system give rise to shifts in optical properties. Relieving strain allows for the incorporation of additional indium nitride, which shifts the wavelength of light emitted by the structure. In order to control strain effects, growth templates were fabricated by several methods (PAA, FIB, EBL). A robust process for fabrication of pores down to 25 nm in diameter has been developed in order to investigate this effect. From this process, a template using e-beam lithography has been created and then growth of (In,Ga)N on this template in a metallorganic chemical vapor deposition system was performed. As (In,Ga)N grows from the GaN substrate, it is naturally strained due to the lattice mismatch. Lateral growth out of the templates relieves strain by allowing the rods to expand as they grow out of the prepared pores. The effect of the diameter of pores on the emission characteristics has been analyzed and a strong logarithmic trend was discovered correlating emission wavelength to pore diameter. In addition to allowing control over the wavelength of emission based on pore diameter, the process that has been developed and demonstrated will allow a distribution of pore sizes that could facilitate color mixing.

  16. First principles study of size and external electric field effects on the atomic and electronic properties of gallium nitride nanostructures

    NASA Astrophysics Data System (ADS)

    Yilmaz, Hulusi

    A comprehensive density functional theory study of atomic and the electronic properties of wurtzite gallium nitride (GaN) nanostructures with different sizes and shapes is presented and the effect of external electric field on these properties is examined. We show that the atomic and electronic properties of [101¯0] facet single-crystal GaN nanotubes (quasi-1D), nanowires (1D) and nanolayers (2D) are mainly determined by the surface to volume ratio. The shape dependent quantum confinement and strain effects on the atomic and electronic properties of these GaN nanostructures are found to be negligible. Based on this similarity between the atomic and electronic properties of the small size GaN nanostructures, we calculated the atomic and electronic properties of the practical size (28.1 A wall thickness) single-crystal GaN nanotubes through computational much economical GaN nanoslabs (nanolayers). Our results show that, regardless of diameter, hydrogen saturated single-crystal GaN tubes with the wall thickness of 28.1 A are energetically stable and they have a noticeably larger band gap with respect to the band gap of bulk GaN. The band gap of unsaturated single-crystal GaN tubes, on the other hand, is always smaller than the band gap of the wurtzite bulk GaN. In a separate study, we show that a transverse electric field induces a homojunction across the diameter of initially semiconducting GaN single-crystal nanotubes and nanowires. The homojunction arises due to the decreased energy of the electronic states in the higher potential region with respect to the energy of those states in the lower potential region under the transverse electric field. Calculations on single-crystal GaN nanotubes and nanowires of different diameter and wall thickness show that the threshold electric field required for the semiconductor-homojunction induction increases with increasing wall thickness and decreases significantly with increasing diameter.

  17. Medical applications and toxicities of gallium compounds.

    PubMed

    Chitambar, Christopher R

    2010-05-01

    Over the past two to three decades, gallium compounds have gained importance in the fields of medicine and electronics. In clinical medicine, radioactive gallium and stable gallium nitrate are used as diagnostic and therapeutic agents in cancer and disorders of calcium and bone metabolism. In addition, gallium compounds have displayed anti-inflammatory and immunosuppressive activity in animal models of human disease while more recent studies have shown that gallium compounds may function as antimicrobial agents against certain pathogens. In a totally different realm, the chemical properties of gallium arsenide have led to its use in the semiconductor industry. Gallium compounds, whether used medically or in the electronics field, have toxicities. Patients receiving gallium nitrate for the treatment of various diseases may benefit from such therapy, but knowledge of the therapeutic index of this drug is necessary to avoid clinical toxicities. Animals exposed to gallium arsenide display toxicities in certain organ systems suggesting that environmental risks may exist for individuals exposed to this compound in the workplace. Although the arsenic moiety of gallium arsenide appears to be mainly responsible for its pulmonary toxicity, gallium may contribute to some of the detrimental effects in other organs. The use of older and newer gallium compounds in clinical medicine may be advanced by a better understanding of their mechanisms of action, drug resistance, pharmacology, and side-effects. This review will discuss the medical applications of gallium and its mechanisms of action, the newer gallium compounds and future directions for development, and the toxicities of gallium compounds in current use.

  18. Medical Applications and Toxicities of Gallium Compounds

    PubMed Central

    Chitambar, Christopher R.

    2010-01-01

    Over the past two to three decades, gallium compounds have gained importance in the fields of medicine and electronics. In clinical medicine, radioactive gallium and stable gallium nitrate are used as diagnostic and therapeutic agents in cancer and disorders of calcium and bone metabolism. In addition, gallium compounds have displayed anti-inflammatory and immunosuppressive activity in animal models of human disease while more recent studies have shown that gallium compounds may function as antimicrobial agents against certain pathogens. In a totally different realm, the chemical properties of gallium arsenide have led to its use in the semiconductor industry. Gallium compounds, whether used medically or in the electronics field, have toxicities. Patients receiving gallium nitrate for the treatment of various diseases may benefit from such therapy, but knowledge of the therapeutic index of this drug is necessary to avoid clinical toxicities. Animals exposed to gallium arsenide display toxicities in certain organ systems suggesting that environmental risks may exist for individuals exposed to this compound in the workplace. Although the arsenic moiety of gallium arsenide appears to be mainly responsible for its pulmonary toxicity, gallium may contribute to some of the detrimental effects in other organs. The use of older and newer gallium compounds in clinical medicine may be advanced by a better understanding of their mechanisms of action, drug resistance, pharmacology, and side-effects. This review will discuss the medical applications of gallium and its mechanisms of action, the newer gallium compounds and future directions for development, and the toxicities of gallium compounds in current use. PMID:20623028

  19. Boron nitride - Composition, optical properties, and mechanical behavior

    NASA Technical Reports Server (NTRS)

    Pouch, John J.; Alterovitz, Samuel A.; Miyoshi, Kazuhisa; Warner, Joseph D.

    1987-01-01

    A low energy ion beam deposition technique was used to grow boron nitride films on quartz, germanium, silicon, gallium arsenide, and indium phosphate. The film structure was amorphous with evidence of a hexagonal phase. The peak boron concentration was 82 at. percent. The carbon and oxygen impurities were in the 5 to 8 at. percent range. Boron-nitrogen and boron-boron bonds were revealed by X-ray photoelectron spectroscopy. The index of refraction varied from 1.65 to 1.67 for films deposited on III-V compound semiconductors. The coefficient of friction for boron nitride in sliding contact with diamond was less than 0.1. The substrate was silicon.

  20. Boron nitride: Composition, optical properties and mechanical behavior

    NASA Technical Reports Server (NTRS)

    Pouch, John J.; Alterovitz, Samuel A.; Miyoshi, Kazuhisa; Warner, Joseph D.

    1987-01-01

    A low energy ion beam deposition technique was used to grow boron nitride films on quartz, germanium, silicon, gallium arsenide, and indium phosphate. The film structure was amorphous with evidence of a hexagonal phase. The peak boron concentration was 82 at %. The carbon and oxygen impurities were in the 5 to 8 at % range. Boron-nitrogen and boron-boron bonds were revealed by X-ray photoelectron spectroscopy. The index of refraction varied from 1.65 to 1.67 for films deposited on III-V compound semiconductors. The coefficient of friction for boron nitride in sliding contact with diamond was less than 0.1. The substrate was silicon.

  1. Boron nitride: composition, optical properties and mechanical behavior

    SciTech Connect

    Pouch, J.J.; Alterovitz, S.A.; Miyoshi, K.; Warner, J.D.

    1987-04-01

    A low energy ion beam deposition technique was used to grow boron nitride films on quartz, germanium, silicon, gallium arsenide, and indium phosphate. The film structure was amorphous with evidence of a hexagonal phase. The peak boron concentration was 82 at %. The carbon and oxygen impurities were in the 5 to 8 at % range. Boron-nitrogen and boron-boron bonds were revealed by x-ray photoelectron spectroscopy. The index of refraction varied from 1.65 to 1.67 for films deposited on III-V compound semiconductors. The coefficient of friction for boron nitride in sliding contact with diamond was less than 0.1. The substrate was silicon.

  2. POLLUTION PREVENTION IN THE SEMICONDUCTOR INDUSTRY THROUGH RECOVERY AND RECYCLING OF GALLIUM AND ARSENIC FROM GAAS POLISHING WASTES

    EPA Science Inventory

    A process was developed for the recovery of both arsenic and gallium from gallium arsenide polishing wastes. The economics associated with the current disposal techniques utilizing ferric hydroxide precipitation dictate that sequential recovery of toxic arsenic and valuble galliu...

  3. Field-effect transistors based on cubic indium nitride

    PubMed Central

    Oseki, Masaaki; Okubo, Kana; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

    2014-01-01

    Although the demand for high-speed telecommunications has increased in recent years, the performance of transistors fabricated with traditional semiconductors such as silicon, gallium arsenide, and gallium nitride have reached their physical performance limits. Therefore, new materials with high carrier velocities should be sought for the fabrication of next-generation, ultra-high-speed transistors. Indium nitride (InN) has attracted much attention for this purpose because of its high electron drift velocity under a high electric field. Thick InN films have been applied to the fabrication of field-effect transistors (FETs), but the performance of the thick InN transistors was discouraging, with no clear linear-saturation output characteristics and poor on/off current ratios. Here, we report the epitaxial deposition of ultrathin cubic InN on insulating oxide yttria-stabilized zirconia substrates and the first demonstration of ultrathin-InN-based FETs. The devices exhibit high on/off ratios and low off-current densities because of the high quality top and bottom interfaces between the ultrathin cubic InN and oxide insulators. This first demonstration of FETs using a ultrathin cubic indium nitride semiconductor will thus pave the way for the development of next-generation high-speed electronics. PMID:24492240

  4. Field-effect transistors based on cubic indium nitride.

    PubMed

    Oseki, Masaaki; Okubo, Kana; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

    2014-02-04

    Although the demand for high-speed telecommunications has increased in recent years, the performance of transistors fabricated with traditional semiconductors such as silicon, gallium arsenide, and gallium nitride have reached their physical performance limits. Therefore, new materials with high carrier velocities should be sought for the fabrication of next-generation, ultra-high-speed transistors. Indium nitride (InN) has attracted much attention for this purpose because of its high electron drift velocity under a high electric field. Thick InN films have been applied to the fabrication of field-effect transistors (FETs), but the performance of the thick InN transistors was discouraging, with no clear linear-saturation output characteristics and poor on/off current ratios. Here, we report the epitaxial deposition of ultrathin cubic InN on insulating oxide yttria-stabilized zirconia substrates and the first demonstration of ultrathin-InN-based FETs. The devices exhibit high on/off ratios and low off-current densities because of the high quality top and bottom interfaces between the ultrathin cubic InN and oxide insulators. This first demonstration of FETs using a ultrathin cubic indium nitride semiconductor will thus pave the way for the development of next-generation high-speed electronics.

  5. Narrow energy band gap gallium arsenide nitride semi-conductors and an ion-cut-synthesis method for producing the same

    DOEpatents

    Weng, Xiaojun; Goldman, Rachel S.

    2006-06-06

    A method for forming a semi-conductor material is provided that comprises forming a donor substrate constructed of GaAs, providing a receiver substrate, implanting nitrogen into the donor substrate to form an implanted layer comprising GaAs and nitrogen. The implanted layer is bonded to the receiver substrate and annealed to form GaAsN and nitrogen micro-blisters in the implanted layer. The micro-blisters allow the implanted layer to be cleaved from the donor substrate.

  6. Gallium arsenide solar cell radiation damage study

    NASA Technical Reports Server (NTRS)

    Maurer, R. H.; Herbert, G. A.; Kinnison, J. D.; Meulenberg, A.

    1989-01-01

    A thorough analysis has been made of electron- and proton- damaged GaAs solar cells suitable for use in space. It is found that, although some electrical parametric data and spectral response data are quite similar, the type of damage due to the two types of radiation is different. An I-V analysis model shows that electrons damage the bulk of the cell and its currents relatively more, while protons damage the junction of the cell and its voltages more. It is suggested that multiple defects due to protons in a strong field region such as a p/n junction cause the greater degradation in cell voltage, whereas the individual point defects in the quasi-neutral minority-carrier-diffusion regions due to electrons cause the greater degradation in cell current and spectral response.

  7. Net Photorefractive Gain In Gallium Arsenide

    NASA Technical Reports Server (NTRS)

    Liu, Tsuen-Hsi; Cheng, Li-Jen

    1990-01-01

    Prerequisite includes applied electric field. Electric field applied to GaAs crystal in which two infrared beams interfere. Depending on quality of sample and experimental conditions, net photorefractive gain obtained. Results offer possibility of new developments in real-time optical processing of signals by use of near-infrared lasers of low power.

  8. Defect characterization in plastically deformed gallium arsenide

    SciTech Connect

    Leipner, H.S.; Huebner, C.; Storbeck, O.; Polity, A.; Krause-Rehberg, R.

    1996-12-31

    The defect spectrum in plastically deformed GaAs is analyzed by positron lifetime measurements. Different types of defects, such as vacancy clusters or antisites, are identified and their thermal annealing behavior is studied.

  9. Indium gallium arsenide microwave power transistors

    NASA Technical Reports Server (NTRS)

    Johnson, Gregory A.; Kapoor, Vik J.; Shokrani, Mohsen; Messick, Louis J.; Nguyen, Richard

    1991-01-01

    Depletion-mode InGaAs microwave power MISFETs with 1-micron gate lengths and up to 1-mm gate widths have been fabricated using an ion-implantation process. The devices employed a plasma-deposited silicon/silicon dioxide gate insulator. The dc I-V characteristics and RF power performance at 9.7 GHz are presented. The output power, power-added efficiency, and power gain as a function of input power are reported. An output power of 1.07 W with a corresponding power gain and power-added efficiency of 4.3 dB and 38 percent, respectively, was obtained. The large-gate-width devices provided over twice the previously reported output power for InGaAs MISFETs at X-band. In addition, output power stability within 1.2 percent over 24 h of continuous operation was achieved. In addition, a drain current drift of 4 percent over 10,000 sec was obtained.

  10. Spalling fracture behavior in (100) gallium arsenide

    NASA Astrophysics Data System (ADS)

    Sweet, Cassi A.

    Record-high conversion efficiencies inherent in III-V solar cells make them ideal for one-sun photovoltaic applications. However, material costs associated with implementation prevent competitive standing with other solar technologies. This dissertation explores controlled exfoliation of III-V single junction photovoltaic devices from (100) GaAs substrates by spalling to enable wafer reuse for material cost reductions. Spalling is a type of fracture that occurs within the substrate of a bilayer under sufficient misfit stress. A spalling crack propagates parallel to the film/substrate interface at a steady-state spalling depth within the substrate. Spalling in (100) GaAs, a semiconductor with anisotropic fracture properties, presents unique challenges. Orientation of the cleavage plane is not parallel to the steady-state spalling depth which results in a faceted fracture surface. A model is developed by modifying Suo and Hutchinson's spalling mechanics to approximate quantitatively the spalling process parameter window and the thickness of the exfoliated film, i.e. spalling depth, for use with (100) GaAs and other semiconductor materials. Experimental data for faceted (100)-GaAs spalling is shown to be in agreement with this model. A faceted surface leads to undesirable waste material for low cost application to the solar industry. Therefore, methods to mitigate the facet size are explored. Trends in facet size and distribution are linked with both the stressor film deposition parameters and the spalling pull velocity. A spalling fracture is a high energy process where damage to the exfoliated material is a concern. Spalled material quality is assessed directly by dislocation density analysis and indirectly by characterization of electrical performance of high quality spalled photovoltaic devices sensitive to material damage such as dislocation and microcrack occurrence. Controlled application of spalling in (100) GaAs is achieved by exfoliation of a high performance single junction solar cell resulting in 18.2% conversion efficiency without the use of an anti-reflective coating. It is shown that spalling in (100) GaAs is a successful device exfoliation process that does not generate defects or cause degradation to device performance.

  11. Position sensitivity in gallium arsenide radiation detectors

    SciTech Connect

    Harper, R.; Hilko, R.A.

    1994-12-31

    For several years, the authors have studied the electrical output of GaAs detectors in response to MeV protons. Beams from the Los Alamos National Laboratory`s tandem Van de Graaff, bunched into pulses of about 0.7-ns width, have been used to drive detectors into the current mode, and fast electronics have enabled characterization of the impulse response shapes and the absolute sensitivities. Recently, the authors extended this line of investigation to measure output-charge spectra in response to low-current beams, in which the count rate was low and pulses due to individual ionizing particles were analyzed. The first part of the work was the measurement of spectra of the output charge of the detectors when bombarded by a beam of MeV-energy protons, which was collimated to a diameter of 0.1 mm. The GaAs detector was mounted on a microadjustable stage just behind the collimator, so that the site of irradiation on the detector could be varied. Output pulses originating from the impacts of individual protons were preamplified with charge-sensitive Lecroy 2004 preamplifiers, shaped with Lecroy 2011 amplifiers, and analyzed with a Lecroy 3500 multichannel analyzer. The second part was the measurement of the time response of the detector to a 0.1 mm-collimated bunched proton beam. The proton bunch width was less than 1 ns, during which time many protons struck the detector, driving it into the current mode where individual proton impacts are unresolved. A possible detector design is suggested by the results. In the past, GaAs time response has been improved by doping or radiation damaging, which introduces traps. The tails can be eliminated, but at the cost of a factor of a thousand in main peak sensitivity. It now appears that by masking off the region of the detector near the negative electrode, the tails can be eliminated with only a factor of about ten loss in peak gain.

  12. Gallium scan

    MedlinePlus

    Liver gallium scan; Bony gallium scan ... You will get a radioactive material called gallium injected into your vein. The gallium travels through the bloodstream and collects in the bones and certain organs. Your health care provider will ...

  13. Effects of post-deposition annealing ambient on band alignment of RF magnetron-sputtered Y2O3 film on gallium nitride

    PubMed Central

    2013-01-01

    The effects of different post-deposition annealing ambients (oxygen, argon, forming gas (95% N2 + 5% H2), and nitrogen) on radio frequency magnetron-sputtered yttrium oxide (Y2O3) films on n-type gallium nitride (GaN) substrate were studied in this work. X-ray photoelectron spectroscopy was utilized to extract the bandgap of Y2O3 and interfacial layer as well as establishing the energy band alignment of Y2O3/interfacial layer/GaN structure. Three different structures of energy band alignment were obtained, and the change of band alignment influenced leakage current density-electrical breakdown field characteristics of the samples subjected to different post-deposition annealing ambients. Of these investigated samples, ability of the sample annealed in O2 ambient to withstand the highest electric breakdown field (approximately 6.6 MV/cm) at 10−6 A/cm2 was related to the largest conduction band offset of interfacial layer/GaN (3.77 eV) and barrier height (3.72 eV). PMID:23360596

  14. Fabrication of conducting-filament-embedded indium tin oxide electrodes: application to lateral-type gallium nitride light-emitting diodes.

    PubMed

    Kim, Hee-Dong; Kim, Kyeong Heon; Kim, Su Jin; Kim, Tae Geun

    2015-11-01

    A novel conducting filament (CF)-embedded indium tin oxide (ITO) film is fabricated using an electrical breakdown method. To assess the performance of this layer as an ohmic contact, it is applied to GaN (gallium nitride) light-emitting diodes (LEDs) as a p-type electrode for comparison with typical GaN LEDs using metallic ITO. The operating voltage and output power of the LED with the CF embedded ITO are 3.93 V and 8.49 mW, respectively, at an injection current of 100 mA. This is comparable to the operating voltage and output power of the conventionally fabricated LEDs using metallic ITO (3.93 V and 8.43 mW). Moreover, the CF-ITO LED displays uniform and bright light emission indicating excellent current injection and spreading. These results suggest that the proposed method of forming ohmic contacts is at least as effective as the conventional method. PMID:26561146

  15. Solubility of gallium arsenide in bismuth-gallium melts

    SciTech Connect

    Yakusheva, N.A.; Chikichev, S.I.

    1988-03-01

    The solubility of GaAs in melts of the system Bi-Ga at 700, 800, and 850/degree/C was determined. For all isotherms of the liquids the existence of a maximum for a Bi concentration in the solvent of approx. 85 at. % and a maximum in the case of a bismuth concentration of approx. 10 at. % are characteristic. The experimental data do not agree with calculations based on the model of regularly associated solutions. For the quasibinary system Bi-GaAs the solubility of As in the interval 600-900/degree/C is described by the expression C/sub As/ = 1.1 /times/ 10/sup /minus/5/ /times/ exp (9.45 /times/ 10/sup /minus/3/ /times/ t) atomic fractions.

  16. Formation of gallium microinclusions in GaAs single crystals

    SciTech Connect

    Vasilenko, N.D.; Gorbatyuk, A.Ya.; Maronchuk, I.E.

    1988-08-01

    In this report we analyze the causes of gallium microinclusion formation in gallium arsenide single crystals. We present a model in which microinclusions result from the decomposition of a supersaturated solid solution. From experimental data available in the literature and calculated kinetic parameters of the model we demonstrate that microinclusion formation in bulk single crystals follows the mechanism of homogeneous nucleation and Brownian coalescence of precipitated liquid gallium metal.

  17. Growth of 1.5 micron gallium indium nitrogen arsenic antimonide vertical cavity surface emitting lasers by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Wistey, Mark Allan

    Fiber optics has revolutionized long distance communication and long haul networks, allowing unimaginable data speeds and noise-free telephone calls around the world for mere pennies per hour at the trunk level. But the high speeds of optical fiber generally do not extend to individual workstations or to the home, in large part because it has been difficult and expensive to produce lasers which emitted light at wavelengths which could take advantage of optical fiber. One of the most promising solutions to this problem is the development of a new class of semiconductors known as dilute nitrides. Dilute nitrides such as GaInNAs can be grown directly on gallium arsenide, which allows well-established processing techniques. More important, gallium arsenide allows the growth of vertical-cavity surface-emitting lasers (VCSELs), which can be grown in dense, 2D arrays on each wafer, providing tremendous economies of scale for manufacturing, testing, and packaging. Unfortunately, GaInNAs lasers have suffered from what has been dubbed the "nitrogen penalty," with high thresholds and low efficiency as the fraction of nitrogen in the semiconductor was increased. This thesis describes the steps taken to identify and essentially eliminate the nitrogen penalty. Protecting the wafer surface from plasma ignition, using an arsenic cap, greatly improved material quality. Using a Langmuir probe, we further found that the nitrogen plasma source produced a large number of ions which damaged the wafer during growth. The ions were dramatically reduced using deflection plates. Low voltage deflection plates were found to be preferable to high voltages, and simulations showed low voltages to be adequate for ion removal. The long wavelengths from dilute nitrides can be partly explained by wafer damage during growth. As a result of these studies, we demonstrated the first CW, room temperature lasers at wavelengths beyond 1.5mum on gallium arsenide, and the first GaInNAs(Sb) VCSELs beyond 1

  18. The sensitivity of the electron transport within bulk zinc-blende gallium nitride to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley

    NASA Astrophysics Data System (ADS)

    Siddiqua, Poppy; O'Leary, Stephen K.

