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Sample records for arsenide gallium nitride

  1. Silicon Nitride For Gallium Arsenide Integrated Circuits

    NASA Astrophysics Data System (ADS)

    Nagle, J.; Morgan, David V.

    1987-04-01

    Gallium Arsenide, unlike silicon does not have a natural oxide with the dielectric and interface qualities of SiO2. As a consequence alternative techniques have to be developed for device and IC processing applications. Plasma deposited silicon nitride films are currently being investigated in many laboratories. This paper will deal with the characterization of such films deposited under a range of gas and plasma deposition conditions. The techniques of Infra Red Spectroscopy and Rutherford backscattering have been used for characterization of both "as deposited layers" and layers which have been annealed up to temperatures of 800 °C, after deposition. The use of RBS for silicon nitride on GaAs is limited since the relatively small nitride spectrum is superimposed on much larger GaAs spectrum. The problem can be removed by placing carbon test substrates alongside the GaAs wafers. This separates the silicon and nitrogen spectra from the substrate enabling enhanced accuracy to be obtained. In this paper the range of results obtained will be discussed in the context of the deposition condition in order to identify the optimum conditions for obtaining a stoichiometric compound and a high quality interface.

  2. Effect of strain on gallium nitride and gallium indium arsenide nitride growth and doping

    NASA Astrophysics Data System (ADS)

    G. S., Sudhir

    GaN and the related (Al,In)N materials are currently used in manufacturing optoelectronic and electronic devices. However, the efficiency of these devices is limited due to lack of high structural quality and of low resistive p-type GaN. The GaN thin films are under strain during growth due to the large lattice mismatch, thermal expansion difference, and low growth temperature. Developing a better understanding of the effect of strain on the properties of thin films is important in furthering our knowledge of thin film growth affecting the performance of III-nitride based devices. Pulsed laser deposition was used to grow thin films of AlN and GaN on sapphire substrates. It is shown that the structure and surface morphology of layers are controlled by the nitrogen partial pressure during the growth. Through these nitrogen pressure related effects, thin films with microstructure ranging from crystalline to amorphous can be produced. A minimal surface root mean square roughness of 0.7 nm for amorphous AlN is obtained which compares well with the substrate roughness of 0.5 nm. Incorporation of impurities changes the lattice constants of thin films of GaN deposited on basal plane sapphire by molecular beam epitaxy. Both Mg (1017 cm-3) and Zn (3 x 10 20 cm-3) doping were found to expand the c lattice parameter by +0.38 x 10-2 and +0.62 x 10 -2, respectively. Oxygen up to concentrations 9 x 10 21 cm-3 is shown to replace nitrogen in GaN thin films reducing the c parameter only by a small amount. Incorporation of Si leads to a large decrease of the c parameter, which can not be attributed to the different size of Ga and Si. It is suggested that doping alters the film stoichiometry by a predicted Fermi level dependence of defect formation energies and thereby, lattice parameters and stress. A proper buffer layer design is shown to increase the incorporation of Mg by two orders of magnitude Finally, the balance of lattice parameter change caused by dopant and native point

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Thin Films of Gallium Arsenide and Gallium Aluminum Arsenide by Metalorganic Chemical Vapor Deposition.

    NASA Astrophysics Data System (ADS)

    Look, Edward Gene Lun

    Low pressure metalorganic chemical vapor deposition (LPMOCVD) of thin films of gallium arsenide (GaAs) and gallium aluminum arsenide (GaAlAs) was performed in a horizontal cold wall chemical vapor deposition (CVD) reactor. The organometallic (group III) sources were triethylgallium (TEGa) and triethylaluminum (TEAl), used in conjunction with arsine (AsH_3) as the group V source. It was found that growth parameters such as growth temperature, pressure, source flow rates and temperatures have a profound effect on the film quality and composition. Depending on the particular combination of conditions, both the surface and overall morphologies may be affected. The films were nondestructively analyzed by Raman and photoreflectance spectroscopies, x-ray diffraction and rocking curve studies, scanning electron microscopy, energy dispersive spectroscopy, Hall measurements and film thicknesses were determined with a step profilometer.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  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. 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.

  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. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. Far-Infrared and Optical Studies of Gallium Arsenide and Aluminum Gallium Arsenide Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    Stanaway, Mark Brian

    Available from UMI in association with The British Library. Requires signed TDF. This thesis reports far-infrared (FIR) and photoluminescence studies, performed at low temperatures (4.2K) and at magnetic fields up to 25T, of selectively and inadvertently doped bulk and low dimensional gallium arsenide (GaAs) and aluminium gallium arsenide (AlGaAs) semiconductor structures grown by molecular beam epitaxy. High-resolution FIR magnetospectroscopy of ultra -high mobility n-GaAs reveals a variety of shallow donor intra-impurity transitions plus spin-split higher Landau level transitions in the photoconductive response. The first observation of polarons bound to D^ - ions in bulk n-GaAs is reported. The excited state spectrum of the confined silicon donor in GaAs/AlGaAs multi-quantum wells (MQWs) has been examined. Narrower linewidths and more higher excited state donor transitions are noted in the present photoconductive investigation compared with previous reports. The electron recombination dynamics has been examined in silicon-doped GaAs/AlGaAs MQWs and homogeneous and sheet -doped bulk n-GaAs samples using time-resolved FIR photoconductivity. The extrinsic response of doped MQW structures suggests a potential use as a fast, sensitive detectors of FIR. FIR transmission measurements are reported for GaAs/AlGaAs quantum wells (QWs) of various widths in magnetic fields of up to 20T, tilted away from the normal to the QW plane by angles up to theta = 50^circ. Deviation of the cyclotron resonance field from a costheta law are interpreted using theoretical models describing Landau level/electric subband coupling. The in-plane magnetic field and excitation power dependence of the photoluminescence intensity of a GaAs/AlGaAs QW spectral feature is interpreted in terms of charge transfer in the QW, using a coupled oscillator model, and the efficiency of nonradiative electronic traps. In-plane magnetic field studies of the photoluminescence from a superlattice structure

  10. Gallium arsenide pilot line for high performance components

    NASA Astrophysics Data System (ADS)

    Vehse, Robert C.; Lapham, E. F.

    1991-08-01

    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. Physical and electrical analysis conclusively demonstrated that the EFET problem was caused by residual AlGaAs remaining in the EFET tubs. For our Self Aligned Refractory Gate Integrated Circuit (SARGIC) process to perform as designed, the FET gates must be placed directly on Gallium Arsenide. Residual AlGaAs increases the FET thresholds and thereby substantially changes device characteristics. We solved the problem by developing a new etch process using a PP etchant (H3PO4 and H2O2). AlGaAs is now completely removed from EFET tubs and EFET threshold control has been restored. With wafer starts suspended and other program work minimized to conserve resources, there was little primary circuit testing. A new result is that the 32-Bit Multiplier is functional at 60 MHz.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Electrospun Gallium Nitride Nanofibers (abstract)

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    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 NH3 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.

  18. Single event upsets in gallium arsenide dynamic logic

    SciTech Connect

    Fouts, D.J. . ECE Dept.); Weatherford, T. ); McMorrow, C.; Melinger, J.S.; Campbell, A.B. )

    1994-12-01

    The advantages and disadvantages of using gallium arsenide (GaAs) dynamic logic in computers and digital systems are briefly discussed, especially with respect to space applications. A short introduction to the topology and operation of GaAs Two-Phase Dynamic FET Logic (TDFL) circuits is presented. Experiments for testing the SEU sensitivity of GaAs TDFL, using a laser to create charge collection events, are described. Results are used to estimate the heavy-ion, soft error rate for TDFL in a spacecraft in geosynchronous orbit, and the dependence of the SEU sensitivity on clock frequency, clock voltage, and clock phase. Analysis of the data includes a comparison between the SEU sensitivities of TDFL and the more common static form of GaAs logic, Directly Coupled FET Logic (DCFL). This is the first reported SEU testing of GaAs dynamic logic.

  19. 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.

  20. Coated gallium arsenide neutron detectors : results of characterizationmeasurements.

    SciTech Connect

    Klann, R. T.; Perret, G.; Sanders, J.

    2006-09-29

    Effective detection of special nuclear materials (SNM) is essential for reducing the threat associated with stolen or improvised nuclear devices. Passive radiation detection technologies are primarily based on gamma-ray detection and subsequent isotope identification or neutron detection (specific to neutron sources and SNM). One major effort supported by the Department of Homeland Security in the area of advanced passive detection is handheld or portable neutron detectors for search and localization tasks in emergency response and interdiction settings. A successful SNM search detector will not only be able to confirm the presence of fissionable materials but also establish the location of the source in as short of time as possible while trying to minimize false alarms due to varying background or naturally occurring radioactive materials (NORM). For instruments based on neutron detectors, this translates to detecting neutrons from spontaneous fission or alpha-n reactions and being able to determine the direction of the source (or localizing the source through subsequent measurements). Polyethylene-coated gallium arsenide detectors were studied because the detection scheme is based on measuring the signal in the gallium arsenide wafers from the electrical charge of the recoil protons produced from the scattering of neutrons from the hydrogen nucleus. The inherent reaction has a directional dependence because the neutron and hydrogen nucleus have equivalent masses. The assessment and measurement of polyethylene-coated gallium arsenide detector properties and characteristics was the first phase of a project being performed for the Department of Homeland Security and the results of these tests are reported in this report. The ultimate goal of the project was to develop a man-portable neutron detection system that has the ability to determine the direction of the source from the detector. The efficiency of GaAs detectors for different sizes of polyethylene layers and

  1. 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.

  2. 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.

  3. Single gallium nitride nanowire lasers.

    PubMed

    Johnson, Justin C; Choi, Heon-Jin; Knutsen, Kelly P; Schaller, Richard D; Yang, Peidong; Saykally, Richard J

    2002-10-01

    There is much current interest in the optical properties of semiconductor nanowires, because the cylindrical geometry and strong two-dimensional confinement of electrons, holes and photons make them particularly attractive as potential building blocks for nanoscale electronics and optoelectronic devices, including lasersand nonlinear optical frequency converters. Gallium nitride (GaN) is a wide-bandgap semiconductor of much practical interest, because it is widely used in electrically pumped ultraviolet-blue light-emitting diodes, lasers and photodetectors. Recent progress in microfabrication techniques has allowed stimulated emission to be observed from a variety of GaN microstructures and films. Here we report the observation of ultraviolet-blue laser action in single monocrystalline GaN nanowires, using both near-field and far-field optical microscopy to characterize the waveguide mode structure and spectral properties of the radiation at room temperature. The optical microscope images reveal radiation patterns that correlate with axial Fabry-Perot modes (Q approximately 10(3)) observed in the laser spectrum, which result from the cylindrical cavity geometry of the monocrystalline nanowires. A redshift that is strongly dependent on pump power (45 meV microJ x cm(-2)) supports the idea that the electron-hole plasma mechanism is primarily responsible for the gain at room temperature. This study is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet-blue coherent light sources. PMID:12618824

  4. Four Terminal Gallium Nitride MOSFETs

    NASA Astrophysics Data System (ADS)

    Veety, Matthew Thomas

    All reported gallium nitride (GaN) transistors to date have been three-terminal devices with source, drain, and gate electrodes. In the case of GaN MOSFETs, this leaves the bulk of the device at a floating potential which can impact device threshold voltage. In more traditional silicon-based MOSFET fabrication a bulk contact can be made on the back side of the silicon wafer. For GaN grown on sapphire substrates, however, this is not possible and an alternate, front-side bulk contact must be investigated. GaN is a III-V, wide band gap semiconductor that as promising material parameters for use in high frequency and high power applications. Possible applications are in the 1 to 10 GHz frequency band and power inverters for next generation grid solid state transformers and inverters. GaN has seen significant academic and commercial research for use in Heterojunction Field Effect Transistors (HFETs). These devices however are depletion-mode, meaning the device is considered "on" at zero gate bias. A MOSFET structure allows for enhancement mode operation, which is normally off. This mode is preferrable in high power applications as the device has lower off-state power consumption and is easier to implement in circuits. Proper surface passivation of seminconductor surface interface states is an important processing step for any device. Preliminary research on surface treatments using GaN wet etches and depletion-mode GaN devices utilizing this process are discussed. Devices pretreated with potassium pursulfate prior to gate dielectric deposition show significant device improvements. This process can be applied to any current GaN FET. Enhancement-mode GaN MOSFETs were fabricated on magnesium doped p-type Wurtzite gallium nitride grown by Metal Organic Chemical Vapor Deposition (MOCVD) on c-plane sapphire substrates. Devices utilized ion implant source and drain which was activated under NH3 overpressure in MOCVD. Also, devices were fabricated with a SiO2 gate dielectric

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Investigation of radiation defects in gallium arsenide under hydrostatic pressure

    SciTech Connect

    Brudnyi, V.N.; Vilisov, A.A.; Diamant, V.M.; Krivorotov, N.P.

    1980-01-01

    The spectral characteristics of gallium arsenide photodiodes irradiated with electrons (2 MeV, 300/sup 0/K) were used to study the influence of hydrostatic compression (up to 8 kbar) and temperature (77--300/sup 0/K) on the energy positions of radiation-defect levels. The pressure coefficients of the spectral positions of the impurity absorption bands at 1.2 and 1.37 eV indicated a genetic relationship between localized states H/sub 0/ (approx.E/sub v/+0.1 eV) and H/sub 1/ (approx.E/sub v/+0.25 eV) and the band extrema E/sub v/(GAMMA/sub 15/) and E/sub c/(GAMMA/sub 1/), respectively. The high piezoresistance coefficient (1/rho)(drho/dP)approx. =3.5 x 10/sup -4/ bar/sup -1/, recorded for the first time for n-type GaAs compensated by electron irradiation, was attributed to the influence of a state split off from the valence band and located in the upper half of the band gap at E/sub c/-0.3--0.4 eV. Isochronous annealing of radiation defects was investigated in the temperature range 300--35/sup 0/K.

  10. Indium gallium nitride/gallium nitride quantum wells grown on polar and nonpolar gallium nitride substrates

    NASA Astrophysics Data System (ADS)

    Lai, Kun-Yu

    Nonpolar (m-plane or a-plane) gallium nitride (GaN) is predicted to be a potential substrate material to improve luminous efficiencies of nitride-based quantum wells (QWs). Numerical calculations indicated that the spontaneous emission rate in a single In0.15Ga0.85N/GaN QW could be improved by ˜2.2 times if the polarization-induced internal field was avoided by epitaxial deposition on nonpolar substrates. A challenge for nonpolar GaN is the limited size (less than 10x10 mm2) of substrates, which was addressed by expansion during the regrowth by Hydride Vapor Phase Epitaxy (HVPE). Subsurface damage in GaN substrates were reduced by annealing with NH3 and N2 at 950°C for 60 minutes. It was additionally found that the variation of m-plane QWs' emission properties was significantly increased when the substrate miscut toward a-axis was increased from 0° to 0.1°. InGaN/GaN QWs were grown by Metalorganic Chemical Vapor Deposition (MOCVD) on c-plane and m-plane GaN substrates. The QWs were studied by cathodoluminescence spectroscopy with different incident electron beam probe currents (0.1 nA ˜ 1000 nA). Lower emission intensities and longer peak wavelengths from c-plane QWs were attributed to the Quantum-confined Stark Effect (QCSE). The emission intensity ratios of m-plane QWs to c-plane QWs decreased from 3.04 at 1 nA to 1.53 at 1000 nA. This was identified as the stronger screening effects of QCSE at higher current densities in c-plane QWs. To further investigate these effects in a fabricated structure, biased photoluminescence measurements were performed on m-plane InGaN/GaN QWs. The purpose was to detect the possible internal fields induced by the dot-like structure in the InGaN layer through the response of these internal fields under externally applied fields. No energy shifts of the QWs were observed, which was attributed to strong surface leakage currents.

  11. 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. PMID:27007502

  12. 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.

  13. 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.

  14. 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.

  15. Ammonothermal Growth of Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Pimputkar, Siddha

    Bulk, single crystal Gallium Nitride (GaN) crystals are essential for enabling high performance electronic and optoelectronic devices by providing arbitrarily oriented, high quality, large, single crystal GaN substrates. Methods of producing single crystals of sufficient size and quality at a rate that would enable successful commercialization has been a major focus for research groups and companies worldwide. Recent advances have demonstrated remarkable improvements, though high cost and lack of high volume production remain key challenges. Major investments in bulk GaN growth were made at UCSB with particular focus on the ammonothermal method. The existing lab was upgraded and a new facility was designed and built with improved experimental setups for ammonothermal growth of GaN. The facilities can simultaneously operate up to 15 reactors of differing designs and capabilities with the ability to grow crystals up to 2 inches in diameter. A novel in-situ technique was devised to investigate the growth chemistry which occurs at typical operating conditions of 3,000 atm and 600 °C. Improvements in ammonothermal GaN include improved growth rates for c-plane by a factor of four to 344 μm/day with an overall record growth rate of 544 μm/day achieved for the (112¯2) plane. Crystal qualities comparable to that of the seed crystal were achieved. Impurity concentrations for transition metals were consistently reduced by a factor of 100 to concentrations below 1017 atoms/cm3. Optical transparency was improved by significantly reducing the yellow coloration typically seen for ammonothermal GaN. Single crystal GaN was successfully grown on large seeds and a 1 inch x ½ inch x ½ inch GaN crystal was demonstrated. To better understand the growth chemistry, models were created for the decomposition of ammonia under growth conditions, with initial experiments performed using the designed in-situ setup to verify the model's accuracy. To investigate the surface morphology and

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Skylab experiment performance evaluation manual. Appendix J: Experiment M555 gallium arsenide single crystal growth (MSFC)

    NASA Technical Reports Server (NTRS)

    Byers, M. S.

    1973-01-01

    Analyses for Experiment M555, Gallium Arsenide Single Crystal Growth (MSFC), to be used for evaluating the performance of the Skylab corollary experiments under preflight, inflight, and post-flight conditions are presented. Experiment contingency plan workaround procedure and malfunction analyses are presented in order to assist in making the experiment operationally successful.

  1. NMR microspectroscopy using 100 microns planar RF coils fabricated on gallium arsenide substrates.

    PubMed

    Peck, T L; Magin, R L; Kruse, J; Feng, M

    1994-07-01

    A family of planar gold RF microcoils were fabricated using microlithography on a gallium arsenide substrate. The microcoils were used in 1H nuclear magnetic resonance (NMR) spectroscopy experiments at 300 MHz (7.05 T). These new microcoils are a key component in the design of integrated MR coils and amplifiers for NMR microspectroscopy. PMID:7523278

  2. Electro-optic modulator for infrared laser using gallium arsenide crystal

    NASA Technical Reports Server (NTRS)

    Walsh, T. E.

    1968-01-01

    Gallium arsenide electro-optic modulator used for infrared lasers has a mica quarter-wave plate and two calcite polarizers to amplitude or phase modulate an infrared laser light source in the wavelength range from 1 to 3 microns. The large single crystal has uniformly high resistivities, is strain free, and comparable in quality to good optical glass.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Homogeneous dispersion of gallium nitride nanoparticles in a boron nitride matrix by nitridation with urea.

    PubMed

    Kusunose, Takafumi; Sekino, Tohru; Ando, Yoichi

    2010-07-01

    A Gallium Nitride (GaN) dispersed boron nitride (BN) nanocomposite powder was synthesized by heating a mixture of gallium nitrate, boric acid, and urea in a hydrogen atmosphere. Before heat treatment, crystalline phases of urea, boric acid, and gallium nitrate were recognized, but an amorphous material was produced by heat treatment at 400 degrees C, and then was transformed into GaN and turbostratic BN (t-BN) by further heat treatment at 800 degrees C. TEM obsevations of this composite powder revealed that single nanosized GaN particles were homogeneously dispersed in a BN matrix. Homogeneous dispersion of GaN nanoparticles was thought to be attained by simultaneously nitriding gallium nitrate and boric acid to GaN and BN with urea. PMID:21128417

  8. 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.

  9. 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).

  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. Thermal expansion of gallium arsenide layers grown by molecular beam epitaxy at low temperatures

    NASA Astrophysics Data System (ADS)

    Leszczynski, M.; Walker, J. F.

    1993-03-01

    The thermal expansion of low-temperature (190-220 °C) MBE grown gallium arsenide (LT GaAs) was measured using x-ray diffraction methods. The experiment was performed in order to observe the influence of high nonstoichiometric excess (about 1%) of arsenic on the thermal expansion of gallium arsenide. The diffraction measurements enabled the simultaneous monitoring of the lattice constants of the LT GaAs layers and their semi-insulating GaAs substrates. Their lattice mismatch was only slightly temperature dependent and decreased by about 5% with a temperature rise from 77 K (in dark) up to 550 K. This means that the value of the thermal expansion coefficient of as-grown LT GaAs was lower only by about 0.05×10-6 K-1 than that of the semi-insulating GaAs substrate. Reduction of arsenic excess by air annealing at 420 °C resulted in the decrease of lattice mismatch and the difference in the thermal expansion. This means that both are related to such point defects as arsenic antisites and interstitials. The experimental results are compared with the previously published data for variously doped gallium arsenide samples.

  12. 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.

  13. 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.

  14. 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

  15. 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)

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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.

  7. 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

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

    NASA Astrophysics Data System (ADS)

    Gaddy, Edward 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. Nonetheless, the benefit of the higher efficiency

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

    2015-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

  15. 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

  16. Carrier depletion and electrical optimization of gallium arsenide plasmonic solar cell with a rear metallic grating

    NASA Astrophysics Data System (ADS)

    Shang, Aixue; Li, Xiaofeng

    2015-02-01

    Plasmonic nanostructures have been extensively considered for photovoltaics due to the outstanding light-trapping capability; however, the intrinsic processes of carrier transport, recombination and collection have seldom been concerned. We report a complete optoelectronic investigation for plasmonic gallium arsenide solar cells (SCs) with a rear silver grating, by especially quantifying the plasmonics-induced photocurrent loss. It is found that, although the plasmonic design shows indeed much improved output photocurrent, its potential in improving the performance of SCs has not been fully exploited since a lot of energy has been wasted in the form of carrier depletion. A further design which electrically separates the plasmonic nanostructure from the core PN junction is verified to be an effective solution in improving the electrical performance of the SCs. The complete optoelectronic consideration is expected to advance the design of plasmonic SCs for thin-film and high-efficiency.

  17. Single event upsets in gallium arsenide pseudo-complementary MESFET logic

    SciTech Connect

    Fouts, D.J.; Wolfe, K.; Van Dyk, S.E.; Weatherford, T.R.; McMorrow, D.; Melinger, J.S.; Tran, L.H.; Campbell, A.B.

    1995-12-01

    An introduction to gallium arsenide (GaAs) Pseudo-Complementary MESFET Logic (PCML) circuits is presented. PCML was developed to reduce the sensitivity of high-speed GaAs logic to radiation-induced single event upsets (SEUs). Experiments for testing the single-event upset (SEU) sensitivity of GaAs PCML integrated circuits (ICs) are described. The results of the experiments are analyzed. This new type of high-speed, low-power, GaAs logic provides decreased sensitivity to SEUs compared to more traditional circuit designs such as Directly-Coupled FET Logic (DCFL). PCML is fully compatible with existing GaAs E/D MESFET fabrication processes, such as those commonly used to make DCFL.

  18. 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.

  19. 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.

  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. 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.

  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. Growth of epitaxial iron nitride ultrathin film on zinc-blende gallium nitride

    SciTech Connect

    Pak, J.; Lin, W.; Wang, K.; Chinchore, A.; Shi, M.; Ingram, D. C.; Smith, A. R.; Sun, K.; Lucy, J. M.; Hauser, A. J.; Yang, F. Y.

    2010-07-15

    The authors report the growth of iron nitride on zinc-blende gallium nitride using molecular beam epitaxy. First, zinc-blende GaN is grown on a magnesium oxide substrate having (001) orientation; second, an ultrathin layer of FeN is grown on top of the GaN layer. In situ reflection high-energy electron diffraction is used to monitor the surface during growth, and a well-defined epitaxial relationship is observed. Cross-sectional transmission electron microscopy is used to reveal the epitaxial continuity at the gallium nitride-iron nitride interface. Surface morphology of the iron nitride, similar to yet different from that of the GaN substrate, can be described as plateau valley. The FeN chemical stoichiometry is probed using both bulk and surface sensitive methods, and the magnetic properties of the sample are revealed.

  4. 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

  5. Nucleation mechanism of gallium-assisted molecular beam epitaxy growth of gallium arsenide nanowires

    SciTech Connect

    Fontcuberta i Morral, A.; Colombo, C.; Abstreiter, G.; Arbiol, J.; Morante, J. R.

    2008-02-11

    Molecular beam epitaxy Ga-assisted synthesis of GaAs nanowires is demonstrated. The nucleation and growth are seen to be related to the presence of a SiO{sub 2} layer previously deposited on the GaAs wafer. The interaction of the reactive gallium with the SiO{sub 2} pinholes induces the formation of nanocraters, found to be the key for the nucleation of the nanowires. With SiO{sub 2} thicknesses up to 30 nm, nanocraters reach the underlying substrate, resulting into a preferential growth orientation of the nanowires. Possibly related to the formation of nanocraters, we observe an incubation period of 258 s before the nanowires growth is initiated.

  6. Focused ion beam-based in situ patterning of gallium arsenide(001) and optical investigations of indium arsenide/gallium arsenide(001)

    NASA Astrophysics Data System (ADS)

    Kalburge, Amol Madhusudan

    This dissertation contributes to the two generic areas of current research focusing on epitaxical semiconductor nanostructures: (i) all in-situ nanostructure synthesis via epitaxical growth on non-planar patterned substrates (NPPS), and via highly strained epitaxical growth on planar substrates, and (ii) optical behaviour of such nanostructures. Towards in-situ nanostructure synthesis via epitaxical growth on NPPS, two Ga+ focused ion beam (FIB) based approaches are explored to create NPPS in-situ. The first approach is a direct-write (i.e. resist-less) approach and uses FIB assisted chlorine etching (FIBCE) to directly create mesas into the GaAs (001) substrate. Systematic investigations of the FIBCE process are carried out to develop a basic understanding necessary for its effective use as a direct-write patterning tool. The second approach is a lithographic approach and uses plasma enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) as an in-situ resist and Ga+ implantation as a resist exposure method. For the in-situ nanostructure synthesis via highly strained epitaxical growth of three-dimensional (3D) islands on planar substrates, systematic optical investigations of the InAs/GaAs (001) system are carried out to both, reveal the potential of the islands as quantum boxes [dubbed quantum dots (QDs)] and optimize their synthesis. Through low temperature photoluminescence and photoluminescence excitation studies we identify the optimum GaAs cap layer growth conditions and demonstrate the QD-like nature of 3D islands. Optical investigations of multiply stacked islands suggest that the size and shape uniformity of islands in the upper stacks improves during the vertical stacking process. Lasing is observed from the laser structures having single and multiple stacks of 2.00ML InAs islands, albeit at wavelengths shorter than the PL maximum. Through systematic optical studies of incremental InAs depositions ranging from 1.00ML to 2.00ML, and with

  7. 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.

  8. 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.

  9. Electron microscopy of gallium nitride growth on polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Webster, R. F.; Cherns, D.; Kuball, M.; Jiang, Q.; Allsopp, D.

    2015-11-01

    Transmission and scanning electron microscopy were used to examine the growth of gallium nitride (GaN) on polycrystalline diamond substrates grown by metalorganic vapour phase epitaxy with a low-temperature aluminium nitride (AlN) nucleation layer. Growth on unmasked substrates was in the (0001) orientation with threading dislocation densities ≈7 × 109 cm-2. An epitaxial layer overgrowth technique was used to reduce the dislocation densities further, by depositing silicon nitride stripes on the surface and etching the unmasked regions down to the diamond substrate. A re-growth was then performed on the exposed side walls of the original GaN growth, reducing the threading dislocation density in the overgrown regions by two orders of magnitude. The resulting microstructures and the mechanisms of dislocation reduction are discussed.

  10. High stability of negative electron affinity gallium arsenide photocathodes activated with Cs and NF3

    NASA Astrophysics Data System (ADS)

    Chanlek, N.; Herbert, J. D.; Jones, R. M.; Jones, L. B.; Middleman, K. J.; Militsyn, B. L.

    2015-09-01

    In this paper we report the first time demonstration under extremely high vacuum (XHV) conditions of the influence of O2, CO2, CO, N2, H2 and CH4 on the quantum efficiency (QE) of negative electron affinity (NEA) gallium arsenide (GaAs) photocathodes activated with Cs and NF3. The photocathodes were exposed to a small quantity (<0.25 Langmuirs) of each gas species under test in a vacuum chamber with a typical base pressure of 1.5× {{10}-11} mbar, thereby minimising the influence of the residual gas in the photocathode response. It was found that exposure to N2, H2 and CH4 does not affect the QE of the photocathodes, whereas exposure to O2 and CO2 lead to a substantial reduction in the QE of the photocathodes. Only small degradation in the QE under CO exposure was observed. Compared to those activated with Cs and O2 in our previous study [1], photocathodes activated with Cs and NF3 are more stable, especially under exposure to CO.

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

    SciTech Connect

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

    1984-09-01

    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.

  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. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. A stress gettering mechanism in semi-insulating, copper-contaminated gallium arsenide

    NASA Astrophysics Data System (ADS)

    Kang, Nam Soo; Zirkle, Thomas E.; Schroder, Dieter K.

    1992-07-01

    We have demonstrated a stress gettering mechanism in semi-insulating, copper-contaminated gallium arsenide (GaAs) using cathodoluminescence (CL), thermally stimulated current spectroscopy (TSC), and low temperature Fourier transform infrared spectroscopy (FTIR). Cathodoluminescence shows a local gettering effect around dislocation cores in bulk semi-insulating GaAs qualitatively. This gettering result was confirmed by low temperature FTIR data, which show absorption features resulting from the transition of electrons from the valence band to copper levels. The energy level of each absorption shoulder corresponds to the various copper levels in GaAs. After gettering, the absorption depth at each shoulder decreases. Thermally stimulated current measurements show changes after copper doping. The characteristic returns to that of uncontaminated GaAs after gettering. On the basis of these qualitative and quantitative data, we conclude that copper was gettered, and we propose a stress gettering mechanism in semi-insulating, copper-contaminated GaAs on the basis of dislocation cores acting as localized gettering sites.

  3. 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.

  4. 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

  5. Gallium nitride-based micro-opto-electro-mechanical systems

    NASA Astrophysics Data System (ADS)

    Stonas, Andreas Robert

    Gallium Nitride and its associated alloys InGaN and AlGaN have many material properties that are highly desirable for micro-electro-mechanical systems (MEMS), and more specifically micro-opto-electro-mechanical systems (MOEMS). The group III-nitrides are tough, stiff, optically transparent, direct bandgap, chemically inert, highly piezoelectric, and capable of functioning at high temperatures. There is currently no other semiconductor system that possesses all of these properties. Taken together, these attributes make the nitrides prime candidates not only for creating new versions of existing device structures, but also for creating entirely unique devices which combine these properties in novel ways. Unfortunately, their chemical resiliency also makes the group III-nitrides extraordinarily difficult to shape into devices. In particular, until this research, no undercut etch technology existed that could controllably separate a selected part of a MEMS device from its sapphire or silicon carbide substrate. This has effectively prevented GaN-based MEMS from being developed. This dissertation describes how this fabrication obstacle was overcome by a novel etching geometry (bandgap-selective backside-illuminated photoelectochemical (BS-BIPEC) etching) and its resulting morphologies. Several gallium-nitride based MEMS devices were created, actuated, and modelled, including cantilevers and membranes. We describe in particular our pursuit of one of the many novel device elements that is possible only in this material system: a transducer that uses an externally applied strain to dynamically change the optical transition energy of a quantum well. While the device objective of a dynamically tunable quantum well was not achieved, we have demonstrated sufficient progress to believe that such a device will be possible soon. We have observed a shift (5.5meV) of quantum well transition energies in released structures, and we have created structures that can apply large biaxial

  6. High growth speed of gallium nitride using ENABLE-MBE

    NASA Astrophysics Data System (ADS)

    Williams, J. J.; Fischer, A. M.; Williamson, T. L.; Gangam, S.; Faleev, N. N.; Hoffbauer, M. A.; Honsberg, C. B.

    2015-09-01

    Films of gallium nitride were grown at varying growth speeds, while all other major variables were held constant. Films grown determine the material impact of the high flux capabilities of the unique nitrogen plasma source ENABLE. Growth rates ranged from 13 to near 60 nm/min. X-ray ω scans of GaN (0002) have FWHM in all samples less than 300 arc sec. Cathodoluminescence shows radiative recombination for all samples at the band edge. In general material quality overall is high with slight degradation as growth speeds increase to higher rates.

  7. 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.

  8. Frequency conversion in free-standing periodically oriented gallium nitride

    NASA Astrophysics Data System (ADS)

    Brown, Christopher G.; Bowman, Steven R.; Hite, Jennifer K.; Freitas, Jaime A.; Kub, Francis J.; Eddy, Charles R.; Vurgaftman, Igor; Meyer, Jerry R.; Leach, Jacob H.; Udwary, Kevin

    2016-03-01

    Gallium nitride's (GaN) material properties of broadband transparency, high thermal conductivity, and wide-band gap make it a promising candidate for high-power frequency conversion devices. The strong internal polarization of GaN leads to large second-order nonlinearity, but conventional phase matching is prevented due to weak birefringence. To obtain efficient nonlinear optic frequency conversion, patterned inversion growth has been developed to induce quasiphase matching (QPM). We have fabricated and tested periodically oriented GaN (PO-GaN) devices to obtain QPM frequency conversion. This report discusses our recent measurements of second harmonic generation resonances for these devices.

  9. 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. PMID:22555695

  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. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

  13. 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.

  14. Low-threshold indium gallium nitride quantum dot microcavity lasers

    NASA Astrophysics Data System (ADS)

    Woolf, Alexander J.

    Gallium nitride (GaN) microcavities with embedded optical emitters have long been sought after as visible light sources as well as platforms for cavity quantum electrodynamics (cavity QED) experiments. Specifically, materials containing indium gallium nitride (InGaN) quantum dots (QDs) offer an outstanding platform to study light matter interactions and realize practical devices, such as on-chip light emitting diodes and nanolasers. Inherent advantages of nitride-based microcavities include low surface recombination velocities, enhanced room-temperature performance (due to their high exciton binding energy, as high as 67 meV for InGaN QDs), and emission wavelengths in the blue region of the visible spectrum. In spite of these advantages, several challenges must be overcome in order to capitalize on the potential of this material system. Such diffculties include the processing of GaN into high-quality devices due to the chemical inertness of the material, low material quality as a result of strain-induced defects, reduced carrier recombination effciencies due to internal fields, and a lack of characterization of the InGaN QDs themselves due to the diffculty of their growth and therefore lack of development relative to other semiconductor QDs. In this thesis we seek to understand and address such issues by investigating the interaction of light coupled to InGaN QDs via a GaN microcavity resonator. Such coupling led us to the demonstration of the first InGaN QD microcavity laser, whose performance offers insights into the properties and current limitations of the nitride materials and their emitters. This work is organized into three main sections. Part I outlines the key advantages and challenges regarding indium gallium nitride (InGaN) emitters embedded within gallium nitride (GaN) optical microcavities. Previous work is also discussed which establishes context for the work presented here. Part II includes the fundamentals related to laser operation, including the

  15. 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.

  16. 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

    SciTech Connect

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

    1981-11-01

    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.

  17. 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.

  18. Analysis of Nitrogen Incorporation in Group III-Nitride-Arsenide Materials Using a Magnetic Sector Secondary-Ion Mass Spectrometry (SIMS) Instrument: Preprint

    SciTech Connect

    Reedy, R. C.; Geisz, J. F.; Kurtz, S. R.; Adams, R. O.; Perkins, C. L.

    2001-10-01

    Presented at the 2001 NCPV Program Review Meeting: Group III-nitride-arsenide materials were studied by SIMS, XRD, and Profiler to determine small amounts of nitrogen that can lower the alloys bandgap significantly.

  19. 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.

  20. 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.

  1. 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.

  2. Modeling and simulation of bulk gallium nitride power semiconductor devices

    NASA Astrophysics Data System (ADS)

    Sabui, G.; Parbrook, P. J.; Arredondo-Arechavala, M.; Shen, Z. J.

    2016-05-01

    Bulk gallium nitride (GaN) power semiconductor devices are gaining significant interest in recent years, creating the need for technology computer aided design (TCAD) simulation to accurately model and optimize these devices. This paper comprehensively reviews and compares different GaN physical models and model parameters in the literature, and discusses the appropriate selection of these models and parameters for TCAD simulation. 2-D drift-diffusion semi-classical simulation is carried out for 2.6 kV and 3.7 kV bulk GaN vertical PN diodes. The simulated forward current-voltage and reverse breakdown characteristics are in good agreement with the measurement data even over a wide temperature range.

  3. Investigation of Structural Phase Transitions on Wurtzite Gallium Nitride Surfaces

    NASA Astrophysics Data System (ADS)

    Chen, Tianjiao; Chinchore, Abhijit; Liu, Yinghao; Wang, Kangkang; Lin, Wenzhi; Smith, Arthur

    2009-03-01

    Surface structures of wurtzite gallium nitride (w-GaN) have been investigated previously,[1][2] and it is well known that above 300K there exist order-disorder phase transitions. For N-polar w-GaN (000-1) at 300K, a family of surface reconstructions occurs, including 1x1, 3x3, 6x6, and c(6x12). Not much is known, however, about what happens to these structures as they are cooled below 300K. We have recently developed a new epitaxy/analysis system, including a sample stage which can be both heated and cooled. The N-polar w-GaN surfaces are prepared using rf N-plasma-assisted molecular beam epitaxy, and monitored in-situ using reflection high energy electron diffraction (RHEED). The approach is to monitor the [11-20] and [10-10] RHEED diffractions during cryogenic cooling, starting with the 1x1 or 3x3 structures. A critical issue to explore is the interrelationship between surface gallium concentration and structural deformation. This study may provide the missing link to new reconstructions of w-GaN recently observed using LT scanning tunneling microscopy.[3] This work is supported by NSF (Grant No. 0730257). [1] A. R. Smith et al., Phys. Rev. Lett. 79, 3934 (1997). [2] A. R. Smith et al., Surface Science 423, 70 (1999). [3] D. Acharya, S.-W. Hla et al., unpublished.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Characteristics of trap-filled gallium arsenide photoconductive switches used in high gain pulsed power applications

    SciTech Connect

    ISLAM,N.E.; SCHAMILOGLU,E.; MAR,ALAN; LOUBRIEL,GUILLERMO M.; ZUTAVERN,FRED J.; JOSHI,R.P.

    2000-05-30

    The electrical properties of semi-insulating (SI) Gallium Arsenide (GaAs) have been investigated for some time, particularly for its application as a substrate in microelectronics. Of late this material has found a variety of applications other than as an isolation region between devices, or the substrate of an active device. High resistivity SI GaAs is increasingly being used in charged particle detectors and photoconductive semiconductor switches (PCSS). PCSS made from these materials operating in both the linear and non-linear modes have applications such as firing sets, as drivers for lasers, and in high impedance, low current Q-switches or Pockels cells. In the non-linear mode, it has also been used in a system to generate Ultra-Wideband (UWB) High Power Microwaves (HPM). The choice of GaAs over silicon offers the advantage that its material properties allow for fast, repetitive switching action. Furthermore photoconductive switches have advantages over conventional switches such as improved jitter, better impedance matching, compact size, and in some cases, lower laser energy requirement for switching action. The rise time of the PCSS is an important parameter that affects the maximum energy transferred to the load and it depends, in addition to other parameters, on the bias or the average field across the switch. High field operation has been an important goal in PCSS research. Due to surface flashover or premature material breakdown at higher voltages, most PCSS, especially those used in high power operation, need to operate well below the inherent breakdown voltage of the material. The lifetime or the total number of switching operations before breakdown, is another important switch parameter that needs to be considered for operation at high bias conditions. A lifetime of {approximately} 10{sup 4} shots has been reported for PCSS's used in UWB-HPM generation [5], while it has exceeded 10{sup 8} shots for electro-optic drivers. Much effort is currently

  10. Simulation studies on the evolution of gallium nitride on a liquid gallium surface under plasma bombardment.

    PubMed

    Vasquez, M R; Flauta, R E; Wada, M

    2008-02-01

    Monte Carlo simulations were conducted to study the formation of gallium-nitride (GaN) layer on liquid gallium (Ga) sputtering target immersed in nitrogen (N(2)) plasma. In the simulation model, N ions were assumed to possess energy equal to the bias voltage applied to the sputtering target with respect to the plasma. The results showed the surface morphology of GaN changed from a relatively smooth GaN on Ga surface at 50 eV N ion energy to a rough surface with GaN dendrites on liquid Ga at 500 eV ion energy. Further increase in N ion energy up to 1 keV resulted in smaller density of GaN dendrites on surface. Increasing surface coverage of Ga by GaN substantially reduced the sputtering yield of Ga from the target. These simulation results were correlated with previously reported experimental observations on liquid Ga surface immersed in the nitrogen plasma of a plasma-sputter-type ion source. PMID:18315225

  11. Short channel effects on gallium nitride/gallium oxide nanowire transistors

    NASA Astrophysics Data System (ADS)

    Yu, J.-W.; Yeh, P.-C.; Wang, S.-L.; Wu, Y.-R.; Mao, M.-H.; Lin, H.-H.; Peng, L.-H.

    2012-10-01

    Gallium nitride/gallium oxide GaN/Ga2O3 nanowire metal-oxide-semiconductor field-effect-transistors are shown to operate at an average electron velocity of ˜1.24 × 107 cm/s and threshold-voltage roll-off of -0.2 V as the transistor gate length Lg reduced from 500 to 50 nm. Improvement of saturation current to 120 μA and unity current/power-gain cut-off frequency to 150/180 GHz is observed on Lg = 50 nm devices. Our study reveals the advantages of using (i) polarization-induced positive charges and high-k dielectric at the {11¯01¯}GaN/{002}Ga2O3 interface to provide carrier confinement and to shield the drain field, and (ii) polarization-induced negative charges at the (0001)GaN/sapphire interface to form a back-barrier to suppress leakage and improve the short-channel transport properties.

  12. 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.

  13. 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

  14. Epitaxial Zinc Oxide Semiconductor Film deposited on Gallium Nitride Substrate

    NASA Astrophysics Data System (ADS)

    McMaster, Michael; Oder, Tom

    2011-04-01

    Zinc oxide (ZnO) is a wide bandgap semiconductor which is very promising for making efficient electronic and optical devices. The goal of this research was to produce high quality ZnO film on gallium nitride (GaN) substrate by optimizing the substrate temperature. The GaN substrates were chemically cleaned and mounted on a ceramic heater and loaded into a vacuum deposition chamber that was pumped down to a base pressure of 3 x 10-7 Torr. The film deposition was preceded by a 30 minute thermal desorption carried in vacuum at 500 ^oC. The ZnO thin film was then sputter-deposited using an O2/Ar gas mixture onto GaN substrates heated at temperatures varying from 20 ^oC to 500 ^oC. Post-deposition annealing was done in a rapid thermal processor at 900 ^oC for 5 min in an ultrapure N2 ambient to improve the crystal quality of the films. The films were then optically characterized using photoluminescence (PL) measurement with a UV laser excitation. Our measurements reveal that ZnO films deposited on GaN substrate held at 200 ^oC gave the best film with the highest luminous intensity, with a peak energy of 3.28 eV and a full width half maximum of 87.4 nm. Results from low temperature (10 K) PL measurements and from x-ray diffraction will also be presented.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. High-field transport studies of bulk gallium nitride and gallium nitride heterostructures

    NASA Astrophysics Data System (ADS)

    Barker, Joy Marie

    This research study reports the fabrication of special geometric test structures and the measurements of transport properties in bulk GaN and AlGaN/GaN heterostructures. A large part of this study was spent examining fabrication issues related to the test structures used in these measurements, due to the fact that GaN processing is still in its infancy. One such issue dealt with surface passivation. Test samples without a surface passivation often failed at electric fields below 50 kV/cm due to surface breakdown. A silicon nitride passivation layer of approximately 200 nm was used to reduce the effects of surface states and premature surface breakdown. Another issue was finding quality contacts for the material, especially in the case of the AlGaN/GaN heterostructure samples. Poor contact performance in the heterostructures plagued the test structures with lower than expected velocities due to carrier injection from the contacts themselves. Using a titanium-rich ohmic contact reduced the contact resistance and stopped the carrier injection. The final test structures had an etch constriction with varying lengths and widths (8 x 2, 10 x 3, 12 x 3, 12 x 4, 15 x 5, and 16 x 4 mum) and massive contacts. A pulsed voltage input and a four-point measurement in a 50 O environment was used to determine the current through and the voltage dropped across the constriction. From these measurements, the drift velocity as a function of the, applied electric field was calculated, and, thus, the velocity-field characteristics in n-type bulk GaN and AlGaN/GaN test structures were determined. These measurements show an apparent saturation velocity near 2.5 x 107 cm/s at 180 kV/cm and 3.1 x 107 cm/s, at a field of 140 kV/cm, for the bulk GAN and AlGaN heterostructure samples, respectively. These experimental drify velocities mark the highest velocities measured in these material to date and confirm the predictions of previous theoretical models using ensemble Monte Carlo simulations

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. 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. PMID:24089824

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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. PMID:20373777

  13. 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.

  14. Gallium nitrogen arsenide and gallium arsenic bismuth: Structural and electronic properties of two resonant state semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Young, Erin Christina

    Semiconductor alloys that are lattice matched to GaAs but have a smaller energy band gap are of interest for numerous applications, including infrared lasers for telecommunications, high efficiency solar cells, and high electron mobility transistors. For high optoelectronic efficiency, these materials must be highly perfect single crystals with low defect densities. In this thesis, two substitutional GaAs-based alloy families, nitrides and bismides, are investigated experimentally. In the first alloy, GaNAs, the addition of N results in a large band gap reduction, though the small size of the N relative to As introduces tensile strain into the lattice, and the high electronegativity of N attracts electrons. The second alloy, GaAsBi, also has a smaller band gap and is formed by the addition of the very large Bi atom to GaAs, which introduces compressive strain and tends to attract holes. The experimental investigations of these alloys focused on elucidating the relationships between the growth process, atomic structure, and electronic properties. Films were grown by molecular beam epitaxy (MBE) with in-situ process monitoring and subject to post-growth structural and electronic characterization. For GaNAs and a related alloy. InGaNAs, degradation in luminescence efficiency, mobility and structural integrity were observed as the nitrogen content of the alloy was increased. A comprehensive study of strain relaxation in compressively strained InGaNAs and InGaAs quantum wells revealed that the nitrogen alloying did not have an effect on the critical thickness for dislocation formation, or the dislocation density in relaxed films. At large lattice mismatch, InGaNAs quantum wells were observed to relax by means of unusually oriented pure edge-type misfit dislocations aligned with <100> directions, likely due to the high stress associated with the large misfit. Use of bismuth as a non-incorporating surfactant during growth was successfully applied to improve the material

  15. Molecular beam epitaxy growth of indium nitride and indium gallium nitride materials for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Trybus, Elaissa

    The objective of the proposed research is to establish the technology for material growth by molecular beam epitaxy (MBE) and fabrication of indium gallium nitride/gallium nitride (InxGa1-xN/GaN) heterojunction solar cells. InxGa1-xN solar cells have the potential to span 90% of the solar spectrum, however there has been no success with high indium (In) incorporation and only limited success with low In incorporation InxGa1-xN. Therefore, this present work focuses on 15--30% In incorporation leading to a bandgap value of 2.3--2.8 eV. This work will exploit the revision of the indium nitride (InN) bandgap value of 0.68 eV, which expands the range of the optical emission of nitride-based devices from ultraviolet to near infrared regions, by developing transparent In xGa1-xN solar cells outside the visible spectrum. Photovoltaic devices with a bandgap greater than 2.0 eV are attractive because over half the available power in the solar spectrum is above the photon energy of 2.0 eV. The ability of InxGa1-xN materials to optimally span the solar spectrum offers a tantalizing solution for high-efficiency photovoltaics. This work presents results confirming the revised bandgap of InN grown on germanium (Ge) substrates and the effects of oxygen contamination on the bandgap. This research adds to the historical discussion of the bandgap value of InN. Using the metal modulated epitaxy (MME) technique in a new, ultra-clean refurbished MBE system, an innovative growth regime is established where In and Ga phase separation is diminished by increasing the growth rate for In xGa1-xN. The MME technique modulates the metal shutters with a fixed duty cycle while maintaining a constant nitrogen flux and proves effective for improving crystal quality and p-type doping. InxGa 1-xN/GaN heterojunction solar cells require p-type doping to create the p-n subcell collecting junction, which facilitates current collection through the electrostatic field created by spatially separated ionized

  16. 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.

  17. Synthesis of high purity gallium nitride powders and growth and characterization of aluminum nitride and gallium nitride bulk single crystals

    NASA Astrophysics Data System (ADS)

    Balkas, Cengiz Mustafa

    Single crystalline platelets of aluminum nitride (AlN) ≤ 1 mm thick have been grown within the range 1950-2250sp°C on silicon carbide (SiC) substrates via sublimation-recondensation in a resistively heated graphite furnace. The source material was sintered AlN. A maximum growth rate of 500 mum/hr was achieved at 2150sp°C and a source-to-seed separation of 4 mm. Crystals grown at high temperatures ranged in color from blue to green due to the incorporation of Si and C from the SiC substrates; those grown at lower temperatures were colorless and transparent. Secondary-ion mass spectroscopy (SIMS) results showed approximately a two order of magnitude decrease in the concentrations of these two impurities in the transparent crystals. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy studies revealed low densities of line and planar defects and a strain free material. The synthesis of high purity, single phase GaN powders was accomplished in a hot wall tube furnace via (1) the reaction of Ga(l) with ammonia (NHsb3) and (2) the conversion of Gasb2Osb3(s). Polyhedra of various shapes were obtained from both processes; some rod-shaped crystals were also observed in the material derived from Gasb2Osb3. The GaN powders produced via the first route were characterized via XRD technique. The diffraction data revealed the material to be single phase with a = 3.1891 A, c = 5.1855 A, in space group P6sb3mc, Z = 2 and Dsb{x} = 6.0886 gr/cmsp3. Scanning electron microscopy revealed a particle size distribution in the ground material between 1 and 5 mum with most of the particles being {≈}1{mu}m. The data obtained in this study was chosen to be the new standard for the powder diffraction pattern for this material by the International Center for Diffraction Data. Single crystals of GaN up to 3 mm in length were grown by sublimation of pellets of this material under an NHsb3 flow. Typical green densities were 50 to 60% of theoretical density

  18. 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

  19. 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%.

  20. Development and testing of gallium arsenide photoconductive detectors for ultra-fast, high dose rate electron and photon radiation measurements

    NASA Astrophysics Data System (ADS)

    Kharashvili, George

    Real time radiation dose measurements often present a challenge in high dose rate environments, like those needed for testing survivability of electronic devices or biological agents. Dosimetry needs at particle accelerator facilities require development of devices with fast (tens of picoseconds or less) response to pulsed radiation, linear response over a wide range of dose rates (up to 1011 Gy/s), high resistance to radiation damage, and successful operation in mixed gamma and neutron environments. Gallium arsenide photoconductive detectors (GaAs PCDs) have been shown to exhibit many of these desirable characteristics, especially the fast time response, when neutron irradiation is used to introduce displacement damage in the crystalline lattice of GaAs, hence improving the time response characteristics of the devices at the expense of their sensitivity. The objective of this project was to develop and test GaAs PCDs for ultra fast, high dose rate electron and bremsstrahlung radiation measurements. Effects of neutron pre-irradiation and detector size on the PCD properties were also investigated. GaAs PCDs with three different neutron irradiation levels (0, ˜1014, and 5 x 1015 n/cm 2 (1-MeV equivalent in GaAs) were fabricated. The devices were tested with 7, 20 and 38-MeV electron pulses produced by linear accelerators operating at the L-band frequency of 1.3-GHz and the S-band frequency of 2.8-GHz. In addition, detector responses at high dose rates were tested with 33-ns wide, 7-MeV maximum energy bremsstrahlung pulses produced by a pulse-power accelerator. The time response characteristics and the dose-rate ranges of application of the GaAs PCDs were determined. Several operational issues were identified. Recommendations on how to improve the PCD fabrication procedure and diagnostic capabilities for the high intensity radiation research are also discussed.

  1. 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

  2. Electronic States in Gallium Arsenide Quantum Wells Probed by Optically Pumped NMR

    NASA Astrophysics Data System (ADS)

    Tycko, R.; Barrett, S. E.; Dabbagh, G.; Pfeiffer, L. N.; West, K. W.

    1995-06-01

    An optical pumping technique was used to enhance and localize nuclear magnetic resonance (NMR) signals from an n-doped GaAs/Al0.1Ga0.9As multiple quantum well structure, permitting direct radio-frequency measurements of gallium-71 NMR spectra and nuclear spin-lattice relaxation rates (1/T_1) as functions of temperature (1.6 K < T < 4.2 K) and the Landau level filling factor (0.66 < ν < 1.76). The measurements reveal effects of electron-electron interactions on the energy levels and spin states of the two-dimensional electron system confined in the GaAs wells. Minima in 1/T_1 at ν≈ 1 and ν≈ 2/3 indicate energy gaps for electronic excitations in both integer and fractional quantum Hall states. Rapid, temperature-independent relaxation at intermediate ν values indicates a manifold of low-lying electronic states with mixed spin polarizations.

  3. 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.

  4. 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.

  5. 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.

  6. Close-spaced vapor transport and photoelectrochemistry of gallium arsenide for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Ritenour, Andrew J.

    The high balance-of-system costs of photovoltaic installations indicate that reductions in absorber cost alone are likely insufficient for photovoltaic electricity to reach grid parity unless energy conversion efficiency is also increased. Technologies which both yield high-efficiency cells (>25%) and maintain low costs are needed. GaAs and related III--V semiconductors are used in the highest-efficiency single- and multi-junction photovoltaics, but the technology is too expensive for non-concentrated terrestrial applications. This is due in part to the limited scalability of traditional syntheses, which rely on expensive reactors and employ toxic and pyrophoric gas-phase precursors such as arsine and trimethyl gallium. This work describes GaAs films made by close-spaced vapor transport, a potentially scalable technique which is carried out at atmospheric pressure and requires only bulk GaAs, water vapor, and a temperature gradient to deposit crystalline films with similar electronic properties to GaAs prepared using traditional syntheses. Although close-spaced vapor transport of GaAs was first developed in 1963, there were few examples of GaAs photovoltaic devices made using this method in the literature at the onset of this project. Furthermore, it was unclear whether close-spaced vapor transport could produce GaAs films appropriate for use in photovoltaics. The goal of this project was to create and study GaAs devices made using close-spaced vapor transport and determine whether the technique could be used for production of grid-connected GaAs photovoltaics. In Chapter I the design of the vapor transport reactor, the chemistry of crystal growth, and optoelectronic characterization techniques are discussed. Chapter II focuses on compositional measurements, doping, and improved electronic quality in CSVT GaAs. Chapter III describes several aspects of the interplay between structure and electronic properties of photoelectrochemical devices. Chapter IV addresses

  7. Anomalous Magneto-Optical Behavior of Rare Earth Doped Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Helbers, Andrew; Mitchell, Brandon; Woodward, Nathaniel; Dierolf, Volkmar

    We have observed unusual magneto-optical properties in rare earth doped gallium nitride. Specifically, the reversal of a magnetic field applied parallel to the c-axis produces unexpected, marked differences in luminescence spectra in several of our samples. Notably, relative emission strengths of Zeeman-split lines from the rare earth ions appear to change when the field is reversed. These effects were not observed in rare earth doped lithium niobate and lithium tantalate, which are also hexagonal and polar. Measurements for erbium doped gallium nitride suggest that these asymmetries seem to be linked to the degree of ferromagnetism of the samples. Results are presented showing these differences. The symmetry of the observed effects requires a perturbation of the RE states with a screw like symmetry. We explore whether this may be accomplished by defects such as threading dislocations. The work related to ferroelectric materials was supported by NSF Grant (DMR-1008075).

  8. 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.

  9. Direct growth of graphene on gallium nitride using C2H2 as carbon source

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Zhao, Yun; Yi, Xiao-Yan; Wang, Guo-Hong; Liu, Zhi-Qiang; Duan, Rui-Rei; Huang, Peng; Wang, Jun-Xi; Li, Jin-Min

    2016-04-01

    Growing graphene on gallium nitride (GaN) at temperatures greater than 900°C is a challenge that must be overcome to obtain high quality of GaN epi-layers. We successfully met this challenge using C2H2 as the carbon source. We demonstrated that graphene can be grown both on copper and directly on GaN epi-layers. The Raman spectra indicated that the graphene films were about 4-5 layers thick. Meanwhile, the effects of the growth temperature on the growth of the graphene films were systematically studied, and 830°C was found to be the optimum growth temperature. We successfully grew high-quality graphene films directly on gallium nitride.

  10. 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

  11. 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

  12. 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

  13. Nitridation and CVD reactions with hydrazine

    SciTech Connect

    Vogt, K.W.; Kohl, P.A.; Abys, J.A.

    1995-10-01

    The low-temperature nitridation of gallium arsenide, silicon and transition metals was investigated using hydrazine. Gallium nitride films were grown on gallium arsenide (GaAs) by direct reaction of the semiconductor surface layers with hydrazine at 200--400 C. Auger electron spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses show that the films are primarily gallium nitride with a small oxide impurity. Thin nitride films ({approximately}15{angstrom}) were grown on silicon by reaction with hydrazine at 300--500 C. Ellipsometry results suggest that the film growth goes through different phases following linear, parabolic and logarithmic functions with time. XPS analysis shows that the nitride films could be formed at much lower temperatures than possible with ammonia (300 vs. 600 C). The formation of numerous transition metal nitrides (Co, Cr, Fe, Mo, Si, Ta, Ti, V, and W) by reaction with hydrazine at 400 C is demonstrated, as well as the chemical vapor deposition of boron nitride films from diborane and hydrazine reactants. The temperature at the mixing point was critical in determining the final composition of the film. A 1-D transport model suggests that the reaction rate at 400 C was kinetically limited. The results also agree qualitatively with thermodynamic equilibrium calculations.

  14. Defects in gallium nitride nanowires: first principles calculations

    SciTech Connect

    Wang, Zhiguo; Li, Jingbo; Gao, Fei; Weber, William J.

    2010-08-15

    Atomic configurations and formation energies of native defects in an unsaturated GaN nanowire grown along the [001] direction and with (100) lateral facets are studied using large-scale ab initio calculation. Cation and anion vacancies, antisites and interstitials in the neutral charge state are all considered. The nitrogen related defects are more stable than the gallium related defects under nitrogen-rich conditions. The configurations of these defects in the core region of the nanowire are same as those in the bulk GaN. The relaxation of vacancies is generally small, but the relaxation around antisite defects is large. The nitrogen interstitial relaxes into a split interstitial configuration. The configurations of the defects in the outermost free surface region are different than those in the core. A Ga atom on the outmost surface is replaced by a Ga interstital, and is ejected on to the surface to become an adsorbed atom. A gallium atom at the outermost surface can also be ejected out to become an adsorbed atom. Nitrogen interstitials form a split-interstitial configuration with one of the nearest-neighbor nitrogens. For a Ga vacancy at the edge of the side plane of the nanowire, nitrogen atom at a gallium site and nitrogen interstitial often induced the formation of N2 molecules with low formation energy, which agrees well with experiment findings [Nano Letters 9, 1844 (2009)].

  15. Gallium arsenide electronics

    NASA Astrophysics Data System (ADS)

    Ghosh, Chuni

    The DOD has instituted a development program for microwave/mm-wave monolithic ICs ('MMICs') that are based on GaAs, in the hope of reducing the cost of EW equipment and of 'smart weapons' employing mm-wave radar guidance, as well as of increasing such electronics' resistance to radiation. MMICs involve the implantation of a complete functional subsystem on a single GaAs chip without internal wire-bonding. While near-term applications are primarily industrial, commercial sales of GaAs MMICs are expected to outnumber military sales by 4:1.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. Structure and Properties of Epitaxial Dielectrics on gallium nitride

    NASA Astrophysics Data System (ADS)

    Wheeler, Virginia Danielle

    GaN is recognized as a possible material for metal oxide semiconductor field effect transistors (MOSFETs) used in high temperature, high power and high speed electronic applications. However, high gate leakage and low device breakdown voltages limit their use in these applications. The use of high-kappa dielectrics, which have both a high permittivity (ε) and high band gap energy (Eg), can reduce the leakage current density that adversely affects MOS devices. La2O3 and Sc2O 3 are rare earth oxides with a large Eg (6.18 eV and 6.3 eV respectively) and a relatively high ε (27 and 14.1 respectively), which make them good candidates for enhancing MOSFET performance. Epitaxial growth of oxides is a possible approach to reducing leakage current and Fermi level pinning related to a high density of interface states for dielectrics on compound semiconductors. In this work, La2O3 and Sc2O 3 were characterized structurally and electronically as potential epitaxial gate dielectrics for use in GaN based MOSFETs. GaN surface treatments were examined as a means for additional interface passivation and influencing subsequent oxide formation. Potassium persulfate (K2(SO4)2) and potassium hydroxide (KOH) were explored as a way to achieve improved passivation and desired surface termination for GaN films deposited on sapphire substrates by metal organic chemical vapor deposition (MOCVD). X-ray photoelectron spectroscopy (XPS) showed that KOH left a nitrogen-rich interface, while K2(SO 4)2 left a gallium-rich interface, which provides a way to control surface oxide formation. K2(SO4)2 exhibited a shift in the O1s peak indicating the formation of a gallium-rich GaOx at the surface with decreased carbon contaminants. GaO x acts as a passivating layer prior to dielectric deposition, which resulted in an order of magnitude reduction in leakage current, a reduced hysteresis window, and an overall improvement in device performance. Furthermore, K2(SO4)2 resulted in an additional 0.4 eV of

  4. 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.

  5. Selective epitaxy of gallium nitride and related materials by metal-organic chemical vapor depostion

    NASA Astrophysics Data System (ADS)

    Kapolnek, David Joseph

    1999-11-01

    Selective epitaxy has been applied to many semiconductor materials for a variety of applications. We have developed basic selective epitaxy processes for Gallium Nitride, an important wide band gap semiconductor. This work has revealed that in many respects, GaN behaves similarly to other semiconductors. This makes possible such applications as regrown FET contacts and other three-dimensional device structures. In addition, selective growth using relatively small mask openings results in highly anisotropic growth that is exploited for a number of other applications. GaN pyramids grown using circular mask openings are ideal structures for GaN electron field emission devices. Lateral epitaxial overgrowth grown with linear mask openings is an exciting process that has recently been used for both GaN dislocation reduction and for buried structures in GaN epitaxial films. The discovery of GaN LEO has resulted in an explosion of research and has been applied in commercial GaN laser diodes. The fundamentals of Gallium Nitride selective epitaxy and the most important applications are contained in this dissertation.