    2016-09-01

    Within the framework of a semi-classical three-valley Monte Carlo simulation approach, we analyze the steady-state and transient electron transport that occurs within bulk zinc-blende gallium nitride. In particular, we examine how the steady-state and transient electron transport that occurs within this material changes in response to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley. These results are then contrasted with those corresponding to a number of other compound semiconductors of interest.

  19. Microwave Nonlinear Modeling and Active Frequency Multiplier Design for High Power Silicon-Carbide and Gallium-Nitride Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Yuk, Kelvin Shing-Tak

    Wide bandgap silicon-carbide (SiC) and gallium-nitride (GaN) FETs are the premier microwave solid-state power technology and are presently being deployed in a variety of commercial applications. However, performance-degrading self-heating and charge-trapping effects create new challenges for characterization and modeling of these devices. Accurate nonlinear models capable of predicting these effects are necessary to maximally exploit the benefits of this emerging, high power density technology. An empirical modeling methodology for the SiC MESFET and GaN HEMT using high power dynamic IV measurements to exploit and characterize self-heating and charge-trapping is applied over a vast range of electrothermal operating conditions. Nonlinear diode modeling and multibias, small-signal techniques are performed to create complete nonlinear models for SiC and GaN FETs, which are capable of predicting DC, pulsed, small- and large-signal RF behavior over a wide range of bias and frequency. The presented models are valid for drain currents beyond 2A, drain voltages greater than 50V and up to 10W at RF. These harmonically-accurate models permit the new application of CAD-based active frequency multiplier design for wide bandgap devices. Frequency doublers and triplers are demonstrated in SiC MESFET and GaN HEMT technology, producing some of the highest power, single-transistor microwave frequency multipliers to date. This work reports SiC- and GaN-based C-band frequency doublers with >5W output power and a GaN-based X-band frequency tripler with 1W output power.

  20. Resonant and nonresonant vibrational excitation of ammonia molecules in the growth of gallium nitride using laser-assisted metal organic chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Golgir, Hossein Rabiee; Zhou, Yun Shen; Li, Dawei; Keramatnejad, Kamran; Xiong, Wei; Wang, Mengmeng; Jiang, Li Jia; Huang, Xi; Jiang, Lan; Silvain, Jean Francois; Lu, Yong Feng

    2016-09-01

    The influence of exciting ammonia (NH3) molecular vibration in the growth of gallium nitride (GaN) was investigated by using an infrared laser-assisted metal organic chemical vapor deposition method. A wavelength tunable CO2 laser was used to selectively excite the individual vibrational modes. Resonantly exciting the NH-wagging mode (v2) of NH3 molecules at 9.219 μm led to a GaN growth rate of 84 μm/h, which is much higher than the reported results. The difference between the resonantly excited and conventional thermally populated vibrational states was studied via resonant and nonresonant vibrational excitations of NH3 molecules. Resonant excitation of various vibrational modes was achieved at 9.219, 10.35, and 10.719 μm, respectively. Nonresonant excitation was conducted at 9.201 and 10.591 μm, similar to conventional thermal heating. Compared to nonresonant excitation, resonant excitation noticeably promotes the GaN growth rate and crystalline quality. The full width at half maximum value of the XRD rocking curves of the GaN (0002) and GaN (10-12) diffraction peaks decreased at resonant depositions and reached its minimum value of 45 and 53 arcmin, respectively, at the laser wavelength of 9.219 μm. According to the optical emission spectroscopic studies, resonantly exciting the NH3 v2 mode leads to NH3 decomposition at room temperature, reduces the formation of the TMGa:NH3 adduct, promotes the supply of active species in GaN formation, and, therefore, results in the increased GaN growth rate.

  1. Self-assembled Multilayers of Silica Nanospheres for Defect Reduction in Non- and Semipolar Gallium Nitride Epitaxial Layers

    PubMed Central

    2015-01-01

    Non- and semipolar GaN have great potential to improve the efficiency of light emitting devices due to much reduced internal electric fields. However, heteroepitaxial GaN growth in these crystal orientations suffers from very high dislocation and stacking faults densities. Here, we report a facile method to obtain low defect density non- and semipolar heteroepitaxial GaN via selective area epitaxy using self-assembled multilayers of silica nanospheres (MSN). Nonpolar (11–20) and semipolar (11–22) GaN layers with high crystal quality have been achieved by epitaxial integration of the MSN and a simple one-step overgrowth process, by which both dislocation and basal plane stacking fault densities can be significantly reduced. The underlying defect reduction mechanisms include epitaxial growth through the MSN covered template, island nucleation via nanogaps in the MSN, and lateral overgrowth and coalescence above the MSN. InGaN/GaN multiple quantum wells structures grown on a nonpolar GaN/MSN template show more than 30-fold increase in the luminescence intensity compared to a control sample without the MSN. This self-assembled MSN technique provides a new platform for epitaxial growth of nitride semiconductors and offers unique opportunities for improving the material quality of GaN grown on other orientations and foreign substrates or heteroepitaxial growth of other lattice-mismatched materials. PMID:27065755

  2. Polar and Nonpolar Gallium Nitride and Zinc Oxide based thin film heterostructures Integrated with Sapphire and Silicon

    NASA Astrophysics Data System (ADS)

    Gupta, Pranav

    This dissertation work explores the understanding of the relaxation and integration of polar and non-polar of GaN and ZnO thin films with Sapphire and silicon substrates. Strain management and epitaxial analysis has been performed on wurtzitic GaN(0001) thin films grown on c-Sapphire and wurtzitic non-polar a-plane GaN(11-20) thin films grown on r-plane Sapphire (10-12) by remote plasma atomic nitrogen source assisted UHV Pulsed Laser Deposition process. It has been established that high-quality 2-dimensional c-axis GaN(0001) nucleation layers can be grown on c-Sapphire by PLD process at growth temperatures as low as ˜650°C. Whereas the c-axis GaN on c-sapphire has biaxially negative misfit, the crystalline anisotropy of the a-plane GaN films on r-Sapphire results in compressive and tensile misfits in the two major orthogonal directions. The measured strains have been analyzed in detail by X-ray, Raman spectroscopy and TEM. Strain relaxation in GaN(0001)/Sapphire thin film heterostructure has been explained by the principle of domain matched epitaxial growth in large planar misfit system and has been demonstrated by TEM study. An attempt has been made to qualitatively understand the minimization of free energy of the system from the strain perspective. Analysis has been presented to quantify the strain components responsible for the compressive strain observed in the GaN(0001) thin films on c-axis Sapphire substrates. It was also observed that gallium rich deposition conditions in PLD process lead to smoother nucleation layers because of higher ad-atom mobility of gallium. We demonstrate near strain relaxed epitaxial (0001) GaN thin films grown on (111) Si substrates using TiN as intermediate buffer layer by remote nitrogen plasma assisted UHV pulsed laser deposition (PLD). Because of large misfits between the TiN/GaN and TiN/Si systems the TIN buffer layer growth occurs via nucleation of interfacial dislocations under domain matching epitaxy paradigm. X-ray and

  3. Computer modelling of aluminum-gallium arsenide/gallium arsenide multilayer photovoltaics. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Wagner, Michael Broderick

    1987-01-01

    The modeled cascade cells offer an alternative to conventional series cascade designs that require a monolithic intercell ohmic contact. Selective electrodes provide a simple means of fabricating three-terminal devices, which can be configured in complementary pairs to circumvent the attendant losses and fabrication complexities of intercell ohmic contacts. Moreover, selective electrodes allow incorporation of additional layers in the upper subcell which can improve spectral response and increase radiation tolerance. Realistic simulations of such cells operating under one-sun AMO conditions show that the seven-layer structure is optimum from the standpoint of beginning-of-life efficiency and radiation tolerance. Projected efficiencies exceed 26 percent. Under higher concentration factors, it should be possible to achieve efficiencies beyond 30 percent. However, to simulate operation at high concentration will require a model for resistive losses. Overall, these devices appear to be a promising contender for future space applications.

  4. Characterization, Modeling and Fabrication of Aluminum Gallium Arsenide/gallium Arsenide Heterojunction Bipolar Transistors.

    NASA Astrophysics Data System (ADS)

    Ozaydin, Melih

    1995-01-01

    Heterojunction bipolar transistors have found broad applications in recent years as a result of intense research. In order to explore and utilize HBTs for a better performance, the carrier transport phenomenon in HBTs needs to be investigated, and the device parameters optimized. Demand for higher speed and smaller dimensions also requires implementation of new fabrication techniques that will make possible the realization of smaller transistor dimensions. In this thesis we analyze physical characteristics, transport mechanisms, modeling, parameter extraction and electron-beam lithography fabrication techniques for self -aligned heterojunction bipolar transistors. We present a new multi-flux method to analyze the emitter-base heterojunction by self-consistent solution of Schrodinger and Poisson equations. The simulation results show transport characteristics of electrons which differ from those found with the commonly used WKB method. Simulation of electron transport in the base region based on a balance equations approach indicates that tunneling electrons give rise to unique transport characteristics in the base of HBTs. A domain-like density profile is found as a result of ballistic and diffusive transport in different parts of the base region. Bias dependent non-equilibrium behavior is found from the I-V measurements of HBTs, and non-equilibrium transport is shown to be responsible for reduction of the recombination rate. Collector-base space charge region is also investigated and utilization of multi-velocity overshoot is shown to reduce the total collector delay time by 10 percent and improve the breakdown voltage by 70 percent. A semi-two-dimensional model is developed to obtain microwave characteristics, as well as the parameter extraction of transistors. For the parameter extraction procedure, a least-squares technique is used. We also develop a self-aligned process using selective dry-etching for heterojunction transistors. Most of the lithography steps are done with electron-beam lithography, where better resolution and alignment accuracy is achieved. Selective dry-etching using CCl_2F _2/He etching gas developed for this process provides excellent control for emitter etching. An etch selectivity of 120:1 or higher is observed. Base mesa is processed with a dry etch process, as well, which produces nearly vertical side walls. This technology permits the base-collector junction area to decrease, when compared to a non-self-aligned process.

  5. Toward the development of a gallium arsenide/aluminum gallium arsenide intersubband laser

    NASA Astrophysics Data System (ADS)

    Riely, Brian Paul

    The 3- to 5-μm and the 8- to-12-μm bands, generally referred to as the mid-infrared (MIWR) and the long wavelength infrared (LWIR) bands, respectively, have long been of great interest to the technical and scientific communities. The two primary reasons for the interest in these bands are that their transmissions as atmospheric windows are close to one, and that the vibration frequencies of several important elements occur in these bands. Therefore, it is highly desirable to have a semiconductor laser with emission in these bands at room temperature. This was recently achieved using an Al 0.48In0.52As/In0.57Ga0.47As type-I quantum-cascade laser. A GaAs/AlGaAs type-I quantum-cascade laser is expected to have less thermal resistance then AlInAs/InGaAs systems, and is also based on more mature materials. My dissertation presents progress made toward developing a LWIR GaAs/AlGaAs type-I quantum-cascade laser. We first present the theoretical foundation on which design parameters, such as scattering times and oscillator strengths, are based. We then discuss the design of the cladding region. The design of the active region was accomplished using a FORTRAN program called SEQUAL, which solves Poisson's and Schrödinger's equations self-consistently. A quantum cascade emitter was designed, and several measurements on the corresponding processed wafer were performed. These measurements included light-current-voltage (LIV) curves and spectral emission data. The encouraging results of these data led to the design of a potential quantum cascade laser with the same active region as the emitter. However, measurements on the processed wafer that corresponded to the laser design revealed some potential problems and gave some insight for an improved design. This measurement information was incorporated into a new design that, along with a waveguide design that had proven to be successful with another group, is expected to lase.

  6. Theory and Experiments on Unstable Resonator and Quantum Well Gallium Arsenide/gallium Aluminum Arsenide Lasers

    NASA Astrophysics Data System (ADS)

    Mittelstein, Michael

    Structures of GaAs/GaAlAs lasers and their performance characteristics are investigated experimentally and theoretically. A self-consistent model for the longitudinal gain and intensity distribution in injection lasers is introduced. The model is applied to unstable-resonator semiconductor lasers to evaluate their lateral losses and quantum efficiencies, and an advanced design is presented. Symmetric, unstable -resonator semiconductor lasers are manufactured and a virtual source point inside the laser more than an order of magnitude narrower than the width of the near field is demonstrated. Young's double-slit experiment is adopted for lateral coherence measurements in semiconductor lasers. A high degree of lateral coherence is found, indicating operation of the unstable-resonator lasers in predominantly one mode. In the pulsed measurements on broad-area, single -quantum-well, graded-index wave-guide, separate-confinement -heterostructure lasers, very high quantum efficiencies, very low losses, and very high output powers are observed. The devices are found to exhibit beam divergence narrower than two times the diffraction limit in single-lobed, far-field patterns. Using these single-quantum-well lasers, the "second quantized-state lasing" is found experimentally, and a simple model is developed to explain it. A general model for the gain spectrum and required current density of quantum-well lasers is introduced. The eigenfunctions and eigenvalues of the charge carriers and optical mode of the transverse structure are used to derive the gain spectrum and current density from the Einstein coefficients. The two-dimensional density of states for the charge carriers and the effective width of the optical mode (not the width of the quantum well) are identified as the dominant parameters. The model includes a new heuristic approach to account for the observed smeared onset of subbands, eliminating convolution calculations. Applications of the model for a typical structure, a conventional double heterostructure and an advanced structure are presented. Structures providing two- and three-dimensional confinement are discussed and are directly compared to conventional and quantum-well structures in terms of laser parameters. The length scale of confinement structures for the optical mode is found to be two orders of magnitude larger than the corresponding length scale for carrier confinement, implying that the single-quantum-well laser is the most adapted structure. The gain-flattened condition that single-quantum -well lasers exhibit near the onset of the second quantized -state lasing is introduced. An external grating-tuned resonator is analyzed, and the coupled cavity formalism is employed to examine conditions for continuous tuning. Predictions for tuning ranges of conventional, double-heterostructure and single-quantum-well lasers are made, and the superiority of the latter on account of pump current density is clarified. Experimentally, broadband tunability exceeding a 10% spectral tuning range of an uncoated quantum-well laser in a simple grating-tuned resonator is demonstrated.

  7. Collector-up aluminum gallium arsenide/gallium arsenide heterojunction bipolar transistors using oxidized aluminum arsenide for current confinement

    NASA Astrophysics Data System (ADS)

    Massengale, Alan Ross

    1998-12-01

    The discovery in 1990 that the wet thermal oxidation of AlAs can create a stable native oxide has added a new constituent, AlAs-oxide, to the AlGaAs/GaAs materials system. Native oxides of high Al mole-fraction AlGaAs are being used to confine electrical and/or optical fields in many types of electronic and optoelectronic structures with very promising results. Among these devices are collector-up heterojunction bipolar transistors (HBTs). Collector-up HBTs offer a means to reduce base-collector capacitance relative to their emitter-up counterparts, and thus to improve device performance. A novel method for fabricating collector-up AlGaAs/GaAs HBTs where an AlAs layer is inserted into the emitter layer and is oxidized in water vapor at 450sp°C has been developed. The resulting AlAs-oxide serves as a current confining layer that constricts collector current flow to the intrinsic portion of the device. Compared to previous methods of fabricating these devices, the process of converting AlAs into an insulator requires only one growth, and does not suffer from implant damage in the base. Because the lateral oxidation of AlAs is a process that proceeds at rates of microns per minute, one of the major challenges facing its implementation is the ability to accurately control the oxidation rate over the wafer, and from one wafer to the next. In the course of work on the oxidation of AlAs, a method to lithographically form lateral oxidation stop layers has been achieved. This technique utilizes impurity induced layer disordering (IILD) in heavily Si-doped buried planes, combined with selective surface patterning and thermal annealing, to create a lateral variation in the Al mole-fraction of the layer to be oxidized.

  8. Aluminum Gallium Nitride (GaN)/GaN High Electron Mobility Transistor-Based Sensors for Glucose Detection in Exhaled Breath Condensate

    PubMed Central

    Chu, Byung Hwan; Kang, Byoung Sam; Hung, Sheng Chun; Chen, Ke Hung; Ren, Fan; Sciullo, Andrew; Gila, Brent P.; Pearton, Stephen J.

    2010-01-01

    Background Immobilized aluminum gallium nitride (AlGaN)/GaN high electron mobility transistors (HEMTs) have shown great potential in the areas of pH, chloride ion, and glucose detection in exhaled breath condensate (EBC). HEMT sensors can be integrated into a wireless data transmission system that allows for remote monitoring. This technology offers the possibility of using AlGaN/GaN HEMTs for extended investigations of airway pathology of detecting glucose in EBC without the need for clinical visits. Methods HEMT structures, consisting of a 3-μm-thick undoped GaN buffer, 30-Å-thick Al0.3Ga0.7N spacer, and 220-Å-thick silicon-doped Al0.3Ga0.7N cap layer, were used for fabricating the HEMT sensors. The gate area of the pH, chloride ion, and glucose detection was immobilized with scandium oxide (Sc2O3), silver chloride (AgCl) thin film, and zinc oxide (ZnO) nanorods, respectively. Results The Sc2O3-gated sensor could detect the pH of solutions ranging from 3 to 10 with a resolution of ∼0.1 pH. A chloride ion detection limit of 10-8 M was achievedt with a HEMT sensor immobilized with the AgCl thin film. The drain–source current of the ZnO nanorod-gated AlGaN/GaN HEMT sensor immobilized with glucose oxidase showed a rapid response of less than 5 seconds when the sensor was exposed to the target glucose in a buffer with a pH value of 7.4. The sensor could detect a wide range of concentrations from 0.5 nM to 125 μM. Conclusion There is great promise for using HEMT-based sensors to enhance the detection sensitivity for glucose detection in EBC. Depending on the immobilized material, HEMT-based sensors can be used for sensingt different materials. These electronic detection approaches with rapid response and good repeatability show potential for the investigation of airway pathology. The devices can also be integrated into a wireless data transmission system for remote monitoring applications. This sensor technology could use the exhaled breath condensate to

  9. Evaluation of the indium gallium nitride/silicon broken-gap heterojunction and its potential application for solar cells

    NASA Astrophysics Data System (ADS)

    Yao, Yuan

    InGaN (especially In-rich alloy) has been actively studied for decades since the band gap of InN was revised downward from ˜2.0 eV to 0.64 eV. The potential applications for alloys of In-rich InGaN hence became apparent. Despite the promising potential, photovoltaic devices based on InGaN have struggled due to a number of key limitations and fundamental physical problems. Firstly, due to the deep excursion of the InN conduction band at the gamma point, defects in InN are almost universally n-type leading to unintentional degenerate doping. This also leads to the problem of electron accumulation at all surfaces and interfaces of InN. Secondly, p-type doping is problematic, partially due to the degenerate doping effect of defects, but it has also been observed that Mg-doping, while leading to a p-type layer, dramatically reduces the quantum efficiency. This thesis explores an alternative approach using n-type InGaN to form a heterojunction with a p-type Si substrate. One potential benefit to using p-type Si as a substrate material for InGaN is that the valence band of Si possibly lines up with the conduction band of InGaN for a specific mole fraction of indium. Such a band alignment is known as a broken gap heterojunction, an example of which is the interface between InAs and AlxGa 1--xSb. The benefits of this broken-gap junction include a low series resistance, high electron mobility, and mobility only weakly dependent on temperature. These properties enable new approach to photovoltaic devices. The InGaN/Si heterojunctions were fabricated by plasma-assisted molecular beam epitaxy under stoichiometric flux conditions. An ultra-thin SiN interface layer was introduced, by Si nitridation process, to passivate the substrate surface and prevent In-Si and Ga-Si eutectic problems. InGaN films with a variety of indium mole fractions were grown by calibrating the In/Ga flux ratio during the deposition. The chemical composition of as-grown films was characterized by x

  10. The Role of Defect Complexes in the Magneto-Optical Properties of Rare Earth Doped Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Mitchell, Brandon

    Wide band gap semiconductors doped with rare earth ions (RE) have shown great potential for applications in optoelectronics, photonics, and spintronics. The 1.54mum Erbium (Er) emission has been extensively utilized in optical fiber communications, and Europium (Eu) is commonly used as a red color component for LEDs and fluorescence lamps. For the realization of spintronic-type devices, a dilutely doped semiconductor that exhibits room temperature ferromagnetic behavior would be desirable. Such behavior has been observed in GaN:Er. Furthermore, it was demonstrated that strain may play an important role in the control of this ferromagnetism; however, this requires further investigation. One motivation of this work is the realization of an all solid state white light source monolithically integrated into III/V nitride semiconductor materials, ideally GaN. For this, the current AlGaAs-based LEDs need to be replaced. One approach for achieving efficient red emission from GaN is dilute doping with fluorescent ions. In this regard, Eu has consistently been the most promising candidate as a dopant in the active layer for a red, GaN based, LED due to the sharp 5D0 to 7F2 transitions that result in red emission around 620nm. The success of GaN:Eu as the active layer for a red LED is based on the ability for the Eu ions to be efficiently excited by electron hole pairs. Thus, the processes by which energy is transferred from the host to the Eu ions has been studied. Complications arise, however, from the fact that Eu ions incorporate into multiple center environments, the structures of which are found to have a profound influence on the excitation pathways and efficiencies of the Eu ion. Therefore the nature of Eu incorporation and the resulting luminescence efficiency in GaN has been extensively investigated. By performing a comparative study on GaN:Eu samples grown under a variety of controlled conditions and using a variety of experimental techniques, the majority site has

  11. Effect of nitridation surface treatment on silicon (1 1 1) substrate for the growth of high quality single-crystalline GaN hetero-epitaxy layer by MOCVD

    NASA Astrophysics Data System (ADS)

    Rahman, Mohd Nazri Abd.; Yusuf, Yusnizam; Mansor, Mazwan; Shuhaimi, Ahmad

    2016-01-01

    A single-crystalline with high quality of gallium nitride epilayers was grown on silicon (1 1 1) substrate by metal organic chemical vapor deposition. The process of nitridation surface treatment was accomplished on silicon (1 1 1) substrate by flowing the ammonia gaseous. Then, it was followed by a thin aluminum nitride nucleation layer, aluminum nitride/gallium nitride multi-layer and a thick gallium nitride epilayer. The influence of in situ nitridation surface treatment on the crystallinity quality of gallium nitride epilayers was studied by varying the nitridation times at 40, 220 and 400 s, respectively. It was shown that the nitridation times greatly affect the structural properties of the grown top gallium nitride epilayer on silicon (1 1 1) substrate. In the (0 0 0 2) and (1 0 1 bar 2) X-ray rocking curve analysis, a narrower value of full width at half-maximum has been obtained as the nitridation time increased. This is signifying the reduction of dislocation density in the gallium nitride epilayer. This result was supported by the value of bowing and root mean square roughness measured by surface profilometer and atomic force microscopy. Furthermore, a crack-free gallium nitride surface with an abrupt cross-sectional structure that observed using field effect scanning electron microscopy was also been obtained. The phi-scan curve of asymmetric gallium nitride proved the top gallium nitride epilayer exhibited a single-crystalline structure.