  6. Improved heat dissipation in gallium nitride light-emitting diodes with embedded graphene oxide pattern

    NASA Astrophysics Data System (ADS)

    Han, Nam; Viet Cuong, Tran; Han, Min; Deul Ryu, Beo; Chandramohan, S.; Bae Park, Jong; Hye Kang, Ji; Park, Young-Jae; Bok Ko, Kang; Yun Kim, Hee; Kyu Kim, Hyun; Hyoung Ryu, Jae; Katharria, Y. S.; Choi, Chel-Jong; Hong, Chang-Hee

    2013-02-01

    The future of solid-state lighting relies on how the performance parameters will be improved further for developing high-brightness light-emitting diodes. Eventually, heat removal is becoming a crucial issue because the requirement of high brightness necessitates high-operating current densities that would trigger more joule heating. Here we demonstrate that the embedded graphene oxide in a gallium nitride light-emitting diode alleviates the self-heating issues by virtue of its heat-spreading ability and reducing the thermal boundary resistance. The fabrication process involves the generation of scalable graphene oxide microscale patterns on a sapphire substrate, followed by its thermal reduction and epitaxial lateral overgrowth of gallium nitride in a metal-organic chemical vapour deposition system under one-step process. The device with embedded graphene oxide outperforms its conventional counterpart by emitting bright light with relatively low-junction temperature and thermal resistance. This facile strategy may enable integration of large-scale graphene into practical devices for effective heat removal.

  7. 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.

  8. 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

  9. 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.

  10. Thin films of aluminum nitride and aluminum gallium nitride for cold cathode applications

    NASA Astrophysics Data System (ADS)

    Sowers, A. T.; Christman, J. A.; Bremser, M. D.; Ward, B. L.; Davis, R. F.; Nemanich, R. J.

    1997-10-01

    Cold cathode structures have been fabricated using AlN and graded AlGaN structures (deposited on n-type 6H-SiC) as the thin film emitting layer. The cathodes consist of an aluminum grid layer separated from the nitride layer by a SiO2 layer and etched to form arrays of either 1, 3, or 5 μm holes through which the emitting nitride surface is exposed. After fabrication, a hydrogen plasma exposure was employed to activate the cathodes. Cathode devices with 5 μm holes displayed emission for up to 30 min before failing. Maximum emission currents ranged from 10-100 nA and required grid voltages ranging from 20-110 V. The grid currents were typically 1 to 104 times the collector currents.

  11. Ab initio calculation of the thermodynamic properties and phase diagram of gallium nitride

    NASA Astrophysics Data System (ADS)

    Zhou, Ying; Wang, Shaofeng; Wang, Rui; Jiang, Na

    2013-12-01

    The thermodynamic properties of gallium nitride (GaN) with wurtzite (WZ) and rocksalt (RS) phases have been investigated by carrying out the first principles-calculations, in which the density-functional theory (DFT) and density-functional perturbation theory (DFPT) have been employed. The quasiharmonic approximation (QHA) has been utilized to estimate the free energies. The phonon dispersion, thermal expansion coefficients, bulk modulus, and heat capacities are presented and provided good agreement with the previous calculation and experimental data. Furthermore, the pressure-temperature (P-T) diagram of WZ-RS phase transition of GaN is predicted and the values of transition pressure range from 32.2 GPa at 0 K to about 21 GPa at 2480 K.

  12. 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.

  13. 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. PMID:22019517

  14. 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.

  15. 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.

  16. Gallium nitride nanoneedles grown in extremely non-equilibrium nitrogen plasma

    NASA Astrophysics Data System (ADS)

    Mangla, O.; Roy, S.

    2016-05-01

    In the present work, gallium nitride (GaN) nanoneedles are grown on quartz substrates using the high fluence ions of GaN produced by hot, dense and extremely non-equlibrium nitrogen plasma in a modified dense plasma focus device. The formation of nanoneedles is obtained from the scanning electron microscopy with mean size of the head of nanoneedles ~ 70 nm. The nanoneedles are found to be poly-crystalline when studied structurally through the X-ray diffraction. The optical properties of nanoneedles studied using absorption spectra which show more absorption for nanoneedles depsoited one shot of ions irradiation. In addition, the band gap of nanoneedles is found to be increased as compared to bulk GaN. The obtained nanoneedles with increased band gap have potential applications in detector systems.

  17. Biological monitoring of arsenic exposure of gallium arsenide- and inorganic arsenic-exposed workers by determination of inorganic arsenic and its metabolites in urine and hair

    SciTech Connect

    Yamauchi, H.; Takahashi, K.; Mashiko, M.; Yamamura, Y. )

    1989-11-01

    In an attempt to establish a method for biological monitoring of inorganic arsenic exposure, the chemical species of arsenic were measured in the urine and hair of gallium arsenide (GaAs) plant and copper smelter workers. Determination of urinary inorganic arsenic concentration proved sensitive enough to monitor the low-level inorganic arsenic exposure of the GaAs plant workers. The urinary inorganic arsenic concentration in the copper smelter workers was far higher than that of a control group and was associated with high urinary concentrations of the inorganic arsenic metabolites, methylarsonic acid (MAA) and dimethylarsinic acid (DMAA). The results established a method for exposure level-dependent biological monitoring of inorganic arsenic exposure. Low-level exposures could be monitored only by determining urinary inorganic arsenic concentration. High-level exposures clearly produced an increased urinary inorganic arsenic concentration, with an increased sum of urinary concentrations of inorganic arsenic and its metabolites (inorganic arsenic + MAA + DMAA). The determination of urinary arsenobetaine proved to determine specifically the seafood-derived arsenic, allowing this arsenic to be distinguished clearly from the arsenic from occupational exposure. Monitoring arsenic exposure by determining the arsenic in the hair appeared to be of value only when used for environmental monitoring of arsenic contamination rather than for biological monitoring.

  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. 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

  20. 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.

  1. 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.

  2. Photoluminescence study of (Er3+ + Yb3+) doped gallium nitride layers fabricated by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Prajzler, Vaclav; Hüttel, Ivan; Spirkova, Jarmila; Oswald, Jiri; Perina, Vratislav; Zavadil, Jiri; Machovic, Vladimír; Burian, Zdenek

    2005-09-01

    Erbium (Er3+) and Ytterbium (Yb3+) ions doped Gallium Nitride (GaN) layers were deposited by RF magnetron sputtering. Deposition was carried out in Ar + N2 gas mixture using Ga and Ga2O3 target as the source of Gallium. For the erbium and ytterbium doping, the Er2O3, Yb2O3 pellets, or Er and Yb powder were laid on the top of the Ga2O3 target. The GaN layers were deposited on silicon and Corning glass substrates. The properties of the GaN layers were investigated by using X-ray diffraction, Raman spectroscopy, absorption spectra and photoluminescence spectra. Prism coupling mode spectroscopy was used to measure the waveguiding properties. The composition of the fabricated samples was determined by using nuclear chemical analysis as Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection Analysis (ERDA). The results of the experiments were evaluated in terms of the relations between the technology approaches and the composition and luminescence properties of the fabricated thin films. Up to now the best results, which can be utilized for a structure operating at 1550 nm (when pumped at 980 nm), were obtained when using (erbium plus ytterbium) metallic powder and Corning glass as the substrate for the deposition.

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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

  8. Structure and properties of dilute nitride gallium arsenic nitride alloy films

    NASA Astrophysics Data System (ADS)

    Reason, Matthew J.

    Dilute nitride semiconductor alloys are useful for a wide range of applications. A fundamental understanding of how various growth regimes affect the structural, optical and electronic properties is needed for further optimization of device performance. This thesis explores these issues in GaAsN. We investigated the temperature-dependent mechanisms of growth for GaAsN films. At low temperatures, limited adatom surface mobility leads to layer-by-layer growth. As the temperature increases, the interplay between adatom surface diffusivity and the step-edge diffusion barrier leads to the formation of "mounds". For sufficiently high temperatures, adatoms overcome the step-edge diffusion barrier, resulting in layer-by-layer growth once again. Using a combination of nuclear reaction analysis and Rutherford backscattering spectrometry, we observe significant composition-dependent incorporation of N into non-substitutional sites, presumably as either N-N or N-As split interstitials. The (2x1) reconstruction is identified as the surface structure which leads to the highest substitutional N incorporation, presumably due to the high number of group V sites per unit area available for N-As surface exchange. For coherently strained films, a comparison of stresses measured via in-situ wafer curvature measurements, with those determined from x-ray rocking curves is used to quantify composition-dependent elastic constant bowing parameters. For films with x>2.5%, we observe that stress relaxation occurs by a combination of elastic relaxation via island formation and plastic relaxation associated with the formation of stacking faults. Optical absorption measurements reveal a substitutional nitrogen composition-dependent band gap energy reduction, which is less significant than typical literature reports. However, when the data are corrected to account for the typical 20% incorporation of non-substitutional nitrogen, all measurements reveal a band gap reduction of ˜125 meV per 1% N

  9. Spintronics: Towards room temperature ferromagnetic devices via manganese and rare earth doped gallium nitride

    NASA Astrophysics Data System (ADS)

    Luen, Melvyn Oliver

    Spintronics is a multidisciplinary field aimed at the active manipulation of spin degrees of freedom in solid-state systems. The goal being the understanding of the interaction between the particle spin and its solid-state environment, and the making of useful devices based on the acquired knowledge. If Moore's law is to continue, then we need to find alternatives to conventional microelectronics. Where conventional electronic devices rely on manipulating charge to produce desired functions, spintronic devices would manipulate both the charge flow and electron spin within that flow. This would add an extra degree of freedom to microelectronics and usher in the era of truly nanoelectronic devices. Research aimed at a whole new generation of electronic devices is underway by introducing electron spin as a new or additional physical variable, and semiconductor devices that exploit this new freedom will operate faster and more efficiently than conventional microelectronic devices and offer new functionality that promises to revolutionize the electronics industry. Long recognized as the material of choice for next-generation solid-state lighting, gallium nitride (GaN) also has proven uses in the field of high power, high frequency field-effect transistors (FETs). But its promise as a material system for spintronic applications may be its ultimate legacy. In this dissertation, the growth of gallium-manganese-nitride (GaMnN) compound semiconductor alloy was investigated through the use of an in-house built metal-organic chemical vapor deposition (MOCVD) reactor. Building on previous investigations of ferromagnetic mechanisms in GaMnN, where ferromagnetism was shown to be carrier mediated, a above room temperature ferromagnetic GaMnN i-p-n diode structure was conceived. This device proved to be the first of its kind in the world, where ferromagnetic properties are controlled via proximity of the mediating holes, upon voltage bias of adjacent structure layers

  10. 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.

  11. About holographic lithography for grating coupler fabrication in gallium nitride grown by MOVPE on sapphire substrate

    NASA Astrophysics Data System (ADS)

    Dylewicz, R.; Patela, S.; Paszkiewicz, R.; Tlaczala, M.; Bartkiewicz, S.; Miniewicz, A.

    2005-09-01

    The use of the holographic lithography method for sub-nano pattering of photoresist layer deposited on bare sapphire substrate as well as on GaN grown by metaloorganic vapour phase epitaxy on Al2O3 is reported. Positive photoresist Shipley SPR700 was first diluted with photoresist thinner and then spin-coated on prepared substrates to obtain layers of final thickness of 227nm. Thin photoresist layer was exposed in the holographic setup with wavelength of 355nm to produce the surface relief grating. After development SEM observations reveled well-defined valleys and ridges of diffraction grating in SPR700 deposited on gallium nitride layer whereas the whole structure on sapphire was strongly affected by the speckles created by reflection from the unpolished back surface of the sapphire substrate. Latter, we confirmed with transmission spectroscopy, that even small amount of light transmitted through the substrate, which is back reflected by the unpolished back-surface of sapphire, canstrongly disturb nano-sized features in photoresist.

  12. 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).

  13. 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

  14. Solution-based functionalization of gallium nitride nanowires for protein sensor development

    NASA Astrophysics Data System (ADS)

    Williams, Elissa H.; Davydov, Albert V.; Oleshko, Vladimir P.; Steffens, Kristen L.; Levin, Igor; Lin, Nancy J.; Bertness, Kris A.; Manocchi, Amy K.; Schreifels, John A.; Rao, Mulpuri V.

    2014-09-01

    A solution-based functionalization method for the specific and selective attachment of the streptavidin (SA) protein to gallium nitride (GaN) nanowires (NWs) is presented. By exploiting streptavidin's strong affinity for its ligand biotin, SA immobilization on GaN NWs was achieved by exposing the GaN NW surface to a 3-aminopropyltriethoxysilane (APTES) solution followed by reaction with biotin. Functionalization of the NWs with APTES was facilitated by the presence of an ≈ 1 nm thick surface oxide layer, which formed on the NWs after exposure to air and oxygen plasma. Biotinylation was accomplished by reacting the APTES-functionalized NWs with sulfo-N-hydroxysuccinimide-biotin at slightly alkaline pH. It was determined that the biotinylated GaN NW surface was specific towards the binding of SA and demonstrated no affinity towards a control protein, bovine serum albumin (BSA). There was however, evidence of non-specific, electrostatic binding of both the SA protein and the BSA protein to the APTES-coated NWs, revealing the importance of the biotinylation step. Successful SA immobilization on the biotinylated GaN NW surface was verified using fluorescence microscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The functionalized GaN NWs demonstrate potential as biosensing platforms for the selective detection of proteins.

  15. Characterization of gallium nitride microsystems within radiation and high-temperature environments

    NASA Astrophysics Data System (ADS)

    Chiamori, Heather C.; Hou, Minmin; Chapin, Caitlin A.; Shankar, Ashwin; Senesky, Debbie G.

    2014-03-01

    New milestones in space exploration can be realized through the development of radiation-hardened, temperature-tolerant materials, sensors and electronics. This enables lightweight systems (reduced packaging requirements) with increased operation lifetimes. Gallium nitride (GaN) is a ceramic, semiconductor material that is stable within high-radiation, high-temperature and chemically corrosive environments. Recently, this material platform has been utilized to realize sensors and electronics for operation under extreme harsh conditions. These devices exploit the two-dimensional electron gas (2DEG) formed at the interface between AlGaN/GaN heterostructures, which is used as the material platform in high electron mobility transistors (HEMTs). In this paper, a review of the advancements in GaN manufacturing technology such as the growth of epitaxially deposited thin films, micromachining techniques and high-temperature metallization is presented. In addition, the compelling results of fabricating and operating micro-scale GaNbased sensors within radiation environments and at elevated temperatures are shown. The paper will close with future directions GaN-based microsystems technology for down-hole, propulsion and space exploration applications.

  16. Heat resistive dielectric multi-layer micro-mirror array in epitaxial lateral overgrowth gallium nitride.

    PubMed

    Huang, Chen-Yang; Ku, Hao-Min; Liao, Wei-Tsai; Chao, Chu-Li; Tsay, Jenq-Dar; Chao, Shiuh

    2009-03-30

    Ta2O5 / SiO2 dielectric multi-layer micro-mirror array (MMA) with 3mm mirror size and 6mm array period was fabricated on c-plane sapphire substrate. The MMA was subjected to 1200 degrees C high temperature annealing and remained intact with high reflectance in contrast to the continuous multi-layer for which the layers have undergone severe damage by 1200 degrees C annealing. Epitaxial lateral overgrowth (ELO) of gallium nitride (GaN) was applied to the MMA that was deposited on both sapphire and sapphire with 2:56 mm GaN template. The MMA was fully embedded in the ELO GaN and remained intact. The result implies that our MMA is compatible to the high temperature growth environment of GaN and the MMA could be incorporated into the structure of the micro-LED array as a one to one micro backlight reflector, or as the patterned structure on the large area LED for controlling the output light. PMID:19333330

  17. 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.

  18. Metasurfaces based on Gallium Nitride High Contrast Gratings at Visible Range

    NASA Astrophysics Data System (ADS)

    Wang, Zhenhai; He, Shumin; Liu, Qifa; Wang, Wei; Wang, Yongjin; Zhu, Hongbo; Grünberg Research Centre Team

    2015-03-01

    Metasurfaces are currently attracting global attention due to their ability to achieve full control of light propagation. However, these metasurfaces have thus far been constructed mostly from metallic materials, which greatly limit the diffraction efficiencies because of the ohmic losses. Semiconducting metasurfaces offer one potential solution to the issue of losses. Besides, the use of semiconducting materials can broaden the applicability of metasurfaces, as they enable facile integration with electronics and mechanical systems and can benefit from mature semiconductor fabrication technologies. We have proposed visible-light metasurfaces (VLMs) capable of serving as lenses and beam deflecting elements based on gallium nitride (GaN) high contrast gratings (HCGs). By precisely manipulating the wave-fronts of the transmitted light, we theoretically demonstrate an HCG focusing lens with transmissivity of 83.0% and numerical aperture of 0.77, and a VLM with beam deflection angle of 6.03° and transmissivity as high as 93.3%. The proposed 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.

  19. 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.

  20. Surface cleaning procedures for thin films of indium gallium nitride grown on sapphire

    NASA Astrophysics Data System (ADS)

    Douglass, K.; Hunt, S.; Teplyakov, A.; Opila, R. L.

    2010-12-01

    Surface preparation procedures for indium gallium nitride (InGaN) thin films were analyzed for their effectiveness for carbon and oxide removal as well as for the resulting surface roughness. Aqua regia (3:1 mixture of concentrated hydrochloric acid and concentrated nitric acid, AR), hydrofluoric acid (HF), hydrochloric acid (HCl), piranha solution (1:1 mixture of sulfuric acid and 30% H 2O 2) and 1:9 ammonium sulfide:tert-butanol were all used along with high temperature anneals to remove surface contamination. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were utilized to study the extent of surface contamination and surface roughness, respectively. The ammonium sulfide treatment provided the best overall removal of oxygen and carbon. Annealing over 700 °C after a treatment showed an even further improvement in surface contamination removal. The piranha treatment resulted in the lowest residual carbon, while the ammonium sulfide treatment leads to the lowest residual oxygen. AFM data showed that all the treatments decreased the surface roughness (with respect to as-grown specimens) with HCl, HF, (NH 4) 2S and RCA procedures giving the best RMS values (˜0.5-0.8 nm).

  1. The effects of rare earth doping on gallium nitride thin films

    NASA Astrophysics Data System (ADS)

    McHale, Stephen R.

    The thermal neutron capture cross section of the rare earth (RE) metal isotope Gd-157 is the largest of all known natural elements, which distinguishes the material as a logical candidate for neutron detection. To address an incomplete understanding of rare earth doped Gallium Nitride (GaN) materials, investigations of the surface electronic structure and interface properties of GaN thin films doped with rare earths (Yb, Er, Gd) were undertaken. Lattice ion occupation, bonding, rare earth 4f occupation, and gold Schottky barrier formation were examined using synchrotron photoemission spectroscopy. Measured Debye temperatures indicate substitutional occupation of Ga sites by RE ions. The occupied RE 4f levels, deep within the valence band, suggest that intra-atomic f-f transitions may be more 'blue' than predicted by theoretical models. Thin layers of gold did not wet and uniformly cover the GaN surface, even with rare earth doping of the GaN. The resultant Schottky barrier heights for GaN:Yb, GaN:Er, and GaN:Gd, are 25--55% larger than those reported at the gold to undoped GaN interface. The utility of gadolinium as a neutron detection material was examined via fundamental nuclear and semiconductor physics. Low charge production and the large range of internal conversion electrons limits charge collection efficiency.

  2. Performance and applications of gallium-nitride monolithic microwave integrated circuits (GaN MMICs)

    NASA Astrophysics Data System (ADS)

    Scott, Jonathan B.; Parker, Anthony E.

    2007-12-01

    The evolution of wide-bandgap semiconductor transistor technology is placed in historical context with other active device technologies. The relative rapidity of GaN transistor development is noted and is attributed to the great parallel activity in the lighting sector and the historical experience and business model from the III-V compound semiconductor sector. The physical performance expectations for wide-bandgap technologies such as Gallium-Nitride Field-Effect Transistors (GaN FETs) are reviewed. We present some device characteristics. Challenges met in characterising, and prospects for modeling GaN FETs are described. Reliability is identified as the final remaining hurdle facing would-be foundries. Evolutionary and unsurprising applications as well as novel and revolutionary applications are suggested. Novel applications include wholly monolithic switchmode power supplies, simplified tools for ablation and diathermy in tissue, and very wide dynamic range circuits for audio or low phase noise signal generation. We conclude that now is the time to embark on circuit design of MMICs in wide-bandgap technology. The potential for fabless design groups to capitalise upon design IP without strong geopraphic advantage is noted.

  3. 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.

  4. Platinum nanoparticles on gallium nitride surfaces: effect of semiconductor doping on nanoparticle reactivity.

    PubMed

    Schäfer, Susanne; Wyrzgol, Sonja A; Caterino, Roberta; Jentys, Andreas; Schoell, Sebastian J; Hävecker, Michael; Knop-Gericke, Axel; Lercher, Johannes A; Sharp, Ian D; Stutzmann, Martin

    2012-08-01

    Platinum nanoparticles supported on n- and p-type gallium nitride (GaN) are investigated as novel hybrid systems for the electronic control of catalytic activity via electronic interactions with the semiconductor support. In situ oxidation and reduction were studied with high pressure photoemission spectroscopy. The experiments revealed that the underlying wide-band-gap semiconductor has a large influence on the chemical composition and oxygen affinity of supported nanoparticles under X-ray irradiation. For as-deposited Pt cuboctahedra supported on n-type GaN, a higher fraction of oxidized surface atoms was observed compared to cuboctahedral particles supported on p-type GaN. Under an oxygen atmosphere, immediate oxidation was recorded for nanoparticles on n-type GaN, whereas little oxidation was observed for nanoparticles on p-type GaN. Together, these results indicate that changes in the Pt chemical state under X-ray irradiation depend on the type of GaN doping. The strong interaction between the nanoparticles and the support is consistent with charge transfer of X-ray photogenerated free carriers at the semiconductor-nanoparticle interface and suggests that GaN is a promising wide-band-gap support material for photocatalysis and electronic control of catalysis. PMID:22738117

  5. 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.

  6. 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. PMID:25479565

  7. 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

  8. Metal-semiconductor-metal ultraviolet photodetectors based on gallium nitride grown by atomic layer deposition at low temperatures

    NASA Astrophysics Data System (ADS)

    Tekcan, Burak; Ozgit-Akgun, Cagla; Bolat, Sami; Biyikli, Necmi; Okyay, Ali Kemal

    2014-10-01

    Proof-of-concept, first metal-semiconductor-metal ultraviolet photodetectors based on nanocrystalline gallium nitride (GaN) layers grown by low-temperature hollow-cathode plasma-assisted atomic layer deposition are demonstrated. Electrical and optical characteristics of the fabricated devices are investigated. Dark current values as low as 14 pA at a 30 V reverse bias are obtained. Fabricated devices exhibit a 15× UV/VIS rejection ratio based on photoresponsivity values at 200 nm (UV) and 390 nm (VIS) wavelengths. These devices can offer a promising alternative for flexible optoelectronics and the complementary metal oxide semiconductor integration of such devices.

  9. 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

  10. 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.

  11. High Active Nitrogen Flux Growth of (Indium) Gallium Nitride by Plasma Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    McSkimming, Brian Matthew

    Plasma-assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) has evolved over the past two decades due to progress in growth science and in the active nitrogen plasma source hardware. The transition from electron cyclotron resonance (ECR) microwave plasma sources to radio frequency (RF) plasma sources has enabled higher growth rates, reduced ion damage and improved operation at higher growth chamber pressures. Even with further improvements in RF plasma sources, PAMBE has remained primarily a research tool partially due to limitations in material growth rates. This dissertation presents results based upon two modifications of a commercially available nitrogen plasma source. These modifications have resulted in record active nitrogen fluxes, and therefore record growth rates of more than 7.6 mum/h. For optimized growth conditions in the standard metal-rich growth regime, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 mumx3 mum) on the order of 1 nm. Secondary ion mass spectroscopy (SIMS) impurity analysis demonstrates unintentional oxygen incorporation of ˜1x1016, comparable to the metal organic chemical vapor deposition (MOCVD) grown template layer. Additionally, a revised universal growth diagram is proposed allowing the rapid determination of the metal flux needed to grow in a specific growth regime for any and all active nitrogen fluxes available. High temperature nitrogen rich PAMBE growth of GaN has been previously demonstrated as a viable alternative to the challenges presented in maintaining the Ga bilayer required by metal rich growth of GaN. This dissertation also present results demonstrating PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ˜100 °C greater than any previously reported PAMBE growth of GaN. Finally, a revised growth diagram is proposed highlighting a large growth window available at high temperatures.

  12. 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.

  13. 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

  14. 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

  15. 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

  16. Hot-Electron Gallium Nitride Two Dimensional Electron Gas Nano-bolometers For Advanced THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Rahul

    Two-dimensional electron gas (2DEG) in semiconductor heterostructures was identified as a promising medium for hot-electron bolometers (HEB) in the early 90s. Up until now all research based on 2DEG HEBs is done using high mobility AlGaAs/GaAs heterostructures. These systems have demonstrated very good performance, but only in the sub terahertz (THz) range. However, above ˜0.5 THz the performance of AlGaAs/GaAs detectors drastically deteriorates. It is currently understood, that detectors fabricated from standard AlGaAs/GaAs heterostructures do not allow for reasonable coupling to THz radiation while maintaining high conversion efficiency. In this work we have developed 2DEG HEBs based on disordered Gallium Nitride (GaN) semiconductor, that operate at frequencies beyond 1THz at room temperature. We observe strong free carrier absorption at THz frequencies in our disordered 2DEG film due to Drude absorption. We show the design and fabrication procedures of novel micro-bolometers having ultra-low heat capacities. In this work the mechanism of 2DEG response to THz radiation is clearly identified as bolometric effect through our direct detection measurements. With optimal doping and detector geometry, impedances of 10--100 O have been achieved, which allow integration of these devices with standard THz antennas. We also demonstrate performance of the antennas used in this work in effectively coupling THz radiation to the micro-bolometers through polarization dependence and far field measurements. Finally heterodyne mixing due to hot electrons in the 2DEG micro-bolometer has been performed at sub terahertz frequencies and a mixing bandwidth greater than 3GHz has been achieved. This indicates that the characteristic cooling time in our detectors is fast, less than 50ps. Due to the ultra-low heat capacity; these detectors can be used in a heterodyne system with a quantum cascade laser (QCL) as a local oscillator (LO) which typically provides output powers in the micro

  17. 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

  18. Threading dislocations in gallium nitride epilayers grown by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Fang, Xiaolong

    Gallium nitride (GaN) epitaxial layers were deposited by metalorganic vapor phase epitaxy on (0001) sapphire. A new approach involving silicon nitride (Si3N4) interlayers deposited on as-grown nucleation layers (NLs) was demonstrated for reducing the density of threading dislocations (TDs). By inserting the Si3N4 interlayer, the metamorphosis of the NL upon thermal annealing was significantly changed as compared to that without the Si3N4 interlayer. Surface roughening upon thermal annealing produced a small number of protrusions from the NLs breaking through the Si3N4 interlayer. Initial GaN overgrowth could then be confined to the exposed protrusions, ensuring a selective area growth mode similar to the epitaxial lateral overgrowth (ELOG) technique. This new technique is referred to as "in situ patterning ELOG". The TD density has been reduced by one to two orders of magnitude as compared to the two-step growth. The improvement of crystal quality was also confirmed by X-ray diffraction and photoluminescence measurements. A comprehensive investigation of morphology and microstructure evolution in GaN NLs and early stage GaN overgrowths was carried out in order to understand the mechanisms of generation and reduction of TDs. Annealed NLs in Si 3N4/GaN NL composites consist of discrete grains with very high density of basal plane stacking faults. The majority of edge dislocations (Burgers vector 1/3<11--20>) emerging from the exposed regions can be generated by reactions in which a Shockley partial dislocation bounding a stacking fault creates a perfect dislocation and another Shockley partial dislocation. These perfect dislocations can bend to form vertical dislocations (VDs) when vertical growth dominates then bend back to from horizontal dislocations (HDs) once lateral overgrowth dominates. Dislocation bending occurs as a result of glide and climb in the presence of stresses and point defects during the early stage of high temperature overgrowth. A significant

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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).

  5. 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.

  6. 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

  7. 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

  8. 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)

  9. A terminal molybdenum arsenide complex synthesized from yellow arsenic.

    PubMed

    Curley, John J; Piro, Nicholas A; Cummins, Christopher C

    2009-10-19

    A terminal molybdenum arsenide complex is synthesized in one step from the reactive As(4) molecule. The properties of this complex with its arsenic atom ligand are discussed in relation to the analogous nitride and phosphide complexes. PMID:19764796

  10. Optimized Spiral Metal-Gallium-Nitride Nanowire Cavity for Ultra-High Circular Dichroism Ultraviolet Lasing at Room Temperature

    NASA Astrophysics Data System (ADS)

    Liao, Wei-Chun; Liao, Shu-Wei; Chen, Kuo-Ju; Hsiao, Yu-Hao; Chang, Shu-Wei; Kuo, Hao-Chung; Shih, Min-Hsiung

    2016-05-01

    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.

  11. 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

  12. 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

  13. Spectroscopic Ellipsometry Measurements of Wurtzite Gallium Nitride Surfaces as a Function of Buffered Oxide Etch Substrate Submersion

    NASA Astrophysics Data System (ADS)

    Szwejkowski, Chester; Constantin, Costel; Duda, John; Hopkins, Patrick; Optical Studies of GaN interfaces Collaboration

    2013-03-01

    Gallium nitride (GaN) is considered the most important semiconductor after the discovery of silicon. Understanding the optical properties of GaN surfaces is imperative in determining the utility and applicability of this class of materials to devices. In this work, we present preliminary results of spectroscopic ellipsometry measurements as a function of surface root mean square (RMS). We used commercially available 5mm x 5mm, one side polished GaN (3-7 μm)/Sapphire (430 μm) substrates that have a wurtzite crystal structure and they are slightly n-type doped. The GaN substrates were cleaned with Acetone (20 min)/Isopropanol(20 min)/DI water (20 min) before they were submerged into Buffered Oxide Etch (BOE) for 10s - 60s steps. This BOE treatment produced RMS values of 1-30 nm as measured with an atomic force microscope. Preliminary qualitative ellipsometric measurements show that the complex refractive index and the complex dielectric function decrease with an increase of RMS. More measurements need to be done in order to provide explicit quantitative results. This work was supported by the 4-VA Collaborative effort between James Madison University and University of Virginia.

  14. 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.

  15. 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.

  16. The role of ammonization on chemical bonding and optical properties of nickel-catalyzed gallium nitride nanowire

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Nickel-catalyzed gallium nitride nanowires (GaN-NWs) were grown on p-type Si (100) substrates using Ga2O3 powder and NH3, N2, and H2 as precursor gases in chemical vapor deposition reactor. The GaN-NWs were characterized by atomic force microscopy (AFM), Fourier transform infrared spectroscopy, Raman spectroscopy, and photoluminescence (PL) spectroscopy to investigate microstructural, structural, optical, and chemical bonding networks of GaN-NW films. AFM shows the formation of GaN-NWs with different diameter. The room temperature PL spectra of GaN-NWs show a broad blue emission band centered at 2.54, 2.69, 2.81, 2.89, and 2.94 eV, which are associated with different electronic transitions. The stokes shift of GaN-NWs reveals the existence of prominent transverse optic and longitudinal optic (LO) peak at 548 and 795 cm-1, respectively. However, the pronounced blue shifting of LO peak was observed with increasing NH3 flow rate indicates considerable stress in NWs.

  17. 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.

  18. 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.

  19. Low-energy ion beam-based deposition of gallium nitride

    NASA Astrophysics Data System (ADS)

    Vasquez, M. R.; Wada, M.

    2016-02-01

    An ion source with a remote plasma chamber excited by a 13.56 MHz radio frequency power was used for low-energy broad ion beam extraction. Optical emission spectral analyses showed the sputtering and postionization of a liquid gallium (Ga) target placed in a chamber separated from the source bombarded by argon (Ar) plasma guided by a bent magnetic field. In addition, an E × B probe successfully showed the extraction of low-energy Ga and Ar ion beams using a dual-electrode extractor configuration. By introducing dilute amounts of nitrogen gas into the system, formation of thin Ga-based films on a silicon substrate was demonstrated as determined from X-ray diffraction and X-ray reflectivity studies.

  20. Low-energy ion beam-based deposition of gallium nitride.

    PubMed

    Vasquez, M R; Wada, M

    2016-02-01

    An ion source with a remote plasma chamber excited by a 13.56 MHz radio frequency power was used for low-energy broad ion beam extraction. Optical emission spectral analyses showed the sputtering and postionization of a liquid gallium (Ga) target placed in a chamber separated from the source bombarded by argon (Ar) plasma guided by a bent magnetic field. In addition, an E × B probe successfully showed the extraction of low-energy Ga and Ar ion beams using a dual-electrode extractor configuration. By introducing dilute amounts of nitrogen gas into the system, formation of thin Ga-based films on a silicon substrate was demonstrated as determined from X-ray diffraction and X-ray reflectivity studies. PMID:26932113

  1. 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.

  2. Ab initio study of the unusual thermal transport properties of boron arsenide and related materials

    NASA Astrophysics Data System (ADS)

    Broido, D. A.; Lindsay, L.; Reinecke, T. L.

    2013-12-01

    Recently, using a first principles approach, we predicted that zinc blende boron arsenide (BAs) will have an ultrahigh lattice thermal conductivity, κ, of over 2000 Wm-1K-1 at room temperature (RT), comparable to that of diamond. Here, we provide a detailed ab initio examination of phonon thermal transport in boron arsenide, contrasting its unconventional behavior with that of other related materials, including the zinc blende crystals boron nitride (BN), boron phosphide, boron antimonide, and gallium nitride (GaN). The unusual vibrational properties of BAs contribute to its weak phonon-phonon scattering and phonon-isotope scattering, which are responsible for its exceptionally high κ. The thermal conductivity of BAs has contributions from phonons with anomalously large mean free paths (˜2 μm), two to three times those of diamond and BN. This makes κ in BAs sensitive to phonon scattering from crystal boundaries. An order of magnitude smaller RT thermal conductivity in a similar material, zinc blende GaN, is connected to more separated acoustic phonon branches, larger anharmonic force constants, and a large isotope mixture on the heavy rather than the light constituent atom. The striking difference in κ for BAs and GaN demonstrates the importance of using a microscopic first principles thermal transport approach for calculating κ. BAs also has an advantageous RT coefficient of thermal expansion, which, combined with the high κ value, suggests that it is a promising material for use in thermal management applications.

  3. 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

  4. 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

  5. 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.

  6. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics - a Comparative Study with Gallium Nitride

    NASA Astrophysics Data System (ADS)

    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.

  7. 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

  8. Growth of Indium Gallium Nitride Nanorings via Metal Organic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Zaidi, Zohair

    III-Nitride nanostructures have been an active area of research recently due to their ability to tune their optoelectronic properties. Thus far work has been done on InGaN quantum dots, nanowires, nanopillars, amongst other structures, but this research reports the creation of a new type of InGaN nanostructure, nanorings. Hexagonal InGaN nanorings were formed using Metal Organic Chemical Vapor Deposition through droplet epitaxy. The nanorings were thoroughly analyzed using x-ray diffraction, photoluminescence, electron microscopy, electron diffraction, and atomic force microscopy. Nanorings with high indium incorporation were achieved with indium content up to 50% that was then controlled using the growth time, temperature, In/Ga ratio and III/N ratio. The analysis showed that the nanoring shape is able to incorporate more indium than other nanostructures, due to the relaxing mechanism involved in the formation of the nanoring. The ideal conditions were determined to be growth of 30 second droplets with a growth time of 1 minute 30 seconds at 770 C to achieve the most well developed rings with the highest indium concentration.

  9. 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.

  10. Investigation of indium gallium nitride facet-dependent nonpolar growth rates and composition for core-shell light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Gîrgel, Ionut; Edwards, Paul R.; Le Boulbar, Emmanuel; Coulon, Pierre-Marie; Sahonta, Suman-Lata; Allsopp, Duncan W. E.; Martin, Robert W.; Humphreys, Colin J.; Shields, Philip A.

    2016-01-01

    Core-shell indium gallium nitride (InGaN)/gallium nitride (GaN) structures are attractive as light emitters due to the large nonpolar surface of rod-like cores with their longitudinal axis aligned along the c-direction. These facets do not suffer from the quantum-confined Stark effect that limits the thickness of quantum wells and efficiency in conventional light-emitting devices. Understanding InGaN growth on these submicron three-dimensional structures is important to optimize optoelectronic device performance. In this work, the influence of reactor parameters was determined and compared. GaN nanorods (NRs) with both {11-20} a-plane and {10-10} m-plane nonpolar facets were prepared to investigate the impact of metalorganic vapor phase epitaxy reactor parameters on the characteristics of a thick (38 to 85 nm) overgrown InGaN shell. The morphology and optical emission properties of the InGaN layers were investigated by scanning electron microscopy, transmission electron microscopy, and cathodoluminescence hyperspectral imaging. The study reveals that reactor pressure has an important impact on the InN mole fraction on the {10-10} m-plane facets, even at a reduced growth rate. The sample grown at 750°C and 100 mbar had an InN mole fraction of 25% on the {10-10} facets of the NRs.

  11. Development of aluminum gallium nitride based optoelectronic devices operating in deep UV and terahertz spectrum ranges

    NASA Astrophysics Data System (ADS)

    Zhang, Wei

    In this research project I have investigated AlGaN alloys and their quantum structures for applications in deep UV and terahertz optoelectronic devices. For the deep UV emitter applications the materials and devices were grown by rf plasma-assisted molecular beam epitaxy on 4H-SiC, 6H-SiC and c-plane sapphire substrates. In the growth of AlGaN/AlN multiple quantum wells on SiC substrates, the AlGaN wells were grown under excess Ga, far beyond than what is required for the growth of stoichiometric AlGaN films, which resulted in liquid phase epitaxy growth mode. Due to the statistical variations of the excess Ga on the growth front we found that this growth mode leads to films with lateral variations in the composition and thus, band structure potential fluctuations. Transmission electron microscopy shows that the wells in such structures are not homogeneous but have the appearance of quantum dots. We find by temperature dependent photoluminescence measurements that the multiple quantum wells with band structure potential fluctuations emit at 240 nm and have room temperature internal quantum efficiency as high as 68%. Furthermore, they were found to have a maximum net modal optical gain of 118 cm-1 at a transparency threshold corresponding to 1.4 x 1017 cm-3 excited carriers. We attribute this low transparency threshold to population inversion of only the regions of the potential fluctuations rather than of the entire matrix. Some prototype deep UV emitting LED structures were also grown by the same method on sapphire substrates. Optoelectronic devices for terahertz light emission and detection, based on intersubband transitions in III-nitride semiconductor quantum wells, were grown on single crystal c-plane GaN substrates. Growth conditions such the ratio of group III to active nitrogen fluxes, which determines the appropriate Ga-coverage for atomically smooth growth without requiring growth interruptions were employed. Emitters designed in the quantum cascade

  12. Growth of Gallium Nitride Nanowires: A Study Using In Situ Transmission Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Diaz Rivas, Rosa Estela

    Owing to their special characteristics, group III-Nitride semiconductors have attracted special attention for their application in a wide range of optoelectronic devices. Of particular interest are their direct and wide band gaps that span from ultraviolet to the infrared wavelengths. In addition, their stronger bonds relative to the other compound semiconductors makes them thermally more stable, which provides devices with longer life time. However, the lattice mismatch between these semiconductors and their substrates cause the as-grown films to have high dislocation densities, reducing the life time of devices that contain these materials. One possible solution for this problem is to substitute single crystal semiconductor nanowires for epitaxial films. Due to their dimensionality, semiconductor nanowires typically have stress-free surfaces and better physical properties. In order to employ semiconductor nanowires as building blocks for nanoscale devices, a precise control of the nanowires' crystallinity, morphology, and chemistry is necessary. This control can be achieved by first developing a deeper understanding of the processes involved in the synthesis of nanowires, and then by determining the effects of temperature and pressure on their growth. This dissertation focuses on understanding of the growth processes involved in the formation of GaN nanowires. Nucleation and growth events were observed in situ and controlled in real-time using an environmental transmission electron microscope. These observations provide a satisfactory elucidation of the underlying growth mechanism during the formation of GaN nanowires. Nucleation of these nanowires appears to follow the vapor-liquid-solid mechanism. However, nanowire growth is found to follow both the vapor-liquid-solid and vapor-solid-solid mechanisms. Direct evidence of the effects of III/V ratio on nanowire growth is also reported, which provides important information for tailoring the synthesis of Ga

  13. Heteroepitaxy of nitrogen-polar, nonpolar, and semipolar gallium nitride by MOCVD

    NASA Astrophysics Data System (ADS)

    Sun, Qian

    summarized and discussed. Mirror-like semipolar (112&barbelow;2) GaN with improved quality has been consistently attained on m-plane sapphire through a two-step growth scheme. And the preliminary results of semipolar (112&barbelow;2) InGaN green quantum wells were very encouraging. We have achieved atomically smooth N-polar (0001&barbelow;) GaN with crystalline quality comparable to that of Ga-polar c-plane GaN by adopting an appropriate nitridation for slightly offcut sapphire substrates, and investigated the challenges in growing high quality N-polar InGaN.

  14. 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...

  15. 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.

  16. MQWs InGaN/GaN LED with embedded micro-mirror array in the epitaxial-lateral-overgrowth gallium nitride for light extraction enhancement.

    PubMed

    Huang, Chen-Yang; Ku, Hao-Min; Liao, Chen-Zi; Chao, Shiuh

    2010-05-10

    Multi-quantum wells (MQWs) InGaN/GaN LEDs, 300 microm x 300 microm chip size, were fabricated with Ta(2)O(5) / SiO(2) dielectric multi-layer micro-mirror array (MMA) embedded in the epitaxiallateral- overgrowth (ELOG) gallium nitride (GaN) on the c-plane sapphire substrate. MQWs InGaN/GaN LEDs with ELOG embedded patterned SiO(2) array (P-SiO(2)) of the same dimension as the MMA were also fabricated for comparison. Dislocation density was reduced for the ELOG samples. 75.2% light extraction enhancement for P-SiO(2)-LED and 102.6% light extraction enhancement for MMA-LED were obtained over the standard LED. We showed that multiple-diffraction with high intensity from the MMA redirected the trap lights to escape from the LED causing the light extraction enhancement. PMID:20588920

  17. 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.

  18. Anodic bonding of gallium arsenide to glass

    NASA Astrophysics Data System (ADS)

    Hök, Bertil; Dubon, Chantal; Ovrén, Christer

    1983-08-01

    We describe a modified anodic bonding technique for hermetic sealing between GaAs and glass, the modification being called for by the formation of a nonadherent oxide layer during the bonding process. We show that this can be avoided by prebaking the glass and performing the bonding operation in a reducing atmosphere. With this technique, strong, hermetic seals can be produced. Parameter dependence has been studied theoretically by solving the continuity equation for a one-dimensional model of the experimental situation. Experimentally, the bonds were evaluated with a number of methods, giving support for a model consisting of a high-field, sodium-depleted zone in the interface region during bond formation. The described technique is of particular interest for optoelectronic devices requiring transparent and hermetic seals.

  19. Epitaxial growth dynamics in gallium arsenide

    NASA Astrophysics Data System (ADS)

    Ballestad, Anders

    The problem of a complete theory describing the far-from-equilibrium statistical mechanics of epitaxial crystal growth remains unsolved. Besides its academic importance, this problem is also interesting from the point of view of device manufacturing. In order to improve on the quality and performance of lateral nanostructures at the lengthscales required by today's technology, a better understanding of the physical mechanisms at play during epitaxial growth and their influence on the evolution of the large-scale morphology is required. In this thesis, we present a study of the morphological evolution of GaAs (001) during molecular beam epitaxy by experimental investigation, theoretical considerations and computational modeling. Experimental observations show that initially rough substrates smooth during growth and annealing towards a steady-state interface roughness, as dictated by kinetic roughening theory. This smoothing indicates that there is no need for a destabilizing step-edge barrier in this material system. In fact, generic surface growth models display a much better agreement with experiments when a weak, negative barrier is used. We also observe that surface features grow laterally, as well as vertically during epitaxy. A growth equation that models smoothing combined with lateral growth is the nonlinear, stochastic Kardar-Parisi-Zhang (KPZ) equation. Simulation fits match the experimentally observed surface morphologies quite well, but we argue that this agreement is coincidental and possibly a result of limited dynamic range in our experimental measurements. In light of these findings, we proceed by developing a coupled growth equations (CGE) model that describes the full morphological evolution of both flat and patterned starting surfaces. The resulting fundamental model consists of two coupled, spatially dependent rate equations that describe the interaction between diffusing adatoms and the surface through physical processes such as adatom diffusion, deposition, and incorporation and detachment at step edges. In the low slope, small amplitude limit, the CGE model reduces to a nonlinear growth equation similar to the KPZ equation. From this, the apparent applicability of the KPZ equation to surface shape evolution is explained. The CGE model is based on fundamental physical processes, and can therefore explain the underlying physics, as well as describe macroscopic pattern evolution during growth.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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 ...

  6. Theoretical and experimental studies of surface processes in the course of molecular-beam epitaxy of gallium nitride

    SciTech Connect

    Bobrovnikova, I. A. Ivonin, I. V.; Novikov, V. A.; Preobrazhenskii, V. V.

    2009-03-15

    The method of atomic-force microscopy has been used to experimentally study the effect of growth conditions on the structure of the surface of epitaxial GaN layers grown by molecular-beam epitaxy. Quantitative values of the density, height, and width of growth centers in relation to the conditions of epitaxy are obtained; the average length of the diffusion path of particles limiting the GaN growth rate have been estimated; and the activation energies and the surface-diffusion coefficients for these particles have been calculated. The equilibrium composition of adsorbed layers at the GaN (0001) surface in a wide range of deposition temperatures and pressures of gallium and nitrogen has been calculated with account taken of the following components: gallium atoms, nitrogen atoms, and NH molecules. On the basis of the comparison of experimental data on the structure of the GaN surface with results of calculations concerning the composition of adsorbed layers on the growth surface, it was assumed that the growth of GaN layers is limited by supply of gallium.

  7. 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.

  8. Elastic Constants of Indium Arsenide at Room Temperature by Resonant Ultrasound Spectroscopy

    NASA Astrophysics Data System (ADS)

    Arammash, Fouzi; Yin, Ming

    2013-03-01

    The three independent elastic constants, C11, C12, and C44 of indium arsenide (InAs) single crystal were determined at room temperature using resonant ultrasound spectroscopy (RUS) technique. We will present and compare our results with those obtained from more conventional measurement techniques. We also compare our results to those of other III-V compound semiconductors such as gallium arsenide (GaAs).

  9. 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

  10. Optical Spectroscopy of Indium Gallium Arsenide/gallium Arsenide Quantum Wells

    NASA Astrophysics Data System (ADS)

    Adams, Stephen J. A.

    1992-01-01

    Available from UMI in association with The British Library. In_{rm x}Ga _{rm 1-x}As/GaAs quantum wells have been studied using optical and magneto -optical techniques. Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been used to determine the valence band offset in these heterostructures which was found to vary between 0.4 for wells with indium concentration x = 0.08 to 0.2 for wells with x = 0.21. An interband magneto-luminescence oscillation (IMLO) technique has been applied to the study of undoped 'multi-single' quantum well samples and the theoretically predicted peaked nature of the exciton binding energy as a function of well width has been observed for the first time in any material system. The conduction band effective mass was also determined in the same samples using Optically Detected Cyclotron Resonance (ODCR) and found to be constant over the range of well widths studied at a value close to that of the bulk, with a suitable correction for strain effects. This result was then combined with the IMLO data, fitted to the theory of Akimoto and Hasegawa, to deduce the hole mass as a function of well width, which was found to increase significantly in narrower wells. PL and PLE data was also obtained from modulation doped quantum wells. The PL involving transitions from highly populated subbands was found to be much broader than the PLE data from unpopulated subbands, where the transitions were strongly excitonic. Furthermore the PL linewidth in n-type samples was somewhat greater than that in p-type samples because of the difference in particle effective mass. Comparison of the Fermi energy deduced from PL in n-type samples with Hall and Shubnikov-de Haas measurements suggested an enhancement in the density-of -states over the value in undoped wells. Interesting effects were also observed in the quantum well luminescence arising from an interaction with GaAs deep levels in the barrier layers. A novel method was used to determine the effective mass renormalisation due to the presence of a two-dimensional electron gas in modulation-doped quantum wells. The technique took advantage of the presence, in the samples studied, of parity-allowed transitions between the two lowest conduction subbands and the lowest valence subband. Landau splittings were observed in the n_{rm c } = 1 to n_{rm v } = 1 recombination in PL and in the n _{rm c} = 2 to n _{rm v} = 1 recombination in PLE, and a comparison of the reduced masses derived from the two sets of Landau fans allowed the effective mass enhancement to be determined. Enhancements of the order of 20%, independent of magnetic field, have been observed in samples with well sheet carrier density of approximately 10^{12}cm ^{-2}.

  11. 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.

  12. 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.

  13. 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.

  14. Advanced design of ultra-thin barrier aluminum nitride/gallium nitride HEMTs; A study of device design, modeling, and analysis

    NASA Astrophysics Data System (ADS)

    Deen, David A.

    Of the III-Nitride family the AlN/GaN heterojunction has demonstrated the largest combined polarization charge and energy band offsets available in the system. Engineering the polarization fields through varying the AlN thickness leads to two-dimensional electron gas densities (2DEGs) that may be tailored between 0.5--5 x 1013 cm-2 . Furthermore, the ultra-thin (< 5 nm) barrier and excellent transport properties of this all binary heterostructure make it well suited for high electron mobility transistor applications where high frequency and high current are required. This work encompasses various design aspects of GaN-based High Electron Mobility Transistors (HEMTs) which ultimately result in the realization of several generations that utilize the AlN/GaN heterostructure. HEMTs fabricated from high-mobility, low sheet resistance heterostructures have achieved drain current densities up to 2.3 A/mm and transconductance of 480 mS/mm, which set new benchmarks for GaN-based HEMTs. Ultra-thin pre-metallization etching has been employed for the first time to reduce ohmic contact resistance for AlN/GaN HEMTs and has enabled small signal frequency performance in excess of 100 GHz. Moll's method for delay time extraction has been utilized to extract an effective electron velocity in the intrinsic region of the AlN/GaN HEMT and was found to be ˜ 1.2 x 107 cm/s. By leveraging the allowable thickness window of the AlN barrier along with the high density 2DEGs that result, several novel HEMT devices have been designed and realized. High Al-content AlxGa 1-xN back barriers have been employed for improved 2DEG confinement in several new variations of the ultra-thin AlN/GaN HEMT. A dual, parallel-channel AlN/GaN-based HEMT structure is designed and realized for the first time as an epitaxial approach to mitigating DC-RF frequency dispersion. These structures emphasize the facilitation of new device designs that are made possible through the particular qualities the Al

  15. 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.

  16. Efficient injection of spin-polarized electrons from manganese arsenide contacts into aluminum gallium arsenide/gallium arsenide spin LEDs

    NASA Astrophysics Data System (ADS)

    Schweidenback, Lars

    In this thesis we describe two spectroscopic projects project on semiconductor heterostructures, as well as putting together and testing a micro-photoluminescence/7 tesla magnet system for the study of micron size two-dimensional crystals. Below we discuss the three parts in more detail. i) MnAs-based spin light emitting diodes. We have studied the injection of spin-polarized electrons from a ferromagnetic MnAs contact into an AlGaAs(n)/GaAs(i)/AlGaAs(p) n-i-p light emitting diode. We have recorder the emitted electroluminescence as function of magnetic field applied at right angles to the device plane in the 7-300 K temperature range. It was found that at 7 Kelvin the emitted light is circularly polarized with a polarization that is proportional to the MnAs contact magnetization with a saturation value of 26% for B > 1.25 tesla. The polarization persists up to room temperature with a saturation value of 6%. ii) Optical Aharonov-Bohm effect in InGaAs quantum wells. The excitonic photoluminescence intensity from InGaAs quantum wells as function of magnetic field exhibits two local maxima superimposed on a decreasing background. The maxima are attributed to the optical Aharonov-Bohm effect of electrons orbiting around a hole localized at the center of an Indium rich InGaAs islands detected by cross sectional scanning tunneling microscopy. Analysis of the position of the maxima yields a value of the electron orbit radius. iii) Micro-Photoluminescence. We have put together a micro-photoluminescence /7 tesla system for the study of two dimensional crystals. The samples are placed inside a continuous flow cryostat whose tail is positioned in the bore of the 7 tesla magnet. A microscope objective is used to focus the exciting laser light and collect the emitted photoluminescence. The system was tested by recording the photoluminescence spectra of WS2 and WSe 2 monolayers at T = 77 K.

  17. 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

  18. 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

  19. 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

  20. 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.

  1. Comparison between experimental and theoretical determination of the local structure of the GaAs1-yNy dilute nitride alloy

    NASA Astrophysics Data System (ADS)

    Ciatto, Gianluca; D'Acapito, Francesco; Sanna, Simone; Fiorentini, Vincenzo; Polimeni, Antonio; Capizzi, Mario; Mobilio, Settimio; Boscherini, Federico

    2005-03-01

    We present a combined experimental and theoretical study of the local structure of the GaAs1-yNy dilute nitride alloy. Experimental results obtained by x-ray absorption spectroscopy have been compared with first-principles density-functional supercell calculations and with the predictions of three different valence force field models. Both experiments and calculations find that inclusion of N induces static disorder in the Ga-As bond length distribution. An increase of the Ga-As bond length upon N incorporation in gallium arsenide has been observed; this is due to the competing effects of the decrease of the free lattice parameter and the tensile strain due to pseudomorphic growth. The different theoretical calculations reproduce more or less accurately this bond length expansion; we discuss the performance of the different valence force field models in predicting the measured bond lengths.

  2. 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.

  3. 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.

  4. The status of gallium arsenide photoemission guns at Jefferson Lab

    SciTech Connect

    M. Poelker; P. Adderley; M. Baylac; J. Brittian; D. Charles; J. Clark; J. Grames; J. Hansknecht; R. Kazimi; M. Stutzman; K. Surles-Law

    2004-10-07

    Highlights of the polarized beam program at CEBAF at Jefferson Lab will be presented. These include successful completion of portions of parity violation experiments G0 Forward Angle and HAPPex II. Experience with commercial modelocked Ti-Sapphire lasers and high polarization strained superlattice GaAs photocathodes will be discussed. Finally, gun charge lifetime measurements made over the course of many years following charge extraction of nearly 3000 C will be presented.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Gallium arsenide (GaAs) power conversion concept

    NASA Technical Reports Server (NTRS)

    Nussberger, A. A.

    1980-01-01

    A summary design analysis of a GaAs power conversion system for the solar power satellite (SPS) is presented. Eight different satellite configuration options for the solar arrays are compared. Solar cell annealing effects after proton irradiation are considered. Mass estimates for the SPS and the effect of solar cell parameters on SPS array design are discussed.

  17. Gallium arsenide 55Fe X-ray-photovoltaic battery

    NASA Astrophysics Data System (ADS)

    Butera, S.; Lioliou, G.; Barnett, A. M.

    2016-02-01

    The effects of temperature on the key parameters of a prototype GaAs 55Fe radioisotope X-ray microbattery were studied over the temperature range of -20 °C to 70 °C. A p-i-n GaAs structure was used to collect the photons from a 254 Bq 55Fe radioisotope X-ray source. Experimental results showed that the open circuit voltage and the short circuit current decreased with increased temperature. The maximum output power and the conversion efficiency of the device decreased at higher temperatures. For the reported microbattery, the highest maximum output power (1 pW, corresponding to 0.4 μW/Ci) was observed at -20 °C. A conversion efficiency of 9% was measured at -20 °C.

  18. Reliability study of refractory gate gallium arsenide MESFETS

    NASA Technical Reports Server (NTRS)

    Yin, J. C. W.; Portnoy, W. M.

    1981-01-01

    Refractory gate MESFET's were fabricated as an alternative to aluminum gate devices, which have been found to be unreliable as RF power amplifiers. In order to determine the reliability of the new structures, statistics of failure and information about mechanisms of failure in refractory gate MESFET's are given. Test transistors were stressed under conditions of high temperature and forward gate current to enhance failure. Results of work at 150 C and 275 C are reported.

  19. 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.

  20. 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.

  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. 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.

  3. Investigation of spin transport and accumulation in aluminum gallium arsenide

    NASA Astrophysics Data System (ADS)

    Misuraca, Jennifer

    This dissertation describes spin injection, transport, and detection experiments from Fe electrodes into a bulk AlGaAs channel. This semiconducting alloy is one of a class of persistent photoconductors, chosen as the spin transport medium because its carrier density can be tuned in a controlled manner via photoexcitation through the metal to insulator transition (MIT) in situ. This allows one to determine the dependence of spin lifetime on a variety of external parameters including carrier density, all on one sample. This research represents the first electrical spin-dependent measurements in this material and describes the dependence of the Hanle signal size and spin lifetime on bias, temperature, and carrier density. The photoexcitation needed to change the carrier density in this material comes from an infrared light-emitting diode (IR LED). The first step of this project was to characterize the new, highly Si doped Al0.3Ga 0.7As heterostructures, in order to determine how the illumination of the sample will affect the parameters of the material. To complete this study, Hall crosses were fabricated from the AlGaAs material and the transport properties were measured between 350 mK and 165 K. The resistivity, carrier density, and mobility were determined as a function of temperature for a variety of different illumination times. From this data, the MIT, scattering mechanisms, and the shape of the band tail of the density of states (DOS) were investigated. In fact, this is the first work to electrically probe the DOS in AlGaAs. Once the materials were characterized, they were used to fabricate lateral spin transport devices. Spin transport and accumulation were studied in detail via Hanle effect measurements, which measure the dephasing of electron spins in a perpendicular magnetic field. From these measurements, the spin lifetime of the material can be calculated, and is in the nanosecond range for all measured carrier densities. The spin lifetimes are measured using three distinct measurement configurations which all give consistent results. The dependence of spin lifetime and Hanle signal size are reported as a function of bias, temperature, and carrier density. This is the first spin transport experiment using a persistently photoconductive material as the spin transport channel in order to change the carrier density of the material in situ. The research in this dissertation successfully provides a framework for the continuation of spin injection and detection studies in this and other alloy semiconductors, and provides insight into how the spin lifetime depends on the doping levels in semiconductors.

  4. Nickel-gallium arsenide high-voltage power Schottky diodes

    NASA Astrophysics Data System (ADS)

    Ashkinazi, G.; Hadas, Tz.; Meyler, B.; Nathan, M.; Zolotarevski, L.; Zolotarevski, O.

    1993-01-01

    A power GaAs Schottky diode (SD) with a chemically deposited Ni barrier was designed, fabricated and tested. The diode has a reverse breakdown voltage VBR of 140 V, forward voltage drop VF (at 50 A/cm 2) of 0.7 V at 23°C, 0.5 V at 150°C and 0.3 V at 250°C, and reverse leakage current densities jR (at -50 V) of 0.1 μA/cm 2 at 23°C and 1 mA/cm 2 at 150°C. Calculated forward and reverse I- V characteristics using a simple self-consistent computer model are in good agreement with measured values. Calculated characteristics of a silicon SD with identical structure parameters, using the same model, show much poorer VBR, VF and jR values. The theoretical maximum value of VBR is physically limited by the largest allowed VF. For a V Fof ⋍1.6 V, V BR.maxis ⋍200 V in Si and ⋍800 simple technology allows manufacturing of large area GaAs Schottky diodes with average currents up to V in GaAs SDs. Our relatively 100 A.

  5. 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.

  6. Radiative recombination and photon recycling in gallium arsenide solar cells

    NASA Astrophysics Data System (ADS)

    Lundstrom, M. S.; Melloch, M. R.; Lush, G. B.; Patkar, M. P.; Young, M.; Durbin, S. M.; Gray, J. L.; MacMillan, H. F.; Keyes, B. M.; Levi, D. H.; Ahrenkiel, R. K.

    1992-12-01

    This talk reviews experimental work to develop a detailed understanding of radiative recombination in n-GaAs. Photoluminescence decay studies of minority carrier lifetimes versus doping in n-GaAs are presented. We show that when the substrate is removed by etching, photon recycling is enhanced, and lifetimes increase by nearly a factor of 10. The doping-dependent absorption coefficient is measured, and detailed balance arguments are used to relate absorption and recombination. Modeling surfaces, verified by comparison with experiments, are used to examine the effects of recycling in conventional solar cells and to explore new design options.

  7. Mixed conduction in semi-insulating gallium arsenide

    NASA Astrophysics Data System (ADS)

    Winter, J. J.; Leupold, H. A.; Ross, R. L.; Ballato, A.

    1982-12-01

    Hall effect and conductivity measurements made on semi-insulating bulk GaAs are examined by a new approach to mixed conduction analysis. Based on Fermi level and electron mobility analyses of conductivity and Hall coefficient, it uses revised values of effective densities of states at the band edges, and electron/hole mobility ratios recently adopted by other workers. The treatment provides a visual analysis of the system in terms of the electrical parameters and impurity densities, and establishes criteria for the onset of mixed conduction.

  8. Galvanomagnetic Properties and Magnetic Domain Structure of Epitaxial Manganese Arsenide Films on Gallium ARSENIDE(001)

    NASA Astrophysics Data System (ADS)

    Park, Moon Chan

    We have studied galvanomagnetic properties and magnetic domain structure of epitaxial ferromagnetic MnAs thin films on GaAs(001) substrates by molecular beam epitaxy in the thickness range 20-200nm. Using data reported here on ordinary and extraordinary Hall effect to determine the field required for perpendicular saturation and using saturation magnetizations reported elsewhere, we determined the shape anisotropy constant in the basal plane of the hexagonal structure to be 3.7(0.6)times10 ^5 erg/cm^3 and the surface anisotropy constant to be -1.3(0.4) erg/cm^2. The negative sign indicates thin enough films will be perpendicularly magnetized. By using magnetic force microscopy on a 100 nm type-B MnAs film we found stripe domains with 180^circ Bloch walls parallel to the easy direction, thereby avoiding the hard c-axis, which in type-B is tilted up 39^circ. out of the film plane. The widths of the domains and the walls are 4.0(0.3) μm and 95(6) nm, respectively. Similar MFM results were obtained for a 100 nm type-A MnAs thin film having hard c-axis in plane, with an average domain width of 11.7(1.2) mum. This domain width agrees with a calculated value using the effective anisotropy constant data. Magnetoresistance versus field shows a linear past beyond the coercive field H _{c} (VSM value +/-324Oe) due to s-d electron scattering as explained by N. F. Mott. Peaks occur at the transition region observed in the vicinity of H_ {c} in the VSM hysteresis loop and are centered at about H_{c}. The peaks are attributed to electron scattering from the domain walls. The electrical resistance showed a rapid increase with temperature beginning about 5 degrees below the Curie temperature (40^circ C) caused by the change in crystal structure from hexagonal to orthorhombic. The resistivities are, respectively, 300(24) and 375(30) muOmega -cm. Comparison with bulk values indicates the large lower temperature value is partly due to the presence of some orthorhombic phase observed in x-ray studies.