  12. Large Signal Characterization of Microwave Gallium Arsenide Mesfets

    NASA Astrophysics Data System (ADS)

    Amaeshi, Lawrence Lemchukwu Nnanyelugo

    Available from UMI in association with The British Library. A large Rf signal characterization of GaAs MESFETs, employing Large Signal S-parameter (LSSP), and waveform distortion analysis techniques, is carried out. A LSSP measurement system, (also applicable to SSSP measurements), including an uncomplicated, direct deembedding technique is developed. A direct technique of measuring the current and voltage waveforms of the microwave signals, at the device terminals, is also developed. Measurements of the LSSPs show that only the input parameters: S^{21} and S_{11} vary with the Rf. The results are explained against reported trends of variation. The non-linear elements are identified, and a subsequent Large Signal Model (LSM) of the DUTs developed and verified. It is demonstrated that LSMs cannot be generalised. However a systematic approach of determining the LSM of a given device is given. An improved model of the transconductance, Gm, in terms of the S-parameters, and a method to determine the LSSP from small signal parameters are developed and verified. The optimum incident Rf to determine the LSSPs at a given bias is given. The flow of forward conduction, rm I_{f} is known to damage, by burn -out, the DUT. A limiting resistor was included in the gate external circuit to limit this effect, when large enough Rf was employed. The interaction of the rm I_{f} with this circuit is investigated, and the self-limiting actions explained. The flow of rm I_{f} is found to degrade the output performance and device power added efficiency also. The waveform distortions are investigated, the main causes--the non-linear elements, and the manner in which they affect the distortions are explored. The non -linearity in the Gm is shown to be the main cause of the output waveform distortion, especially before the onset of forward conduction by the gate Schottky diode. While the forward conduction, I_{it f}, and the non-linearity in the depletion capacitance are responsible for the input waveform distortion, hence are secondary causes of output waveform distortions. In particular, the flow of I_{it f}, due to large Vgs > 0, causes the saturation of the drain voltage, hence the output power. But the waveforms were, in particular, insensitive to the output conductance. (Abstract shortened by UMI.).

  13. Some observations of heated gallium arsenide heteroface solar cells

    NASA Technical Reports Server (NTRS)

    Friesen, W. J.

    1985-01-01

    GaAlAs/GaAs heteroface solar cells used in space offer advantages of higher operating temperatures and recovery from radiation damage using thermal annealing. Experiments were conducted to examine the effects on the room temperature photovoltaic properties of cells due to heating in a vacuum at temperatures encountered in radiation damage annealing. Some degradation of photovoltaic properties was observed for all the cells that were heated. The lifetime, due to heating, for a 20-percent degradation in output power was estimated for cells heated at 200 C and 400 C. The results for cells that were heated at 200 C for 1750 hours indicate a lifetime of at least 3 years. The results for cells that were heated at 400 C for 264 hours indicate that lifetimes in the range of 350 hours to 1400 hours may be expected. The results indicate that for cells that must be heated at 400 C the selection of fabrication techniques and materials is particularly important.

  14. Spin transport measurements in gallium arsenide quantum dots

    NASA Astrophysics Data System (ADS)

    Folk, Joshua Alexander

    This thesis presents a series of measurements investigating the spin physics of lateral quantum dots, defined electrostatically in the 2-D electron gas at the interface of a GaAs/AlGaAs heterostructure. The experiments span a range from open dots, where the leads of the dot carry at least one fully transmitting mode, to closed dots, where the leads are set to be tunnel barriers. For open dots, spin physics is inferred from measurements of conductance fluctuations; the effects of spin degeneracy in the orbital levels as well as a spin-orbit interaction are observed. In the closed dot measurements, ground state spin transitions as electrons are added to the dot may be determined from the motion of Coulomb blockade peaks in an in-plane magnetic field. In addition, this thesis demonstrates for the first time a direct measurement of the spin polarization of current emitted from a quantum dot, or a quantum point contact, during transport. These experiments make use of a spin-sensitive focusing geometry in which a quantum point contact serves as a spin analyzer for the mesoscopic device under test. Measurements are presented both in the open dot regime, where good agreement with theory is found, as well as the closed dot regime, where the data defies a simple theoretical explanation.

  15. Closed loop coherent control of electronic transitions in gallium arsenide.

    PubMed

    Singha, Sima; Hu, Zhan; Gordon, Robert J

    2011-06-16

    A genetic algorithm was used to control the photoluminesce-nce (PL) from GaAs(100). A spatial light modulator (SLM) used feedback from the emission to optimize the spectral phase profile of an ultrashort laser pulse. Most of the experiments were performed using a sine phase function to optimize the integrated PL spectrum over a specified wavelength range, with the amplitude and period of the phase function treated as genetic parameters. An order of magnitude increase in signal was achieved after only one generation, and an optimized waveform, consisting of three equally spaced pulses approximately 0.8 ps apart, was obtained after 15 generations. The effects of fluence, polarization, relative phase of the subpulses, and spectral range of the optimized PL were investigated. In addition, preliminary experiments were performed using the phases of individual pixels of the SLM as genetic variables. The PL spectrum is identified with recombination of electron-hole pairs in the L-valley of the Brillouin zone. Control is achieved by coherent manipulation of plasma electrons. It is proposed that hot electrons excite lattice phonons, which in turn scatter carriers into the L-valley.

  16. Optical Effects in Microwave Gallium-Arsenide Mesfet Oscillators.

    NASA Astrophysics Data System (ADS)

    Sun, Horng-Jye

    The effects of DC and pulse light illumination on microwave GaAs MESFET oscillators are studied. Two kinds of optical operation--optical tuning and optical switching--are presented and evaluated. For optical tuning, the oscillation frequency decreases with light. The maximum tuning range depends principally on oscillator mode (common-source, common-drain, or common-gate), with 2.2% at X band and 3.8% at S band being achieved in common-source mode at a light intensity of 0.5 mW/mm('2). A theoretical model has been developed to calculate the tuning range mode dependence. The RF power output of the MESFET oscillators generally increases 1 or 2 dB with light. The drain current increases approximately 30% at the light intensity of 0.5 mW/mm('2). A first-order approximation assuming the power output variation is mainly due to the optical-induced drain current variation gives good agreement (average error within 10%) between measured and calculated power output. For optical switching, two switching modes (optically -on and optically-off) were observed, with oscillator switching between no oscillation and 7.5 mW power output when illuminated by a 2 mW laser diode. The optical response of microwave GaAs MESFET oscillators is attributed to capture of holes by hole traps in the Schottky gate depletion region. Two kinds of hole traps--one having an emission time constant about 8 us, another having a time constant around seconds--contribute to the optical responses of the oscillator. The changes in oscillation frequency and power output decrease at high speed optical modulation rate, becoming about 10% of the constant light illuminated changes at light PRF of 1 MHz and negligibly small at 10 MHz. Only the optically induced frequency jump due to impedance looping of oscillator external circuits has a high speed response capability.

  17. a 9-BIT, Pipelined Gallium Arsenide Analog-Digital Converter

    NASA Astrophysics Data System (ADS)

    Breevoort, Cornelius Marius

    1992-01-01

    Excellent Short Take-Off and Landing (STOL) performance is achieved by Upper Surface Blowing (USB) aircraft as a result of mounting high by-pass turbofan engines over the forward part of the wing. High lift levels are generated by directing the engine exhaust over the wing upper surface to entrain additional airflow and by using the Coanda effect to turn the exhaust flow downward over a large radius "Coanda" flap. Commercial application of USB technology could reduce airport congestion and community noise if future configurations can be designed with economically acceptable cruise drag levels. An experimental investigation of the high speed aerodynamics of USB aircraft configurations has been conducted to accurately define the magnitude and causes of the powered configuration cruise drag. A highly instrumented wind tunnel model of a realistic USB configuration has been used which permitted parametric variations in the number and spanwise location of the nacelles and accurately modeled the engine power effects with turbofan propulsion simulators. The measured force data provides an accurate definition of the cruise drag penalty associated with each configuration and the constructed pressure contour plots provide detailed insight into their causes. It was found that the high speed aerodynamics of USB configurations is a complex interaction of jet induced and wing transonic flowfields. The presence of the nacelles on the wing upper surface created a severe drag penalty which increased with freestream Mach number, power setting and angle of attack. The more widely spaced two nacelle configurations exhibited improved flowfields at moderate Mach numbers but suffered from drag levels comparable to the baseline configuration for high speed cruise conditions. At high Mach numbers and power settings, all of the tested configurations displayed strong shocks and separated zones in the wing/nacelle junction regions. Detailed discussions of the causes of the cruise drag penalty and recommended future design improvements are presented.

  18. Diffusion-bonded-stacked gallium arsenide for mid- infrared generation

    NASA Astrophysics Data System (ADS)

    Gordon, Leslie Ann

    One of the limiting factors in mid-infrared nonlinear generation is the availability of adequate crystals. Current mid-infrared nonlinear crystals suffer from poor thermal properties and/or high absorption, minimizing their usefulness for high-peak and high-average-power conversion. While new materials are continually being explored, more than 15 years may be necessary to develop and test a new crystal, with no guarantee of final success. A new nonlinear material has been synthesized, combining the knowledge from two existing fields: quasi- phasematching (QPM) and diffusion bonding. QPM allows the use of well known semiconductors which are not birefringent, but which have good thermal properties, high damage thresholds, and high nonlinear coefficients. Diffusion bonding provides a robust monolithic structure. Prior to this work, bonded semiconductor structures were single interface, with little attention to optical losses. During this work, techniques were developed to precisely thin and clean the wafers in preparation for bonding. Two generations of bonding furnaces were designed and built to provide uniform temperatures and pressures, fully adjustable and repeatable bonding parameters, and multiple-interface capabilities. GaAs wafers were stacked with alternating crystal orientation, and annealed under compression to diffusion bond the interfaces. The quasi-phasematching was controlled by the wafer thickness. Diffusion-bonded stacks of 2 to 50-layers were bonded, and demonstrated close to theoretical conversion efficiency of second- harmonic generation of CO2 laser radiation. The quality of the bonds was affected by surface cleanliness and contact uniformity of the interfaces. Conversion efficiency was limited by fabrication techniques, chiefly accurate wafer thinning and process- induced bulk losses. Diffusion-bonded-stacked structures can be optimized for all types of nonlinear devices. This technology can be expanded to other well known semiconductors, and is limited only by transparency range and minimum possible wafer thickness.

  19. Gallium arsenide-based long-wavelength quantum dot lasers

    NASA Astrophysics Data System (ADS)

    Park, Gyoungwon

    2001-09-01

    GaAs-based long-wavelength quantum dot lasers have long been studied for applications to optical interconnects. The zero-dimensional confinement potential of quantum dots opens possibility of novel devices. Also, the quantum dot itself shows very interesting characteristics. This dissertation describes the development of GaAs-based 1.3 μm quantum dot lasers and the research on the unique characteristics of quantum dot ensemble. InGaAs quantum dots grown using molecular beam epitaxy in submonolayer deposition have extended wavelength around 1.3 μm and well resolved energy levels that can be described by three-dimensional harmonic oscillator model assuming parabolic confining potential. Lasing transitions from various InGaAs quantum dot energy levels are obtained from edge-emitting lasers. With optimized quantum dot active region and device structure, continuous-wave, room-temperature lasing operation around 1.3 μm is achieved with very low threshold current. Lateral confinement of carriers and photons in the cavity with AlxO y using wet-oxidation technique results in low waveguide loss, which lowers the threshold further. InGaAs quantum dot lasers have almost temperature- insensitive lasing threshold below ~200 K with very low threshold current density close to transparency current density. The rapid increase of threshold current along with temperature above ~200 K is due to thermal excitation of carriers into the higher energy levels and increase of non-radiative recombination. Quasi- equilibrium model for carrier dynamics shows that the optical gain of quantum dot ensemble is strongly temperature dependent, and that the separation between quantum dot energy levels plays an important role in the temperature dependence of the device characteristics. Several predictions of the model are compared with the experimental results. Lasing operation with less temperature-sensitivity is achieved from InAs quantum dot lasers with increased level separation.

  20. Ion-beam induced isolation of gallium arsenide layers

    NASA Astrophysics Data System (ADS)

    Sengupta, D.; Zemanski, J. M.; Williams, J. S.; Johnson, S. T.; Pogany, A. P.

    1989-07-01

    Epitaxial (n +-n) layers on semi-insulating GaAs samples were implanted with 60 keV He + ions at elevated temperatures. Samples were analysed to provide sheet resistivity, Hall mobility and carrier depth profiles using electrical measurement techniques and damage distributions using TEM and Rutherford backscattering and channeling. All of the data were correlated to identify the optimum conditions to achieve electrical isolation. Elevated temperature He + implants have been found to create uniform, single step isolation of GaAs layers. Isolation of the GaAs layers can be enhanced and stabilised further by a suitable post-implantation annealing process.

  1. Gallium arsenide based surface plasmon resonance for glucose monitoring

    NASA Astrophysics Data System (ADS)

    Patil, Harshada; Sane, Vani; Sriram, G.; Indumathi, T. S; Sharan, Preeta

    2015-07-01

    The recent trends in the semiconductor and microwave industries has enabled the development of scalable microfabrication technology which produces a superior set of performance as against its counterparts. Surface Plasmon Resonance (SPR) based biosensors are a special class of optical sensors that become affected by electromagnetic waves. It is found that bio-molecular recognition element immobilized on the SPR sensor surface layer reveals a characteristic interaction with various sample solutions during the passage of light. The present work revolves around developing painless glucose monitoring systems using fluids containing glucose like saliva, urine, sweat or tears instead of blood samples. Non-invasive glucose monitoring has long been simulated using label free detection mechanisms and the same concept is adapted. In label-free detection, target molecules are not labeled or altered, and are detected in their natural forms. Label-free detection mechanisms involves the measurement of refractive index (RI) change induced by molecular interactions. These interactions relates the sample concentration or surface density, instead of total sample mass. After simulation it has been observed that the result obtained is highly accurate and sensitive. The structure used here is SPR sensor based on channel waveguide. The tools used for simulation are RSOFT FULLWAVE, MEEP and MATLAB etc.

  2. Research on gallium arsenide diffused junction solar cells

    NASA Technical Reports Server (NTRS)

    Borrego, J. M.; Ghandi, S. K.

    1984-01-01

    The feasibility of using bulk GaAs for the fabrication of diffused junction solar cells was determined. The effects of thermal processing of GaAs was studied, and the quality of starting bulk GaAs for this purpose was assessed. These cells are to be made by open tube diffusion techniques, and are to be tested for photovoltaic response under AMO conditions.

  3. Gallium arsenide solar cell efficiency: Problems and potential

    NASA Technical Reports Server (NTRS)

    Weizer, V. G.; Godlewski, M. P.

    1985-01-01

    Under ideal conditions the GaAs solar cell should be able to operate at an AMO efficiency exceeding 27 percent, whereas to date the best measured efficiencies barely exceed 19 percent. Of more concern is the fact that there has been no improvement in the past half decade, despite the expenditure of considerable effort. State-of-the-art GaAs efficiency is analyzed in an attempt to determine the feasibility of improving on the status quo. The possible gains to be had in the planar cell. An attempt is also made to predict the efficiency levels that could be achieved with a grating geometry. Both the N-base and the P-base BaAs cells in their planar configurations have the potential to operate at AMO efficiencies between 23 and 24 percent. For the former the enabling technology is essentially in hand, while for the latter the problem of passivating the emitter surface remains to be solved. In the dot grating configuration, P-base efficiencies approaching 26 percent are possible with minor improvements in existing technology. N-base grating cell efficiencies comparable to those predicted for the P-base cell are achievable if the N surface can be sufficiently passivated.

  4. Image processing using Gallium Arsenide (GaAs) technology

    NASA Technical Reports Server (NTRS)

    Miller, Warner H.

    1989-01-01

    The need to increase the information return from space-borne imaging systems has increased in the past decade. The use of multi-spectral data has resulted in the need for finer spatial resolution and greater spectral coverage. Onboard signal processing will be necessary in order to utilize the available Tracking and Data Relay Satellite System (TDRSS) communication channel at high efficiency. A generally recognized approach to the increased efficiency of channel usage is through data compression techniques. The compression technique implemented is a differential pulse code modulation (DPCM) scheme with a non-uniform quantizer. The need to advance the state-of-the-art of onboard processing was recognized and a GaAs integrated circuit technology was chosen. An Adaptive Programmable Processor (APP) chip set was developed which is based on an 8-bit slice general processor. The reason for choosing the compression technique for the Multi-spectral Linear Array (MLA) instrument is described. Also a description is given of the GaAs integrated circuit chip set which will demonstrate that data compression can be performed onboard in real time at data rate in the order of 500 Mb/s.

  5. Gallium Arsenide welded panel technology for advanced spaceflight applications

    NASA Technical Reports Server (NTRS)

    Lillington, D. R.; Gillanders, M. S.; Garlick, G. F. J.; Cavicchi, B. T.; Glenn, G. S.; Tobin, S. P.

    1989-01-01

    A significant impediment to the widespread use of GaAs solar cells in space is the cost and weight of the GaAs substrate. In order to overcome these problems, Spectrolab is pursuing thin cell technologies encompassing both liquid phase epitaxy (LPE) GaAs on GaAs and MOCVD GaAs on Ge cells. Spectrolab's experience in the manufacture of 4 to 6 mil 2 cm x 4 cm GaAs cells on a LPE production line is discussed. By thinning the cells at a late state of processing, production yields comparable to 12 mil cells have been achieved. Data are presented showing that GaAs cells can be welded without degradation and have achieved minimum average efficiencies of 18 percent AM0, 28 C with efficiencies up to 20 percent. Spectrolab, in conjunction with Spire Corporation has also been pursuing GaAs on Ge cell technology in support of larger area lighter weight power systems. Data are presented showing that individual 2 cm x 2 cm, 8 mil cell efficiencies up to 21.7 percent have been achieved. Efficiencies up to 24 percent AM0 will be possible by optimizing the GaAs/Ge interface. Cells have been welded without degradation using silver interconnects and have been laid down on an aluminum honeycomb/graphite facesheet substrate to produce a small coupon. The efficiency was 18.1 percent at AM0, 28 C.

  6. Optical computing and image processing using photorefractive gallium arsenide

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Liu, Duncan T. H.

    1990-01-01

    Recent experimental results on matrix-vector multiplication and multiple four-wave mixing using GaAs are presented. Attention is given to a simple concept of using two overlapping holograms in GaAs to do two matrix-vector multiplication processes operating in parallel with a common input vector. This concept can be used to construct high-speed, high-capacity, reconfigurable interconnection and multiplexing modules, important for optical computing and neural-network applications.

  7. Electrical characterization of plasma-grown oxides on gallium arsenide

    NASA Technical Reports Server (NTRS)

    Hshieh, F. I.; Bhat, K. N.; Ghandhi, S. K.; Borrego, J. M.

    1985-01-01

    Plasma-grown GaAs oxides and their interfaces have been characterized by measuring the electrical properties of metal-oxide-semiconductor capacitors and of Schottky junctions. The current transport mechanism in the oxide at high electrical field was found to be Frankel-Poole emission, with an electron trap center at 0.47 eV below the conduction band of the oxide. The interface-state density, evaluated from capacitance and conductance measurements, exhibits a U-shaped interface-state continuum extending over the entire band gap. Two discrete deep states with high concentration are superimposed on this continuum at 0.40 and 0.70 eV below the conduction band. The results obtained from measurements on Schottky junctions have excluded the possibility that these two deep states originate from plasma damage. Possible origins of these states are discussed in this paper.

  8. Noise-margin limitations on gallium-arsenide VLSI

    NASA Technical Reports Server (NTRS)

    Long, Stephen I.; Sundaram, Mani

    1988-01-01

    Two factors which limit the complexity of GaAs MESFET VLSI circuits are considered. Power dissipation sets an upper complexity limit for a given logic circuit implementation and thermal design. Uniformity of device characteristics and the circuit configuration determines the electrical functional yield. Projection of VLSI complexity based on these factors indicates that logic chips of 15,000 gates are feasible with the most promising static circuits if a maximum power dissipation of 5 W per chip is assumed. While lower power per gate and therefore more gates per chip can be obtained by using a popular E/D FET circuit, yields are shown to be small when practical device parameter tolerances are applied. Further improvements in materials, devices, and circuits wil be needed to extend circuit complexity to the range currently dominated by silicon.

  9. Annealing Studies of Metals and Arsenic on Gallium Arsenide.

    NASA Astrophysics Data System (ADS)

    Chiang, Terry Teh-I.

    1990-01-01

    PES (photoelectron spectroscopy) has been used to examine the mechanism of Schottky barrier formation in GaAs. The experiments are performed on metal/GaAs interfaces grown under UHV (ultra-high vacuum) conditions. The approach is to take three representative models of Schottky barrier formation and examine their applicability to three representative metal/GaAs interfaces. The three models are selected so as to encompass the key ideas of all the various proposed mechanisms and they are: (i) Effective work function (EWF) model, (ii) Metal induced gap states (MIGS) model, and (iii) Advanced unified defect model (AUDM). The high temperature annealing experiments help to distinguish between the three models and the results clearly suggest a different Schottky barrier formation mechanism dominating in each of the interfaces studied: As/GaAs (EWF model), Ag/GaAs (MIGS model), and Al/GaAs (AUDM). This indicates that a single mechanism may dominate in a particular metal/GaAs interface, but, in general, there will be contributions from several different mechanisms due to the complexity of the metal/GaAs interface. Therefore, any generalized Schottky barrier theory with predictive powers must take a multi-mechanism approach. For the As/GaAs interface, the high temperature annealing process causes the As overlayer to desorb and the surface Fermi level to become unpinned. Assuming the Fermi level pinning is due to the As overlayer (EWF model), desorption of the As overlayer naturally results in Fermi level unpinning. For the Ag/GaAs interface, the high temperature annealing process causes the Ag overlayer to cluster into large islands and the surface Fermi level to also become unpinned. It is suggested that this is because the Fermi level pinning is dominated by MIGS from metallic Ag (MIGS model) and the clustering results in metallic Ag covering a smaller fraction of the GaAs surface. For the Al/GaAs interface, the high temperature annealing process produces an enhancement in the replacement reaction of Ga by Al, but it does not cause the surface Fermi level to become unpinned. For this particular interface, it is suggested that the Fermi level pinning is dominated by As/Ga antisite defects (AUDM) and apparently they are not being annealed out.