  9. Electrical and optical study of an indium gallium arsenide/gallium arsenide multi-quantum well structure for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    An, Sangwoo

    2000-08-01

    InGaAs is a III-V material system that has recently attracted a lot of interest for possible optoelectronic applications. When grown over a GaAs substrate, it provides an example of a strained-layer system, due to the lattice mismatch of the layers. As long as the strained layers are grown shorter than a critical thickness, the material is pseudomorphic and presents no catastrophic degrading. Thus, it can be used for different devices, such as lasers, detectors, switches, and spatial light modulators. In this work a low-dimensional structure, composed of different stacks of InGaAs quantum wells embedded in a matrix of GaAs barriers, is investigated. This work addresses a number of important issues involving material properties and basic physical effects. In addition it discloses the concept of an improved, multicolor, spatial light modulator. Material information about InGaAs is abundant but not exhaustive as for the GaAs system. We have performed an in-depth spectroscopic study of a complex structure, composed of serially grown stacks of stepped quantum wells, where it is possible, in principle, to observe large Stark shifts. In this sample we have studied the formation of electrical high and low-field domains along the multi-quantum well region with a number of spectroscopic techniques. Electrical and optical measurements have been performed and have given an extensive characterization of the sample. Experimental results closely match theoretical calculations performed under the effective mass approximation. Excitonic peaks at room temperatures have been clearly resolved, a first for InGaAs stepped quantum well samples. Formation and expansion of electric field domains along the shallow multi-quantum well region have been recorded. For the first time an observation of the interplay of high field domains involving shallow quantum well levels and resonances in the continuum, have been observed. New techniques to probe such high field domains have been developed. And finally, we have proposed the concept of an improved multi-color spatial light modulator, based on a single-voltage control of the Stark shifts induced by the expansion of high field domains along the sample.

  10. 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.

  11. 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.

  12. Isoelectronic Traps in Gallium Phosphide

    NASA Astrophysics Data System (ADS)

    Christian, Theresa; Alberi, Kirstin; Beaton, Daniel; Fluegel, Brian; Mascarenhas, Angelo

    2015-03-01

    Isoelectronic substitutional dopants can result in strongly localized exciton traps within a host bandstructure such as gallium arsenide (GaAs) or gallium phosphide (GaP). These traps have received great attention for their role in the anomalous bandgap bowing of nitrogen or bismuth-doped GaAs, creating the dramatic bandgap tunability of these unusual dilute alloys. In the wider, indirect-bandgap host material GaP, these same isoelectronic dopants create bound states within the gap that can have very high radiative efficiency and a wealth of discrete spectral transitions illuminating the symmetry of the localized excitonic trap state. We will present a comparative study of nitrogen and bismuth isoelectronic traps in GaP. Research was supported by the U. S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division under contract DE-AC36-08GO28308 and by the Department of Energy Office of Science Graduate Fellowship Program (DOE SCGF), made possible in part by the American Recovery and Reinvestment Act of 2009, administered by ORISE-ORAU under contract no. DE-AC05-06OR23100.

  13. 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.

  14. 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.

  15. Gallium self-diffusion in gallium arsenide: A study using isotope heterostructures

    SciTech Connect

    Wang, Lei; Hsu, L.; Haller, E.E. |; Erickson, J.W.; Fischer, A.; Eberl, K.; Cardona, M.

    1996-09-01

    Ga self-diffusion was studied with secondary-ion mass spectroscopy in {sup 69}GaAs/{sup 71}GaAs isotope heterostructures grown by molecular beam epitaxy on GaAs substrates. Results show that the Ga self- diffusion coefficient in intrinsic GaAs can be described accurately with D = (43{+-}25 cm{sup 2}s{sup -1})exp(-4.24{+-}0.06 eV/k{sub B}T) over 6 orders of magnitude between 800 and 1225 C under As-rich condition. Experimental results combined with theoretical calculations strongly suggest Ga vacancy being the dominant native defect controlling the diffusion. No significant doping effects were observed in samples where the substrates were doped with Te up to 4x10{sup 17}cm{sup -3} or Zn up to 1x10{sup 19}cm{sup -3}.

  16. 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

  17. One dimensional and two dimensional growth of indium(gallium)arsenic on gallium arsenide surfaces

    NASA Astrophysics Data System (ADS)

    Wen, Hong

    In this dissertation, the development of one dimensional (1D) InGaAs quantum wires (QWRs) and two dimensional (2D) InGaAs growth have been performed by Molecular Beam Epitaxy (MBE) using unconventional methods. For the QWRs growth, the GaAs (311)A surface is selected because of its unique step-like surface reconstruction. Three stages (initiation, growth and overgrowth) of InGaAs wire evolution have been investigated. In the first stage, the previously believed InGaAs wire-like structures on GaAs (311)A were confirmed to be real QWRs. The growth mode of the wires was SK growth. The reason for the 1D InGaAs growth on GaAs (311)A, instead of three dimensional (3D) growth, is discussed. In second stage, the shape of In0.4Ga0.6As wires is assigned as a triangle bounded by two side facets with indices of {11,5,2}. The side facet incline angle changes with different growth coverage but was not sensitive to indium composition in deposited material. In the third stage, 3D InGaAs islands were formed on wires. When indium composition was high, the high built up strain supported islands formation by consuming wetting layer. When InGaAs deposition coverage was high, less accumulated strain in the growth layer led to the dots formation with consuming of the wires. The growth of wires at different temperatures was also performed. It was found that the length of wires increased as temperature increased. The vertical multilayer stacking growth technique was confirmed to grow longer and more organized InGaAs wires. Two approaches were explored to achieve 2D growth of InGaAs on GaAs. The first approach was depositing In0.53Ga0.47As, which is lattice matched to InP, on GaAs (100) with an unconventional V/III flux ratio of 2. The As-deficient growing condition suppressed the 3D islands growth. The second approach was depositing InAs on GaAs (111)B vicinal substrate. STM images combined with PL measurement showed that the strain relaxed through ragged step edge formation and Ga-In intermixing for low InAs deposition, and through the formation of step bunching and dislocations for thicker depositions.

  18. 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.

  19. 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

  20. Gallium fluoroarsenates.

    PubMed

    Marshall, Kayleigh L; Armstrong, Jennifer A; Weller, Mark T

    2015-07-28

    Six new phases in the gallium-fluoride-arsenate system have been synthesised hydrofluorothermally using a fluoride-rich medium and "HAsF6" (HF : AsF5) as a reactant. RbGaF3(H2AsO4), KGaF(H2AsO4) and [piperazine-H2]2[Ga2F8(HAsO4)]·H2O have one dimensional structures, [DABCO-H2]2[Ga4F7O2H(AsO4)2]·4H2O consists of two dimensionally connected polyhedral layers, while GaF(AsO3[OH,F])2 and (NH4)3Ga4F9(AsO4)2 both have three-dimensionally connected polyhedral frameworks. PMID:26095086

  1. First-Principles Determination of Ultrahigh Thermal Conductivity of Boron Arsenide: A Competitor for Diamond?

    NASA Astrophysics Data System (ADS)

    Lindsay, L.; Broido, D. A.; Reinecke, T. L.

    2013-07-01

    We have calculated the thermal conductivities (κ) of cubic III-V boron compounds using a predictive first principles approach. Boron arsenide is found to have a remarkable room temperature κ over 2000Wm-1K-1; this is comparable to those in diamond and graphite, which are the highest bulk values known. We trace this behavior in boron arsenide to an interplay of certain basic vibrational properties that lie outside of the conventional guidelines in searching for high κ materials, and to relatively weak phonon-isotope scattering. We also find that cubic boron nitride and boron antimonide will have high κ with isotopic purification. This work provides new insight into the nature of thermal transport at a quantitative level and predicts a new ultrahigh κ material of potential interest for passive cooling applications.

  2. Enthalpy of formation of gallium nitride

    SciTech Connect

    Ranade, M.R.; Tessier, F.; Navrotsky, A.; Leppert, V.J.; Risbud, S.H.; DiSalvo, F.J.; Balkas, C.M.

    2000-05-04

    A major discrepancy in the literature concerning the enthalpy of formation of GaN has been resolved using oxidative oxide melt solution calorimetry. Four samples of differing nitrogen contents were measured by dropping them into molten 3Na{sub 2}O{center_dot}4MoO{sub 3} in a calorimeter at 975 K with oxygen gas bubbling through the solvent. The samples were characterized by X-ray diffraction, chemical analysis, transmission electron microscopy, particle size analysis, and BET measurements. The enthalpy of drop solution (kJ/g) varied approximately linearly with nitrogen content. Extrapolated to stoichiometric GaN, the data yield a value of {minus}156.8 {+-} 16.0 kJ/mol for the standard enthalpy of formation from the elements at 298 K. The relatively large error reflects the deviation of individual points from the straight line rather than uncertainties in each set of data for a given sample. This new directly measured enthalpy of formation is in excellent agreement with that obtained from the temperature dependence of the equilibrium pressure of nitrogen over GaN, {minus}157.7 kJ/mol, measured by Madar et al. and Karpinski and Porowski. This value of {minus}156.8 kJ/mol should replace the commonly tabulated value of {minus}110 kJ/mol determined by Hahn and Juza using combustion calorimetry on an uncharacterized sample over 50 years ago.

  3. Gallium Nitride: Charge Neutrality Level and Interfaces

    NASA Astrophysics Data System (ADS)

    Brudnyi, V. N.

    2016-03-01

    An analysis of experimental data revealed the dependence of the metal/ n-GaN GaN(0001) barrier height on the metal work function, as predicted by the model that takes into account the charge neutrality level of the semiconductor. In case of the metal/ p-GaN(Mg) barriers, significant scatter of the corresponding experimental data is observed and pinning of the near-surface Fermi level near E v + 2.5 eV takes place in most structures, which is due to the influence of high density of interface defect states formed during the process of the GaN doping by Mg impurity.

  4. Single-crystal gallium nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Goldberger, Joshua; He, Rongrui; Zhang, Yanfeng; Lee, Sangkwon; Yan, Haoquan; Choi, Heon-Jin; Yang, Peidong

    2003-04-01

    Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized by using carbon nanotubes and porous membranes as templates, or by thin-film rolling. These nanotubes, however, are either amorphous, polycrystalline or exist only in ultrahigh vacuum. The growth of single-crystal semiconductor hollow nanotubes would be advantageous in potential nanoscale electronics, optoelectronics and biochemical-sensing applications. Here we report an `epitaxial casting' approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30-200nm and wall thicknesses of 5-50nm. Hexagonal ZnO nanowires were used as templates for the epitaxial overgrowth of thin GaN layers in a chemical vapour deposition system. The ZnO nanowire templates were subsequently removed by thermal reduction and evaporation, resulting in ordered arrays of GaN nanotubes on the substrates. This templating process should be applicable to many other semiconductor systems.

  5. Annealing of ion implanted gallium nitride

    SciTech Connect

    Tan, H.H.; Williams, J.S.; Zou, J.; Cockayne, D.J.; Pearton, S.J.; Zolper, J.C.; Stall, R.A.

    1998-03-01

    In this paper, we examine Si and Te ion implant damage removal in GaN as a function of implantation dose, and implantation and annealing temperature. Transmission electron microscopy shows that amorphous layers, which can result from high-dose implantation, recrystallize between 800 and 1100{degree}C to very defective polycrystalline material. Lower-dose implants (down to 5{times}10{sup 13}cm{sup {minus}2}), which are not amorphous but defective after implantation, also anneal poorly up to 1100{degree}C, leaving a coarse network of extended defects. Despite such disorder, a high fraction of Te is found to be substitutional in GaN both following implantation and after annealing. Furthermore, although elevated-temperature implants result in less disorder after implantation, this damage is also impossible to anneal out completely by 1100{degree}C. The implications of this study are that considerably higher annealing temperatures will be needed to remove damage for optimum electrical properties. {copyright} {ital 1998 American Institute of Physics.}

  6. Gallium nitride nanostructures: Synthesis, characterization and applications

    NASA Astrophysics Data System (ADS)

    Kente, Thobeka; Mhlanga, Sabelo Dalton

    2016-06-01

    GaN nanostructures have been extensively studied due to their important properties and applications in many fields. The recent synthesis and uses of these nanostructures have been reviewed. The different synthesis methods such as catalyst-assisted and catalyst-free methods to make GaN nanostructures and different reaction conditions have been also reviewed. This review covers the synthesis, growth mechanism, crystalline structure, properties, applications, structural and optical characterization of GaN nanostructures.

  7. 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.

  8. Microstructures of aluminum gallium nitride epitaxial layers

    NASA Astrophysics Data System (ADS)

    Wise, Adam

    Stress relief mechanisms and microstructures of AlxGa 1-xN thin films were investigated by growing samples by MBE and MOCVD. For investigation of stress relief mechanisms, a series of eight GaN samples were grown using MOCVD with AlxGa1-xN interlayers ranging from xAl=0.14 to xAl=1. Each successive interlayer in a given sample was increased in thickness and followed by a GaN probe-layer. A multi-beam optical stress sensor (MOSS) was used to monitor the stress in the sample during the growth process and determine the onset of stress relaxation. The thicknesses determined for stress relief onset in the interlayers were compared with calculations of Griffith's Criterion for hexagonal thin films and found to closely follow the predicted thicknesses of surface crack formation. For investigation of microstructures in AlxGa1-xN thin films, several sets of samples were grown by MOCVD, with varying pressure, temperature, and composition, and by MBE with varying temperature. The samples were examined by transmission electron microscopy, including [101¯0] selected area electron diffraction (SAED) patterns and weak beam dark field images taken with g=(0002) and g=(1¯21¯0). The MOCVD samples with composition variation were examined with [112¯0] SAED patterns, and the MBE-grown samples were examined using z-contrast imaging. All the MOCVD samples showed signs of ordering, while none of the MBE-grown samples did. In addition, the ordering was shown to be forming as thin plates of ordered material on the (0001) planes, anisotropic within the plane. Some MBE-grown samples were shown to have strong composition modulations arranged in bands arranged parallel to the surface of the sample, due to a balance between strain energy in the samples and the interfacial energy occurring between regions of high and low xAl. The samples grown by MOCVD were shown to have signs of phase separation in addition to the ordering observed. These samples show enhanced ordering in the system when there is low surface mobility. Phase separation will destroy the more quickly forming ordering in the samples, but lower surface mobility will inhibit the formation of strong phase separation, preserving the ordered structure.

  9. 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.

  10. 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.

  11. 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.

  12. Tuning indium arsenide quantum dot electronic structure using (indium aluminum gallium)arsenide capping layers and application to infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Kim, Eui-Tae

    This dissertation contributes to the subjects of (i) molecular beam epitaxical growth and characterization of strain-driven self-assembled InAs/GaAs coherent island based quantum dots (QDs), (ii) manipulation of such InAs QD electronic states and associated transitions utilizing AlxGa 1-xAs, InxGa1-xAs, or InxAl yGa1-x-yAs capping layers, and (iii) application of such InAs/(InAlGa)As QDs to infrared photodetectors (QDIPs). A slow-growth-rate (at 0.054 ML/sec) QD formation is introduced to realize high-quality uniform InAs/(InAlGa)As QDs. Such QDs are characterized utilizing photoluminescence (PL), PL excitation spectroscopy, atomic force microscopy, and transmission electron microscopy. The QD growth kinetics is discussed by comparing with commonly employed relatively fast-growth-rate (at 0.22 ML/sec) QD formation. To manipulate electronic states and associated transitions of such InAs/GaAs QDs, part of the GaAs capping layer is replaced with AlxGa 1-xAs, InxGa1-xAs, or InxAlyGa1-x-yAs layers. Al xGa1-xAs insertions result in blueshifted inter- and intraband transition wavelengths (with respect to those of InAs/GaAs QDs) because of the enhanced confinement potential. By contrast, InxGa 1-xAs insertions allow redshifted inter- and intraband transition wavelengths because of overall lowering of the confinement potential via strain relief and chemical difference effects. Moreover, the InxGa 1-xAs layer regions between the InAs QDs act as a quantum well (QW) having its own energy states. Indeed, we find that the long-wavelength IR (LWIR) photoresponse involves QD intraband transitions to final states that are likely coupled to the QW electron energy states. To further the objective of controlled manipulation of the electronic states in InAs QDs, we introduce the notion of a lateral potential confinement layer (LPCL) whose judicious placement during island capping allows selective impact on ground and excited electron and hole states. Finally, as an application of self-assembled epitaxical island QDs, we have performed a comprehensive study on n-i(5 QD layers)-n QDIPs. The QDIP performance is significantly enhanced by introducing AlxGa 1-xAs dark current blocking layers into the QDIP active regions. The Al0.2Ga0.8As-QDIP shows the highest 77 K detectivity for a QDIP to-date: 9.6 x 109 cmHz1/2/W at 6.2 mum. We also tailor detection bands of QDIPs to the LWIR (8--14 mum) regime using InxGa1-xAs strain-relieving capping layers that also act as QWs. (Abstract shortened by UMI.)

  13. 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)

  14. 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.

  15. 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 ...

  16. 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.

  17. 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.

  18. 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.

  19. Gallium-containing anticancer compounds

    PubMed Central

    Chitambar, Christopher R

    2013-01-01

    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 cross resistance 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. PMID:22800370

  20. Theoretical study of IR and photoelectron spectra of small gallium-arsenide clusters

    SciTech Connect

    Pouchan, Claude; Marchal, Rémi; Hayashi, Shinsuke

    2015-01-22

    Relative stabilities of small Ga{sub n}As{sub m} clusters, as well as their structural electronic and vibrational properties, were computed and analysed using a CCSD(T) reference method since experimental data in this area are sparse or unknown. With the aim of investigating larger clusters, we explored several DFT functionals and basis sets able to mimic the reliable CCSD(T) approach. Among them, the PBE0/SBKJC+sp,d appears as the most efficient to describe the structural and vibrational properties since average differences of about 0.042Å and 5.1cm{sup −1} were obtained for bond lengths and fundamental vibrational frequencies, respectively for the first small clusters [1] of the series found from our GSAM method [2]. As further test, this model is used in order to investigate and revisit an experimental IR spectrum of Ga{sub n}As{sub m} mixture previously published by Li et al. [3]. More complicated is the difficulty which arises in the electronic description due to the presence of numerous low lying electronic states nearly degenerated to correctly describe the electronic structure. The case of Ga{sub 2}As will be discussed and the photoelectron spectra of the Ga{sub 2}As anion reanalyzed on the ground of our calculations [4] comparatively to the experimental spectra obtained by Neumark and co-workers [5].

  1. 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.

  2. A customizable commercial miniaturized 320×256 indium gallium arsenide shortwave infrared camera

    NASA Astrophysics Data System (ADS)

    Huang, Shih-Che; O'Grady, Matthew; Groppe, Joseph V.; Ettenberg, Martin H.; Brubaker, Robert M.

    2004-10-01

    The design and performance of a commercial short-wave-infrared (SWIR) InGaAs microcamera engine is presented. The 0.9-to-1.7 micron SWIR imaging system consists of a room-temperature-TEC-stabilized, 320x256 (25 μm pitch) InGaAs focal plane array (FPA) and a high-performance, highly customizable image-processing set of electronics. The detectivity, D*, of the system is greater than 1013 cm-√Hz/W at 1.55 μm, and this sensitivity may be adjusted in real-time over 100 dB. It features snapshot-mode integration with a minimum exposure time of 130 μs. The digital video processor provides real time pixel-to-pixel, 2-point dark-current subtraction and non-uniformity compensation along with defective-pixel substitution. Other features include automatic gain control (AGC), gamma correction, 7 preset configurations, adjustable exposure time, external triggering, and windowing. The windowing feature is highly flexible; the region of interest (ROI) may be placed anywhere on the imager and can be varied at will. Windowing allows for high-speed readout enabling such applications as target acquisition and tracking; for example, a 32x32 ROI window may be read out at over 3500 frames per second (fps). Output video is provided as EIA170-compatible analog, or as 12-bit CameraLink-compatible digital. All the above features are accomplished in a small volume < 28 cm3, weight < 70 g, and with low power consumption < 1.3 W at room temperature using this new microcamera engine. Video processing is based on a field-programmable gate array (FPGA) platform with a soft-embedded processor that allows for ease of integration/addition of customer-specific algorithms, processes, or design requirements. The camera was developed with the high-performance, space-restricted, power-conscious application in mind, such as robotic or UAV deployment.

  3. Lattice constant variation and complex formation in zincblende gallium manganese arsenide

    NASA Astrophysics Data System (ADS)

    Schott, G. M.; Faschinger, W.; Molenkamp, L. W.

    2001-09-01

    We perform high resolution x-ray diffraction on GaMnAs mixed crystals as well as on GaMnAs/GaAs and GaAs/MnAs superlattices for samples grown by low-temperature molecular-beam epitaxy under different growth conditions. Although all samples are of high crystalline quality and show narrow rocking curve widths and pronounced finite thickness fringes, the lattice constant variation with increasing manganese concentration depends strongly on the growth conditions: For samples grown at substrate temperatures of 220 and 270 °C, the extrapolated relaxed lattice constant of Zincblende MnAs is 0.590 nm and 0.598 nm, respectively. This is in contrast to low-temperature GaAs, for which the lattice constant decreases with increasing substrate temperature.

  4. 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.

  5. Shunt diode analysis using light emission for gallium arsenide solar cell predictability

    NASA Astrophysics Data System (ADS)

    Kilmer, Louis C.; Honsberg, Christiana; Phillips, James E.; Barnett, Allen M.

    The use of light emission as a defect analysis technique has been expanded to better differentiate the types of shunt defects and analyze their effects on GaAs solar cells. Light emission from full-size 2-cm x 2-cm space solar cells was detected, recorded, digitized, and enhanced in order to analyze the low-level light emission and the shunt diode's effects. Shunt diodes are of particular importance because they have been found to be the type of defect which is most likely to degrade and cause failure in GaAs solar cells. To analyze how the shunt diodes affect the quality of the solar cell, the pattern of light emission must be studied. In studying the low-level light emission, it was found that the pattern of light emission is different than that of the high-level light emission. The different light patterns show the changing effects of the shunt diodes. It is concluded that the shunt diode dominates over the junction diode at low values of current and that the junction diode dominates over the shunt diode at high values of current.

  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. Processing, mechanisms, and applications in p-zinc sulphur selenide:nitrogen/p(+) gallium arsenide heterostructures

    NASA Astrophysics Data System (ADS)

    Hong, Hyesook

    This research addresses the electrical and optical properties of II-VI compound semiconductors, namely ZnSe and the family, for applications to blue-green lasers or photodetectors. To realize such devices, forming the p-n junction is crucial. The difficulty in obtaining in-situ p-type Zn(S)Se using molecular beam epitaxy (MBE) or metalorganic chemical vapor deposition (MOCVD) prompted N-ion implantation on undoped material to obtain the required doping into ZnSSe epilayers with various ion energy and doses to study p-type properties of ZnSSe. To activate the implanted species as acceptors for ZnSSe and remove damage from ion bombardment, an optimum post annealing condition was sought through photoluminescence, current-voltage (I-V), and capacitance-voltage (C-V) measurements. This study showed doping concentration between 10sp{17}{-}10sp{13} cmsp{-3} from C-V measurements due to a Gaussian depth profile of ion bombardment. MBE grown p-type ZnSSe on psp +GaAs (100) substrates with RF plasma in-situ doping was studied for possible application for heterostructure devices. To study the electrical properties of this material, proper Ohmic system on the psp+GaAs side were sought due to the low thermal budget. Schottky contacts were deposited on the ZnSSe surface with various metals to extract Schottky parameters. As a device application, nitrogen implanted p-i-n devices were fabricated using the optimum post annealing condition. Nitrogen ions were implanted into the MBE grown undoped ZnSe/ZnSe:Cl/nsp+GaAs (100) substractes. A quasi-uniform p-layer doping profile was obtained, using nitrogen ions at multiple energies and ion doses. These devices exhibited a responsivity of 0.025 A/W at a wavelength of 460 nm through the top 200 A thick metal contracts. Metal semiconductor photodetectors were fabricated with undoped 0.5 mum and 2.0 mum thick ZnSe epilayers on semi-insulating GaAs substrates. A dielectric multilayer hard mask technique was employed to aid in metal deposition at liquid temperature. Metal was deposited by evaporation with the substrate at 77 K and vacuum of 10sp{-7} Torr. By using the Ti-Sapphire ultra fast femto-second laser, the bandwidth and speed of these devices was studied using a Fourier transform method.

  8. Evaluation of semiconductor specimens by X-ray analysis. [considering germanium and gallium arsenide structures

    NASA Technical Reports Server (NTRS)

    Walter, H. U.

    1975-01-01

    Germanium and GaAs crystals were investigated for studies on photovoltaic effects, chemical etching and epitaxial growth according to the overall objective to assess the defect structure of single crystalline materials. A brief survey of basic theory and topographical techniques is provided; examples of topographs are presented.

  9. Photoemission from activated gallium arsenide. I. Very-high-resolution energy distribution curves

    NASA Astrophysics Data System (ADS)

    Drouhin, H.-J.; Hermann, C.; Lampel, G.

    1985-03-01

    The energy distribution curves (EDC's) of the photoelectrons emitted from the (100) face of a p-type doped (~1019 cm-3) GaAs crystal, activated to negative electron affinity in ultrahigh-vacuum conditions, is investigated. The study is performed at 300 and 120 K under well-focused Kr+-laser excitation and with a very-high-energy resolution (20 meV). The analysis of the EDC's as a function of the photon energy, mainly at low temperature, is shown to provide a very direct picture of the GaAs band structure away from the Brillouin-zone center. The experimental results are well fitted by a spherical, nonparabolic k-->.p--> perturbation calculation of the coupled conduction and valence bands, for electron kinetic energies up to 1 eV in the central Γ valley. The essential role played by the subsidiary L and X minima in the energy relaxation and photoemission processes is evidenced. The main contribution to the total emitted current is due to electrons which were thermalized in the bulk Γ minimum and have lost an average energy ~=130 meV in the band-bending region prior to emission into vacuum. The band-bending value is shown to be >=0.5 eV. The yield and time evolution of GaAs photocathodes are discussed. This detailed study leads to a reexamination of the pioneer work of L. W. James and J. L. Moll [Phys. Rev. 183, 740 (1969)] and to a good understanding of the photoemission properties of activated GaAs.

  10. Scalable synthesis of vertically aligned, catalyst-free gallium arsenide nanowire arrays: towards optimized optical absorption

    NASA Astrophysics Data System (ADS)

    Yao, Maoqing; Madaria, Anuj R.; Chi, ChunYung; Huang, Ningfeng; Lin, Chenxi; Povinelli, Michelle L.; Dapkus, P. Daniel; Zhou, Chongwu

    2012-06-01

    Recently nanostructure materials have emerged as a building block for constructing next generation of photovoltaic devices. Nanowire based semiconductor solar cells, among other candidates, have shown potential to produce high efficiency. In a radial pn junction light absorption and carrier collection can be decoupled. Also nanowires can increase choice of materials one can use to fabricate high efficiency tandem solar cells by relaxing the lattice-match constraint. Here we report synthesis of vertical III-V semiconducting nanowire arrays using Selective-Area Metal Organic Chemical Vapor Deposition (SA-MOCVD) technique, which can find application in various optoelectronic devices. We also demonstrate nanosphere lithography (NSL) patterning techniques to obtain ordered pattern for SAMOCVD. Reflection spectrum of nanowires array made by this technique shows excellent light absorption performance without additional anti-reflection coating layer. Thus, we show that highly ordered nanowire structure is 'not needed' to maximize the absorption in vertical nanowire array. Our scalable approach for synthesis of vertical semiconducting nanowire can have application in high throughput and low cost optoelectronic devices including photovoltaic devices.

  11. Ultrafast coherent studies of excitons and excitonic complexes in doped and undoped gallium arsenide quantum wells

    NASA Astrophysics Data System (ADS)

    Busch, Alexander Anthony

    2003-10-01

    This thesis reports a systematic study of near-band edge linear and nonlinear optical properties of doped and undoped semiconductor multiple quantum well samples, aimed at quantifying and separating the numerous contributions to the overall material response from photon excitation. Information obtained from both linear absorption and nonlinear, degenerate four-wave-mixing experiments is compared with elaborate numerical simulations. Accurate measures of 1S--2S binding energies and dephasing rates as a function of temperature from 5 to 40 K is established. The biexciton binding energy and dephasing rate over the temperature range 5 to 40 K is measured and, by comparison with theories reported in the literature, it is found that localization effects have a significant influence on the biexciton binding energy in 5 nm quantum wells. The first systematic attempt to quantitatively account for the continuum contribution to nonlinear response by fitting a series of spectra obtained at various input laser pulse detunings was conducted. Unique evidence for coherent beating between multi-exciton/free electron complexes in lightly doped material was also found.

  12. Characterization of high-purity arsine and gallium arsenide epilayers grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Feng, Jun; Clement, Ryan; Raynor, Mark

    2008-11-01

    Impurities present in the metal organic chemical vapor deposition (MOCVD) process gases and precursors can have a significant effect on the performance of III-V compound semiconductor devices. High-purity arsine purified using chemical, adsorption and distillation techniques, has been characterized for impurities by using high sensitivity gas analysis methods and low temperature photoluminescence (PL) of GaAs epilayers. Permanent gas, hydrocarbon and dopant impurities can all be removed using these purification methods to below the detection limit of instrumentation (low nmol mol -1-pmol mol -1, depending on method). Capability to remove water vapor to single digit nmol mol -1 levels is also demonstrated and cylinder depletion studies show that gas-phase arsine, with consistently low H 2O, can be delivered from the cylinder, even well after phase break. Low temperature PL measurements are made on 10 μm GaAs/GaAs grown with three different arsine sources. Well-resolved near-band emission characteristics of high-purity n-type GaAs is obtained with high-purity distilled arsine. PL of epilayers grown with less pure arsine show the presence of Ge as well as elevated levels of Mg and Zn, incorporated from the trimethylgallium. The incorporation of O from an arsine cylinder containing H 2O at 200 nmol mol -1 results in reduced full width at half maximum (FWHM) of the near-band emission and decreased ( D0, X) and ( F, X) intensity, highlighting the importance of minimizing H 2O impurity.

  13. 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.

  14. Optical evaluation of indium gallium arsenide phosphide double-heterostructure material for injection lasers

    SciTech Connect

    Degani, J.; Besomi, P.; Wilt, D.P.; Nelson, R.J.; Wilson, R.B.

    1983-12-01

    Optical methods used for evaluation of InGaAsP double-heterostructure (DH) material are described. The photoluminescence (PL) efficiency of the active layer in DH wafers and its spatial variation are shown to be correlated with the threshold current density of the broad area lasers processed from the corresponding wafers. The simultaneous measurement of the PL signal and the transmitted intensity of the excitation source through the active layer is a useful technique for monitoring imperfection in the active layer. The sheet conductivity of the epitaxial p layers and p-n junction misplacement can be determined from the variation of the PL signal as a function of the power of the optical pump source. In addition, conventional spectrally and spatially resolved PL indicates the compositional homogeneity and the doping concentration of the active layer. In general, we find the 1.06-..mu..m yttrium aluminum garnet (YAG) laser to be a most convenient tool for evaluation of InGaAsP DH material.