  10. Photoelastic coupling in gallium arsenide optomechanical disk resonators.

    PubMed

    Baker, Christopher; Hease, William; Nguyen, Dac-Trung; Andronico, Alessio; Ducci, Sara; Leo, Giuseppe; Favero, Ivan

    2014-06-16

    We analyze the magnitude of the radiation pressure and electrostrictive stresses exerted by light confined inside GaAs semiconductor WGM optomechanical disk resonators, through analytical and numerical means, and find the electrostrictive stress to be of prime importance. We investigate the geometric and photoelastic optomechanical coupling resulting respectively from the deformation of the disk boundary and from the strain-induced refractive index changes in the material, for various mechanical modes of the disks. Photoelastic optomechanical coupling is shown to be a predominant coupling mechanism for certain disk dimensions and mechanical modes, leading to total coupling gom and g(0) reaching respectively 3 THz/nm and 4 MHz. Finally, we point towards ways to maximize the photoelastic coupling in GaAs disk resonators, and we provide some upper bounds for its value in various geometries.

  11. Optically rewritable patterns of nuclear magnetization in gallium arsenide.

    PubMed

    King, Jonathan P; Li, Yunpu; Meriles, Carlos A; Reimer, Jeffrey A

    2012-06-26

    The control of nuclear spin polarization is important to the design of materials and algorithms for spin-based quantum computing and spintronics. Towards that end, it would be convenient to control the sign and magnitude of nuclear polarization as a function of position within the host lattice. Here we show that, by exploiting different mechanisms for electron-nuclear interaction in the optical pumping process, we are able to control and image the sign of the nuclear polarization as a function of distance from an irradiated GaAs surface. This control is achieved using a crafted combination of light helicity, intensity and wavelength, and is further tuned via use of NMR pulse sequences. These results demonstrate all-optical creation of micron scale, rewritable patterns of positive and negative nuclear polarization in a bulk semiconductor without the need for ferromagnets, lithographic patterning techniques, or quantum-confined structures.

  12. Laser Ablation of Gallium Arsenide in Different Solutions

    SciTech Connect

    Ganeev, R.A.; Kuroda, H.; Ryasnyanskii, A.I.

    2005-12-15

    The optical, structural, and nonlinear optical characteristics of GaAs nanoparticles obtained by laser ablation in different liquids were investigated. Thermally induced self-defocusing in GaAs solutions was observed using both a high pulse repetition rate and nanosecond pulses. In studying the nonlinear optical characteristics of GaAs solutions using picosecond and femtosecond pulses, two-photon absorption was observed. The nonlinear absorption coefficient of an aqueous GaAs solution measured by the Z-scan technique and the nonlinear susceptibility of GaAs nanoparticles were, respectively, 0.7 x 10{sup -9} cm W{sup -1} and 2 x 10{sup -9} esu at a wavelength of 795 nm.

  13. Gallium arsenide digital integrated circuits - A systems perspective

    NASA Astrophysics Data System (ADS)

    Kanopoulos, Nick

    The characteristics of GaAs electronic components and their integration into digital circuits are examined in an introduction for graduate engineering students. Chapters are devoted to GaAs components, GaAs logic-gate design, GaAs logic circuits, GaAs digital-IC design principles, packaging, high-speed testing and design for testability, and GaAs insertion into system design. Diagrams, drawings, and exercises for each chapter are included.

  14. Design and microfabrication of a lateral excited gallium arsenide biosensor

    NASA Astrophysics Data System (ADS)

    Bienaime, A.; Liu, L.; Elie-Caille, C.; Leblois, T.

    2012-02-01

    GaAs crystal presents some interesting perspectives for resonant biosensors due to its piezoelectric and good mechanical properties and the opportunity to bio-functionalize the surface. Moreover, GaAs can be micromachined by wet etching in several solutions, which constitutes a batch and low-cost process of fabrication. The lateral field excitation (LFE) is used to generate bulk acoustic waves. The main advantage of LFE is the possibility to measure in liquid media, moreover reduced aging and increased frequency stability are also ensured. In this study, an analytical modelization is used to determine the orientations of the vibrating membrane and the electric field that give satisfactory metrological performances. Electrical performances are discussed as a function of geometrical parameters. A simulation based on a Finite Element Modelization is performed in order to optimize the design of the resonant structure. The microfabrication process of the structure is presented. The choice of etchants is discussed in terms of etching rates and surface textures. Several steps of the fabrication of the sensing area structure are shown and characterized. Finally, the active area is fabricated according to the theoretical and experimental results of this study.

  15. Integrated planar gallium arsenide Schottky mixers for submillimeter wavelength receivers

    NASA Astrophysics Data System (ADS)

    Marazita, Steven Michael

    1999-11-01

    Two integration technologies have been investigated. The first is the quartz upside-down inverted device (QUID) technology invented at JPL. Through this research QUID mixers operating at 240 GHz were fabricated and tested, thereby demonstrating the technology using UVa fabrication equipment and processes. A major drawback of the QUID integration process is that a layer of epoxy is used to adhere the diodes an metal films to the quartz. This epoxy is lossy and suffers from reliability concerns related to long term robustness and out-gassing. Through this research, the QUID process was extended to include a new etch step which removes the epoxy from all areas of circuit except between the quartz substrate and the attached layers. This resulted in the best published planar mixer sensitivity in the 200 to 300 GHz frequency range. This process was also transferred to JPL, where it helped improve the bandwidth of their 640 GHz mixers to meet the requirements of NASA's EOS-MLS mission. The new etch process does not remove the layer of epoxy that is trapped in the critical region between the anode/finger and the quartz substrate. To avoid this concern, a new fabrication process was developed. The Method of Adhesion by Spin-on-dielectric Temperature Enhanced Reflow (MASTER) uses a novel semiconductor to substrate bonding process to eliminate the necessity of epoxy bonding. This process was fully developed and integrated mixers were fabricated for 585 GHz, 640 GHz, and 1 THz. The 585 GHz mixers were fully designed using computer modeling tools, were extremely easy to assemble, and most importantly exhibited record performance, Tsys = 1631 K, T mix = 1135 K, Lmix = 6.5 dB (all DSB). This result was accomplished without the use of mechanical tuning elements and was consistent for four assembled mixers, showing an unprecedented level of repeatability. Through this dissertation research a new semiconductor on quartz integration technology has been created. This technology was demonstrated through the design, fabrication, and testing of a 585 GHz integrated mixer that is the most sensitive room temperature mixer ever reported for operation above 500 GHz. It is also the first planar mixer to outperform the best whisker contacted components in this frequency range. In addition to improved sensitivity, the new integrated technology offers greater bandwidth without reliance on mechanical tuners, a simplified design process, easier assembly, and drastically improved repeatability. As this integration technology is applied to mixers and multipliers throughout the terahertz range, it will significantly improve performance and reduce costs. Thus, this research has made an important contribution toward the creation of a commercially viable terahertz technology base. (Abstract shortened by UMI.)

  16. Gallium arsenide (GaAs) solar cell modeling studies

    NASA Technical Reports Server (NTRS)

    Heinbockel, J. H.

    1980-01-01

    Various models were constructed which will allow for the variation of system components. Computer studies were then performed using the models constructed in order to study the effects of various system changes. In particular, GaAs and Si flat plate solar power arrays were studied and compared. Series and shunt resistance models were constructed. Models for the chemical kinetics of the annealing process were prepared. For all models constructed, various parametric studies were performed.

  17. Fabrication and characterisation of gallium arsenide ambipolar quantum point contacts

    SciTech Connect

    Chen, J. C. H. Klochan, O.; Micolich, A. P.; Hamilton, A. R.; Das Gupta, K.; Sfigakis, F.; Ritchie, D. A.; Trunov, K.; Wieck, A. D.; Reuter, D.

    2015-05-04

    We show that ballistic one-dimensional channels can be formed in an ambipolar device fabricated on a high mobility Al{sub 0.34}Ga{sub 0.66}As/GaAs heterostructure. Both electron and hole quantised conductances can be measured in the same one-dimensional channel. We have used this device to compare directly the subband spacings of the two charge carriers in the same confining potential and used this to compare the electron and hole effective masses.

  18. Supralinear photoconductivity of copper doped semi-insulating gallium arsenide

    SciTech Connect

    Schoenbach, K.H.; Joshi, R.P.; Peterkin, F.; Druce, R.L.

    1995-05-15

    We report on the intensity dependent supralinear photoconductivity in GaAs:Si:Cu material. The results of our measurements show that the effective carrier lifetime can change over two orders of magnitude with variations in the intensity of the optical excitation. A threshold intensity level has been observed and can be related to the occupancy of the deep copper level. Numerical simulations have also been carried out to analyze the trapping dynamics. The intensity dependent lifetimes obtained from the simulations match the experimental data very well. Finally, based on the nonlinear intensity dependence of the effective lifetimes, a possible low-energy phototransistor application for the GaAs:Cu material system is presented. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  19. Gallium arsenide enhances digital signal processing in electronic warfare

    NASA Astrophysics Data System (ADS)

    Hoffman, B.; Apte, D.

    1985-07-01

    The higher electron mobility and velocity of GaAs digital signal processing IC devices for electronic warfare (EW) allow operation times that are several times faster than those of ICs based on silicon. Particular benefits are foreseen for the response time and broadband capability of ECM systems. Many data manipulation methods can be implemented in emitter-coupled logic (ECL) GaAs devices, and digital GaAs RF memories are noted to show great promise for improved ECM system performance while encompassing microwave frequency and chirp signal synthesis, repeater jamming, and multiple false target generation. EW digital frequency synthesizers are especially in need of GaAS IC technology, since bandwidth and resolution have been limited by ECL technology to about 250 MHz.

  20. Gallium arsenide changes the shape of airborne radar

    NASA Astrophysics Data System (ADS)

    Nathanson, Harvey C.; Driver, Mike C.; Thomas, R. Noel

    1987-04-01

    An evaluation is made of the intrinsic properties and projected performance capabilities of GaAs ICs, with a view to the impact of their use on military radars and such other electronic devices as wideband low noise amplifiers, power amplifiers, broadband phase shifters, and electronic attenuators. For these, GaAs offers higher electron velocity for high frequencies, broader bandwidth, and higher RF efficiency than other semiconductor technologies. The complexity of GaAs power monolithics has been doubling every nine months, and systems-on-a-wafer are expected to become available as IC yields increase. GaAs CCD imagers and memories will combine on-chip image scanning with monolithic microwave ICs for ultrahigh speed image processing.

  1. Third Working Meeting on Gallium Arsenide Solar Cells

    NASA Technical Reports Server (NTRS)

    Walker, G. H. (Compiler)

    1976-01-01

    Research results are reported for GaAs Schottky barrier solar cells, GaAlAs/GaAs heteroface solar cells, and GaAlAs graded band gap solar cells. Related materials studies are presented. A systems study for GaAs and Si solar concentrator systems is given.

  2. Gallium complexes and solvent extraction of gallium

    SciTech Connect

    Coleman, J.P.; Graham, C.R.; Monzyk, B.F.

    1988-05-03

    This patent describes a process for recovering gallium from aqueous solutions containing gallium which comprises contacting such a solution with an organic solvent containing at least 2% by weight of a water-insoluble N-organo hydroxamic acid having at least about 8 carbon atoms to extract gallium, and separating the gallium loaded organic solvent phase from the aqueous phase.

  3. Incorporation and diffusion of dopants in gallium arsenide, indium phosphide and indium gallium arsenide: Implications for devices

    NASA Astrophysics Data System (ADS)

    Tandon, Ashish

    Incorporation and diffusion of dopants in the InP, InGaAs and GaAs material systems by atmospheric pressure organometallic vapor phase epitaxy (APOMVPE) is discussed. A better understanding of the role point defect mechanisms play in driving dopant diffusion in III-V compounds has been obtained from experimental results. A study of Fermi level pinning at the surface of InP, InGaAs and GaAs is presented to explain the anomalously fast diffusion of dopants (such as Zn and Be which reside on the group III sublattice) observed in the base region of InP/InGaAs HBTs. Experimental results indicated that the Fermi level is not pinned at the surface of InGaAs while it appears to be pinned close to the valence band in InP. The Fermi level pinning at the surface of GaAs was found to vary with the crystal orientation. A solution to the problem of obtaining p-type base in InP/InGaAs HBTs has been presented in the form of carbon doped (p-type) InGaAs. The effects of growth temperature, V/III ratio and dopant source partial pressure on the concentration and mobility of holes in carbon doped InGaAs epilayers are reported. Record doping levels with negligible dopant passivation have been attained for carbon doped InGaAs epilayers. Studies linking dopant passivation to macroscopic defect formation are presented. A culmination of these findings in the growth and fabrication of InP/InGaAs HBTs with low base resistance and moderate gains is reported. A design resulting in the improvement of the collector-base breakdown voltage in InGaAs diodes is also discussed. The chemical treatment and history of the substrate were shown to play an important role in the diffusion of dopants in grown epilayers. Chlorine based compounds, thermal oxidation of the surface and growth of buffer layers (between the substrate and the epilayer) reduced diffusion in the epilayer. Sodium based compounds and anodic oxides tend to enhance dopant diffusion in the epilayer. A theoretical model for calculating dopant profiles has been developed and the simulated results show good agreement with experimental data. The model accounts for charged point defects, electric fields and Fermi level pinning at the surface.

  4. Ultrafast electronic dynamics in unipolar n-doped indium gallium arsenide/gallium arsenide self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Wu, Zong-Kwei J.

    2006-12-01

    Photodetectors based on intraband infrared absorption in the quantum dots have demonstrated improved performance over its quantum well counterpart by lower dark current, relative temperature insensitivity, and its ability for normal incidence operation. Various scattering processes, including phonon emission/absorption and carrier-carrier scattering, are critical in understanding device operation on the fundamental level. In previous studies, our group has investigated carrier dynamics in both low- and high-density regime. Ultrafast electron-hole scattering and the predicted phonon bottleneck effect in intrinsic quantum dots have been observed. Further examination on electron dynamics in unipolar structures is presented in this thesis. We used n-doped quantum dot in mid-infrared photodetector device structure to study the electron dynamics in unipolar structure. Differential transmission spectroscopy with mid-infrared intraband pump and optical interband probe was implemented to measure the electron dynamics directly without creating extra electron-hole pair, Electron relaxation after excitation was measured under various density and temperature conditions. Rapid capture into quantum dot within ˜ 10 ps was observed due to Auger-type electron-electron scattering. Intradot relaxation from the quantum dot excited state to the ground state was also observed on the time scale of 100 ps. With highly doped electron density in the structure, the inter-sublevel relaxation is dominated by Auger-type electron-electron scattering and the phonon bottleneck effect is circumvented. Nanosecond-scale recovery in larger-sized quantum dots was observed, not intrinsic to electron dynamics but due to band-bending and built-in voltage drift. An ensemble Monte Carlo simulation was also established to model the dynamics in quantum dots and in goad agreement with the experimental results. We presented a comprehensive picture of electron dynamics in the unipolar quantum dot structure. Although the phonon bottleneck is circumvented with high doped electron density, relaxation processes in unipolar quantum dots have been measured with time scales longer than that of bipolar systems. The results explain the operation principles of the quantum dot infrared photodetector on a microscopic level and provide basic understanding for future applications and designs.

  5. Threshold extension of gallium arsenide/aluminum(x) gallium(1-x) arsenide terahertz detectors and switching in heterostructures

    NASA Astrophysics Data System (ADS)

    Rinzan, Mohamed B.

    In this work, homojunction interfacial workfunction internal photoemission (HIWIP) detectors based on GaAs, and heterojunction interfacial workfunction internal photoemission (HEIWIP) detectors based mainly on the GaAs/Al xGa1-xAs material system are presented. Design principles of HIWIP and HEIWIP detectors, such as free carrier absorption, photocarrier generation, photoemission, and responsivity, are discussed in detail. Results of p-type HIWIPs based on GaAs material are presented. Homojunction detectors based on p-type GaAs were found to limit their operating wavelength range. This is mainly due to band depletion arising through carrier transitions from the heavy/light hole bands to the split off band. Designing n-type GaAs HIWIP detectors is difficult as it is strenuous to control their workfunction. Heterojunction detectors based on GaAs/AlxGa 1-xAs material system will allow tuning their threshold wavelength by adjusting the alloy composition of the Al xGa1-xAs barrier, while keeping a fixed doping density in the emitter. The detectors covered in this work operate from 1 to 128 microm (300 to 2.3 THz). Enhancement of detector response using resonance cavity architecture is demonstrated. Threshold wavelength extension of HEIWIPs by varying the Al composition of the barrier was investigated. The threshold limit of ˜ 3.3 THz (92 microm), due to a practical Al fraction limit of ˜ 0.005, can be overcome by replacing GaAs emitters in GaAs/AlxGa1-xAs HEIWIPs with AlxGa1-xAs emitters. As the initial step, terahertz absorption for 1 microm-thick Be-doped AlxGa1-xAs epilayers (with different Al fraction and doping density) grown on GaAs substrates was measured. The absorption probability of the epilayers was derived from these absorption measurements. Based on the terahertz absorption results, an AlxGa1-xAs/GaAs HEIWIP detector was designed and the extension of threshold frequency ( f0) to 2.3 THz was successfully demonstrated. In a different study, switching in GaAs/AlxGa1- xAs heterostructures from a tunneling dominated low conductance branch to a thermal emission dominated high conductance branch was investigated. This bistability leads to neuron-like voltage pulses observed in some heterostructure devices. The bias field that initiates the switching was determined from an iterative method that uses feedback information, such as carrier drift velocity and electron temperature, from hot carrier transport. The bias voltage needed to switch the device was found to decrease with the increasing device temperature.

  6. Chemical mechanical polishing of Indium phosphide, Gallium arsenide and Indium gallium arsenide films and related environment and safety aspects

    NASA Astrophysics Data System (ADS)

    Matovu, John Bogere

    As scaling continues with advanced technology nodes in the microelectronic industry to enhance device performance, the performance limits of the conventional substrate materials such as silicon as a channel material in the front-end-of-the-line of the complementary metal oxide semiconductor (CMOS) need to be surmounted. These challenges have invigorated research into new materials such as III-V materials consisting of InP, GaAs, InGaAs for n-channel CMOS and Ge for p-channels CMOS to enhance device performance. These III-V materials have higher electron mobility that is required for the n-channel while Ge has high hole mobility that is required for the p-channel. Integration of these materials in future devices requires chemical mechanical polishing (CMP) to achieve a smooth and planar surface to enable further processing. The CMP process of these materials has been associated with environment, health and safety (EH&S) issues due to the presence of P and As that can lead to the formation of toxic gaseous hydrides. The safe handling of As contaminated consumables and post-CMP slurry waste is essential. In this work, the chemical mechanical polishing of InP, GaAs and InGaAs films and the associated environment, health and safety (EH&S) issues are discussed. InP removal rates (RRs) and phosphine generation during the CMP of blanket InP films in hydrogen peroxide-based silica particle dispersions in the presence and absence of three different multifunctional chelating carboxylic acids, namely oxalic acid, tartaric acid, and citric acid are reported. The presence of these acids in the polishing slurry resulted in good InP removal rates (about 400 nm min-1) and very low phosphine generation (< 15 ppb) with very smooth post-polish surfaces (0.1 nm RMS surface roughness). The optimized slurry compositions consisting of 3 wt % silica, 1 wt % hydrogen peroxide and 0.08 M oxalic acid or citric acid that provided the best results on blanket InP films were used to evaluate their planarization capability of patterned InP-STI structures of 200 mm diameter wafers. Cross sectional scanning electron microscope (SEM) images showed that InP in the shallow trench isolation structures was planarized and scratches, slurry particles and smearing of InP were absent. Additionally, wafers polished at pH 6 showed very low dishing values of about 12-15 nm, determined by cross sectional SEM. During the polishing of blanket GaAs, GaAs RRs were negligible with deionized water or with silica slurries alone. They were relatively high in aq. solutions of H2O2 alone and showed a strong pH dependence, with significantly higher RRs in the alkaline region. The addition of silica particles to aq. H2O2 did not increase the GaAs RRs significantly. The evolution of arsenic trihydride (AsH3) during the dissolution of GaAs in aq. H2O2 solution was similarly higher in the basic pH range than in neutral pH or in the acidic pH range. However, no AsH3 was measured during polishing, evidently because of the relatively high water solubility of AsH3. The work done on InGaAs polishing shows that InGaAs RR trends are different from those observed for InP or GaAs. InGaAs RRs at pH 2 are higher than those at pH 10 and highest at pH 4. Dissolution rates (DRs), Fourier Transform Infrared Spectroscopy (FTIR), contact angles, X-Ray Photoelectron Spectroscopy (XPS), X-Ray Fluorescence Spectroscopy (XRF), zeta potential measurements and calculated Gibbs free energy changes of the reactions involved during polishing and gas formation were used to discuss the observed RRs and hydride gas generation trends and to propose the reaction pathways involved in the material removal and in hydride gas generation mechanisms.