  15. 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.

  16. Optical Spectroscopy Studies of Body Centered Cubic Cobalt and Gallium Arsenide Quantum Well Heterostructures.

    NASA Astrophysics Data System (ADS)

    Subramanian, Suresh

    Brillouin light scattering was used to study the elastic and magnetic properties of several films (up to 357A thick) of body centered cubic (bcc) cobalt (Co). Bcc Co is an artificial phase of Co stabilized on a lattice matched GaAs substrate. The elastic constants were extracted from the measured surface phonon dispersion. The c _{11} and c_{44 } elastic constants soften (40%) from the corresponding hcp values whereas c_{12} remains unchanged. While theoretical calculations agree with our measured c_{11} and c_{12}, the calculated value of c_{44} is considerably larger than our measured value. Spin wave dispersion studies of the surface and exchange dominated modes yield information on the exchange stiffness, gyromagnetic ratios and anisotropies. Specific to some samples is the presence of large uniaxial volume anisotropies. A simple magnetoelasticity model explains the origin of these uniaxial anisotropies. Using c _{rm ij}'s measured for these films and the film-substrate lattice mismatch, we obtain good agreement between the anisotropies measured from spin wave dispersions and the results of the magnetoelasticity calculations. Continuous wave (cw) and time resolved photoluminescence (PL) spectroscopy were used to study exciton lifetimes in growth interrupted (< 50A thick) GaAs/AlGaAs single quantum wells. Growth interruption gives rise to smooth interfaces with island formation where well widths vary by 1 monolayer. Exciton localization at these islands is evident as doublet structures in the cw PL which shows a switching in the oscillator strength from low to high energy with increasing temperature. Complementary time resolved experiments reveal that both excitons have the same lifetimes. These results enable us to place limits on island sizes formed during growth interruption. The identical lifetimes measured for both excitons is interpreted in terms of length scales on which the in-plane potential fluctuations occur during growth interruption. Time resolved studies were also performed as a function of carrier density (n) on similar GaAs/AlGaAs quantum wells. At low densities (n < 10 ^{10} cm^ {-2}), we observe the expected linear dependence of exciton lifetime on temperature. When n ~ 10^{11} cm^{-2}, the PL decay deviates strongly from a mono-exponential and displays cooling behavior. For n ~ 10 ^{12} cm^{ -2} (> critical Mott density), a new mono-exponential decay is observed at the onset of the decay with a characteristic lifetime of 500 ps which is nearly independent of temperature. This initial mono -exponential is followed by the cooling pattern observed previously at intermediate densities. Temperature is used as a means to probe the underlying characteristics of this high density PL decay. It is likely that the initial mono -exponential is due to electron-hole plasma recombination.

  17. 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. PMID:26552880

  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. Resonant Raman Scattering as a Probe of Intrinsic Defects in Gallium-Arsenide

    NASA Astrophysics Data System (ADS)

    Berg, Robert Scott

    This thesis presents a series of Raman scattering measurements performed on GaAs samples that have been irradiated with either high energy electrons or neutrons. The irradiation creates fairly high concentrations (10('17) - 10('18) cm(' -3)) of intrinsic defects. It is demonstrated that Raman scattering can give useful information about such defects. One important result of this work is the observation of new and relatively sharp peaks in the Raman spectra of the irradiated samples. These are attributed to vibrational modes of a specific point defect created by the irradiation. On the basis of annealing experiments it is concluded that one of thes modes is most likely associated with an As vacancy. The observed polarization dependence suggests that this can be a "breathing" vibration of the atoms surrounding the vacancy. In addition, experiments were performed that measured the lineshape of the enhancement of the Raman cross section of both the intrinsic and extrinsic modes near the band gap of GaAs using a tunable near infra-red laser. It was observed that the enhancement of the defect introduced modes was strong relative to the enhancement of the allowed TO phonon, which itself exhibits a strong enhancement. The observed enhancement lineshape can be explained by assuming that the scattering involving the defect induced modes occurs via a fourth order process. During this process quasi-momentum conservation is relaxed when electrons or holes scatter elastically from defects. On the basis of this model it is concluded that the strong resonant enhancement occurs when the vibrational modes involved have a component that is well localized around a defect. Thus resonant Raman scattering has greater sensitivity to motion within the first few lattice constants surrounding a point defect and is well suited to provide microscopic information about such defects. Another important conclusion is that the strong enhancement of the Raman cross section of the defect induced modes should be present at critical points other than the fundamental gap.

  20. The electronic and structural properties of the silicon-gallium arsenide(110) interface

    NASA Astrophysics Data System (ADS)

    Dunstan, P. R.; Wilks, S. P.; Burgess, S. R.; Pan, M.; Williams, R. H.; Cammack, D. S.; Clark, S. A.

    1998-01-01

    The passivation properties of the Sisbnd GaAs(110) interface have been studied using scanning tunnelling microscopy/spectroscopy (STM/STS) and soft X-ray photoemission spectroscopy (SXPS). Silicon has been deposited at room temperature and STM images show the sub-monolayer growth of silicon islands on the GaAs substrate. The electrical properties of these islands together with the clean surface have been investigated using scanning tunnelling spectroscopy (STS). The spectroscopy clearly illustrates the difference in electrical properties between atomically flat regions of GaAs as compared to those containing defects or steps, i.e. where surface band bending occurs. We have investigated the use of sub-monolayer Si coverages to modify the electronic structure of the surface. Height variations of 3-4Åacross Si islands and 2Åacross steps on the GaAs surface have also been observed using the STM. STS spectra, collected simultaneously with the STM image, showed the Si to have semiconducting properties differing from that of crystalline Si and the GaAs substrate. Comparisons between the STM and STS results together with SXPS have provided a correlation between the structural, electrical and chemical nature of the Si/GaAs(110) interface.

  1. Miniaturized 320x256 indium gallium arsenide SWIR camera for robotic and unmanned aerial vehicle applications

    NASA Astrophysics Data System (ADS)

    Ettenberg, Martin H.; O'Grady, Matthew T.; Huang, Shih-Che; Cohen, Marshall J.

    2003-09-01

    We describe a new InGaAs SWIR microcamera developed for robotic and UAV applications. The camera has a volume less than 27 cm3, weighs less than 100 g, and consumes less than 1.4 W. The camera operates with the focal plane array at room temperature and is sensitive to the 0.9 μm to 1.7 μm SWIR band with a detectivity, D*, greater than (formula available in paper). The InGaAs focal plane array has 320x256 pixels on a 25 μm pitch. It features snapshot-mode integration with a minimum exposure time of 500 ns making it ideally suited for all-solid-state range-gated imaging. The full-frame readout rate is greater than 400 frames per second. The built-in windowing feature is highly flexible with as many as 8 arbitrarily shaped regions-of-interest can be located anywhere (including overlapping) on the imager. Eight 64 x 64 regions of interest (ROIs), for example, can be read out faster than 1000 frames per second with a single 64 x 64 ROI read out faster than 5000 frames per second enabling high speed target acquisition and tracking applications.

  2. Diffusion of zinc in gallium arsenide with the participation isovalent impurities

    NASA Astrophysics Data System (ADS)

    Karlina, L. B.; Vlasov, A. S.; Ber, B. Y.; Kazantsev, D. Y.

    2015-12-01

    The diffusion of Zn into GaAs in the presence of indium and phosphorus was studied. Zn diffusion was performed from the gas phase in a hydrogen flow under isothermal conditions (670 °C). A GaAs substrate was annealed in In and P vapors in a separate chamber. The annealing conditions simulated the memory effect of a MOVPE reactor and/or the cross-doping during the growth of multilayer structures based on III-V alloys. The aim of the current research was to study the effects of In and P on the Zn diffusion processes in GaAs. The results obtained by secondary-ion mass spectrometry show that, upon a pre-treatment with In and P, both the incorporation efficiency and the diffusion rate of Zn increase. Measurements by Raman spectroscopy confirm the increase in the free-hole concentration in the sub-surface layers in pre-annealed samples. The influence of In and P on the diffusion process was observed at concentrations higher than 1017 cm-3. Optical characterization reveals changes in the defect distribution in the GaAs samples. The changes of the recombination processes, caused by In and P, depend on the indium vs. phosphorus ratio. The effective Zn diffusion rate is controlled by this ratio.

  3. 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.

  4. 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.

  5. Cubic zirconia as a species permeable coating for zinc diffusion in gallium arsenide

    SciTech Connect

    Bisberg, J.E.; Dabkowski, F.P.; Chin, A.K.

    1988-10-31

    Diffusion of zinc into GaAs through an yttria-stabilized cubic zirconia (YSZ) passivation layer has been demonstrated with an open-tube diffusion method. Pure zinc or GaAs/Zn/sub 2/As/sub 3/ sources produced high quality planar p-n junctions. The YSZ layer protects the GaAs surface from excessive loss of arsenic, yet is permeable to zinc, allowing its diffusion into the semiconductor. The YSZ films, deposited by electron beam evaporation, were typically 2000 A thick. Zinc diffusion coefficients (D/sub T/) at 650 /sup 0/C in the YSZ passivated GaAs ranged from 3.6 x 10/sup -10/ cm/sup 2//min for the GaAs/Zn/sub 2/As/sub 3/ source to 1.9 x 10/sup -9/ cm/sup 2//min for the pure zinc source. Doping concentrations for both YSZ passivated and uncapped samples were approximately 5 x 10/sup 19/ cm/sup -3/.

  6. Growth and characterization of indium gallium arsenide photocathodes for extended near infrared imaging

    NASA Astrophysics Data System (ADS)

    Bourree, Loig Erwan Richard

    Near infrared InGaAs photocathodes were designed and grown using molecular beam epitaxy (MBE), a high quality semiconductor growth technique, for the purpose of expanding the current spectral range of generation 3 image intensifier tubes to a 1000nm wavelength while maintaining a high quantum efficiency. Previous authors who have attempted this task have reported low sensitivity compared to the standard GaAs photocathodes and associated this drawback with the compositional mismatch from growing InGaAs epilayers onto GaAs substrates. Our approach differed from these previous authors by using MBE for the semiconductor growth instead of a vapor phase epitaxy technique that had been employed. In addition, to reduce the inherent lattice mismatch between the InGaAs photoemissive layer and the substrate, structures deviating from standard GaAs photocathodes were created, to include lattice-mismatch reducing buffers. These buffers are composed of ternary alloys with graded composition. Utilizing a variety of characterization techniques to determine growth parameters (thickness, doping, composition, crystallinity) a high level of control and reproducibility was achieved on our photocathode structures. Overall, negative electron affinity activation performed on our InGaAs photocathodes showed improvements in their white light photoresponse (PR) resulting from the inclusion of these buffers. Studies performed using room temperature photoluminescence, Raman spectroscopy and atomic force microscopy were employed to attempt relating these increases in PR to changes in material parameters and are presented in this dissertation.

  7. Gallium Arsenide Quantum Well Devices for Detection and Nonlinear Optics in the Mid-Infrared

    NASA Astrophysics Data System (ADS)

    Grave, Ilan

    The basic physical limits for infrared detection based on intersubband processes in semiconductor quantum wells are presented. An evaluation of the potential of GaAs intersubband detectors and a comparison with other systems is attempted. It is shown that the performances of the single GaAs detector falls short with respect to the single HgCdTe detector. Still, the performances of GaAs intersubband detectors answer the needs of many conceivable applications; this fact, together with the maturity, integrability and uniformity of the cheaper GaAs technology might make these detectors the choice for many future applications and systems. Optimization of parameters in the design and epitaxial growth of these structures yield standard intersubband detectors with very respectable performances at reasonable cooling costs. The narrow bandwidth and the lack of post-growth tunability limit the capability and versatility of intersubband detection. A new kind of intersubband detector, the multi -stack integrated detector, is conceived in an attempt to address these issues. This detector can operate in a number of modes; it can have a narrow or wide bandwidth of detection, and even a voltage-controlled expandable bandwidth. Among its features a multi-color option and a switching-peak option for combined or alternate color detection. The underlying physics involves the formation, expansion and readjustment of electric field high and low domains along the multi-quantum well region. Additional topics in the physics and applications of intersubband processes for detection of infrared light are explored: a band-gap design involving a variably-spaced superlattice barrier, is investigated by photocurrent spectroscopy. The experiments reveal the subtle breaking of the parity selection rules, and also the possibility of detecting infrared light at shorter wavelengths than previously thought possible in the GaAs/AlGaAs system. The second part of this thesis deals with the study and observation of enhanced nonlinear optical effects at the mid infrared, close to intersubband resonances. Second harmonic generation is obtained around 5 mu m. Third-order effects are then investigated in different experimental configurations, including the first observation of phase conjugation based on these nonlinearities. Very large third-order susceptibilities and intensity-dependent refractive indices are deduced from the experimental results.

  8. 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.

  9. Improved defect analysis of Gallium Arsenide solar cells using image enhancement

    NASA Technical Reports Server (NTRS)

    Kilmer, Louis C.; Honsberg, Christiana; Barnett, Allen M.; Phillips, James E.

    1989-01-01

    A new technique has been developed to capture, digitize, and enhance the image of light emission from a forward biased direct bandgap solar cell. Since the forward biased light emission from a direct bandgap solar cell has been shown to display both qualitative and quantitative information about the solar cell's performance and its defects, signal processing techniques can be applied to the light emission images to identify and analyze shunt diodes. Shunt diodes are of particular importance because they have been found to be the type of defect which is likely to cause failure in a GaAs solar cell. The presence of a shunt diode can be detected from the light emission by using a photodetector to measure the quantity of light emitted at various current densities. However, to analyze how the shunt diodes affect the quality of the solar cell the pattern of the light emission must be studied. With the use of image enhancement routines, the light emission can be studied at low light emission levels where shunt diode effects are dominant.

  10. 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.

  11. 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%).

  12. 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.

  13. 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.

  14. 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.

  15. Surface reconstructions and morphology of indium gallium arsenide compound semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Riposan, Alexandru

    Lattice-matched In0.53Ga0.47As/InP(001) and compressively strained In0.27Ga0.73As/GaAs(001) and In0.81Ga 0.19As/InP(001) compound semiconductor layers were grown by molecular beam epitaxy (MBE) and analyzed by in-situ scanning tunneling microscopy (STM) and ex-situ atomic force microscopy (AFM). Regular (4x3) and irregular (nx3) alloy reconstructions were observed at all compositions. In addition, the strained surfaces contain alpha2(2x4) and beta2(2x4) reconstructions at the lower and higher In compositions, respectively. New models were proposed for the (4x3) reconstruction, which are consistent with the experimental results and obey the electron counting rule. In these models, the (4x3) reconstruction is As-rich, but contains As-metal heterodimers, in addition to As dimers and metal dimers. These models can also be used to compose disordered (nx3) surfaces while still obeying the electron counting rule. The experiments suggest that the (2x4) reconstructions are favored by compressive misfit strain and are enriched in In compared with the (4x3)/(nx3) reconstructions. At moderate misfit strains and temperatures, the critical film thickness for three-dimensional (3D) growth is increased by increasing the As overpressure during film deposition. This effect provides an additional method to control the transition to 3D growth and has applications in device fabrication. Large 3D islands form during the annealing of planar pseudomorphic In 0.27Ga0.73As/GaAs films, and later disappear with continuing annealing. These islands are different from those formed during film deposition. The formation of these features is strain-driven, while their dissolution is triggered by In desorption. A step instability was also observed during annealing at this composition, consisting in the cusping of step edges and the formation of surface pits and step bunches. The driving force for this instability is likely the creation of new step line due to the compressive strain, through step undulation due to the large step separation. The nucleation of 3D pits during the growth of In0.27Ga 0.73As/GaAs compressively strained films is a localized phenomenon, occurring only in the proximity of 3D islands and at small island separation. The nucleation of pits in these regions was attributed to a reduced critical pit size, as a result of the overlapping strain fields of 3D islands and a reduced adatom density between islands.

  16. 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.

  17. Element Resolved Spin Configuration in Ferromagnetic Manganese-Doped Gallium Arsenide

    NASA Astrophysics Data System (ADS)

    Keavney, D. J.; Wu, D.; Freeland, J. W.; Johnston-Halperin, E.; Awschalom, D. D.; Shi, J.

    2003-10-01

    We report induced Ga and As moments in ferromagnetic Ga1-xMnxAs detected using x-ray magnetic circular dichroism at the Mn, Ga, and As L3,2 edges. Across a broad composition range, we find As and Ga dichroism signals which indicate an As 4s moment coupled antiparallel to the Mn 3d moment, and a smaller parallel Ga 4s moment. The Ga moment follows that of Mn in both doping and tempera­ture dependence. These results are consistent with recent predictions of induced GaAs host moments and support the model of carrier-mediated ferromagnetic ordering involving As-derived valence band states.

  18. Dual-band technology on indium gallium arsenide focal plane arrays

    NASA Astrophysics Data System (ADS)

    Dixon, Peter; Hess, Cory D.; Li, Chuan; Ettenberg, Martin; Trezza, John

    2011-06-01

    While InGaAs-based SWIR imaging technology has been improved dramatically over the past 10 years, the motivation remains to reduce Size Weight and Power (SWaP) for applications in Intelligence Surveillance and Reconnaissance (ISR). Goodrich ISR Systems, Princeton (Sensors Unlimited, Inc.) has continued to improve detector sensitivity. Additionally, SUI is working jointly with DRS-RSTA to develop innovative techniques for manufacturing dual-band focal planes to provide next generation technology for not only reducing SWaP for SWIR imagers, but also to combine imaging solutions for providing a single imager for Visible Near-SWIR (VNS) + LW imaging solutions. Such developments are targeted at reducing system SWaP, cost and complexity for imaging payloads on board UASs as well as soldier deployed systems like weapon sights. Our motivation is to demonstrate capability in providing superior image quality in fused LWIR and SWIR imaging systems, while reducing the total system SWaP and cost by enabling Short Wave and Thermal imaging in a single uncooled imager. Under DARPA MTO awarded programs, a LW bolometer (DRS-RSTA) is fabricated on a Short Wave (SW) InGaAs Vis-SWIR (SUI-Goodrich) Imager. The combined imager is a dual-band Sensor-Chip Assembly which is capable of imaging in VIS-SWIR + LW. Both DRS and Goodrich have developed materials and process enhancements to support these dual-band platform investigations. The two imagers are confocal and coaxial with respect to the incident image plane. Initial work has completed a single Read Out Integrated Circuit (ROIC) capable of running both imagers. The team has hybridized InGaAs Focal planes to 6" full ROIC wafers to support bolometer fabrication onto the SW array.

  19. Fluorescent lifetime measurements of rare-earth elements in gallium arsenide. Master's thesis

    SciTech Connect

    Topp, D.J.

    1990-12-01

    Lifetime measurements of the excited states of three GaAs semiconductors doped with the rare earth elements Erbium (Er), Praseodymium (Pr), and Thulium (Tm) has been studied using a pulsed nitrogen laser and germanium detector. The measurements were made with an experimental set up with a system response time of 0.34 microseconds. A 330 milliwatt nitrogen laser with a wavelength of 3370 angstroms was used to excite transitions of the rare earth elements.

  20. The effect of dislocations on the performance of gallium arsenide solar cells

    NASA Astrophysics Data System (ADS)

    Zolper, John C.; Barnett, Allen M.

    The dependence on dislocation density of GaAs solar cell performance is modeled. Reductions in short-circuit current are calculated with an effective diffusion length that is dependent on dislocation density. The electronic properties of the dislocations were examined to predict reductions in open-circuit voltage. The dislocations in n-type GaAs are modeled as inverted p-type regions based on the properties of GaAs grain boundaries and GaAs surfaces. These inverted regions form low-voltage diodes that act in parallel with the bulk GaAs diode and degrade open-circuit voltage. This approach predicts that GaAs solar cells on Si substrates with dislocation densities of 10 to the 6th/sq cm can attain AM1.5 efficiencies of 20 percent.

  1. Gamma Ray Detector Using Gallium Arsenide to Develop an Electrode Detector

    SciTech Connect

    Knoll, G.F.

    1999-03-26

    The emphasis of the DOE-funded detector project at the University of Michigan has been on the improvement of the performance of room-temperature gamma ray spectrometers. We have concentrated on the material known as CZT, a blend of cadmium and zinc tellurides, as the material of primary interest.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Oxidation of gallium arsenide in a plasma multipole device. Study of the MOS structures obtained

    NASA Technical Reports Server (NTRS)

    Gourrier, S.; Mircea, A.; Simondet, F.

    1980-01-01

    The oxygen plasma oxidation of GaAs was studied in order to obtain extremely high frequency responses with MOS devices. In the multipole system a homogeneous oxygen plasma of high density can easily be obtained in a large volume. This system is thus convenient for the study of plasma oxidation of GaAs. The electrical properties of the MOS diodes obtained in this way are controlled by interface states, located mostly in the upper half of the band gap where densities in the 10 to the 13th power/(sq cm) (eV) range can be estimated. Despite these interface states the possibility of fabricating MOSFET transistors working mostly in the depletion mode for a higher frequency cut-off still exists.

  7. 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.

  8. 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.

  9. 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.

  10. Spatially resolved localized vibrational mode spectroscopy of carbon in liquid encapsulated Czochralski grown gallium arsenide wafers

    SciTech Connect

    Yau, Waifan.

    1988-04-01

    Substitutional carbon on an arsenic lattice site is the shallowest and one of the most dominant acceptors in semi-insulating Liquid Encapsulated Czochralski (LEC) GaAs. However, the role of this acceptor in determining the well known W'' shape spatial variation of neutral EL2 concentration along the diameter of a LEC wafer is not known. In this thesis, we attempt to clarify the issue of the carbon acceptor's effect on this W'' shaped variation by measuring spatial profiles of this acceptor along the radius of three different as-grown LEC GaAs wafers. With localized vibrational mode absorption spectroscopy, we find that the profile of the carbon acceptor is relatively constant along the radius of each wafer. Average values of concentration are 8 {times} 10E15 cm{sup -3}, 1.1 {times} 10E15 cm{sup -3}, and 2.2 {times} 10E15 cm{sup -3}, respectively. In addition, these carbon acceptor LVM measurements indicate that a residual donor with concentration comparable to carbon exists in these wafers and it is a good candidate for the observed neutral EL2 concentration variation. 22 refs., 39 figs.

  11. 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.

  12. Design and implementation of high sensitive CCD on gallium arsenide based miniaturized spectrometer

    NASA Astrophysics Data System (ADS)

    Zheng, Jiamin; Shen, Jianhua; Guo, Fangmin

    2013-08-01

    In this paper, a method on how to design and implement a miniaturized spectrometer with low-light-level (LLL) CCD on GaAs is introduced. The optical system uses a blazed grating as the dispersive element and a 1×64 CCD on GaAs as the sensor. We apply a highly integrated Cortex-M4 MCU (STM32F407), to build the data acquisition and analysis unit, providing Wi-Fi interface to communicate with the PC software. It can complete the tasks like data acquisition, digital filtering, spectral display, network communication, human-computer interaction etc.

  13. Feasibility investigation of growing gallium arsenide single crystals in ribbon form

    NASA Technical Reports Server (NTRS)

    Richardson, D. L.

    1975-01-01

    Polycrystalline GaAs ribbons have been grown in graphite boats by passage of a wide zone through B2O3 encapsulated feed stock, confined by a quartz cover plate. By controlling the heat flow in the graphite boat and controlling the zoning rate, large grained, single phase polycrystalline samples with directional solidification and good thickness control were achieved. Arsenic vaporization was effectively suppressed at the melting point of GaAs by the B2O3 moat and 3 atmospheres of pressure. A vertical constrained-zone-melting apparatus with a B2O3 moat seal, rf heating, and water cooling on the bottom will be used to control the heat flow and temperature patterns required for growth of single crystal ribbons.

  14. DFT investigations of structural and electronic properties of gallium arsenide (GaAs)

    NASA Astrophysics Data System (ADS)

    Anua, N. Najwa; Ahmed, R.; Saeed, M. A.; Shaari, A.; Haq, Bakhtiar Ul

    2012-09-01

    First principles calculations for structural and electronic properties of GaAs have been reported using a full potential linearized augmented plane wave (FP-LAPW) scheme of calculations developed within density functional theory (DFT). We use in this study local density approximation (LDA), Perdew-Burke-Ernzerhof parameterized generalized gradient approximation (PBE-GGA), Wu-Cohen parameterized GGA (WC-GGA) executed in WIEN2k code. In addition, to calculate band structure with high accuracy we used modified Becke-Johnson exchange potential (MBJ) + LDA approach. Our calculated lattice constant with GGA-WC is in good agreement to experimental value than LDA and PBE-GGA. Whereas our calculations for the band structure show that MBJ+ LDA approach gives much better results for band gap value as compared to other exchange correlation approaches.

  15. Intersubband transitions in strained indium gallium arsenide quantum wells for multi-color infrared detector applications

    NASA Astrophysics Data System (ADS)

    Workman, Clayton Lee

    Intersubband transitions in InxGa1- xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy (MBE) were studied. The conduction band offset for this material system is larger than that of the well-known GaAs/AlGaAs system, thus making it possible to design, grow and fabricate quantum well infrared photodetectors operational in the 5--8 mum and 10--14 mum spectral regions with minimal dark current. InxGa 1-xAs/AlGaAs MQWs were grown by MBE with indium compositions ranging from x = 0.10 to 0.15 verified by in situ RHEED oscillations and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy in both the Brewster's angle and waveguide configuration. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ˜12% did not result in intersubband transitions at silicon doping levels of 2 x 10 18 cm-3. New structures were grown, with a thick linear graded InxGa1- xAs buffer below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in In xGa1-xAs wells with indium compositions of x = .20 when grown on top of the linear graded buffer (LGB). Three-color device structures consisting of InxGa1-xAs triple-coupled MQWs were grown with and without the LGB. FTIR measurements revealed that without the LGB, intersubband transitions were not present in the three-color structure. However, with the LGB intersubband transitions were measured. Only one intersubband peak was observed in the three-color structures in the Brewster angle configuration---possibly due to nonuniformity in the sample growth. In the waveguide configuration, an additional higher energy peak was observed which other groups have attributed to multiple internal reflections off the many layers in the structure. One three-color structure with an LGB layer and 21.4% indium showed multiple peaks in the waveguide configuration, but no peaks in the Brewster angle configuration. Due to the complex nature of the waveguide, it is difficult to compare the measured peaks with the expected values. However, this sample showed the most promising results in terms of multi-color detection behavior.

  16. The stopping of energetic silicon, phosphorus and sulfur ions in nickel, copper, germanium and gallium arsenide

    NASA Astrophysics Data System (ADS)

    Nigam, Mohit

    Accurate knowledge of stopping powers is essential for these for quantitative analysis and surface characterization of thin films using ion beam analysis (IBA). These values are also of interest in radiobiology and radiotherapy, and in ion-implantation technology where shrinking feature sizes puts high demands on the accuracy of range calculations. A theory that predicts stopping powers and ranges for all projectile-target combinations is needed. The most important database used to report the stopping powers is the SRIM/TRIM program developed by Ziegler and coworkers. However, other researchers report that at times, these values differ significantly from experimental values. In this study the stopping powers of Si, P and S ions have been measured in Ni, Cu, Ge and GaAs absorbers in the energy range ˜2--10 MeV. For elemental films of Ni, Cu and Ge, the stopping of heavy ions was measured using a novel ERD (Elastic Recoil Detection) based technique. In which an elastically recoiled lighter atom is used to indirectly measure the energy of the incoming heavy ion using a surface barrier detector. In this way it was possible to reduce the damage and to improve the FVVHM of the detector. The results were compared to SRIM-2000 predictions and other experimental measurements. A new technique derived from Molecular Beam Epitaxy (MBE) was developed to prepare stoichiometric GaAs films on thin carbon films for use in transmission ion beam experiments. The GaAs films were characterized using X-ray Photoelectron Spectroscopy (XPS) and Particle Induced X-ray Emission (PIXE). These films were used to investigate the stopping powers of energetic heavy ions in GaAs and to provide data for the calculation of Bethe-Block parameters in the framework of the Modified Bethe-Block theory. As a result of this study, stopping power data are available for the first time for Si and P ions in the energy range 2--10 MeV stopping in GaAs absorbers.

  17. Nuclear magnetization in gallium arsenide quantum dots at zero magnetic field

    PubMed Central

    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. PMID:24500329

  18. Growth and characterization of indium gallium arsenide (0.0 gallium arsenide wafers and the evolution of indium arsenide quantum dots grown on these substrates

    NASA Astrophysics Data System (ADS)

    Ghanad-Tavakoli, Shahram

    InxGa1-xAs (0.00 ≤ x ≤ 0.42) metamorphic pseudosubstrate layers (MSLs) were studied as a means to change the lattice constant of the substrates and to modify the growth conditions of InAs quantum dots (QDs) by varying the strain. The MSLs showed symmetrical mosaicity about the <110> axes but the spread was different in the two orthogonal [110] and [11¯0] directions. The anisotropy in the mosaic spread in two <110> directions was correlated to asymmetry of kinks and multilevel-terrace growth front during the growth of InxGa1-xAs buffer layers. X-ray and electron diffraction along with the least squares criterion can interchangeably be employed to determine the lattice constant of the MSLs. It is possible to grow a defect free MSL with employing a compositional undershoot relative to the terminating buffer layer. Asymmetric tilt was found in an In0.42Ga0.58As MSL grown on a singular (001) GaAs substrate with an initial layer of a low temperature (< 300°C) grown InGaP prior to the growth of step-graded InxGa1-xAs (x = 0.02 to 0.42) buffer layers. The tilt around [11¯0] axis was correlated with the imbalance of the tilt component of the Burgers vector (BV) of the 60° alpha-dislocations. Climb and jog formation of beta-dislocations in the presence of P-interstitials were considered as a plausible mechanism for multiplication of the like-sign BV alpha-dislocations. These results show that an asymmetric tilt boundary can be induced in mismatched heterointerfaces grown on singular substrates. The evolution of InAs QDs on InxGa1-xAs (0.0 ≤ x ≤ 0.3) MSLs on GaAs substrates was studied. The results indicate that the ratio of the height (h) over lateral diameter ( d) of the QDs decreases with decreasing strain (i.e. the morphology of the coherent islands evolve toward a uniform film morphology ( hd = 0) with decreasing strain). This evolution is analogous to the current understating of strained uniform films where the tetragonality of the uniform film decreases with decreasing strain. The photoluminescence of the buried In(Ga)As QDs increases with increasing In (decreasing Ga) mole fraction of the underlying MSL; and thin strain-reducing capping layers do not significantly shift the PL. Modelling the experimental data suggests that Ga is incorporated in InAs QDs and the incorporation was estimated to linearly depend on the Ga mole fraction of the underlying InxGa1-xAs MSL indicating mass transport from the substrate at the growth temperature (≅ 500°C).

  19. Gallium interactions with Zircaloy

    SciTech Connect

    Woods, A.L.; West, M.K.