  7. Development of gallium nitride-based ultraviolet and visible light-emitting diodes using hydride vapor-phase epitaxy and molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Cabalu, Jasper Sicat

    Much of the work done on ultraviolet (UV) and visible III-Nitrides-based light emitting diodes (LEDs) involves growth by metal-organic chemical vapor deposition (MOCVD). In this dissertation, the growth, development, and fabrication of III-Nitrides-based UV and visible LEDs with very high photon conversion and extraction efficiencies using hydride vapor-phase epitaxy (HVPE) and radio frequency (rf) plasma-assisted molecular beam epitaxy (PAMBE) is presented. High-power electrically-pumped UV-LEDs based on GaN/AlGaN multiple quantum wells (MQWs) emitting at 340 nm and 350 nm have been fabricated in a flip-chip configuration and evaluated. Under pulsed operation, UV-LEDs emitting at 340 nm have output powers that saturate, due to device heating, at approximately 3 mW. Devices emitting at 350 nm show DC operation output powers as high as 4.5 mW under 200 mA drive current. These results were found to be equivalent with those of UV-LEDs produced by the MOCVD and HVPE methods. The concept of using textured MQWs on UV-LED structures was tested by optical pumping of GaN/AlGaN MQWs grown on textured GaN templates. Results show highly enhanced (>700 times) blue-shifted photoluminescence (PL) at 360 nm compared to similarly produced MQWs on smooth GaN templates whose PL emission is red-shifted. These results are attributed partly to enhancement in light extraction efficiency (LEE) and partly to enhancement in internal quantum efficiency (IQE). The origin of the increase in IQE is partly due to reduction of the quantum-confined Stark effect (QCSE) on QW-planes not perpendicular to the polarization direction and partly due to charge redistribution in the QWs caused by the polarization component parallel to the planes of the QWs. Similar studies have been done for visible LEDs using InGaN/GaN MQWs. Growth of LED structures on textured GaN templates employing textured MQW-active regions resulted in the production of dichromatic (430 nm and 530 nm) phosphorless white LEDs with

  8. Noise in gallium nitride-based quantum well structures used for nanometer devices in the frequency range 1 Hz--3 Mhz and temperature range 77K--324K

    NASA Astrophysics Data System (ADS)

    Duran, Rolando Silvano

    Electronic noise has been investigated in AlxGa1-x N/GaN Modulation-Doped Field Effect Transistors (MODFETs) of submicron dimensions, grown for us by MBE (Molecular Beam Epitaxy) techniques at Virginia Commonwealth University by Dr. H. Morkoc and coworkers. Some 20 devices were grown on a GaN substrate, four of which have leads bonded to source (S), drain (D), and gate (G) pads, respectively. Conduction takes place in the quasi-2D layer of the junction (xy plane) which is perpendicular to the quantum well (z-direction) of average triangular width ˜3 nm. A non-doped intrinsic buffer layer of ˜5 nm separates the Si-doped donors in the AlxGa1-xN layer from the 2D-transistor plane, which affords a very high electron mobility, thus enabling high-speed devices. Since all contacts (S, D, and G) must reach through the AlxGa1-xN layer to connect internally to the 2D plane, parallel conduction through this layer is a feature of all modulation-doped devices. While the shunting effect may account for no more than a few percent of the current IDS, it is responsible for most excess noise, over and above thermal noise of the device. The excess noise has been analyzed as a sum of Lorentzian spectra and 1/f noise. The Lorentzian noise has been ascribed to trapping of the carriers in the AlxGa1-xN layer. A detailed, multitrapping generation-recombination noise theory is presented, which shows that an exponential relationship exists for the time constants obtained from the spectral components as a function of 1/kT. The trap depths have been obtained from Arrhenius plots of log (tauT2) vs. 1000/T. Comparison with previous noise results for GaAs devices shows that: (a) many more trapping levels are present in these nitride-based devices; (b) the traps are deeper (farther below the conduction band) than for GaAs. Furthermore, the magnitude of the noise is strongly dependent on the level of depletion of the AlxGa1-xN donor layer, which can be altered by a negative or positive gate bias

  9. Graded-refractive-index structures on gallium nitride-based light-emitting diodes for light-extraction-efficiency enhancement and far-field-emission control

    NASA Astrophysics Data System (ADS)

    Mont, Frank Wilhelm

    Light-emitting diodes (LEDs) represent the next generation of lighting and illumination sources. There are many challenges yet to be solved for nitride-based LEDs such as enhancing the internal quantum efficiency and enhancing the light-extraction efficiency (LEE). Both challenges need to be overcome to obtain highly efficient devices. Semiconductor materials used for LEDs have large refractive indices ( n = 2.5 to 3.5) in contrast to air (n = 1.0) or encapsulant materials (n ≈ 1.5), resulting in total internal reflection losses and high Fresnel reflection losses at semiconductor-air and semiconductor-encapsulant interfaces thereby limiting light extraction. Frequently, single-layer anti-reflection (AR) coatings are used in optical devices to eliminate reflection. However such single-layer coatings eliminate reflection at only a single wavelength and angle of incidence. In this dissertation, we demonstrate that broadband omni-directional AR characteristics are attainable by grading the refractive index of the AR coating from the substrate index to the ambient index. Furthermore, micro-patterning of graded-refractive-index (GRIN) coatings deposited on top of GaInN LEDs is demonstrated to enhance light-output power through the extraction of light that would otherwise be waveguided. Three-dimensional ray-tracing simulations for GRIN micro-pillars on GaInN LEDs predict a LEE enhancement of 85% over uncoated LEDs when the pillar height is half the pillar diameter. The theory, simulation, and fabrication steps needed to realize such a device are developed. In Chapter 1, a review of LED fundamentals is given. Furthermore, modern methods to achieve high light-extraction efficiency for LEDs are discussed. In Chapter 2, the fabrication and characterization of GRIN multi-layer structures are discussed. A method to achieve tunable-refractive-index coatings using co-sputtering is demonstrated. Ellipsometry, reflectance, and transmittance measurements of the GRIN coatings

  10. Growth and analysis of gallium arsenide-gallium antimonide single and two-phase nanoparticles

    NASA Astrophysics Data System (ADS)

    Schamp, Crispin T.

    When evaluating the path of phase transformations in systems with nanoscopic dimensions one often relies on bulk phase diagrams for guidance because of the lack of phase diagrams that show the effect of particle size. The GaAs-GaSb pseudo-binary alloy is chosen for study to gain insight into the size dependence of solid-solubility in a two-phase system. To this end, a study is performed using independent laser ablation of high purity targets of GaAs and GaSb. The resultant samples are analyzed by transmission electron microscopy. Experimental results indicate that GaAs-GaSb nanoparticles have been formed with compositions that lie within the miscibility gap of bulk GaAs-GaSb. An unusual nanoparticle morpohology resembling the appearance of ice cream cones has been observed in single component experiments. These particles are composed of a spherical cap of Ga in contact with a crystalline cone of either GaAs or GaSb. The cones take the projected 2-D shape of a triangle or a faceted gem. The liquid Ga is found to consistently be of spherical shape and wets to the widest corners of the cone, suggesting an energy minimum exists at that wetting condition. To explore this observation a liquid sphere is modeled as being penetrated by a solid gem. The surface energies of the solid and liquid, and interfacial energy are summed as a function of penetration depth, with the sum showing a cusped minimum at the penetration depth corresponding to the waist of the gem. The angle of contact of the liquid wetting the cone is also calculated, and Young's contact angle is found to occur when the derivative of the total energy with respect to penetration depth is zero, which can be a maximum or a minimum depending on the geometrical details. The spill-over of the meniscus across the gem corners is found to be energetically favorable when the contact angle achieves the value of the equilibrium angle; otherwise the meniscus is pinned at the corners.

  11. Application of the bounds-analysis approach to arsenic and gallium antisite defects in gallium arsenide

    DOE PAGESBeta

    Wright, A. F.; Modine, N. A.

    2015-01-23

    The As antisite in GaAs (AsGa) has been the subject of numerous experimental and theoretical studies. Recent density-functional-theory (DFT) studies report results in good agreement with experimental data for the +2, +1, and 0 charge states of the stable EL2 structure, the 0 charge state of the metastable EL2* structure, and the activation energy to transform from EL2* to EL2 in the 0 charge state. However, these studies did not report results for EL2* in the -1 charge state. In this paper, we report new DFT results for the +2, +1, 0, and -1 charge states of AsGa, obtained usingmore » a semilocal exchange-correlation functional and interpreted using a bounds-analysis approach. In good agreement with experimental data, we find a -1/0 EL2* level 0.06 eV below the conduction-band edge and an activation energy of 0.05 eV to transform from EL2* to EL2 in the -1 charge state. While the Ga antisite in GaAs (GaAs) has not been studied as extensively as AsGa, experimental studies report three charge states (-2, -1, 0) and two levels (-2/-1, -1/0) close to the valence-band edge. Recent DFT studies report the same charge states, but the levels are found to be well-separated from the valence-band edge. To resolve this disagreement, we performed new DFT calculations for GaAs and interpreted them using a bounds analysis. The analysis identified the -1 and 0 charge states as hole states weakly bound to a highly-localized -2 charge state. Moreover, the -2/-1, -1/0 levels were found to be near the valence-band edge, in good agreement with the experimental data.« less

  12. Application of the bounds-analysis approach to arsenic and gallium antisite defects in gallium arsenide

    SciTech Connect

    Wright, A. F.; Modine, N. A.

    2015-01-23

    The As antisite in GaAs (AsGa) has been the subject of numerous experimental and theoretical studies. Recent density-functional-theory (DFT) studies report results in good agreement with experimental data for the +2, +1, and 0 charge states of the stable EL2 structure, the 0 charge state of the metastable EL2* structure, and the activation energy to transform from EL2* to EL2 in the 0 charge state. However, these studies did not report results for EL2* in the -1 charge state. In this paper, we report new DFT results for the +2, +1, 0, and -1 charge states of AsGa, obtained using a semilocal exchange-correlation functional and interpreted using a bounds-analysis approach. In good agreement with experimental data, we find a -1/0 EL2* level 0.06 eV below the conduction-band edge and an activation energy of 0.05 eV to transform from EL2* to EL2 in the -1 charge state. While the Ga antisite in GaAs (GaAs) has not been studied as extensively as AsGa, experimental studies report three charge states (-2, -1, 0) and two levels (-2/-1, -1/0) close to the valence-band edge. Recent DFT studies report the same charge states, but the levels are found to be well-separated from the valence-band edge. To resolve this disagreement, we performed new DFT calculations for GaAs and interpreted them using a bounds analysis. The analysis identified the -1 and 0 charge states as hole states weakly bound to a highly-localized -2 charge state. Moreover, the -2/-1, -1/0 levels were found to be near the valence-band edge, in good agreement with the experimental data.

  13. A study to investigate the chemical stability of gallium phosphate oxide/gallium arsenide phosphide

    NASA Technical Reports Server (NTRS)

    Kuhlman, G. J.

    1979-01-01

    The elemental composition with depth into the oxide films was examined using secondary ion mass spectrometry. Results indicate that the layers are arsenic-deficient through the bulk of the oxide and arsenic-rich near both the oxide surface and the oxide-semiconductor interface region. Phosphorus is incorporated into the oxide in an approximately uniform manner. The MIS capacitor structures exhibited deep-depletion characteristics and hysteresis indicative of electron trapping at the oxide-semiconductor interface. Post-oxidation annealing of the films in argon or nitrogen generally results in slightly increased dielectric leakage currents and decreased C-V hysteresis effects, and is associated with arsenic loss at the oxide surface. The results of bias-temperature stress experiments indicate that the major instability effects are due to changes in the electron trapping behavior. No changes were observed in the elemental profiles following electrical stressing, indicating that the grown films are chemically stable under device operating conditions.

  14. Spectroscopy of oxide-gallium nitride interfaces

    NASA Astrophysics Data System (ADS)

    Craft, Hughes Spalding

    GaN-based devices are of interest for applications requiring high-frequency, high-power operation at elevated temperatures. As in traditional, silicon-based devices, integration of semiconducting phases with insulators is critical. Additionally, applications involving the integration of GaN with polar oxides such as perovskite ferroelectrics have been proposed, due to the coupling that may be achieved between the respective polar vector. Devices utilizing such a coupling behavior would make possible two-dimensional electron gases of high charge densities that could be modulated by the oxide's polarization. The current status of oxide-GaN research is far behind that of oxide-Si research, and large-scale realization of GaN devices will require detailed understanding of oxide-GaN interfaces. This thesis focuses on the characterization of several oxide-GaN interfaces using x-ray photoelectron spectroscopy (XPS), as well as the identification of issues relating to the GaN surface. The rocksalt oxides MgO and CaO have been proposed as candidates for GaN MOSFET gate oxides, passivating layers, and buffer layers in GaN-ferroelectric structures. Thus, knowledge of film growth modes and band alignments is critical. Utilizing in-vacuo molecular beam epitaxy (MBE) and XPS, the growth of MgO on GaN was found to occur by the Volmer-Weber mode, with coalescence occurring at ˜12 nm. This coalescence behavior was not found to affect the band alignment. As measured by XPS, the valence band offset at the MgO-GaN interface is 1.2 +/- 0.2 eV, leading to a conduction band offset of 3.5 eV. A similar study was undertaken for the CaO-GaN system, in which more rapid coalescence was observed, leading to the conclusion of a Stranski-Krastanov growth mode. The difference in coalescence behavior is attributed to the increased reactivity of the CaO surface. The band offsets at the CaO-GaN interface were found to be 1.0 +/- 0.2 eV at the valence band, and 2.5 eV at the conduction band. The band structures measured in this thesis are considered to be sufficient for limiting leakage current by Schottky emission for high-temperature devices. Surface chemical stability of rocksalt oxides is a known issue with respect to hydroxylation through water adsorption. XPS characterization of water uptake was performed using the O 1s photoelectron line after several in-vacuo exposures, culminating in a one-hour exposure to a water/oxygen mixture at 1 x 10-6 Torr. Characterization of polycrystalline MgO showed a saturating coverage of --OH groups at approximately 1 monolayer, regardless of exposure. CaO films exhibited increased reactivity, with hydroxyl coverage increasing to 3 monolayers, in addition to a similar amount of physisorbed water, suggesting the possibility for further reaction. Complete recovery of both oxide surfaces is shown to be achievable using mild vacuum anneals. Finally, the surface of GaN has been characterized with respect to several issues encountered during these investigations. GaN surfaces are found to be significantly Garich, with surface stoichiometries routinely in excess of Ga2N. Several wet chemistries for GaN preparation were evaluated for their ability to modify the electrical behavior of subsequently grown oxide films. XPS could not unambiguously identify any change in surface chemistry that promotes these effects. Finally, p-type GaN films were noted to consistently possess greater oxide contamination in the as-grown state. Typical n-type or undoped GaN were marked by submonolayer quantities of oxide surface coverage, while p-type GaN typically exhibited coverages in the 1-2 nm scale. This difference has been found to be due to the p-type dopant activation anneal, during which GaN oxidation cannot be suppressed.

  15. Ohmic contacts to Gallium Nitride materials

    NASA Astrophysics Data System (ADS)

    Greco, Giuseppe; Iucolano, Ferdinando; Roccaforte, Fabrizio

    2016-10-01

    In this review article, a comprehensive study of the mechanisms of Ohmic contact formation on GaN-based materials is presented. After a brief introduction on the physics of Ohmic contacts, a resume of the most important results obtained in literature is reported for each of the systems taken in consideration (n-type GaN, p-type GaN and AlGaN/GaN heterostructures). The optimal metallization schemes and processing conditions to obtain low resistance Ohmic contacts are presented, discussing the role of the single metals composing the stack and the modification induced by the thermal annealing, either on the metal layers or at the interface with GaN. Physical insights on the mechanism of Ohmic contact formation have been gained by correlating the temperature dependence of the electrical parameters with a morphological/structural analysis of the interface. In the case of the AlGaN/GaN systems, the influence of the heterostructure parameters on the Ohmic contacts has been taken into account adapting the classical thermionic field emission model to the presence of the two dimensional electron gas (2DEG). Finally, the state of the art of "Au-free" metallization to AlGaN/GaN heterostructures is also presented, being this latter a relevant topic for the integration of GaN technology on large scale Silicon devices fabs.

  16. Growth process for gallium nitride porous nanorods

    SciTech Connect

    Wildeson, Isaac Harshman; Sands, Timothy David

    2015-03-24

    A GaN nanorod and formation method. Formation includes providing a substrate having a GaN film, depositing SiN.sub.x on the GaN film, etching a growth opening through the SiN.sub.x and into the GaN film, growing a GaN nanorod through the growth opening, the nanorod having a nanopore running substantially through its centerline. Focused ion beam etching can be used. The growing can be done using organometallic vapor phase epitaxy. The nanopore diameter can be controlled using the growth opening diameter or the growing step duration. The GaN nanorods can be removed from the substrate. The SiN.sub.x layer can be removed after the growing step. A SiO.sub.x template can be formed on the GaN film and the GaN can be grown to cover the SiO.sub.x template before depositing SiN.sub.x on the GaN film. The SiO.sub.x template can be removed after growing the nanorods.

  17. Iron arsenide superconductors what is the glue?

    SciTech Connect

    Hinks, D. G.; Materials Science Division

    2009-06-01

    Is superconductivity in the iron arsenides conventional? The large isotope effect on both the magnetic and superconducting transitions may indicate that magnetic fluctuations are involved in the superconducting pairing.

  18. Recovery of gallium and arsenic from GaAs wafer manufacturing slurries

    SciTech Connect

    Jadvar, R.; McCoy, B.J. ); Ford, B.; Galt, J. )

    1991-11-01

    Lapping and polishing slurries from the gallium arsenide (GaAs) wafer manufacturing process were used to develop simple and inexpensive methods for separation and recovery of valuable gallium and toxic arsenic. The lapping slurry, containing GaAs, glycerol, alumina, iron oxide, and water, is treated by a process involving water addition, dissolution of GaAs, mixing, sedimentation, decantation, and evaporation. The polishing slurry, containing GaAs, silica, sodium bicarbonate, sodium hypochlorite and water, is treated simply by a repetitive cycle of adding water, mixing, settling, decanting, and evaporating. After treatment, the slurries contain less than 5 ppm of dissolved arsenic and are considered non-hazardous.

  19. Mechanical strength and tribological behavior of ion-beam deposited boron nitride films on non-metallic substrates

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Buckley, Donald H.; Pouch, John J.; Alterovitz, Samuel A.; Sliney, Harold E.

    1987-01-01

    An investigation was conducted to examine the mechanical strength and tribological properties of boron nitride (BN) films ion-beam deposited on silicon (Si), fused silica (SiO2), gallium arsenide (GaAs), and indium phosphide (InP) substrates in sliding contact with a diamond pin under a load. The results of the investigation indicate that BN films on nonmetallic substrates, like metal films on metallic substrates, deform elastically and plastically in the interfacial region when in contact with a diamond pin. However, unlike metal films and substrates, BN films on nonmetallic substrates can fracture when they are critically loaded. Not only does the yield pressure (hardness) of Si and SiO2 substrates increase by a factor of 2 in the presence of a BN film, but the critical load needed to fracture increases as well. The presence of films on the brittle substrates can arrest crack formation. The BN film reduces adhesion and friction in the sliding contact. BN adheres to Si and SiO2 and forms a good quality film, while it adheres poorly to GaAs and InP. The interfacial adhesive strengths were 1 GPa for a BN film on Si and appreciably higher than 1 GPa for a BN film on SiO2.

  20. Investigations in gallium removal

    SciTech Connect

    Philip, C.V.; Pitt, W.W.; Beard, C.A.

    1997-11-01

    Gallium present in weapons plutonium must be removed before it can be used for the production of mixed-oxide (MOX) nuclear reactor fuel. The main goal of the preliminary studies conducted at Texas A and M University was to assist in the development of a thermal process to remove gallium from a gallium oxide/plutonium oxide matrix. This effort is being conducted in close consultation with the Los Alamos National Laboratory (LANL) personnel involved in the development of this process for the US Department of Energy (DOE). Simple experiments were performed on gallium oxide, and cerium-oxide/gallium-oxide mixtures, heated to temperatures ranging from 700--900 C in a reducing environment, and a method for collecting the gallium vapors under these conditions was demonstrated.

  1. Gallium nitrate revisited.

    PubMed

    Chitambar, Christopher R

    2003-04-01

    Gallium nitrate, the nitrate salt of the "near-metal" element gallium, is highly effective in the treatment of cancer-related hypercalcemia. Unlike bisphosphonates, gallium nitrate is effective in both parathyroid hormone-related protein-mediated and non-parathyroid hormone-related protein-mediated hypercalcemia. Gallium nitrate's effects on bone are clearly different from those of bisphosphonates. Gallium nitrate enhances calcium and phosphate content of bone and has direct, noncytotoxic effects on osteoclasts at markedly lower doses than those used for the treatment of cancer-related hypercalcemia. The drug may have clinical application in a variety of disorders associated with accelerated bone loss, including multiple myeloma. Gallium nitrate was originally evaluated as an antitumor agent. Its antitumor activity occurs at somewhat higher doses than those used in the treatment of cancer-related hypercalcemia. Gallium nitrate has substantial single-agent activity in the treatment of advanced lymphoma, particularly diffuse large cell lymphoma, small lymphocytic lymphoma, and follicular lymphoma. Because of its profile, including a different mechanism of action and minimal myelosuppression, the drug merits further evaluation in the treatment of advanced lymphoma. Gallium nitrate also has activity in advanced bladder cancer and may be useful in patients with metastatic or unresectable disease failing first-line chemotherapy regimens. Gallium nitrate exhibits a range of dose-dependent pharmacologic actions that provide a basis for its therapeutic potential in a variety of diseases and warrants further investigational evaluation as an antiresorptive and antitumor agent. PMID:12776253

  2. Characterization and reliability of aluminum gallium nitride/gallium nitride high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Douglas, Erica Ann

    Compound semiconductor devices, particularly those based on GaN, have found significant use in military and civilian systems for both microwave and optoelectronic applications. Future uses in ultra-high power radar systems will require the use of GaN transistors operated at very high voltages, currents and temperatures. GaN-based high electron mobility transistors (HEMTs) have proven power handling capability that overshadows all other wide band gap semiconductor devices for high frequency and high-power applications. Little conclusive research has been reported in order to determine the dominating degradation mechanisms of the devices that result in failure under standard operating conditions in the field. Therefore, it is imperative that further reliability testing be carried out to determine the failure mechanisms present in GaN HEMTs in order to improve device performance, and thus further the ability for future technologies to be developed. In order to obtain a better understanding of the true reliability of AlGaN/GaN HEMTs and determine the MTTF under standard operating conditions, it is crucial to investigate the interaction effects between thermal and electrical degradation. This research spans device characterization, device reliability, and device simulation in order to obtain an all-encompassing picture of the device physics. Initially, finite element thermal simulations were performed to investigate the effect of device design on self-heating under high power operation. This was then followed by a study of reliability of HEMTs and other tests structures during high power dc operation. Test structures without Schottky contacts showed high stability as compared to HEMTs, indicating that degradation of the gate is the reason for permanent device degradation. High reverse bias of the gate has been shown to induce the inverse piezoelectric effect, resulting in a sharp increase in gate leakage current due to crack formation. The introduction of elevated temperatures during high reverse gate bias indicated that device failure is due to the breakdown of an unintentional gate oxide. RF stress of AlGaN/GaN HEMTs showed comparable critical voltage breakdown regime as that of similar devices stressed under dc conditions. Though RF device characteristics showed stability up to a drain bias of 20 V, Schottky diode characteristics degraded substantially at all voltages investigated. Results from both dc and RF stress conditions, under several bias regimes, confirm that the primary root for stress induced degradation was due to the Schottky contact. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)

  3. Molecular Beam Epitaxial Growth and Characterization of Mismatched Indium Gallium Arsenide and Indium Aluminum Arsenide Layers on Indium Phosphide

    NASA Astrophysics Data System (ADS)

    Bennett, Brian R.

    Mismatched epitaxial layers of In_ {x}Ga_{1-x}As and In_{y}Al_ {1-y}As were grown on (001) InP by molecular beam epitaxy. The layers were characterized by a technique we developed known as variable azimuthal-angle ellipsometry. It reveals large optical anisotropy for many strained layers. We attribute the anisotropy to strain-induced surface roughening during growth. Samples were also characterized by high -resolution x-ray diffraction (HRXRD) to assess layer quality as well as composition and strain. HRXRD measurements reveal orthorhombic distortion of partially relaxed layers of InGaAs and InAlAs in tension or compression, with preferential strain relief in the (110) direction. We show that HRXRD epilayer peak width and interference fringes are sensitive, non-destructive criteria to judge the structural quality of strained heterostructures. For layers ranging from 300 to 10,000 A, with lattice mismatch of +/- 1% or less, the crystalline quality consistently remains high to thicknesses up to 3-9 times the Matthews -Blakeslee critical layer thickness. We investigated the thermal stability of these layers, using HRXRD to measure structural changes caused by high-temperature anneals. We also compared the electron mobility of modulation-doped heterostructures before and after annealing. Both techniques demonstrate that our high-quality strained layers are stable to temperatures of at least 800-850^circ C. We explain this result by the limited sources available for the nucleation of misfit dislocations. The findings are applied to the design and growth of high-performance pseudomorphic InAlAs/InGaAs/InP heterostructure field-effect transistors with layers exceeding the Matthews-Blakeslee limit. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

  4. Strain compensation technique in indium arsenide/gallium arsenide SAQD structure grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Nuntawong, Noppadon

    This dissertation describes the investigations of the strain-compensation technique for stacked InAs/GaAs self assembled quantum dot (SAQD) structures grown by MOCVD. The effects of the strain-compensated (SC) layers have been investigated using several methods. High-resolution x-ray diffractrometry (XRD) is used to quantify the reduction of overall strain. Atomic force microscopy (AFM) reveals that the SC layer improves QD uniformity and reduces defect density. An increase in photoluminescence (PL) intensity has been observed. The combination of strain compensation and In flushing method, to dissolve large islands and prevent further defect propagation in the stacked QD active region, has been described. Experimental and mathematical treatments of the reduction of strain field in the compensated structure has been conducted. We identify two types of strain in stacked SAQD samples, homogeneous and localized. For homogeneous strain, we use high-resolution x-ray diffraction spectra to quantify the net strain in each sample, which indicate strain reduction of > 36% can be accomplished. For localized strain, which can not be observed by regular XRD techniques, an evaluating method has been proposed. As the localized field propagates, the strain energy diffuses and the maximum of the strain field reduces. Thus, the probability of strain coupling between QD layers is inversely proportional to the spacer thickness. By studying the strain coupling probability as a function of the spacer thickness, a 19% reduction of localized strain within SC structures has been evaluated. Finally, room temperature ground state lasing with an emission wavelength between 1250-1270 nm have been realized. The obtained threshold current density of 108 A/cm2 is the lowest value so far from MOCVD-based QD device emitting near 1.3 mum, which would be promising for application to light source in near-infrared optical communication systems.

  5. Substrate engineering for defect reduction and microstructure control in the growth of indium arsenide on (100) gallium arsenide

    NASA Astrophysics Data System (ADS)

    Ganesan, Suryanarayanan

    The development of devices based on InAs, GaSb, and AlSb, semiconductors that possess narrow band-gaps and 0.61 nm lattice parameters, has been limited by the defects that ensue in epitaxial films that typically are grown on commercial semi-insulating, but 7% lattice-mismatched, GaAs substrates. The studies described in this dissertation investigate the application of a lateral epitaxial overgrowth technique for defect reduction and microstructure control to the InAs/GaAs heteroepitaxial system by exploring the development of microstructure at various stages of island and film growth in conventional and lateral overgrowth epitaxy (that is, on unpatterned and mask-patterned substrates, respectively). For a range of growth conditions, InAs films on unpatterned (100) GaAs substrates exhibit not only the threading dislocations characteristic of largely mismatched epitaxial films, but also systematic tilting within micron-scale InAs domains. Alteration of the pattern and magnitude of the tilt achieved by varying the growth conditions and/or introducing mask-patterned substrates suggest that not only chemical and kinetic, but also physical constraints can direct microstructural evolution during growth. Backscattered electron Kikuchi pattern-based orientation imaging was used to investigate the origin of the improved epitaxial alignment that is realized when InAs films were grown on mask-patterned (100) GaAs substrates. The island size at coalescence was shown to be critical in determining whether a single or two-fold, four-fold or six-fold epitaxial orientation relationship(s) is (are) present in the film. The evolution of tilt with increasing island size is attributed to the particulars of the misfit dislocation network that forms, which appears to evolve in this epitaxial system as the island grows, in accordance with a model proposed by Spencer and Tersoff [1,2]. Sub-micron (˜0.5 mum or less) island sizes at coalescence appear to lead to a single orientation aligned with the GaAs. This work shows that spatial constraints imposed at the early stages of growth, in this case through use of a mask-patterned substrate, can be used to promote coalescence at small island size as an alternative or parallel approach to setting growth conditions (temperature, precursor stoichiometry, etc.) in order to control the defect nucleation and microstructure. References. [1]. B.J. Spencer, and J. Tersoff, Appl. Phys. Lett. 77 (1997) 2533. [2]. B.J. Spencer, and J. Tersoff, Phys. Rev. B63 (2001) 205424.

  6. Synthesis and characterization of some rare earth arsenides. Technical report

    SciTech Connect

    Schurr, J.N.

    1987-09-10

    Solid solutions of a new material, holmium niobium arsenide, were synthesized, and the binary arsenides NdAs and HoAs were prepared. Chemical analyses showed that both were arsenic-deficient. Lattice parameters were determined for NdAs and HoAs. It was established that a range of arsenic solubility exists in the binary arsenides where no change in lattice parameter is observed. High-temperature thermal analyses were conducted on all arsenides. NdAs and HoAs exhibited arenic volatilization upon heating.

  7. Lung gallium scan

    MedlinePlus

    ... inflammation in the lungs, most often due to sarcoidosis or a certain type of pneumonia. Normal Results ... up very little gallium. What Abnormal Results Mean Sarcoidosis Other respiratory infections, most often pneumocystis jirovecii pneumonia ...

  8. Preventing Supercooling Of Gallium

    NASA Technical Reports Server (NTRS)

    Massucco, Arthur A.; Wenghoefer, Hans M.; Wilkins, Ronnie

    1994-01-01

    Principle of heterogeneous nucleation exploited to prevent gallium from supercooling, enabling its use as heat-storage material that crystallizes reproducibly at its freezing or melting temperature of 29 to 30 degrees C. In original intended application, gallium used as heat-storage material in gloves of space suits. Terrestrial application lies in preparation of freezing-temperature reference samples for laboratories. Principle of heterogeneous nucleation also exploited similarly in heat pipes filled with sodium.

  9. Formation of highly n-doped gallium arsenide layers by rapid thermal oxidation followed by rapid thermal annealing of silicon-capped gallium arsenide

    NASA Astrophysics Data System (ADS)

    Sadana, D. K.; de Souza, J. P.; Cardone, F.

    1991-03-01

    Carrier concentrations at a level of ≳1×1019 cm-3 were achieved when Si-capped GaAs underwent rapid thermal oxidation (RTO) in Ar+0.1% O2 ambient at 850-1000 °C for 10-60 s followed by rapid thermal annealing (RTA) in Ar ambient at 850-950 °C. Carrier concentrations in the RTO only samples were in the range of 2-5×1018 cm-3. Kinetic data on the diffusion of Si under RTO and RTO+RTA conditions are presented. The enhancement in the electrical activation of the diffused Si during RTA appears to be partly due to its local atomic rearrangement and partly due to redistribution in the GaAs. Ohmic contacts to the doped layer were made using Au-Ge-Ni alloy and contact resistances of ≲0.1 Ω mm were obtained.

  10. Electrodeposition of gallium for photovoltaics

    DOEpatents

    Bhattacharya, Raghu N.

    2016-08-09

    An electroplating solution and method for producing an electroplating solution containing a gallium salt, an ionic compound and a solvent that results in a gallium thin film that can be deposited on a substrate.

  11. Functionalization of nitrogen-doped carbon nanotubes with gallium to form Ga-CNx-multi-wall carbon nanotube hybrid materials

    NASA Astrophysics Data System (ADS)

    Simmons, Trevor J.; Hashim, Daniel P.; Zhan, Xiaobo; Bravo-Sanchez, Mariela; Hahm, Myung Gwan; López-Luna, Edgar; Linhardt, Robert J.; Ajayan, Pulickel M.; Navarro-Contreras, Hugo; Vidal, Miguel A.

    2012-08-01

    In an effort to combine group III-V semiconductors with carbon nanotubes, a simple solution-based technique for gallium functionalization of nitrogen-doped multi-wall carbon nanotubes has been developed. With an aqueous solution of a gallium salt (GaI3), it was possible to form covalent bonds between the Ga3+ ion and the nitrogen atoms of the doped carbon nanotubes to form a gallium nitride-carbon nanotube hybrid at room temperature. This functionalization was evaluated by x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy

  12. Low Field Transport Properties of a Gallium ARSENIDE/GALLIUM(1-X)ALUMINUM(X)ARSENIC Superlattice

    NASA Astrophysics Data System (ADS)

    Warren, Graham James

    Available from UMI in association with The British Library. Requires signed TDF. This thesis presents some low field mobility, thermopower and Hall factor results for a GaAs/Ga _{1-x}Al_{x}As superlattice. For these calculations, acoustic phonon scattering and polar optic phonon scattering are considered. For the acoustic phonon calculation, the zero magnetic field Boltzmann equation is solved using the relaxation time approximation to give the mobility and thermopower results. The thermopower results show a positive peak which is a direct consequence of the small scale of the structure of the superlattice. The polar optic phonon results are obtained using both the relaxation time approximation, which is not strictly valid in this case, and also by an exact numerical iterative method. This shows the relaxation time mobility results to be less than the exact numerical solution by up to a factor of about two. This is due to the inelasticity of the scattering mechanism and the anisotropic nature of the miniband structure. The Hall factors are calculated using a novel method. Using this method, it is not necessary to solve the non-zero magnetic field Boltzmann equation. Instead, the zero magnetic field Boltzmann equation is solved for two perpendicular orientations of applied electric field, and these zero magnetic field distribution functions are then used to simply calculate the Hall factors. The deviations of the resulting Hall factors from one can give direct information about the form of the miniband structure. Some simple analytical calculations are used to complement the numerical results.

  13. Characterization and Modeling of Indium Gallium Antimonide Avalanche Photodiode and of Indium Gallium Arsenide Two-band Detector

    NASA Technical Reports Server (NTRS)

    2006-01-01

    A model of the optical properties of Al(x)Ga(1-x)As(y)Sb(1-y) and In(x)Ga(1-x)As(y)Sb(1-y) is presented, including the refractive, extinction, absorption and reflection coefficients in terms of the optical dielectric function of the materials. Energy levels and model parameters for each binary compound are interpolated to obtain the needed ternaries and quaternaries for various compositions. Bowing parameters are considered in the interpolation scheme to take into account the deviation of the calculated ternary and quaternary values from experimental data due to lattice disorders. The inclusion of temperature effects is currently being considered.

  14. Group III-nitride thin films grown using MBE and bismuth

    DOEpatents

    Kisielowski, Christian K.; Rubin, Michael

    2000-01-01

    The present invention comprises growing gallium nitride films in the presence of bismuth using MBE at temperatures of about 1000 K or less. The present invention further comprises the gallium nitride films fabricated using the inventive fabrication method. The inventive films may be doped with magnesium or other dopants. The gallium nitride films were grown on sapphire substrates using a hollow anode Constricted Glow Discharge nitrogen plasma source. When bismuth was used as a surfactant, two-dimensional gallium nitride crystal sizes ranging between 10 .mu.m and 20 .mu.m were observed. This is 20 to 40 times larger than crystal sizes observed when GaN films were grown under similar circumstances but without bismuth. It is thought that the observed increase in crystal size is due bismuth inducing an increased surface diffusion coefficient for gallium. The calculated value of 4.7.times.10.sup.-7 cm.sup.2 /sec. reveals a virtual substrate temperature of 1258 K which is 260 degrees higher than the actual one.

  15. Group III-nitride thin films grown using MBE and bismuth

    DOEpatents

    Kisielowski, Christian K.; Rubin, Michael

    2002-01-01

    The present invention comprises growing gallium nitride films in the presence of bismuth using MBE at temperatures of about 1000 K or less. The present invention further comprises the gallium nitride films fabricated using the inventive fabrication method. The inventive films may be doped with magnesium or other dopants. The gallium nitride films were grown on sapphire substrates using a hollow anode Constricted Glow Discharge nitrogen plasma source. When bismuth was used as a surfactant, two-dimensional gallium nitride crystal sizes ranging between 10 .mu.m and 20 .mu.m were observed. This is 20 to 40 times larger than crystal sizes observed when GaN films were grown under similar circumstances but without bismuth. It is thought that the observed increase in crystal size is due bismuth inducing an increased surface diffusion coefficient for gallium. The calculated value of 4.7.times.10.sup.-7 cm.sup.2 /sec. reveals a virtual substrate temperature of 1258 K which is 260 degrees higher than the actual one.

  16. Gallium-containing anticancer compounds.

    PubMed

    Chitambar, Christopher R

    2012-06-01

    There is an ever pressing need to develop new drugs for the treatment of cancer. Gallium nitrate, a group IIIa metal salt, inhibits the proliferation of tumor cells in vitro and in vivo and has shown activity against non-Hodgkin's lymphoma and bladder cancer in clinical trials. Gallium can function as an iron mimetic and perturb iron-dependent proliferation and other iron-related processes in tumor cells. Gallium nitrate lacks crossresistance with conventional chemotherapeutic drugs and is not myelosuppressive; it can be used when other drugs have failed or when the blood count is low. Given the therapeutic potential of gallium, newer generations of gallium compounds are now in various phases of preclinical and clinical development. These compounds hold the promise of greater anti-tumor activity against a broader spectrum of cancers. The development of gallium compounds for cancer treatment and their mechanisms of action will be discussed.

  17. Hafnium nitride buffer layers for growth of GaN on silicon

    DOEpatents

    Armitage, Robert D.; Weber, Eicke R.

    2005-08-16

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  18. Ultrafast scanning tunneling microscopy (STM) using a photoexcited low-temperature-grown gallium arsenide tip

    SciTech Connect

    Donati, G.P.; Some, D.; Rodriguez, G.; Taylor, A.J.

    1998-08-01

    In the quest for atomic spatial and picosecond temporal resolutions, several groups have integrated an STM tip with an ultrafast optoelectronic switch that gates the tunneling current from the tip. The authors report a novel ultrafast STM tip consisting of a cleaved GaAs substrate with a 1-{micro}m thick epilayer of low-temperature-grown GaAs (LT-GaAs) deposited on the face. since LT-GaAs has a carrier lifetime of 1 ps, the photo-excitatin of the tip with an ultrafast above-bandgap pulse provides carriers for the tunneling current and photoconductively gates the current from the tip with picoseconds time resolution. The authors use this tip to detect picosecond voltage transients on a coplanar stripline.

  19. Radiation Effects in ALUMINUM(X)GALLIUM(1-X)ARSENIDE and Indium-Phosphorus

    NASA Astrophysics Data System (ADS)

    Cross, T. A.

    Available from UMI in association with The British Library. Radiation effects in Al_{ rm x}Ga_{rm 1-x}As and InP produced by hydrogen ion bombardment have been studied using mainly electrical resistivity measurements and thermal annealing techniques. Multiple energy ion bombardments at 400 keV to 100 keV were used in most experiments at beam power densities of below 100 mW cm^{-2}. Two terminal, through layer, resistivity measurements were made on Al_{rm x}Ga _{rm 1-x}As:Se with Al mole fraction, x, from 0 (GaAs) to 0.82. In all cases, a maximum resistivity of 1E8 to 1E10 ohm cm was achieved with proton or deuteron bombardment. As x is increased from 0 the resistivity maximum rises gradually from 1E8 to 1E10 ohm cm at x = 0.45 and then gently falls. This behaviour has been explained by considering a single deep level with an activation energy which varies with x in a similar manner to that of the shallow donor levels in Al_{rm x}Ga _{rm 1-x}As. Using an interdigital contact geometry, the first in-situ measurements of the change in Al_ {rm x}Ga_{rm 1-x}As resistivity with ion dose have been made. This has enabled repeated irradiation-measurement cycles, resulting in a rapid determination of the resistivity behaviour and a more accurate measurement of the optimum ion dose for maximum resistivity. The observed anomalously efficient carrier removal of deuterons in GaAs:Si has not been observed in any GaAs:Se or Al_{rm x}Ga _{rm 1-x}As:Se. Proton bombardment is less efficient in GaAs:Si than in GaAs:Se, perhaps due to a parasitic interaction of the protons with the silicon donor species. The thermal stability of the isolation in Al _{rm x}Ga_ {rm 1-x}As:Se, over the whole composition range, appears to be suitable for device applications if post-implant process steps are kept below 400^ circC. Whilst the isolation in InP was observed to be stable to up to 300^circC, some indications of room temperature annealing were noted. The electrical properties of proton and deuteron bombarded material appear to be closely similar. However, preliminary Rutherford Back Scattering (RBS) and optical absorption measurements on Al_{rm x}Ga_{rm 1-x} As samples have indicated differences. RBS has shown the level of disorder introduced by deuteron bombardments to be slightly higher than expected compared with proton bombardments. Optical absorption has shown the optical activity of the deuteron induced damage to be more intense. (Abstract shortened by UMI.).

  20. Deformation of the surface of gallium arsenide during the deposition of gold

    SciTech Connect

    Briantseva, T. A. Lioubtchenko, D. V.; Markov, I. A.; Ten, Yu. A.

    2011-12-15

    Deformation phenomena of near-surface GaAs layers are studied using surface acoustic waves during the deposition of Au and the irradiation of the semiconductor surface by the light of a heated evaporator. It is shown that, in the case of Au deposition, the near-surface layers are plasticized due to the phase transformations in the Au-Ga-As system, while upon irradiation of the GaAs surface with light, a coarse-grained layer with liquid-like interlayers is formed. As a result, the type of surface deformations and their relaxation time change. The integral temporal characteristics of the surface acoustic wave, such as the variation integrals of its rate and dissipated power, reflect the processes occurring on the surface in the real-time mode. In summary, they reflect the current magnitude of the resulting deformation. The parameters of occurring processes such as activation energy and relaxation time are determined.

  1. Characterization of gallium arsenide X-ray mesa p-i-n photodiodes at room temperature

    NASA Astrophysics Data System (ADS)

    Lioliou, G.; Meng, X.; Ng, J. S.; Barnett, A. M.

    2016-03-01

    Two GaAs mesa p+-i-n+ photodiodes intended for photon counting X-ray spectroscopy, having an i layer thickness of 7 μm and diameter of 200 μm, have been characterized electrically, for their responsivity at the wavelength range 580 nm to 980 nm and one of them for its performance at detection of soft X-rays, at room temperature. Dark current and capacitance measurements as a function of applied forward and reverse bias are presented. The results show low leakage current densities, in the range of nA/cm2 at the maximum internal electric field (22 kV/cm). The unintentional doping concentration of the i layer, calculated from capacitance measurements, was found to be <1014 cm-3. Photocurrent measurements were performed under visible and near infrared light illumination for both diodes. The analysis of these measurements suggests the presence of a non-active (dead) layer (0.16 μm thickness) at the p+ side top contact interface, where the photogenerated carriers do not contribute to the photocurrent, possibly due to recombination. One of the diodes, D1, was also characterized as detector for room temperature photon counting X-ray spectroscopy; the best energy resolution achieved (FWHM) at 5.9 keV was 745 eV. The noise analysis of the system, based on spectra obtained at different shaping times and applied reverse biases, showed that the dominant source of noise is the dielectric noise. It was also calculated that there was at least (165±24) eV charge trapping noise at 0 V.

  2. Size-effects in indium gallium arsenide nanowire field-effect transistors

    NASA Astrophysics Data System (ADS)

    Zota, Cezar B.; Lind, E.

    2016-08-01

    We fabricate and analyze InGaAs nanowire MOSFETs with channel widths down to 18 nm. Low-temperature measurements reveal quantized conductance due to subband splitting, a characteristic of 1D systems. We relate these features to device performance at room-temperature. In particular, the threshold voltage versus nanowire width is explained by direct observation of quantization of the first sub-band, i.e., band gap widening. An analytical effective mass quantum well model is able to describe the observed band structure. The results reveal a compromise between reliability, i.e., VT variability, and on-current, through the mean free path, in the choice of the channel material.

  3. Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field.

    PubMed

    Sallen, G; Kunz, S; Amand, T; Bouet, L; Kuroda, T; Mano, T; Paget, D; Krebs, O; Marie, X; Sakoda, K; Urbaszek, B

    2014-01-01

    Optical and electrical control of the nuclear spin system allows enhancing the sensitivity of NMR applications and spin-based information storage and processing. Dynamic nuclear polarization in semiconductors is commonly achieved in the presence of a stabilizing external magnetic field. Here we report efficient optical pumping of nuclear spins at zero magnetic field in strain-free GaAs quantum dots. The strong interaction of a single, optically injected electron spin with the nuclear spins acts as a stabilizing, effective magnetic field (Knight field) on the nuclei. We optically tune the Knight field amplitude and direction. In combination with a small transverse magnetic field, we are able to control the longitudinal and transverse components of the nuclear spin polarization in the absence of lattice strain--that is, in dots with strongly reduced static nuclear quadrupole effects, as reproduced by our model calculations.

  4. Ultrafast pump-probe spectroscopy in gallium arsenide at 25 T.

    PubMed

    Curtis, Jeremy A; Tokumoto, Takahisa; Nolan, Nicholas K; McClintock, Luke M; Cherian, Judy G; McGill, Stephen A; Hilton, David J

    2014-10-01

    We have performed high-fluence, nondegenerate pump-probe spectroscopy in the Split Florida-Helix magnet at 25 T and 15 K. The electronic component of our ultrafast differential reflectivity can be described with a simplified four-level approximation to determine the scattering and recombination rates. Ultrafast oscillations are well described by a coherent acoustic phonon model. Our free-space ultrafast spectroscopic technique will permit future experimental investigations to study novel photoinduced phase transitions and complex interactions in correlated electron systems, which will require the high pulse energies of our free-space alternative.

  5. Antibody molecules discriminate between crystalline facets of a gallium arsenide semiconductor.

    PubMed

    Artzy Schnirman, Arbel; Zahavi, Efrat; Yeger, Hadas; Rosenfeld, Ronit; Benhar, Itai; Reiter, Yoram; Sivan, Uri

    2006-09-01

    Seamless integration of biomolecules with manmade materials will most likely rely on molecular recognition and specific binding. In the following we show that combinatorial antibody libraries, based on the vast repertoire of the human immune system, can be harnessed to generate such binders. As a demonstration, we isolate antibody fragments that discriminate and bind selectively GaAs (111A) facets as opposed to GaAs (100). The isolated antibodies are utilized for exclusive localization of a fluorescent dye on (111A) surfaces in a structure comprising a mixture of (100) and (111A) surfaces. The potential importance of structure rigidity to facet recognition is suggested vis-a-vis published experiments with short and longer peptides.