    1999-01-01

    This study focuses on the effects of gallium ion implantation into zircaloy cladding material to investigate the effects that gallium may have in a reactor. High fluence ion implantation of Ga ions was conducted on heated Zircaloy-4 in the range of 10{sup 16}--10{sup 18} Ga ions/cm2. Surface effects were studied using SEM and electron microprobe analysis. The depth profile of Ga in the Zircaloy was characterized with Rutherford backscattering and SIMS techniques. Results indicate that the Zirc-4 is little affected up to a fluence of 10{sup 17} Ga ions/cm{sup 2}. After implantation of 10{sup 18} Ga ions/cm{sup 2}, sub-grain features on the order of 2 {micro}m were observed which may be due to intermetallic compound formation between Ga and Zr. For the highest fluence implant, Ga content in the Zirc-4 reached a saturation value of between 30 and 40 atomic %; significant enhanced diffusion was observed but gallium was not seen to concentrate at grain boundaries.

  20. 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.

  1. 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.

  2. Gallium--A smart metal

    USGS Publications Warehouse

    Foley, Nora; Jaskula, Brian

    2013-01-01

    Gallium is a soft, silvery metallic element with an atomic number of 31 and the chemical symbol Ga. The French chemist Paul-Emile Lecoq de Boisbaudran discovered gallium in sphalerite (a zinc-sulfide mineral) in 1875 using spectroscopy. He named the element "gallia" after his native land of France (formerly Gaul; in Latin, Gallia). The existence of gallium had been predicted in 1871 by Dmitri Mendeleev, the Russian chemist who published the first periodic table of the elements. Mendeleev noted a gap in his table and named the missing element "eka-aluminum" because he determined that its location was one place away from aluminum in the table. Mendeleev thought that the missing element (gallium) would be very much like aluminum in its chemical properties, and he was right. Solid gallium has a low melting temperature (~29 degrees Celsius, or °C) and an unusually high boiling point (~2,204 °C). Because of these properties, the earliest uses of gallium were in high-temperature thermometers and in designing metal alloys that melt easily. The development of a gallium-based direct band-gap semiconductor in the 1960s led to what is now one of the most well-known applications for gallium-based products--the manufacture of smartphones and data-centric networks.

  3. 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.

  4. Gallium phosphide energy converters

    NASA Technical Reports Server (NTRS)

    Sims, P. E.; DiNetta, Louis C.; DuganCavanagh, K.; Goetz, M. A.

    1996-01-01

    Betavoltaic power supplies based on gallium phosphide can supply long term low-level power with high reliability. Results are presented for GaP devices powered by Ni-63 and tritiarated phosphors. Leakage currents as low as 1.2 x 10(exp -17) A/cm(exp 2) have been measured and the temperature dependence of the reverse saturation current is found to have ideal behavior. A small demonstration system has been assembled that generates and stores enough electricity to light up an LED.

  5. Functionalization of nitrogen-doped carbon nanotubes with gallium to form Ga-CN(x)-multi-wall carbon nanotube hybrid materials.

    PubMed

    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

    2012-08-17

    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 (GaI(3)), it was possible to form covalent bonds between the Ga(3+) 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. PMID:22825368

  6. Preparation of a smooth GaN-Gallium solid-liquid interface

    NASA Astrophysics Data System (ADS)

    de Jong, A. E. F.; Vonk, V.; Ruat, M.; Boćkowski, M.; Kamler, G.; Grzegory, I.; Honkimäki, V.; Vlieg, E.

    2016-08-01

    We discuss the preparation of an atomically flat solid-liquid interface between solid gallium nitride and liquid gallium using in situ surface X-ray diffraction to probe the interface roughness. For the creation of this interface it is necessary to start the experiment with liquid gallium which first etches into the solid at a temperature of 823 K in a nitrogen free ambient. After this rigorous cleaning procedure there is perfect wetting between solid and liquid. The roughness created due to the fast etching of the solid has to be repaired at a nitrogen pressure of 10-20 bar and a temperature around 1150 K. The (2,1) crystal truncation rod data are excellently described by a surface model having 0±0.1 Å roughness, which indicates a successful repair. The lateral length scale on which the roughness is determined has a lower limit of 750±50 Å.

  7. Technique for depositing silicon dioxide on indium arsenide improves adhesion

    NASA Technical Reports Server (NTRS)

    1970-01-01

    Planar array processing of indium arsenide wafers includes dicing into a prescribed geometry, then cleaning and drying, and finally pre-oxidizing in an oxygen atmosphere at 500 degrees C. The last step forms an oxide interface between the InAs surface and a glow discharge deposited layer of silicon dioxide.

  8. Gallium Safety in the Laboratory

    SciTech Connect

    Cadwallader, L.C.

    2003-05-07

    A university laboratory experiment for the US Department of Energy magnetic fusion research program required a simulant for liquid lithium. The simulant choices were narrowed to liquid gallium and galinstan (Ga-In-Sn) alloy. Safety information on liquid gallium and galinstan were compiled, and the choice was made to use galinstan. A laboratory safety walkthrough was performed in the fall of 2002 to support the galinstan experiment. The experiment has been operating successfully since early 2002.

  9. Gallium Safety in the Laboratory

    SciTech Connect

    Lee C. Cadwallader

    2003-06-01

    A university laboratory experiment for the US Department of Energy magnetic fusion research program required a simulant for liquid lithium. The simulant choices were narrowed to liquid gallium and galinstan (Ga-In-Sn) alloy. Safety information on liquid gallium and galinstan were compiled, and the choice was made to use galinstan. A laboratory safety walkthrough was performed in the fall of 2002 to support the galinstan experiment. The experiment has been operating successfully since early 2002.

  10. Discriminating a deep gallium antisite defect from shallow acceptors in GaAs using supercell calculations

    NASA Astrophysics Data System (ADS)

    Schultz, Peter A.

    2016-03-01

    For the purposes of making reliable first-principles predictions of defect energies in semiconductors, it is crucial to distinguish between effective-mass-like defects, which cannot be treated accurately with existing supercell methods, and deep defects, for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite defect GaA s is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a conceptual framework of level patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as BA s. This systematic approach determines that the gallium antisite supercell results has signatures inconsistent with an effective mass state and cannot be the 78/203 shallow double acceptor. The properties of the Ga antisite in GaAs are described, total energy calculations that explicitly map onto asymptotic discrete localized bulk states predict that the Ga antisite is a deep double acceptor and has at least one deep donor state.

  11. Discriminating a deep gallium antisite defect from shallow acceptors in GaAs using supercell calculations

    DOE PAGESBeta

    Schultz, Peter A.

    2016-03-01

    For the purposes of making reliable first-principles predictions of defect energies in semiconductors, it is crucial to distinguish between effective-mass-like defects, which cannot be treated accurately with existing supercell methods, and deep defects, for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite defect GaAs is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a conceptual framework of level patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as BAs. This systematicmore » approach determines that the gallium antisite supercell results has signatures inconsistent with an effective mass state and cannot be the 78/203 shallow double acceptor. Lastly, the properties of the Ga antisite in GaAs are described, total energy calculations that explicitly map onto asymptotic discrete localized bulk states predict that the Ga antisite is a deep double acceptor and has at least one deep donor state.« less

  12. Discriminating a deep defect from shallow acceptors in supercell calculations: gallium antisite in GaAs

    NASA Astrophysics Data System (ADS)

    Schultz, Peter

    To make reliable first principles predictions of defect energies in semiconductors, it is crucial to discriminate between effective-mass-like defects--for which existing supercell methods fail--and deep defects--for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite GaAs is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a framework of level occupation patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as BAs. This systematic analysis determines that the gallium antisite is inconsistent with a shallow state, and cannot be the 78/203 shallow double acceptor. The properties of the Ga antisite in GaAs are described, predicting that the Ga antisite is a deep double acceptor and has two donor states, one of which might be accidentally shallow. -- Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  13. Development of gallium nitride-based PNP heterojunction bipolar transistors

    NASA Astrophysics Data System (ADS)

    Green, Daniel S.

    GaN-based electronics have progressed mightily in the last 15 years. The primary focus of this development has been the AlGaN/GaN heterostructure FET, with the commercialization of this device in progress. Bipolar transistors however offer a few key potential advantages over the FET device, including the primary advantage of normally off operation. Additionally, the pnp heterostructure bipolar transistor (HBT) in particular offers more attractive base performance relative to the npn HBT. The pnp HBT also serves as an excellent test vehicle for the several material parameters of p-Gan that remain poor defined. However, implementation of the pnp HBT has been limited by the difficulty contacting p-GaN collector material. This work was designed to demonstrate and understand the pnp HBT. The research served as both an engineering challenge as well as an investigation of physical parameters governing the transport in the device. In order to remedy the poor collector contact available with buried p-GaN, a transformation diode HBT structure was introduced that added an n-type subcollector the HBT structure. This allowed for good collector contact at the cost of introducing an offset voltage to the HBT performance due to the turn-on voltage of the transformation diode under normal operation. The first transformation diode HBT in GaN was successful demonstrated. In order to improve the transformation diode performance, successive design iterations were performed to isolate the performance limiting elements. Device designs were implemented to mitigate saturated hole velocity, as well as to decrease base transit time through aggressive base scaling and compositional grading. Physical simulations and modelling of device non-idealities were used to understand actual device performance. Hole lifetime and saturated hole velocity were identified as primary contributors to lower than expected performance device performance. Successive device iterations yielded HBT performance of beta ˜ 2 for a current density of ˜ 50 A cm-2.

  14. Defect reduction in gallium nitride using cantilever epitaxy.

    SciTech Connect

    Mitchell, Christine Charlotte

    2003-08-01

    Cantilever epitaxy (CE) has been developed to produce GaN on sapphire with low dislocation densities as needed for improved devices. The basic mechanism of seeding growth on sapphire mesas and lateral growth of cantilevers until they coalesce has been modified with an initial growth step at 950 C. This step produces a gable with (11{bar 2}2) facets over the mesas, which turns threading dislocations from vertical to horizontal in order to reduce the local density above mesas. This technique has produced material with densities as low as 2-3x10{sup 7}/cm{sup 2} averaged across extended areas of GaN on sapphire, as determined with AFM, TEM and cathodoluminescence (CL). This density is about two orders of magnitude below that of conventional planar growths; these improvements suggest that locating wide-area devices across both cantilever and mesa regions is possible. However, the first implementation of this technique also produced a new defect: cracks at cantilever coalescences with associated arrays of lateral dislocations. These defects have been labeled 'dark-block defects' because they are non-radiative and appear as dark rectangles in CL images. Material has been grown that does not have dark-block defects. Examination of the evolution of the cantilever films for many growths, both partial and complete, indicates that producing a film without these defects requires careful control of growth conditions and crystal morphology at multiple steps. Their elimination enhances optical emission and uniformity over large (mm) size areas.

  15. Ab Initio Calculations of Excited Carrier Dynamics in Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Jhalani, Vatsal; Bernardi, Marco

    Bulk wurtzite GaN is the primary material for blue light-emission technology. The radiative processes in GaN are regulated by the dynamics of excited (or so-called ``hot'') carriers, through microscopic processes not yet completely understood. We present ab initio calculations of electron-phonon (e-ph) scattering rates for hot carriers in GaN. Our work combines density functional theory to compute the electronic states, and density functional perturbation theory to obtain the phonon dispersions and e-ph coupling matrix elements. These quantities are interpolated on fine Brillouin zone grids with maximally localized Wannier functions, to converge the e-ph scattering rates within 5 eV of the band edges. We resolve the contribution of the different phonon modes to the total scattering rate, and study the impact on the relaxation times of the long-range Fröhlich interaction due to the longitudinal-optical phonon modes.

  16. Review of using gallium nitride for ionizing radiation detection

    NASA Astrophysics Data System (ADS)

    Wang, Jinghui; Mulligan, Padhraic; Brillson, Leonard; Cao, Lei R.

    2015-09-01

    With the largest band gap energy of all commercial semiconductors, GaN has found wide application in the making of optoelectronic devices. It has also been used for photodetection such as solar blind imaging as well as ultraviolet and even X-ray detection. Unsurprisingly, the appreciable advantages of GaN over Si, amorphous silicon (a-Si:H), SiC, amorphous SiC (a-SiC), and GaAs, particularly for its radiation hardness, have drawn prompt attention from the physics, astronomy, and nuclear science and engineering communities alike, where semiconductors have traditionally been used for nuclear particle detection. Several investigations have established the usefulness of GaN for alpha detection, suggesting that when properly doped or coated with neutron sensitive materials, GaN could be turned into a neutron detection device. Work in this area is still early in its development, but GaN-based devices have already been shown to detect alpha particles, ultraviolet light, X-rays, electrons, and neutrons. Furthermore, the nuclear reaction presented by 14N(n,p)14C and various other threshold reactions indicates that GaN is intrinsically sensitive to neutrons. This review summarizes the state-of-the-art development of GaN detectors for detecting directly and indirectly ionizing radiation. Particular emphasis is given to GaN's radiation hardness under high-radiation fields.

  17. Metallic impurities in gallium nitride grown by molecular beam epitaxy

    SciTech Connect

    McHugo, S.A.; Krueger, J.; Kisielowski, C.

    1997-04-01

    Transition metals are often encountered in trace amounts in semiconductors. They have been extensively studied in most elemental and compound systems, since they form deep donor and/or acceptor levels which usually degrade the electronic and optical material properties. Only very little is known about transition metals in recent III-V semiconducting materials, such as GaN, AlN and InN. These few studies have been done exclusively on Metal-Organic Chemical Vapor Deposition (MOCVD) or Hybrid Vapor Phase Epitaxy HVPE-grown GaN. Preliminary x-ray fluorescence studies at the Advanced Light Source, beamline 10.3.1, Lawrence Berkeley National Laboratory have revealed that GaN materials grown by Molecular Beam Epitaxy (MBE) have Fe, Ni and Cr as the dominant transition metal contaminants. This finding is commensurate with the extremely high concentrations of hydrogen, carbon and oxygen (up to 10{sup 20} cm{sup {minus}3}) measured by Secondary Ion Mass Spectroscopy (SIMS). Preliminary work using the mapping capabilities of the x-ray fluorescence microprobe revealed the metal impurities were inhomogeneously distributed over the film. Future work of this collaboration will be to find a correlation between the existence of transition metals in MBE films, as revealed by x-ray fluorescence, and Photoluminescence (PL) spectra taken in the infrared region. Also, the authors will make use of the 1 {mu}m spatial resolution of x-ray microprobe to locate the contaminants in relation to structural defects in the GaN films. Because of the large strain caused by the lattice mismatch between the GaN films and the substrates, the films grow in a columnar order with high densities of grain boundaries and dislocations. These structural defects offer preferential sites for metal precipitation or agglomeration which could degrade the optical properties of this material more so than if the impurities were left dissolved in the GaN.

  18. Review of using gallium nitride for ionizing radiation detection

    SciTech Connect

    Wang, Jinghui; Mulligan, Padhraic; Cao, Lei R.; Brillson, Leonard

    2015-09-15

    With the largest band gap energy of all commercial semiconductors, GaN has found wide application in the making of optoelectronic devices. It has also been used for photodetection such as solar blind imaging as well as ultraviolet and even X-ray detection. Unsurprisingly, the appreciable advantages of GaN over Si, amorphous silicon (a-Si:H), SiC, amorphous SiC (a-SiC), and GaAs, particularly for its radiation hardness, have drawn prompt attention from the physics, astronomy, and nuclear science and engineering communities alike, where semiconductors have traditionally been used for nuclear particle detection. Several investigations have established the usefulness of GaN for alpha detection, suggesting that when properly doped or coated with neutron sensitive materials, GaN could be turned into a neutron detection device. Work in this area is still early in its development, but GaN-based devices have already been shown to detect alpha particles, ultraviolet light, X-rays, electrons, and neutrons. Furthermore, the nuclear reaction presented by {sup 14}N(n,p){sup 14}C and various other threshold reactions indicates that GaN is intrinsically sensitive to neutrons. This review summarizes the state-of-the-art development of GaN detectors for detecting directly and indirectly ionizing radiation. Particular emphasis is given to GaN's radiation hardness under high-radiation fields.

  19. The Behavior of Ion-Implanted Hydrogen in Gallium Nitride

    SciTech Connect

    Myers, S.M.; Headley, T.J.; Hills, C.R.; Han, J.; Petersen, G.A.; Seager, C.H.; Wampler, W.R.

    1999-01-07

    Hydrogen was ion-implanted into wurtzite-phase GaN, and its transport, bound states, and microstructural effects during annealing up to 980 C were investigated by nuclear-reaction profiling, ion-channeling analysis, transmission electron microscopy, and infrared (IR) vibrational spectroscopy. At implanted concentrations 1 at.%, faceted H{sub 2} bubbles formed, enabling identification of energetically preferred surfaces, examination of passivating N-H states on these surfaces, and determination of the diffusivity-solubility product of the H. Additionally, the formation and evolution of point and extended defects arising from implantation and bubble formation were characterized. At implanted H concentrations 0.1 at.%, bubble formation was not observed, and ion-channeling analysis indicated a defect-related H site located within the [0001] channel.

  20. Modeling of Gallium Nitride Hydride Vapor Phase Epitaxy

    NASA Technical Reports Server (NTRS)

    Meyyappan, Meyya; Arnold, James O. (Technical Monitor)

    1997-01-01

    A reactor model for the hydride vapor phase epitaxy of GaN is presented. The governing flow, energy, and species conservation equations are solved in two dimensions to examine the growth characteristics as a function of process variables and reactor geometry. The growth rate varies with GaCl composition but independent of NH3 and H2 flow rates. A change in carrier gas for Ga source from H2 to N2 affects the growth rate and uniformity for a fixed reactor configuration. The model predictions are in general agreement with observed experimental behavior.

  1. Codoping of magnesium with oxygen in gallium nitride nanowires

    SciTech Connect

    Wang, Zhiguo; Li, Jingbo; Gao, Fei; Weber, William J.

    2010-03-08

    Co-doping of p-type GaN nanowires with Mg and oxygen was investigated using first-principles calculations. The Mg becomes a deep acceptor in GaN nanowires with high ionization energy due to the quantum confinement. The ionization energy of Mg doped GaN nanowires containing passivated Mg-O complex decreases with increasing the diameter, and reduces to 300 meV as the diameter of the GaN nanowire is larger than 2.01 nm, which indicates that Mg-O co-doping is suitable for achieving p-type GaN nanowires with larger diameters. The co-doping method to reduce the ionization energy can be effectively used in other semiconductor nanostructures.

  2. Nanostructures of Indium Gallium Nitride Crystals Grown on Carbon Nanotubes

    PubMed Central

    Park, Ji-Yeon; Man Song, Keun; Min, Yo-Sep; Choi, Chel-Jong; Seok Kim, Yoon; Lee, Sung-Nam

    2015-01-01

    Nanostructure (NS) InGaN crystals were grown on carbon nanotubes (CNTs) using metalorganic chemical vapor deposition. The NS-InGaN crystals, grown on a ~5-μm-long CNT/Si template, were estimated to be ~100–270 nm in size. Transmission electron microscope examinations revealed that single-crystalline InGaN NSs were formed with different crystal facets. The observed green (~500 nm) cathodoluminescence (CL) emission was consistent with the surface image of the NS-InGaN crystallites, indicating excellent optical properties of the InGaN NSs on CNTs. Moreover, the CL spectrum of InGaN NSs showed a broad emission band from 490 to 600 nm. Based on these results, we believe that InGaN NSs grown on CNTs could aid in overcoming the green gap in LED technologies. PMID:26568414

  3. Auger Recombination in Indium Gallium Nitride: Experimental Evidence

    NASA Astrophysics Data System (ADS)

    Krames, Michael

    2010-03-01

    Progress in InGaN-based light-emitting diode (LED) technology has resulted in white-light emitters with efficiencies far exceeding those of conventional light sources such as tungsten-filament-based incandescence and mercury-vapor based fluorescence. Indeed, by now efficacies exceeding 150 lumens per Watt for InGaN-based phosphor-converted white LEDs are claimed, which represent a 90% energy savings compared to the conventional incandescent (i.e., ``light bulb'') solution. However, these high performance levels are obtained under conditions of very low forward current-density for the InGaN LED and do not represent true operating conditions (nor cost-effective utilization) for the device. In order to reduce the cost (and thus increase market penetration of) solid-state lighting, more lumens per unit of semiconductor area are required which in practice necessitates higher drive current densities. Unfortunately, at these higher driver current densities, the internal quantum efficiency of InGaN-based LEDs is observed to decrease significantly. In the fall of 2007, researchers at the Advanced Laboratories of Philips Lumileds were the first to propose Auger recombination as the root-cause mechanism in InGaN which was behind this ``efficiency droop'' [1]. They further proposed to circumvent the problem by employing InGaN-based active region designs that maintain low carrier density, and demonstrated an LED device design that reaches a maximum quantum efficiency above 200 A/cm2, compared to ˜1-10 A/cm^2 for typical multiple-quantum-well heterostructures [2]. In this talk we will review the experimental evidence for Auger recombination in InGaN, beginning with the early work from 2007 and then considering additional work from more recent efforts to better understand the details behind this loss mechanism. [4pt] [1] Y. C. Shen, G. O. M"uller, S. Watanabe, N. F. Gardner, A. Munkholm, and M. R. Krames, ``Auger recombination in InGaN measured by photoluminescence'', Appl. Phys. Lett. 91, 141101 (2007). [0pt] [2] N. F. Gardner, G. O. M"uller, Y. C. Shen, G. Chen, S. Watanabe, W. G"otz, and M. R. Krames, ``Blue-emitting InGaN--GaN double-heterostructure light-emitting diodes reaching maximum quantum efficiency above 200 A/cm^2'', Appl. Phys. Lett. 91, 243506 (2007).

  4. MOCVD growth of gallium nitride with indium surfactant

    NASA Astrophysics Data System (ADS)

    Won, Dong Jin

    In this thesis research, the effect of indium surfactant on Ga-polar and N-polar GaN films grown at 950 °C by MOCVD on various substrates such as Si-face SiC, bulk GaN, Si(111), and C-face SiC was studied to investigate the stress relaxation mechanism, structural, and optical properties of GaN films which were modified by the indium surfactant. The effect of indium surfactant on GaN films grown on SiC was studied first. In the 1.8 microm thick Ga-polar GaN films grown on lattice-mismatched Si-face SiC substrates utilizing indium surfactant at 950 °C, inverted hexagonal pyramid surface defects, so-called V-defects which consist of six (1011) planes, formed at threading dislocations on the GaN surface, which gave rise to the relaxation of compressive misfit stress in an elastic way. Simultaneously, enhanced surface mobility of Ga and N adatoms with indium surfactant lead to improved 2D growth, which may be contradictory to the formation of surface defects like V-defects. In order to find the driving force for V-defect formation in the presence of indium, a nucleation and growth model was developed, taking into consideration the strain, surface, and dislocation energies modified by indium surfactant. This model found that the V-defect formation can be energetically preferred since indium reduces the surface energy of the (1011) plane, which gives rise to the V-defect formation and growth that can overcome the energy barrier at the critical radius of the V-defect. These Ga-polar GaN films were found to be unintentionally doped with Si. Thus, an investigation into the effect of intentional Si doping at a constant TMIn flow rate on GaN films was also performed. Si turned out to be another important factor in the generation of V-defects because Si may be captured at the threading dislocation cores by forming Si -- N bonds, acting as a mask to locally prevent GaN growth. This behavior appeared to assist the initiation of the V-defect which enables V-defects to easily grow beyond the critical radius. Thus, introduction of indium surfactant and Si doping was found to be the most favorable conditions for V-defect formation in Ga-polar GaN films grown on Si-face SiC substrates. The nucleation and growth model predicted that V-defects may not form in homoepitaxy because the energy barrier for V-defect formation approaches infinity due to zero misfit stress. When indium surfactant and Si dopant were introduced simultaneously during the homoepitaxial growth, V-defects did not form in 1.8 microm thick Ga-polar GaN films grown at 950 °C on bulk GaN that had very low threading dislocation density, as predicted by the nucleation and growth model. Ga-polar GaN films grown on Si(111) substrates using indium surfactant showed that additional tensile stress was induced by indium with respect to the reference GaN. Since cracking is known to be a stress relaxation mechanism for tension, the In-induced additional tensile stress is thus detrimental to the GaN films which experience the tensile thermal stress associated with the difference in coefficient of thermal expansion between GaN and the substrate during cooling after growth. The generation of tensile stress by indium seemed correlated with a reduction of V-defects since a high density of V-defects formed under the initial compressive stress at the GaN nucleation stage and then V-defect density decreased as the film grew. Even though the initial misfit stress of the GaN film grown on Si(111) was lower than that of GaN grown on SiC, a high density of V-defects were created under the initial compressive stress. Therefore, the high density of threading dislocations was believed to strongly drive the V-defect formation under In-rich conditions. Consequently, without using high quality bulk GaN substrates, V-defects could not be avoided in Ga-polar GaN films grown on foreign substrates such as Si-face SiC and Si(111) in the presence of indium surfactant and Si dopants during growth. Thus, N-polar GaN films were investigated using vicinal C-face SiC substrates because a theoretical study utiliz

  5. Density and morphology adjustments of gallium nitride nanowires

    NASA Astrophysics Data System (ADS)

    Teker, Kasif

    2013-10-01

    This paper presents the morphology and density adjustments of GaN nanostructures via CVD process. GaN nanostructure growth has been carried out using Ga and NH3 as source materials with various catalyst materials, such as Au, Ni, Ag, and Fe between 800 and 1100 °C. The investigation has focused on the effects of process parameters, such as growth temperature and catalyst materials on the GaN nanowire morphology and density. Low temperature (<950 °C) growth runs resulted in microscale-faceted crystals and short nanorods regardless of the catalyst type or reactor pressure. Conversely, high temperature (1100 °C) growth runs resulted in ultra-dense interwoven long nanowires with multi-prong growth mechanism. A detailed analysis for the transition from microscale-faceted crystals to ultra-dense multi-prong-grown GaN nanowires is provided. Furthermore, electrical characteristics of the grown nanowires have been demonstrated through a very efficient fabrication scheme. Consequently, multi-prong growth mechanism reduces catalyst contamination and produces high density of long nanowires, which is very crucial for scale-up manufacturing opportunities.

  6. Nanostructures of Indium Gallium Nitride Crystals Grown on Carbon Nanotubes.

    PubMed

    Park, Ji-Yeon; Man Song, Keun; Min, Yo-Sep; Choi, Chel-Jong; Seok Kim, Yoon; Lee, Sung-Nam

    2015-01-01

    Nanostructure (NS) InGaN crystals were grown on carbon nanotubes (CNTs) using metalorganic chemical vapor deposition. The NS-InGaN crystals, grown on a ~5-μm-long CNT/Si template, were estimated to be ~100-270 nm in size. Transmission electron microscope examinations revealed that single-crystalline InGaN NSs were formed with different crystal facets. The observed green (~500 nm) cathodoluminescence (CL) emission was consistent with the surface image of the NS-InGaN crystallites, indicating excellent optical properties of the InGaN NSs on CNTs. Moreover, the CL spectrum of InGaN NSs showed a broad emission band from 490 to 600 nm. Based on these results, we believe that InGaN NSs grown on CNTs could aid in overcoming the green gap in LED technologies. PMID:26568414

  7. Nanostructures of Indium Gallium Nitride Crystals Grown on Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Park, Ji-Yeon; Man Song, Keun; Min, Yo-Sep; Choi, Chel-Jong; Seok Kim, Yoon; Lee, Sung-Nam

    2015-11-01

    Nanostructure (NS) InGaN crystals were grown on carbon nanotubes (CNTs) using metalorganic chemical vapor deposition. The NS-InGaN crystals, grown on a ~5-μm-long CNT/Si template, were estimated to be ~100-270 nm in size. Transmission electron microscope examinations revealed that single-crystalline InGaN NSs were formed with different crystal facets. The observed green (~500 nm) cathodoluminescence (CL) emission was consistent with the surface image of the NS-InGaN crystallites, indicating excellent optical properties of the InGaN NSs on CNTs. Moreover, the CL spectrum of InGaN NSs showed a broad emission band from 490 to 600 nm. Based on these results, we believe that InGaN NSs grown on CNTs could aid in overcoming the green gap in LED technologies.

  8. Crystal quality and growth evolution of aluminum nitride on silicon carbide

    NASA Astrophysics Data System (ADS)

    Moe, Craig G.; Wu, Yuan; Keller, Stacia; Speck, James S.; Denbaars, Steven P.; Emerson, David

    2006-05-01

    High quality base layer aluminum nitride films have become increasingly desirable with the advent of deep ultraviolet (<280 nm) emitters for water purification, solid state lighting, and biochemical detection applications. In this study, the influence of the MOCVD growth conditions on the structural properties of aluminum nitride grown on silicon carbide, both as-delivered and chemomechanically polished, was studied. Pre-deposition nitridation of the SiC substrate, growth temperature, growth rate, ammonia flow (V/III ratio), and gallium surfactants were explored. Films were analyzed with transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction.

  9. Advanced processing of gallium nitride and gallium nitride-based devices: Ultra-high temperature annealing and implantation incorporation

    NASA Astrophysics Data System (ADS)

    Yu, Haijiang

    This dissertation is focused on three fields: ultra-high temperature annealing of GaN, activation of implanted GaN and the implantation incorporation into AlGaN/GaN HEMT processing, with an aim to increase the performance, manufacturability and reliability of AlGaN/GaN HEMTs. First, the ultra high temperature (around 1500°C) annealing of MOCVD grown GaN on sapphire has been studied, and a thermally induced threading dislocation (TD) motion and reaction are reported. Using a rapid thermal annealing (RTA) approach capable of heating 2 inch wafers to around 1500°C with 100 bar N2 over-pressure, evidence of dislocation motion was first observed in transmission electron microscopy (TEM) micrographs of both planar and patterned GaN films protected by an AIN capping layer. An associated decrease in x-ray rocking curve (XRC) full-width-half-maximum (FWHM) was also observed for both the symmetric and asymmetric scans. After annealing, the AIN capping layer remained intact, and optical measurements showed no degradation of the opto-electronic properties of the films. Then activation annealing of Si implants in MOCVD grown GaN has been studied for use in ohmic contacts. Si was implanted in semi-insulating GaN at 100 keV with doses from 5 x 1014 cm-2 to 1.5 x 1016 cm-2. Rapid thermal annealing at 1500°C with 100 bar N2 over-pressure was used for dopant activation, resulting in a minimum sheet resistance of 13.9 O/square for a dose of 7 x 1015 cm-2. Secondary ion mass spectroscopy measurements showed a post-activation broadening of the dopant concentration peak by 20 nm (at half the maximum), while X-Ray triple axis o-2theta scans indicated nearly complete implant damage recovery. Transfer length method measurements of the resistance of Ti/Al/Ni/Au contacts to activated GaN:Si (5 x 1015 cm-2 at 100 keV) indicated lowest contact resistances of 0.07 Omm and 0.02 Omm for as-deposited and subsequently annealed contacts, respectively. Finally, the incorporation of Si implantation into AlGaN/GaN high electron mobility transistor processing has been first demonstrated. An ultra-high temperature (1500°C) rapid thermal annealing technique was developed for the activation of Si dopants implanted in the source and drain. In comparison to control devices processed by conventional fabrication, the implanted device with nonalloyed ohmic contact showed comparable device performance with a contact resistance of 0.4 Omm Imax 730 mA/mm ft/f max; 26/62 GHz and power 3.4 W/mm on sapphire. These early results demonstrate the feasibility of implantation incorporation into GaN based device processing as well as the potential to increase yield, reproducibility and reliability in AlGaN/GaN HEMTs.

  10. Gallium phosphide energy converters

    NASA Technical Reports Server (NTRS)

    Sims, P. E.; Dinetta, L. C.; Goetz, M. A.