  6. Gallium arsenide surface chemistry and surface damage in a chlorine high density plasma etch process

    NASA Astrophysics Data System (ADS)

    Eddy, C. R., Jr.; Glembocki, O. J.; Leonhardt, D.; Shamamian, V. A.; Holm, R. T.; Thoms, B. D.; Butler, J. E.; Pang, S. W.

    1997-11-01

    In an effort to monitor ion-driven surface chemistry in the high density plasma etching of GaAs by Cl2/Ar plasma chemistries, we have applied mass spectrometry and careful substrate temperature control. Etch product chlorides were mass analyzed while the substrate temperature was monitored by optical bandgap thermometry and as pressure (neutral flux), microwave power (ion flux) and rf bias of the substrate (ion energy) were varied. By ensuring that the substrate temperature does not deviate during process variations, the changes in product mass peak intensities are a direct measure of changes in the ionassisted surface chemistry which promotes anisotropic etching. Experimental results show that ion-assisted surface chemistry is optimum when sufficient Cl and Cl+ are present in the incident plasma flux. These conditions are met at low coupled microwave powers (<300 W) and low total process pressures (<1.0 mTorr) for input gas mixtures of 25% Cl2 in Ar. Three mechanistic regions are identified for surface chemistry as a function of incident ion energy: 1) largely thermal chemistry for <50 eV; 2) ion-assisted chemistry for 50 200 eV; and 3) sputtering for >200 eV. Photoreflectance measurements of the surface Fermi level show significant damage for ion energies >75 eV. However, in situ and ex situ surface passivations can recover the surface Fermi level for up to 200 eV ion energies, in good correlation to the onset of sputtering and subsurface damage. Thus, anisotropic, low damage pattern transfer is possible for ion energies between 50 and 200 eV.

  7. The Photoresponse of the Gallium Arsenide Metal Semiconductor Field Effect Transistor

    NASA Astrophysics Data System (ADS)

    Paolella, Arthur

    The combining of optical and microwave technology is imminent, especially the integration of optical and microwave circuit functions on the same circuit or chip. Exploring the properties of the metal semiconductor field effect transistor (MESFET) as an optical detector for the detection of microwave and control signals in fiber optic links make sense because the MESFET is the main active component of GaAs MMICs. In this thesis, photocurrents and photovoltages of three MESFETs were measured as a function of the optical input (wavelength, intensity and modulation frequency), electrical input (gate voltage and gate resistance), and device characteristics. A model of the photoresponse, based on the drift and diffusion equations for the current density was developed, which established the internal photovoltaic effect at the channel-substrate interface as the dominant mechanism for the generation of photocurrent in the MESFET. The gain, bandwidth and gain-bandwidth products for each of the major photoeffects were determined mathematically. A maximum photocurrent of 16 mA, and an internal photovoltage of -0.5 volts was measured at 3.5 mW of optical power. The addition of a resistance in the gate circuit enhanced the photoresponse. With a resistor of 1 MOmega, the maximum photocurrent produced was 84.0 mA, resulting from an external photovoltage of 3.07 volts. The dynamic photoresponse of the MESFET as measured, showed a strong dependence with the intensity of the optical signal as well as with bias. The low frequency response varied from -15 dB to -41 dB, and the bandwidth changed from 50 MHz to 5 MHz as the optical signal decreased 18 dB. The low frequency response and bandwidth also showed strong dependence of bias. The low frequency response varied over a 7 dB range and the bandwidth changed from 45 MHz to 100 MHz as the gate was reversed biased (0 to -3.0 volts). Used as an optical detector, the MESFET function successfully in controlling the gain (15 dB) and phase (360^circ) of a T/R module as well as in switching functions of microwave MMICs. The techniques used were compatible with present MMIC processing technology.

  8. Thermodynamics and kinetics of phase formation of thin-film metal on gallium arsenide

    SciTech Connect

    Chang, Y.A.

    1988-01-01

    Objectives are to study the thermodynamics and kinetics of reactions between selected metals and GaAs in the bulk and thin-film forms. Even though micro-electronics devices are made of thin-films, their reactions cannot be rationalized without an understanding of the bulk phenomena. In fact, it is our belief that if we understand the thermodynamics and kinetics of the bulk reactions, we can forecast what may happen in thin-films, with perhaps the exception of epitaxial formations. In order to understand the bulk reactions between metals and GaAs, we need to know (1) the ternary phase diagram of Ga-As-M, (2) the diffusion path of GaAs/M in the bulk form and (3) reaction sequence between GaAs and M. Results obtained for items (2) and (3) in the bulk form are correlated with the results obtained for thin films. This paper summarizes the results obtained for several GaAs/M systems.

  9. A new multihit digital TDC implemented in a gallium arsenide ASIC

    SciTech Connect

    Hazen, E.; Dye, S.T.; Gergin, E.; Jenko, M.; Lozic, T.; Mavretic, A.; Orlov, D.; Varner, G. ); Jaworski, M. )

    1994-08-01

    A deep-ocean laboratory for the study of neutrino astrophysics and particle physics is under construction. Phase 1 of the Deep Underwater Muon and Neutrino Detection (DUMAND) experiment is scheduled for initial deployment during the fall of 1993. The experiment detects Cerenkov radiation from high energy muons, and hadronic and electromagnetic cascades, using a volume array of photomultiplier tubes (PMTs) buoyed off the ocean bottom. Event energies and muon trajectories are reconstructed using timing and pulse-height information from the PMTs. To achieve angular resolution of one degree, timing accuracy of one nanosecond is required. A monolithic multi-hit digital TDC (time-to-digital converter) has been developed for the DUMAND 2 experiment. This TDC has a 27 channel pipelined architecture, with a 1ns least count. An overview of the performance requirements and implementation in a GaAs gate array is described here.

  10. Gallium Arsenide detectors for X-ray and electron (beta particle) spectroscopy

    NASA Astrophysics Data System (ADS)

    Lioliou, G.; Barnett, A. M.

    2016-11-01

    Results characterizing GaAs p+-i-n+ mesa photodiodes with a 10 μm i layer for their spectral response under illumination of X-rays and beta particles are presented. A total of 22 devices, having diameters of 200 μm and 400 μm, were electrically characterized at room temperature. All devices showed comparable characteristics with a measured leakage current ranging from 4 nA/cm2 to 67 nA/cm2 at an internal electric field of 50 kV/cm. Their unintentionally doped i layers were found to be almost fully depleted at 0 V due to their low doping density. 55Fe X-ray spectra were obtained using one 200 μm diameter device and one 400 μm diameter device. The best energy resolution (FWHM at 5.9 keV) achieved was 625 eV using the 200 μm and 740 eV using the 400 μm diameter device, respectively. Noise analysis showed that the limiting factor for the energy resolution of the system was the dielectric noise; if this noise was eliminated by better design of the front end of the readout electronics, the achievable resolution would be 250 eV. 63Ni beta particle spectra obtained using the 200 μm diameter device showed the potential utility of these detectors for electron and beta particle detection. The development of semiconductor electron spectrometers is important particularly for space plasma physics; such devices may find use in future space missions to study the plasma environment of Jupiter and Europa and the predicted electron impact excitation of water vapor plumes from Europa hypothesized as a result of recent Hubble Space Telescope (HST) UV observations.

  11. Electron microscopy of an aluminum layer grown on the vicinal surface of a gallium arsenide substrate

    SciTech Connect

    Lovygin, M. V. Borgardt, N. I.; Kazakov, I. P.; Seibt, M.

    2015-03-15

    A thin Al layer grown by molecular-beam epitaxy on a misoriented GaAs (100) substrate is studied by transmission electron microscopy. Electron diffraction data and bright-field, dark-field, and high-resolution images show that, in the layer, there are Al grains of three types of crystallographic orientation: Al (100), Al (110), and Al (110)R. The specific structural features of the interfaces between the differently oriented grains and substrate are studied by digital processing of the high-resolution images. From quantitative analysis of the dark-field images, the relative content and sizes of the differently oriented grains are determined. It is found that atomic steps at the substrate surface cause an increase in the fraction and sizes of Al (110)R grains and a decrease in the fraction of Al (100) grains, compared to the corresponding fractions and sizes in the layer grown on a singular substrate surface.

  12. Gallium arsenide single crystal solar cell structure and method of making

    NASA Technical Reports Server (NTRS)

    Stirn, Richard J. (Inventor)

    1983-01-01

    A production method and structure for a thin-film GaAs crystal for a solar cell on a single-crystal silicon substrate (10) comprising the steps of growing a single-crystal interlayer (12) of material having a closer match in lattice and thermal expansion with single-crystal GaAs than the single-crystal silicon of the substrate, and epitaxially growing a single-crystal film (14) on the interlayer. The material of the interlayer may be germanium or graded germanium-silicon alloy, with low germanium content at the silicon substrate interface, and high germanium content at the upper surface. The surface of the interface layer (12) is annealed for recrystallization by a pulsed beam of energy (laser or electron) prior to growing the interlayer. The solar cell structure may be grown as a single-crystal n.sup.+ /p shallow homojunction film or as a p/n or n/p junction film. A Ga(Al)AS heteroface film may be grown over the GaAs film.

  13. Photoemission study of the adsorption of nitric oxide on gallium arsenide (110) at low temperature

    SciTech Connect

    Bermudez, V.M. ); Williams, R.T. Physics Department, Wake Forest University, Winston-Salem, NC ); Williams, G.P. Jr.; Rowe, M.W.; Liu, H.; Wu, A. ); Sadeghi, H.R.; Rife, J.C. )

    1990-05-01

    Photoelectron spectroscopy with synchrotron radiation has been used to study changes in the region of the valence band and Ga and As 3{ital d} core levels of GaAs (110) resulting from exposure to nitric oxide (NO) at substrate temperatures of 40--140 K. Up to about 60 K, NO physisorbs. Thermal and photochemical effects have been observed during annealing of the adsorbed layer or irradiation by the monochromatized synchrotron radiation beam. At about 70 K, a distinct molecular species forms along with adsorbed O. This species, which desorbs and/or dissociates above about 90 K, is identified as nitrous oxide (N{sub 2}O ) on the basis of comparison with similar data for N{sub 2}O condensed on GaAs. Pre-adsorbed O inhibits N{sub 2}O formation, suggesting that the GaAs surface participates actively in the process. Above about 100 K, only O adsorption is observed, occurring by a mechanism different from that leading to O adsorption at lower temperature.

  14. X-ray studies of III-V native oxide/gallium arsenide interface

    NASA Astrophysics Data System (ADS)

    Cheong, Seong-Kyun

    Three x-ray techniques have been employed to study wet-thermal native oxides of AlGaAs on GaAs. For these materials, a knowledge of the role of As at the interface is important for understanding Fermi-level pinning and is a central issue in efforts to develop high performance III-V MOSFET devices. This study is focused on how the As is incorporated at the interface, the interfacial strain, and related local structural parameters. X-ray absorption fine-structure spectroscopy (XAFS) was used to determine the site of residual As in wet-oxidized Al0.96Ga0.04As. In a ˜0.5 mum oxide film removed from its GaAs substrate, the remaining As atoms were found to be coordinated with oxygen in the form of amorphous As oxides, with a mixture of ˜80% As3+ and ˜20% As 5+ sites. These two sites are locally similar to As2O 3 and As2O5. Through this measurement, no evidence of interstitial or substitutional As, As precipitates, or GaAs was seen, implying that less than 10% of the As atoms are in these forms. To characterize the oxide structure in both the oxide film and the interfacial region, x-ray reflectivity and reflection-mode XAFS experiments were performed for a thin (300 A) oxidized AlxGa1-xAs (x = 0.96) film grown on GaAs. X-ray reflectivity studies showed that the composition of the surface oxidized film is not homogeneous as a function of depth. Reflection-mode XAFS, which uses the total external reflection of x-rays to confine an x-ray beam to the interfacial region, provided details of the local environment of As atoms at the interface of the oxide/GaAs. Analysis through this technique revealed that As atoms are in the form of mixed As oxides, with the local environment appearing to resemble As2O3 and As 2O5 in the interfacial region, which is consistent with the above observation from the isolated oxide film.

  15. Properties of aluminum gallium arsenide native oxides for integrated photonics and optoelectronics applications

    NASA Astrophysics Data System (ADS)

    Luo, Yong

    2001-12-01

    The properties of AlGaAs native oxides have been investigated and single heterostructure (SH) and double heterostructure (DH) native oxide planar waveguides have been realized. Prism coupling, secondary ion mass spectrometry (SIMS), Fourier transform infrared (FTIR) transmission spectroscopy and other techniques are used to characterize the oxide waveguides. Propagation losses are measured for SH native oxide waveguides. The presence of hydroxyl (OH) groups in AlGaAs native oxides is shown to slightly increase the waveguide loss at λ = 1.55 μm. The wet thermal oxidation process has been extensively investigated for AlxGa1-xAs over a wide range of Al compositions (0.3 < x < 0.9). An improvement in the process for oxidation of low Al composition AlxGa1-xAs (x < 0.8) has been achieved by controllably adding trace quantities of O2 to the N 2 + H2O process gas. The complicated effects of O2 + N2 ``mixed carrier gas'' on oxidation rates and the surface quality of oxides have been investigated and applied to reduce the propagation loss of a SH waveguide. The role of added O2 has been analyzed in relation to the possible chemical reactions involved. The effects of mixed carrier gas on the lateral oxidation of Al0.98Ga 0.02As is also explored but shown to be negligible. Two modified AlGaAs SHs designed for reduced planar oxide waveguide propagation loss have also been processed and characterized, with losses as low as 4 dB/cm at λ = 1.55 μm achieved. Finally, in other experimental results it is shown that ``deep-oxidation'' (i.e., through a quantum well heterostructure (QWH) containing a low Al composition waveguide and GaAs quantum well) can be attained by using controllably-mixed O2 + N2 carrier gas, which effectively modifies the oxidation rate selectivity between high and low x AlxGa1-xAs. This achievement eliminates the need for the additional impurity induced layer disordering (IILD) process step used in prior deep- oxidation technology to intermix high and low x AlxGa1-xAs in preparation for oxidation. Deep-oxidation enables the realization of strongly-confined, curved optical waveguides required for routing signals around an optical ``chip.'' This discovery greatly simplifies the process to a more manufacturable and, thus, commercially viable level, and may stimulate further advances in optoelectronics devices and photonic integrated circuits.

  16. Ion implantation of silicon in gallium arsenide: Damage and annealing characterizations

    NASA Astrophysics Data System (ADS)

    Pribat, D.; Dieumegard, D.; Croset, M.; Cohen, C.; Nipoti, R.; Siejka, J.; Bentini, G. G.; Correra, L.; Servidori, M.

    1983-05-01

    The purpose of this work is twofold: (i) to study the damage induced by ion implantation, with special attention to low implanted doses; (ii) to study the efficiency of annealing techniques — particularly incoherent light annealing — in order to relate the electrical activity of implanted atoms to damage annealing. We have used three methods to study the damage induced by ion implantation: (1) RBS (or nuclear reactions) in random or in channeling geometry (2) RX double crystal diffractometry and (3) electrical measurements (free carrier profiling). Damage induced by silicon implantation at doses >10 14at/cm 2 can be monitored by all three techniques. However, the sensitivity of RBS is poor and hence this technique is not useful for low implantation doses. As device technology requires dopant levels in the range of 5 × 10 12 atoms/cm 2, we are particularly interested to the development of analytical techniques able to detect the damage at this implantation level. The sensitivity of such techniques was checked by studying homogeneously doped (5 × 10 16 e -/cm 3) and semi-insulating GaAs samples implanted with 3 × 10 12 silicon atoms/cm 2 at 150 keV. The substrate temperature during implantation was 200°C. The damage produced in these samples and its subsequent annealing are evidenced by strong changes in X-ray double crystal diffraction spectra. This method hence appears as a good monitoring technique. Annealing of the implanted layers has been performed using incoherent light sources (xenon lamps) either in flash or continuous conditions. Reference samples have also been thermally annealed (850°C, 20 min in capless conditions). The results are compared, and the electrical carrier profiles obtained after continuous incoherent light irradiation indicate that the implanted silicon atoms are almost dully activated. The advantages and disadvantages of incoherent light irradiation are discussed (surface oxidation, surface damage) in comparison with standard thermal treatment.

  17. N + doping of gallium arsenide by rapid thermal oxidation of a silicon cap

    NASA Astrophysics Data System (ADS)

    Sadana, D. K.; de Souza, J. P.; Cardone, F.

    1990-10-01

    Shallow (<200 nm) Si profiles with doping levels in excess of 2×1018 cm-3 were reproducively obtained in GaAs by rapid thermal oxidation (RTO) of Si caps (50 or 160 nm) in 0.1% O2/Ar ambient at 850-1050 °C. The doping level as well as distribution of the diffused Si can be controlled by the thickness of the Si cap, RTO temperature, RTO time, and oxygen level in the annealing ambient. It appears that the generation of Si interstitials at the oxidizing surface of the Si cap during RTO is responsible for the Si diffusion into the underlying GaAs substrate.

  18. System architecture of a gallium arsenide one-gigahertz digital IC tester

    NASA Technical Reports Server (NTRS)

    Fouts, Douglas J.; Johnson, John M.; Butner, Steven E.; Long, Stephen I.

    1987-01-01

    The design for a 1-GHz digital integrated circuit tester for the evaluation of custom GaAs chips and subsystems is discussed. Technology-related problems affecting the design of a GaAs computer are discussed, with emphasis on the problems introduced by long printed-circuit-board interconnect. High-speed interface modules provide a link between the low-speed microprocessor and the chip under test. Memory-multiplexer and memory-shift register architectures for the storage of test vectors are described in addition to an architecture for local data storage consisting of a long chain of GaAs shift registers. The tester is constructed around a VME system card cage and backplane, and very little high-speed interconnect exists between boards. The tester has a three part self-test consisting of a CPU board confidence test, a main memory confidence test, and a high-speed interface module functional test.

  19. A 25.5 percent AMO gallium arsenide grating solar cell

    NASA Technical Reports Server (NTRS)

    Weizer, V. G.; Godlewski, M. P.

    1985-01-01

    Recent calculations have shown that significant open circuit voltage gains are possible with a dot grating junction geometry. The feasibility of applying the dot geometry to the GaAs cell was investigated. This geometry is shown to result in voltages approach 1.120 V and efficiencies well over 25 percent (AMO) if good collection efficiency can be maintained. The latter is shown to be possible if one chooses the proper base resistivity and cell thickness. The above advances in efficiency are shown to be possible in the P-base cell with only minor improvements in existing technology.

  20. Radiation and temperature effects in gallium arsenide, indium phosphide, and silicon solar cells

    NASA Technical Reports Server (NTRS)

    Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.; Statler, R. L.

    1987-01-01

    The effects of radiation on performance are determined for both n+p and p+n GaAs and InP cells and for silicon n+p cells. It is found that the radiation resistance of InP is greater than that of both GaAs and Si under 1-MeV electron irradiation. For silicon, the observed decreased radiation resistance with decreased resistivity is attributed to the presence of a radiation-induced boron-oxygen defect. Comparison of radiation damage in both p+n and n+p GaAs cells yields a decreased radiation resistance for the n+p cell attributable to increased series resistance, decreased shunt resistance, and relatively greater losses in the cell's p-region. For InP, the n+p configuration is found to have greater radiation resistance than the p+n cell. The increased loss in this latter cell is attributed to losses in the cell's emitter region. Temperature dependency results are interpreted using a theoretical relation for dVoc/dT, which predicts that increased Voc should result in decreased numerical values for dPm/dT. The predicted correlation is observed for GaAs but not for InP, a result which is attributed to variations in cell processing.

  1. Heat treatment of bulk gallium arsenide using a phosphosilicate glass cap

    NASA Technical Reports Server (NTRS)

    Mathur, G.; Wheaton, M. L.; Borrego, J. M.; Ghandhi, S. K.

    1985-01-01

    n-type bulk GaAs crystals, capped with chemically vapor-deposited phosphosilicate glass, were heat treated at temperatures in the range of 600 to 950 C. Measurements on Schottky diodes and solar cells fabricated on the heat-treated material, after removal of a damaged surface layer, show an increase in free-carrier concentration, in minority-carrier-diffusion length, and in solar-cell short-circuit current. The observed changes are attributed to a removal of lifetime-reducing acceptorlike impurities, defects, or their complexes.

  2. Automated assembly of Gallium Arsenide and 50-micron thick silicon solar cell modules

    NASA Technical Reports Server (NTRS)

    Mesch, H. G.

    1984-01-01

    The TRW automated solar array assembly equipment was used for the module assembly of 300 GaAs solar cells and 300 50 micron thick silicon solar cells (2 x 4 cm in size). These cells were interconnected with silver plated Invar tabs by means of welding. The GaAs cells were bonded to Kapton graphite aluminum honeycomb graphite substrates and the thin silicon cells were bonded to 0.002 inch thick single layer Kapton substrates. The GaAs solar cell module assembly resulted in a yield of 86% and the thin cell assembly produced a yield of 46% due to intermittent sticking of weld electrodes during the front cell contact welding operation. (Previously assembled thin cell solar modules produced an overall assembly yield of greater than 80%).

  3. Radiation and temperature effects in gallium arsenide, indium phosphide and silicon solar cells

    NASA Technical Reports Server (NTRS)

    Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.; Statler, R. L.

    1987-01-01

    The effects of radiation on performance are determined for both n(+)p and p(+)n GaAs and InP cells and for silicon n(+)p cells. It is found that the radiation resistance of InP is greater than that of both GaAs and Si under 1 MeV electron irradiation. For silicon, the observed decreased radiation resistance with decreased resistivity is attributed to the presence of a radiation induced boron-oxygen defect. Comparison of radiation damage in both p(+)n and n(+)p GaAs cells yields a decreased radiation resistance for the n(+)p cell attributable to increased series resistance, decreased shunt resistance, and relatively greater losses in the cell's p-region. For InP, the n(+)p configuration is found to have greater radiation resistance than the p(+)n cell. The increased loss in this latter cell is attributed to losses in the cell's emitter region. Temperature dependency results are interpreted using a theoretical relation for dVoc/cT which predicts that increased Voc should results in decreased numerical values for dPm/dT. The predicted correlation is observed for GaAs but not for InP a result which is attributed to variations in cell processing.

  4. A 25.5 percent AM0 gallium arsenide grating solar cell

    NASA Technical Reports Server (NTRS)

    Weizer, V. G.; Godlewski, M. P.

    1985-01-01

    Recent calculations have shown that significant open circuit voltage gains are possible with a dot grating junction geometry. The feasibility of applying the dot geometry to the GaAs cell was investigated. This geometry is shown to result in voltage approach 1.120 V and efficiencies well over 25 percent (AM0) if good collection efficiency can be maintained. The latter is shown to be possible if one chooses the proper base resistivity and cell thickness. The above advances in efficiency are shown to be possible in the P-base cell with only minor improvements in existing technology.

  5. Depletion layer recombination effects on the radiation damage hardness of gallium arsenide cells

    NASA Technical Reports Server (NTRS)

    Garlick, G. F. J.

    1985-01-01

    The significant effect of junction depletion layer recombination on the efficiency of windowed GaAs cells was demonstrated. The effect becomes more pronounced as radiation damage occurs. The depletion is considered for 1 MeV electron fluences up to 10 to the 16th power e/sq m. The cell modeling separates damage in emitter and base or buffer layers using different damage coefficients is reported. The lower coefficient for the emitter predicts less loss of performance at fluences greater than 10 to the 15th power e/sq cm. A method for obtaining information on junction recombination effects as damage proceeds is described; this enables a more complete diagnosis of damage to be made.

  6. Growth and characterization of epitaxial aluminum layers on gallium-arsenide substrates for superconducting quantum bits

    NASA Astrophysics Data System (ADS)

    Tournet, J.; Gosselink, D.; Miao, G.-X.; Jaikissoon, M.; Langenberg, D.; McConkey, T. G.; Mariantoni, M.; Wasilewski, Z. R.

    2016-06-01

    The quest for a universal quantum computer has renewed interest in the growth of superconducting materials on semiconductor substrates. High-quality superconducting thin films will make it possible to improve the coherence time of superconducting quantum bits (qubits), i.e., to extend the time a qubit can store the amplitude and phase of a quantum state. The electrical losses in superconducting qubits highly depend on the quality of the metal layers the qubits are made from. Here, we report on the epitaxy of single-crystal Al (011) layers on GaAs (001) substrates. Layers with 110 nm thickness were deposited by means of molecular beam epitaxy at low temperature and monitored by in situ reflection high-energy electron diffraction performed simultaneously at four azimuths. The single-crystal nature of the layers was confirmed by ex situ high-resolution x-ray diffraction. Differential interference contrast and atomic force microscopy analysis of the sample’s surface revealed a featureless surface with root mean square roughness of 0.55 nm. A detailed in situ study allowed us to gain insight into the nucleation mechanisms of Al layers on GaAs, highlighting the importance of GaAs surface reconstruction in determining the final Al layer crystallographic orientation and quality. A highly uniform and stable GaAs (001)-(2× 4) reconstruction reproducibly led to a pure Al (011) phase, while an arsenic-rich GaAs (001)-(4× 4) reconstruction yielded polycrystalline films with an Al (111) dominant orientation. The near-atomic smoothness and single-crystal character of Al films on GaAs, in combination with the ability to trench GaAs substrates, could set a new standard for the fabrication of superconducting qubits.

  7. Exciton Relaxation and Minority-Carrier Transport in Gallium Arsenide/aluminum

    NASA Astrophysics Data System (ADS)

    Zhang, Hong

    The ultrafast relaxation of the excitons in GaAs/AlGaAs multiple quantum well (MQW) structures and the tunneling of minority-carrier in n-doped triple-barrier GaAs/AlAs resonant tunneling structures (RTS) have been investigated by laser spectroscopy. Picosecond photoinduced reflectance (PR), time-integrated and time-resolved photoluminescence (PL) (by single-photon-correlation and excitation-correlation techniques) and photoconductance (PhC) measurements have been applied in these studies. Three different excitation-probing configurations have been employed in time-resolved PR experiments. In medium excitation power conditions, the spectra can be fitted with a sum of two single exponential forms. The long-short components are related to exciton recombination decay and more complex processes with exciton-exciton or carrier-exciton interactions, respectively. From excitation correlation experiments, the recombination lifetimes of excitons in both thick- and thin-barrier MQWs have been obtained and are consistent with the results of the time -resolved PR. The carrier tunneling processes in the RTS have been studied by time-resolved PL and PhC. The minority -carrier sequential tunneling was found to take a key role in the time-dependence of the PL Intensities. A model based on the minority-carrier tunneling was able to explain the time-resolved PL, and from this the hole tunneling time and the total decay time of excitons in the wells have been obtained. In the PhC experiment the tunneling information of the majority-carrier electrons has been acquired. The reasons for the absence of hole resonant tunneling have been discussed.

  8. Architecture and design of a 500-MHz gallium-arsenide processing element for a parallel supercomputer

    NASA Technical Reports Server (NTRS)

    Fouts, Douglas J.; Butner, Steven E.

    1991-01-01

    The design of the processing element of GASP, a GaAs supercomputer with a 500-MHz instruction issue rate and 1-GHz subsystem clocks, is presented. The novel, functionally modular, block data flow architecture of GASP is described. The architecture and design of a GASP processing element is then presented. The processing element (PE) is implemented in a hybrid semiconductor module with 152 custom GaAs ICs of eight different types. The effects of the implementation technology on both the system-level architecture and the PE design are discussed. SPICE simulations indicate that parts of the PE are capable of being clocked at 1 GHz, while the rest of the PE uses a 500-MHz clock. The architecture utilizes data flow techniques at a program block level, which allows efficient execution of parallel programs while maintaining reasonably good performance on sequential programs. A simulation study of the architecture indicates that an instruction execution rate of over 30,000 MIPS can be attained with 65 PEs.

  9. Optical properties of erbium-doped aluminum-gallium-arsenide native oxides

    NASA Astrophysics Data System (ADS)

    Kou, Leigang

    In this study, native oxides of Al-bearing III-V compound semiconductors are explored as a host material for erbium ions with potential for integration in the AlGaAs alloy system. Using room temperature photoluminescence and lifetime measurements, the AlGaAs native oxide has been shown to be a much better host for Er 3+ than the unoxidized semiconductors themselves. Furthermore, various luminescence quench ing mechanisms, including arsenic quenching, hydroxyl (OH) group quenching and concentration quenching, are investigated in order to optimize the process. Ampoule annealing with arsenic overpressure has been used to show the effect of arsenic quenching. Fourier transform infrared (FTIR) transform spectra of oxide films thermally oxidized in water (H2O) vapor reveal the existence of OH groups, which act as luminescence quenching centers. However, such OH groups may not be intrinsic to the wet oxidation process, but appear instead to come primarily from the adsorption of moisture from the atmosphere due to the porous nature of the native oxide and strong affinity of OH radical to the oxide. This is supported by the fact that FTIR spectra of oxide films oxidized in deuterated water (D2O) show the presence of OH groups instead of OD groups. In order to fabricate an Er-doped planar waveguide amplifier, a high Er concentration is essential. However, the photoluminescence intensity of Er3+ does not increase linearly as the Er concentration increases because the shorter distance among Er 3+ ions introduces strong ion-ion interactions which reduce the excited Er3+ ion population through non-radiative transitions. High-temperature annealing has been employed as an effective post-processing step to activate Er3+ ions and remove OH groups. The annealing process parameters (temperature, time and gas ambient) have been optimized. The optimal annealing temperature, however, is reduced by arsenic quenching mechanism particular to AlGaAs oxide/semiconductor system. The oxidation process has also been optimized through the addition of a small amount of O2 to the process gas, which results in a more O-rich local environment around the Er3+ ions, effectively coordinating more optically-active Er3+ and preventing Er cluster formation.

  10. Planar Gallium arsenide nanowire arrays for nanoelectronics: Controlled growth, doping, characterization, and devices

    NASA Astrophysics Data System (ADS)

    Dowdy, Ryan Stewart

    The Vapor-Liquid-Solid (VLS) mechanism is a bottom-up approach to produce onedimensional semiconductor structures, or nanowires. VLS nanowires are formed via a chemical or physical deposition process, where a metallic nanoparticle (seed) facilitates the growth. Nanowire growth diameter is strongly correlated to seed size, therefore top-down patterning can control site location and diameter of nanowire growth. Nanowires are sought after for their potential use as a manageable way produce small dimensioned semiconductor features without the need of expensive lithographic techniques. VLS nanowires commonly grow out-of-plane with respect to their growth substrate, resulting in difficulty with integrating VLS nanowires into existing device processing which is intended for planar geometries. Nanowires are typically removed from the substrate, which requires painstaking and uneconomical methods to pattern and align the nanowires. Planar nanowires are a potential solution to this issue; they grow in-plane on the substrate surface, epitaxially attached along its entire axis. Planar nanowires, as is, can be integrated into any preexisting planar semiconductor process, combining the advantages of nanowires with increased manufacturability. In this dissertation, planar GaAs nanowires are grown using metal organic chemical vapor deposition (MOCVD) with Au nanoparticles as the liquid metal seed. Growth occurs across multiple substrates to elucidate the mechanism behind planar nanowire growth direction. Knowledge gained by observing planar nanowire growth is used to precisely control nanowire growth direction. Subsequently the doping of planar nanowires is explored and unique phenomena related to the p-type doping of planar nanowires are investigated and discussed. The advantages of using planar nanowires are demonstrated through the controlled growth and doping of planar nanowires, and ultimately fabrication of electronic devices using conventional planar process techniques without the need for vertical nanowire processes or nanowire transferring. Devices are characterized and results are presented with discussion. The next steps for the future of planar nanowires are presented with initial results highlighting future applications and issues that must be solved. Chapter 1 is an introduction to the history of Vapor-Liquid-Solid nanowires, and as well as a brief overview of the accomplishments of the field and highlighting unsolved issues. Chapter 2 introduces the planar nanowire and discusses the motivation behind researching planar nanowires as a potential solution to the fundamental problems with vertical VLS nanowires. Chapter 3 gives a short background into VLS nanowire growth and properties, introduction to MOCVD growth and reactor design, and material properties of GaAs, the semiconductor material of interest in this dissertation. Chapter 4 presents the experimental details of planar GaAs nanowire growth on various substrates and the concept of projection theory to determined planar nanowire growth direction, as well as intrinsic growth phenomena. Chapter 5 delves into the doping of planar nanowires, both n-type and p-type. The morphological changes and perturbations to planar nanowire that are caused by p-type dopants are discussed. Chapter 6 demonstrates electrical devices such as MESFETS, inverting amplifiers and p-n diodes fabricated using planar GaAs nanowires as the active structure. Devices performance and metrics are discussed in this chapter. Chapter 7 outlines several future directions for planar nanowires and presents initial results in a variety of areas such as potential devices, modeling opportunities and fundamental issues that need to be solved.

  11. Morphology- and orientation-controlled gallium arsenide nanowires on silicon substrates.

    PubMed

    Ihn, Soo-Ghang; Song, Jong-In; Kim, Tae-Wook; Leem, Dong-Seok; Lee, Takhee; Lee, Sang-Geul; Koh, Eui Kwan; Song, Kyung

    2007-01-01

    GaAs nanowires were epitaxially grown on Si(001) and Si(111) substrates by using Au-catalyzed vapor-liquid-solid (VLS) growth in a solid source molecular beam epitaxy system. Scanning electron microscopy analysis revealed that almost all the GaAs nanowires were grown along <111> directions on both Si substrates for growth conditions investigated. The GaAs nanowires had a very uniform diameter along the growth direction. X-ray diffraction data and transmission electron microscopy analysis revealed that the GaAs<111> nanowires had a mixed crystal structure of the hexagonal wurtzite and the cubic zinc-blende. Current-voltage characteristics of junctions formed by the epitaxially grown GaAs nanowires and the Si substrate were investigated by using a current-sensing atomic force microscopy.

  12. A simple soft lithographic nanopatterning of gold on gallium arsenide via galvanic displacement.

    PubMed

    Lim, Hyuneui; Noh, Jung-Hyun; Choi, Dae-Geun; Kim, Wan-Doo; Maboudian, Roya

    2010-08-01

    Nanoscale patterning of gold layers on GaAs substrate is demonstrated using a combination of soft lithographic molding and galvanic displacement deposition. First, an electroless deposition method has been developed to plate gold on GaAs with ease and cost-effectiveness. The electroless metallization process is performed by dipping the GaAs substrates into a gold salt solution without any reducing agents or additives. The deposition proceeds via galvanic displacement in which gold ions in the aqueous solution are reduced by electrons arising from the GaAs substrate itself. The deposition rate, surface morphology and adhesion property can be modulated by the plating parameters such as the choice of acids and the immersion time. Second, soft lithographic patterning of nanodots, nanorings, and nanolines are demonstrated on GaAs substrates with hard-polydimethylsiloxane (h-PDMS) mold and plasma etching. This method can be easily applied to the metallization and nanopatterning of gold on GaAs surfaces.

  13. The E1-E2 center in gallium arsenide is the divacancy.

    PubMed

    Schultz, Peter A

    2015-02-25

    Based on defect energy levels computed from first-principles calculations, it is shown the E1-E2 center in irradiated GaAs cannot be due to an isolated arsenic vacancy. The only simple intrinsic defect with levels compatible with E1 and E2 is the divacancy. The arsenic monovacancy is reassigned to the E3 center in irradiated GaAs. These new assignments are shown to reconcile a number of seemingly contradictory experimental observations.

  14. Origin of optical losses in gallium arsenide disk whispering gallery resonators.

    PubMed

    Parrain, David; Baker, Christophe; Wang, Guillaume; Guha, Biswarup; Santos, Eduardo Gil; Lemaitre, Aristide; Senellart, Pascale; Leo, Giuseppe; Ducci, Sara; Favero, Ivan

    2015-07-27

    Whispering gallery modes in GaAs disk resonators reach half a million of optical quality factor. These high Qs remain still well below the ultimate design limit set by bending losses. Here we investigate the origin of residual optical dissipation in these devices. A Transmission Electron Microscope analysis is combined with an improved Volume Current Method to precisely quantify optical scattering losses by roughness and waviness of the structures, and gauge their importance relative to intrinsic material and radiation losses. The analysis also provides a qualitative description of the surface reconstruction layer, whose optical absorption is then revealed by comparing spectroscopy experiments in air and in different liquids. Other linear and nonlinear optical loss channels in the disks are evaluated likewise. Routes are given to further improve the performances of these miniature GaAs cavities.

  15. Electrochemical sensing of membrane potential and enzyme function using gallium arsenide electrodes functionalized with supported membranes.

    PubMed

    Gassull, Daniel; Ulman, Abraham; Grunze, Michael; Tanaka, Motomu

    2008-05-01

    We deposit phospholipid monolayers on highly doped p-GaAs electrodes that are precoated with methyl-mercaptobiphenyl monolayers and operate such a biofunctional electrolyte-insulator-semiconductor (EIS) setup as an analogue of a metal-oxide-semiconductor setup. Electrochemical impedance spectra measured over a wide frequency range demonstrate that the presence of a lipid monolayer remarkably slows down the diffusion of ions so that the membrane-functionalized GaAs can be subjected to electrochemical investigations for more than 3 days with no sign of degradation. The biofunctional EIS setup enables us to translate changes in the surface charge density Q and bias potentials Ubias into the change in the interface capacitance Cp. Since Cp is governed by the capacitance of semiconductor space charge region CSC, the linear relationships obtained for 1/Cp2 vs Q and 1/Cp2 vs Ubias suggests that Cp can be used to detect the surface charges with a high sensitivity (1 charge per 18 nm2). Furthermore, the kinetics of phospholipids degradation by phospholipase A2 can also be monitored by a significant decrease in diffusion coefficients through the membrane by a factor of 104. Thus, the operation of GaAs membrane composites established here allows for electrochemical sensing of surface potential and barrier capability of biological membranes in a quantitative manner.

  16. Soft-mask fabrication of gallium arsenide nanomembranes for integrated quantum photonics.

    PubMed

    Midolo, L; Pregnolato, T; Kiršanskė, G; Stobbe, S

    2015-12-01

    We report on the fabrication of quantum photonic integrated circuits based on suspended GaAs membranes. The fabrication process consists of a single lithographic step followed by inductively coupled-plasma dry etching through an electron-beam-resist mask and wet etching of a sacrificial layer. This method does not require depositing, etching, and stripping a hard mask, greatly reducing fabrication time and costs, while at the same time yielding devices of excellent structural quality. We discuss in detail the procedures for cleaning the resist residues caused by the plasma etching and present a statistical analysis of the etched feature size after each fabrication step.

  17. Gallium arsenide integrated circuits for professional broadband applications up to 3 GHz approximately

    NASA Astrophysics Data System (ADS)

    Weidlich, H.; Pettenpaul, E.; Petz, F. A.

    1983-03-01

    A GaAs-FET-technology for the manufacture of fast GaAs broadband IC's was developed with: local ion implantation for the channel and the contact region; Si3N4 cap for annealing and in process surface protection; gold based metallizations in a modified lift-off technique; and a second Si3N4 layer on top of the metallizations for safe enclosure of the active areas and as dielectric for metal insulator metal coupling capacitors. The gains with this technology approximate those of the silicon planar technology. An antenna amplifier with 20 dB gain from 40 to 1000 MHz and a noise figure of about 4 dB was tested in different modifications with integrated load transistors and with external load inductors. The stages are cascadable without matching, so higher gains are possible. An amplifier for measurement equipment with 2 GHz bandwidth and 16 dB gain was constructed with selected antenna amplifier samples using real load resistors. Monolithic integrated differential amplifier stages show gain factors of up to 35 dB with 22 MHz 3 dB-bandwidth suitable for a 2 stage operational amplifier with dB gain and 14 MHz bandwidth.

  18. 1.55 um aluminum gallium indium arsenide strained MQW laser diodes

    NASA Astrophysics Data System (ADS)

    Yang, Chi

    At the 1.55 mum eye-safe, telecommunications operating wavelength, semiconductor diode lasers must have low threshold currents and operate at high temperatures without thermoelectric coolers. Existing diode lasers in this wavelength range based on the GaInAsP/InP materials system are very sensitive to operating temperature. To obtain high temperature, high power 1.55 mum semiconductor diode lasers, the AlGaInAs/InP materials system with strained quantum well (QW) active regions was investigated with the goal of improving temperature performance. A set of lasers with active regions consisting of different numbers of QWs (2 to 4) and different QW strains (1.2% and 1.6%) were designed taking into account the quaternary alloy bandgap of AlGaInAs, the effect of strain on the bandgap, and the quantum size effects within the QW. The active region growth temperature was optimized using photoluminescence intensity. The wafers were first processed into broad-area lasers and measured under pulsed injection. The characteristic threshold current temperature, T0, for all AlGaInAs lasers was higher (60-70 K) than for GaInAsP lasers. No strong dependence of temperature parameters on strain was observed, while properties varied significantly with the number of QWs. With more QWs, both internal efficiency and T0 increases, but internal loss increases, reducing the characteristic temperature of the differential efficiency T1. The results show that uncooled laser operation at 1.55 mum is very promising with strained AlGaInAs QWs. Ridge waveguide devices demonstrated low threshold and high output power as well as good temperature performance under continuous wave operation. Devices with different ridge heights were fabricated from one wafer and their performance was compared. It was found that current spreading was significant in these devices and a simple current density-versus-applied voltage analysis was developed to determine the spreading factor. The analysis shows that the current spreading was not effectively limited until etching went below the doped cladding layer. A recombination coefficient analysis was performed to investigate the effect of strain on Auger recombination predicted by theory. An indirect method to infer both the nonradiative recombination coefficient and the Auger recombination coefficient was initially used. The measured values of the recombination coefficients were consistent with theoretical predictions and measurements based on other material systems. The Auger recombination was lower than expected, indicating that Auger recombination is reduced in these strained QWs. To understand the carrier dynamics, impedance measurements were carried out for the first time in AlGaInAs strained QW lasers. A small-signal, sub-threshold equivalent circuit model was derived from the laser rate equations to model the measured laser impedance. Several characteristic carrier lifetimes were obtained directly from these electrical impedance measurements. From the temperature dependence of the QW escape time, it was found that hole rather than electron leakage is dominant in the AlGaInAs system due to the relatively low valence band offset. This may explain why the improvement of T0 in AlGaInAs QW 1.55 mum active regions is limited.

  19. Spin-lattice relaxation in p-type gallium arsenide single crystals

    NASA Astrophysics Data System (ADS)

    Zerrouati, K.; Fabre, F.; Bacquet, G.; Bandet, J.; Frandon, J.; Lampel, G.; Paget, D.

    1988-01-01

    An optical-pumping technique is used to measure the spin-relaxation time of photogenerated conduction electrons in several p-type GaAs single crystals doped with various amounts of acceptors in the 1.7-300 K temperature range. Our experimental results are compared with those of the literature and with the predictions of the existing theoretical calculations. From about 10 K, the Bir-Aronov-Pikus (BAP) mechanism is found to be relevant for moderately doped (1017-1018 cm-3), up to about 150 K, or degenerate (up to 300 K) semiconductors, using the electronic temperature, deduced from the luminescence spectra, rather than the sample temperature. The D'yakonov-Perel' (DP) process was found to be active above 200 K for moderately doped samples and from about 80 K to room temperature for samples doped in the (1.6-6)×1016-cm-3 acceptor-concentration range. Our original results obtained at liquid-helium temperatures at whatever the doping level cannot be explained either by the DP mechanism or by the BAP process.

  20. Temperature dependent characterization of gallium arsenide X-ray mesa p-i-n photodiodes

    NASA Astrophysics Data System (ADS)

    Lioliou, G.; Meng, X.; Ng, J. S.; Barnett, A. M.

    2016-03-01

    Electrical characterization of two GaAs p+-i-n+ mesa X-ray photodiodes over the temperature range 0 °C to 120 °C together with characterization of one of the diodes as an X-ray detector over the temperature range 0 °C to 60 °C is reported as part of the development of photon counting X-ray spectroscopic systems for harsh environments. The randomly selected diodes were fully etched and unpassivated. The diodes were 200 μm in diameter and had 7 μm thick i layers. The leakage current density was found to increase from (3 ± 1) nA/cm-2 at 0 °C to (24.36 ± 0.05) μA/cm-2 at 120 °C for D1 and from a current density smaller than the uncertainty (0.2 ± 1.2) nA/cm-2 at 0 °C to (9.39 ± 0.02) μA/cm-2 at 120 °C for D2 at the maximum investigated reverse bias (15 V). The best energy resolution (FWHM at 5.9 keV) was achieved at 5 V reverse bias, at each temperature; 730 eV at 0 °C, 750 eV at 20 °C, 770 eV at 40 °C, and 840 eV at 60 °C. It was found that the parallel white noise was the main source of the photopeak broadening only when the detector operated at 60 °C, at 5 V, 10 V, and 15 V reverse bias and at long shaping times (>5 μs), whereas the sum of the dielectric noise and charge trapping noise was the dominant source of noise for all the other spectra.