    1995-01-01

    Gallium phosphide (GaP) energy converters may be successfully deployed to provide new mission capabilities for spacecraft. Betavoltaic power supplies based on the conversion of tritium beta decay to electricity using GaP energy converters can supply long term low-level power with high reliability. High temperature solar cells, also based on GaP, can be used in inward-bound missions greatly reducing the need for thermal dissipation. Results are presented for GaP direct conversion devices powered by Ni-63 and compared to the conversion of light emitted by tritiarated phosphors. Leakage currents as low as 1.2 x 10(exp -17) A/sq cm have been measured and the temperature dependence of the reverse saturation current is found to have ideal behavior. Temperature dependent IV, QE, R(sub sh), and V(sub oc) results are also presented. These data are used to predict the high-temperature solar cell and betacell performance of GaP devices and suggest appropriate applications for the deployment of this technology.

  11. 49 CFR 173.162 - Gallium.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 2 2014-10-01 2014-10-01 false Gallium. 173.162 Section 173.162 Transportation... PACKAGINGS Non-bulk Packaging for Hazardous Materials Other Than Class 1 and Class 7 § 173.162 Gallium. (a) Except when packaged in cylinders or steel flasks, gallium must be packaged in packagings which meet...

  12. 49 CFR 173.162 - Gallium.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 2 2010-10-01 2010-10-01 false Gallium. 173.162 Section 173.162 Transportation... PACKAGINGS Non-bulk Packaging for Hazardous Materials Other Than Class 1 and Class 7 § 173.162 Gallium. (a) Except when packaged in cylinders or steel flasks, gallium must be packaged in packagings which meet...

  13. 49 CFR 173.162 - Gallium.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 2 2011-10-01 2011-10-01 false Gallium. 173.162 Section 173.162 Transportation... PACKAGINGS Non-bulk Packaging for Hazardous Materials Other Than Class 1 and Class 7 § 173.162 Gallium. (a) Except when packaged in cylinders or steel flasks, gallium must be packaged in packagings which meet...

  14. 49 CFR 173.162 - Gallium.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 2 2013-10-01 2013-10-01 false Gallium. 173.162 Section 173.162 Transportation... PACKAGINGS Non-bulk Packaging for Hazardous Materials Other Than Class 1 and Class 7 § 173.162 Gallium. (a) Except when packaged in cylinders or steel flasks, gallium must be packaged in packagings which meet...

  15. 49 CFR 173.162 - Gallium.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 2 2012-10-01 2012-10-01 false Gallium. 173.162 Section 173.162 Transportation... PACKAGINGS Non-bulk Packaging for Hazardous Materials Other Than Class 1 and Class 7 § 173.162 Gallium. (a) Except when packaged in cylinders or steel flasks, gallium must be packaged in packagings which meet...

  16. - and Photo-Modulation Studies of Semiconductors: I. Diluted Magnetic Semiconductors. I. Gallium-Arsenide - - Arsenide, Zinc-Selenide and Cadmium - Manganese - Telluride Heterostructures.

    NASA Astrophysics Data System (ADS)

    Lee, Yung-Rai

    1987-09-01

    The reflectivity and transmission spectra of the diluted magnetic semiconductors (DMS) were investigated using piezo- and photo-modulation techniques. The spectra for Cd_{rm 1-x}Mn _{rm x}Te and Zn _{rm 1-x}Mn _{rm x}Te show a characteristic exciton A of the zinc blende DMS. The energy E _{A}, linear in x, is given by 1.595 + 1.592x (eV) for Cd_{rm 1-x}Mn_{rm x} Te and 2.376 + 0.820x (eV) for Zn_ {rm 1-x}Mn_{ rm x}Te at liquid helium temperature, yielding E _{A} = 3.187(3.196) eV for the "hypothetical" zinc blende MnTe. For the wurtizite DMS's, such as Cd_{rm 1-x} Mn_{rm x}Se, signatures characteristic of the crystal field split valence band--the A and the B exciton--are observed for electric vector {rm (vec{E}) } perpendicular and parallel to the c -axis, respectively. For x <=q 0.35, Zn _{rm 1-x}Mn _{rm x}Se has the zinc blende structure; correspondingly only one exciton feature appears in the spectrum. For x > 0.35, two exciton features are observed consistent with the wurtzite structure of Zn_{rm 1-x}Mn _{rm x}Se for higher x. A signature with a sign opposite to that of free exciton is observed at ~ 2.2 eV for Cd _{rm 1-x}Mn _{rm x}Te and Cd _{rm 1-x}Mn_ {rm x}Se for x > 0.4 and for all x in Zn_{rm 1 -x}Mn_{rm x} Te and Zn_{rm 1-x} Mn_{rm x}Se. The feature, identified with a Mn^{2+} internal transition, shows no x dependence. In addition, we have observed signatures associated with imperfections in the crystals. In the magnetoreflectivity measurements, the Mn^{2+} transition fails to show any observable Zeeman shift or splitting when examined in magnetic fields up to 15.58 T. In contrast, the free exciton exhibits huge Zeeman splittings, a consequence of the large Mn^{2+}-band electron exchange interaction. These observations favor the assignment of ^6 A_1(^6 S) to ^4 T _1(^4 G) to the 2.2 eV Mn ^{2+} transition where the levels are associated with the crystal-field-split 3 d ^5 manifold of Mn^{2+ }. We have also applied the piezo- and photo-modulation techniques to investigate the electronic transitions associated with the MBE grown GaAs/Al_{rm x}Ga_{rm 1-x} As quantum well structures and pseudomorphic ZnSe epilayers and the LPE grown Cd_{rm 1-x}Mn_{rm x} Te epilayers. Our results obtained at temperatures down to that of liquid helium with single-, double-, and multiple-quantum wells reveal electronic transitions in the wells, the barriers and the buffer layer with exceptional clarity. The effects of coupling in the double and multiple quantum wells are clearly identified. The results of the 0.1 μm ZnSe epilayer show "heavy hole"--"light hole" splitting in the heterostructure.

  17. High precision radiometry using an indium arsenide/indium gallium arsenide quantum dot-in-a-well infrared focal plane array

    NASA Astrophysics Data System (ADS)

    Andrews, Jonathan R.

    Sensitivity, noise and performance criteria were evaluated for different varieties of InAs/InGaAs quantum dots-in-a-well (DWELL) and quantum dots-in-a-double-well (double DWELL) focal plane arrays (FPAs). These characteristics were measured and compared to those measured from a commercial quantum well infrared photodetector (QWIP) in the same experimental setup to allow a side-by-side comparison of these devices with many system variables held constant. The QWIP device was expected to perform the best, due to its higher number of active regions and enhancement grating, but the performance of the other devices was unknown. The DWELL and double DWELL samples were grown by molecular beam epitaxy (MBE) and fabricated into 320 x 256 pixel FPAs with indium bumps via standard lithography at the University of New Mexico. All samples, including the 320 x 256 pixel QWIPs were hybridized to Indigo Systems Corporation ISC9705 read out integrated circuits and device performance was measured with the SE-IR Corporation CamIRa test system at part cooling of 60°K, 70°K and 80°K. The QWIP performed best at lower device cooling, but could not operate at 80°K. The DWELL device demonstrated favorable operation at 60°K, but performance at 70°K was poor and the device did not perform at 80°K. Both double DWELL devices under test performed well across all device temperatures. The mean NEDT for the DWELL was 143°mK and the two double DWELL devices were 105.7°mK and 160.6°mK at 60°K part temperature. The double DWELL devices showed the lower noise and higher responsivity at higher device temperatures. This document also reviewed methods of non-uniformity correction and suggested methods to improve performance and results by carefully choosing the method of correction and the values.

  18. High pressure nitriding

    SciTech Connect

    Jung, M.; Hoffmann, F.T.; Mayr, P.; Minarski, P.

    1995-12-31

    The aim of the presented research project is the development of a new high pressure nitriding process, which avoids disadvantages of conventional nitriding processes and allows for new applications. Up to now, a nitriding furnace has been constructed and several investigations have been made in order to characterize the influence of pressure on the nitriding process. In this paper, connections between pressure in the range of 2 to 12 atm and the corresponding nitride layer formation for the steel grades AISI 1045, H11 and a nitriding steel are discussed. Results of the nitride layer formation are presented. For all steel grades, a growth of nitride layers with increasing pressure was obtained. Steels with passive layers, as the warm working steel H11, showed a better nitriding behavior at elevated pressure.

  19. Mineral resource of the month: gallium

    USGS Publications Warehouse

    Jaskula, Brian

    2009-01-01

    The metal element gallium occurs in very small concentrations in rocks and ores of other metals — native gallium is not known. As society gets more and more high-tech, gallium becomes more useful. Gallium is one of only five metals that are liquid at or close to room temperature. It has one of the longest liquid ranges of any metal (29.8 degrees Celsius to 2204 degrees Celsius) and has a low vapor pressure even at high temperatures. Ultra-pure gallium has a brilliant silvery appearance, and the solid metal exhibits conchoidal fracture similar to glass.

  20. The 3-5 semiconductor solid solution single crystal growth. [low gravity float zone growth experiments using gallium indium antimonides and cadmium tellurides

    NASA Technical Reports Server (NTRS)

    Gertner, E. R.

    1980-01-01

    Techniques used for liquid and vapor phase epitaxy of gallium indium arsenide are described and the difficulties encountered are examined. Results show that the growth of bulk III-V solid solution single crystals in a low gravity environment will not have a major technological impact. The float zone technique in a low gravity environment is demonstrated using cadmium telluride. It is shown that this approach can result in the synthesis of a class of semiconductors that can not be grown in normal gravity because of growth problems rooted in the nature of their phase diagrams.

  1. Potential effects of gallium on cladding materials

    SciTech Connect

    Wilson, D.F.; Beahm, E.C.; Besmann, T.M.; DeVan, J.H.; DiStefano, J.R.; Gat, U.; Greene, S.R.; Rittenhouse, P.L.; Worley, B.A.

    1997-10-01

    This paper identifies and examines issues concerning the incorporation of gallium in weapons derived plutonium in light water reactor (LWR) MOX fuels. Particular attention is given to the more likely effects of the gallium on the behavior of the cladding material. The chemistry of weapons grade (WG) MOX, including possible consequences of gallium within plutonium agglomerates, was assessed. Based on the calculated oxidation potentials of MOX fuel, the effect that gallium may have on reactions involving fission products and possible impact on cladding performance were postulated. Gallium transport mechanisms are discussed. With an understanding of oxidation potentials and assumptions of mechanisms for gallium transport, possible effects of gallium on corrosion of cladding were evaluated. Potential and unresolved issues and suggested research and development (R and D) required to provide missing information are presented.

  2. Discovery of earth-abundant nitride semiconductors by computational screening and high-pressure synthesis

    PubMed Central

    Hinuma, Yoyo; Hatakeyama, Taisuke; Kumagai, Yu; Burton, Lee A.; Sato, Hikaru; Muraba, Yoshinori; Iimura, Soshi; Hiramatsu, Hidenori; Tanaka, Isao; Hosono, Hideo; Oba, Fumiyasu

    2016-01-01

    Nitride semiconductors are attractive because they can be environmentally benign, comprised of abundant elements and possess favourable electronic properties. However, those currently commercialized are mostly limited to gallium nitride and its alloys, despite the rich composition space of nitrides. Here we report the screening of ternary zinc nitride semiconductors using first-principles calculations of electronic structure, stability and dopability. This approach identifies as-yet-unreported CaZn2N2 that has earth-abundant components, smaller carrier effective masses than gallium nitride and a tunable direct bandgap suited for light emission and harvesting. High-pressure synthesis realizes this phase, verifying the predicted crystal structure and band-edge red photoluminescence. In total, we propose 21 promising systems, including Ca2ZnN2, Ba2ZnN2 and Zn2PN3, which have not been reported as semiconductors previously. Given the variety in bandgaps of the identified compounds, the present study expands the potential suitability of nitride semiconductors for a broader range of electronic, optoelectronic and photovoltaic applications. PMID:27325228

  3. Discovery of earth-abundant nitride semiconductors by computational screening and high-pressure synthesis

    NASA Astrophysics Data System (ADS)

    Hinuma, Yoyo; Hatakeyama, Taisuke; Kumagai, Yu; Burton, Lee A.; Sato, Hikaru; Muraba, Yoshinori; Iimura, Soshi; Hiramatsu, Hidenori; Tanaka, Isao; Hosono, Hideo; Oba, Fumiyasu

    2016-06-01

    Nitride semiconductors are attractive because they can be environmentally benign, comprised of abundant elements and possess favourable electronic properties. However, those currently commercialized are mostly limited to gallium nitride and its alloys, despite the rich composition space of nitrides. Here we report the screening of ternary zinc nitride semiconductors using first-principles calculations of electronic structure, stability and dopability. This approach identifies as-yet-unreported CaZn2N2 that has earth-abundant components, smaller carrier effective masses than gallium nitride and a tunable direct bandgap suited for light emission and harvesting. High-pressure synthesis realizes this phase, verifying the predicted crystal structure and band-edge red photoluminescence. In total, we propose 21 promising systems, including Ca2ZnN2, Ba2ZnN2 and Zn2PN3, which have not been reported as semiconductors previously. Given the variety in bandgaps of the identified compounds, the present study expands the potential suitability of nitride semiconductors for a broader range of electronic, optoelectronic and photovoltaic applications.

  4. Discovery of earth-abundant nitride semiconductors by computational screening and high-pressure synthesis.

    PubMed

    Hinuma, Yoyo; Hatakeyama, Taisuke; Kumagai, Yu; Burton, Lee A; Sato, Hikaru; Muraba, Yoshinori; Iimura, Soshi; Hiramatsu, Hidenori; Tanaka, Isao; Hosono, Hideo; Oba, Fumiyasu

    2016-01-01

    Nitride semiconductors are attractive because they can be environmentally benign, comprised of abundant elements and possess favourable electronic properties. However, those currently commercialized are mostly limited to gallium nitride and its alloys, despite the rich composition space of nitrides. Here we report the screening of ternary zinc nitride semiconductors using first-principles calculations of electronic structure, stability and dopability. This approach identifies as-yet-unreported CaZn2N2 that has earth-abundant components, smaller carrier effective masses than gallium nitride and a tunable direct bandgap suited for light emission and harvesting. High-pressure synthesis realizes this phase, verifying the predicted crystal structure and band-edge red photoluminescence. In total, we propose 21 promising systems, including Ca2ZnN2, Ba2ZnN2 and Zn2PN3, which have not been reported as semiconductors previously. Given the variety in bandgaps of the identified compounds, the present study expands the potential suitability of nitride semiconductors for a broader range of electronic, optoelectronic and photovoltaic applications. PMID:27325228

  5. Liquid gallium rotary electric contract

    NASA Technical Reports Server (NTRS)

    Przybyszewski, J. S.

    1969-01-01

    Due to its low vapor pressure, gallium, when substituted for mercury in a liquid slip ring system, transmits substantial amounts of electrical current to rotating components in an ultrahigh vacuum. It features low electrical loss, little or no wear, and long maintenance-free life.

  6. Gallium scan in intracerebral sarcoidosis

    SciTech Connect

    Makhija, M.C.; Anayiotos, C.P.

    1981-07-01

    Sarcoidosis involving the nervous system probably occurs in about 4% of patients. The usefulness of brain scintigraphy in these cases has been suggested. In this case of cerebral sarcoid granuloma, gallium imaging demonstrated the lesion before treatment and showed disappearance of the lesion after corticosteroid treatment, which correlated with the patient's clinical improvement.

  7. Preparation of uranium nitride

    DOEpatents

    Potter, Ralph A.; Tennery, Victor J.

    1976-01-01

    A process for preparing actinide-nitrides from massive actinide metal which is suitable for sintering into low density fuel shapes by partially hydriding the massive metal and simultaneously dehydriding and nitriding the dehydrided portion. The process is repeated until all of the massive metal is converted to a nitride.

  8. Epitaxial Deposition of Low-Defect Aluminum Nitride and Aluminum Gallium Nitride Films

    NASA Astrophysics Data System (ADS)

    Jain, Rakesh

    The bjective of my research was to develop low-defect AlN and AlGaN templates to enable pseudo-homoepitaxial deposition of UV-LEDs. Two approaches have been used to achieve this objective. Firstly, hydride vapor phase epitaxy (HVPE) process was used to prepare thick AlN films with lower defect density. Interactions of dislocations in thicker films result in their annihilation. Secondly, since thick films grown on sapphire tend to crack beyond a critical thickness (3-5 mum), epitaxial lateral overgrowth (ELOG) approach was employed to eliminate cracking and to further reduce the defect density. The growth technique was switched from HVPE to Metalorganic chemical vapor deposition (MOCVD) due to much improved material quality with the later method. An HVPE growth system was first designed and constructed from ground up [1]. It is a vertical system with a quartz chamber and a resistively heated furnace. AlCl3 and NH3 were used as the precursors. AlCl3 was generated by passing HCl gas (diluted with H2) through Al metal source. A linear relationship between growth rate and HCl flow rate indicated that the growth rate is limited by mass transportation. Growth parameters including temperature, chamber pressure and V/III ratio were optimized to improve the film quality. Thick films of AlN with thicknesses exceeding 25 mum were grown with growth rates as high as 20 mum/hr [2]. AFM study revealed that surface roughness of HVPE grown AlN films strongly depends on the growth rate. The lowest RMS roughness for HVPE grown film was 1.9 nm. These films had typical (002) full-width at half maximum (FWHM) values ranging from 24 -- 400 arcsec, depending on the growth rate of the respective films. The crystalline quality of the films was also found to be deteriorating as the growth rate increased. It is inferred that the growth mode changes from two dimensional to three dimensional at higher growth rates due to reduced adatom migration length. PL spectrum exhibited near-band-edge (NBE) emission line along with broader deep level-related bands, presumably due to donor-acceptor and band-acceptor transitions. Etch-pit density measurement revealed threading dislocation density of 1x109 cm-2, which is at least 5 times smaller than conventionally grown MOCVD films. AlN and AlGaN films grown on sapphire substrate tend to crack and even peel off beyond a critical thickness of 2 -- 5 mum. To prevent thick films from cracking, ELOG technique was utilized. This technique has been successfully employed to deposit several hundred micrometers thick crack-free GaN films, which demonstrate 2-3 orders of magnitude reduction in TDD. Crack-free thick layers of AlN and AlGaN were deposited using ELOG technique. MOCVD was used as the growth method due to improved material quality. Trimethylaluminum (TMAl), trimethylgallium (TMGa) and ammonia (NH3) were used as the precursors. The growth was performed under low pressure with H2 as the carrier gas. First about 2 mum thick AlGaN layers were deposited on c-plane sapphire substrates. Such thin AlGaN layers, grown without any dislocation reduction technique, usually show TDD in the mid 1010 cm-2 range. Linear trench patterns along [11¯00] AlGaN were fabricated in the AlGaN layers using conventional photolithography and RIE (reactive ion etching). The patterns included 2 mum wide mesas with 5 mum wide trenches. The trenched templates were reloaded into the MOCVD chamber for overgrowth of AlN and high Al-content AlGaN. The overgrowth was carried out at a temperature of 1200 °C with the growth rate of 1 to 2 mum/hr. Migration enhanced MOCVD (MEMOCVDRTM) [3] was combined with ELOG approach to develop a novel Migration Enhanced Lateral Epitaxial Overgrowth (MELEO) technique [4]. As part of this novel technique, precursor pulses were varied to control the ratio of lateral/vertical growth rate. Coalescence related low-angle grain boundaries and edge dislocations were reduced by promoting coherent coalescence using MELEO technique. Fully coalesced, AlN and AlGaN films with thicknesses as high as 30 mum were deposited. SEM w

  9. Epitaxial growth of aluminum nitride and gallium nitride via supersonic beams seeded with ammonia

    NASA Astrophysics Data System (ADS)

    Torres, Victor Mario

    1999-11-01

    The research presented in this Thesis was aimed at depositing epitaxial AlN and GaN films on 6H-SiC(0001) substrates using via supersonic beams seeded with NH3. This deposition technique allowed for the tuning of the NH3 kinetic energy ranging from 0.03 to 0.81 eV. A dissociative chemisorption energy barrier of 0.3 +/- 0.1 eV was experimentally estimated for NH3 on GaN(0001) by measuring the film growth rate as a function of NH3 kinetic energy. The low value of the energy barrier did not suffice to account for the temperatures in excess of 700°C required for GaN growth via gas source molecular beam epitaxy using NH3 and evaporated Ga. The requirement that Ga droplets do not form on the growth surface was deemed as a more satisfactory explanation since the activation energy for Ga droplet evaporation is 2.8 eV. In separate experiments, it was determined that the crystallinity of Al epitaxial layers deposited on 6H-SiC(0001) substrates was enhanced if the substrates were etched in a 5% hydrogen in helium mixture at 1600°C under atmospheric pressure. The improvement in crystallinity was correlated to the surface morphology of the etched substrates which were free of surface scratches and contained extended terrace separated by 15A steps. The supersonic beam seeded with NH3 was used as a nitrogen source to deposit GaN homoepitaxial layers in the low energy electron microscope. This experiment enabled in situ studies of the growth process. A Ga-to-NH 3 flux ratio ≥1 was required that for epitaxial growth of smooth GaN films with a (0001) orientation at 670°C. The maximum permissible Ga flux was found to be equal to the flux required for Ga condensation at a given temperature. Films containing patch-like structures were obtained at the Ga condensation flux. A stepped film surface was obtained exclusively when the initial surface displayed steps.

  10. Hall effect and photoconductivity lifetime studies of gallium nitride, indium nitride, and mercury cadmium telluride

    NASA Astrophysics Data System (ADS)

    Swartz, Craig H.

    A deep understanding of both carrier recombination and transport is necessary for semiconductor engineering, particularly in defining the ultimate limits of performance for a given device before spending the resources to perfect its fabrication. Hall effect measurements utilizing a variable magnetic field are necessary to discriminate between conduction in epitaxial layers and conduction originating at the surface or at an interfacial layer. For thick hydride vapor phase epitaxy (HVPE) grown GaN, variable field Hall measurements revealed the presence of small but significant lower mobility surface and interface electrons which would otherwise lead to errors in interpreting the electrical properties. In addition, QMSA analysis of the measurements indicates that thick GaN samples contain a large spread in electron mobility values, most likely with depth. For molecular beam epitaxial InN, it was found that electrical measurements are affected by surface charge conduction, as well as the non-uniformity of mobility and carrier concentration with depth. Both of these effects mask the surprisingly high quality of the material close to the surface. Photoconductance lifetime and variable-magnetic-field Hall and transient measurements were performed on a series of undoped, In-doped and As-doped HgCdTe grown by MBE and MOCVD. N-type layers often significantly influence the interpretation of the electrical measurements. Even the best Low Wavelength Infrared (LWIR) n-type material still appears to be dominated by defect-related recombination, as intrinsic lifetimes calculated with full band structure can be well above those measured. Mid-Wavelength Infrared (MWIR) lifetimes increase somewhat with carrier concentration, as if the n-type doping process were passivating Schockley-Read-Hall (SRH) defects. P-type MWIR films lie mainly below the predicted values, and their relationship between concentration and lifetime is essentially unchanged by growth technique, indicating that a fundamental native defect is responsible for the recombination. Those with lifetimes above the predicted values have anomalous temperature dependences when measured, and often a non-exponential photoconductive decay characteristic of minority carrier traps. Deep level trap concentrations in GaN can harm performance in many desired applications. Deep Level Transient Spectroscopy (DLTS) measurement on MBE GaN suggest that the trapping center concentration drops with temperature below 770°C.

  11. Laser doping and metallization of wide bandgap materials: silicon carbide, gallium nitride, and aluminum nitride

    NASA Astrophysics Data System (ADS)

    Salama, Islam Abdel Haleem

    A laser direct write and doping (LDWD) system is designed and utilized for direct metallization and selective area doping in different SiC polytypes, GaN and in dielectrics including AlN. Laser direct metallization in 4H- and 6H-SiC generates metal-like conductive phases that are produced as both rectifying and ohmic contacts without metal deposition. Nd:YAG (lambda = 532, 1064 nm) nanosecond pulsed laser irradiation in SiC induces carbon-rich conductive phases by thermal decomposition of SiC while UV excimer (lambda = 193 nm) laser irradiation produces a silicon-rich phase due to selective carbon photoablation. Linear transmission line method (TLM) pattern is directly fabricated in single crystals SiC by pulsed laser irradiation allowing characterization of the laser fabricated metal-like contacts. Activation of a self focusing effect at the frequency doubled Nd:YAG laser irradiation (lambda = 532 nm) allows to fabricate buried metal like contacts in SiC wafers while maintaining their device-ready surface condition. Gas immersion laser doping (GILD) and laser doping from a molten precursor are utilized to dope both GaN and SiC. Trimethylaluminum (TMAl) and nitrogen are the precursors used to produce p-type and n-type doped SiC; respectively. Nd:YAG and excimer laser nitrogen doping in SiC epilayer and single crystal substrates increases the dopant concentration by two orders of magnitude and produces both deep (500--600 nm) and shallow (50 nm) junctions, respectively. Laser assisted effusion/diffusion is introduced and utilized to dope Al in SiC wafers. Using this technique, a150 nm p-type doped junction is fabricated in semi-insulating 6H- and n-type doped 4H-SiC wafers. Laser-induced p-type doping of Mg in single crystal GaN is conducted using Bis-magnesium dihydrate [Mg(TMHD)2]. Mg concentration and penetration depth up to 10 20--1021 cm-3 and 5mum, respectively are achieved using various laser doping techniques. Laser direct writing and doping (LDWD) is a viable method for processing wide bandgap materials for electronics and optoelectronics devices applications. It effectively reduces the number of fabrication steps and allows for selective area doping and direct metallization without metal deposition.

  12. Evaluation of critical materials for five advanced design photovoltaic cells with an assessment of indium and gallium

    SciTech Connect

    Watts, R.L.; Gurwell, W.E.; Jamieson, W.M.; Long, L.W.; Pawlewicz, W.T.; Smith, S.A.; Teeter, R.R.

    1980-05-01

    The objective of this study is to identify potential material supply constraints due to the large-scale deployment of five advanced photovoltaic (PV) cell designs, and to suggest strategies to reduce the impacts of these production capacity limitations and potential future material shortages. This report presents the results of the screening of the five following advanced PV cell designs: polycrystalline silicon, amorphous silicon, cadmium sulfide/copper sulfide frontwall, polycrystalline gallium arsenide MIS, and advanced concentrator-500X. Each of these five cells is screened individually assuming that they first come online in 1991, and that 25 GWe of peak capacity is online by the year 2000. A second computer screening assumes that each cell first comes online in 1991 and that each cell has 5 GWe of peak capacity by the year 2000, so that the total online cpacity for the five cells is 25 GWe. Based on a review of the preliminary basline screening results, suggestions were made for varying such parameters as the layer thickness, cell production processes, etc. The resulting PV cell characterizations were then screened again by the CMAP computer code. Earlier DOE sponsored work on the assessment of critical materials in PV cells conclusively identtified indium and gallium as warranting further investigation as to their availability. Therefore, this report includes a discussion of the future availability of gallium and indium. (WHK)

  13. Gallium antimonide texturing for enhanced light extraction from infrared optoelectronics devices

    NASA Astrophysics Data System (ADS)

    Wassweiler, Ella; Toor, Fatima

    2016-06-01

    The use of gallium antimonide (GaSb) is increasing, especially for optoelectronic devices in the infrared wavelengths. It has been demonstrated in gallium nitride (GaN) devices operating at ultraviolet (UV) wavelengths, that surface textures increase the overall device efficiency. In this work, we fabricated eight different surface textures in GaSb to be used in enhancing efficiency in infrared wavelength devices. Through chemical etching with hydrofluoric acid, hydrogen peroxide, and tartaric acid we characterize the types of surface textures formed and the removal rate of entire layers of GaSb. Through optimization of the etching recipes we lower the reflectivity from 35.7% to 1% at 4 μm wavelength for bare and textured GaSb, respectively. In addition, we simulate surface textures using ray optics in finite element method solver software to provide explanation of our experimental findings.

  14. Ca4As3 – a new binary calcium arsenide

    PubMed Central

    Hoffmann, Andrea V.; Hlukhyy, Viktor; Fässler, Thomas F.

    2015-01-01

    The crystal structure of the binary compound tetra­calcium triarsenide, Ca4As3, was investigated by single-crystal X-ray diffraction. Ca4As3 crystallizes in the Ba4P3 structure type and is thus a homologue of isotypic Sr4As3. The unit cell contains 32 Ca2+ cations, 16 As3− isolated anions and four centrosymmetric [As2]4– dumbbells. The As atoms in each of the dumbbells are connected by a single bond, thus this calcium arsenide is a Zintl phase. PMID:26870427

  15. Epitaxial Deposition Of Germanium Doped With Gallium

    NASA Technical Reports Server (NTRS)

    Huffman, James E.

    1994-01-01

    Epitaxial layers of germanium doped with gallium made by chemical vapor deposition. Method involves combination of techniques and materials used in chemical vapor deposition with GeH4 or GeCl4 as source of germanium and GaCl3 as source of gallium. Resulting epitaxial layers of germanium doped with gallium expected to be highly pure, with high crystalline quality. High-quality material useful in infrared sensors.

  16. Tuberculosis peritonitis: gallium-67 scintigraphic appearance.

    PubMed

    Sumi, Y; Ozaki, Y; Hasegawa, H; Shindoh, N; Katayama, H; Tamamoto, F

    1999-06-01

    Tuberculosis peritonitis is a rare manifestation of extrapulmonary tuberculosis. The results of gallium-67 scintigraphy of three patients with tuberculosis peritonitis were reviewed to assess its usefulness in the diagnosis of this condition. Tuberculosis peritonitis was associated with diffuse or focal abdominal localization and decreased hepatic accumulation of gallium-67. These gallium-67 scan features of tuberculosis peritonitis may help to optimize the diagnosis and management of this disease. PMID:10435380

  17. Recovering gallium from residual bayer process liquor

    NASA Astrophysics Data System (ADS)

    Afonso de Magalhães, Maria Elizabeth; Tubino, Matthieu

    1991-06-01

    Gallium is normally obtained by direct electrolysis as a by-product from Bayer process residual liquor at an aluminum processing plant. However, to permit any net accumulation of the metal, the gallium concentration must be at least about 0.3 g/l in the liquor. This article describes a continuous process of extraction with organic solvents and rhodamine-B, followed by a re-extraction step into aqueous media. The final product is a solid containing up to 18 wt.% Ga in a solid mixture of hydroxides and oxides of gallium and aluminum. This final product can then be electrolyzed to recover the gallium more efficiently.

  18. Fabrication Processes for Surface-Emitting via External 45-DEGREE Reflectors, High-Power via Arrayed Ridge - Single-Mode Phase-Locked Aluminum Gallium Arsenide/gallium Arsenide Semiconductor Laser Sources.

    NASA Astrophysics Data System (ADS)

    Porkolab, Gyorgy Arpad

    The fabrication of monolithically integrated configurations of semiconductor lasers incorporating multiple functions is still an open issue today in engineering. A useful set of functions to integrate are: surface-emitting, high -power, phase-locked, single-mode, and collimated laser beam output. In this work new materials and advanced fabrication processes are developed for integrating the first four of the five functions listed. The interest in semiconductor lasers is due to their greater than 90% internal quantum efficiency in converting current-flux to photon-flux, their small size and weight, and their wavelength range from 400 to 1,550 nm. Multitudes of applications are possible for semiconductor laser sources ranging from the low-volume market of satellite-based communications systems to the high-volume market of image display screens. Semimetallic amorphous carbon (SMAC) thin film is introduced as an etch mask for chemically assisted ion beam etching (CAIBE) resulting in smooth etched facets in AlGaAs/GaAs at normal- and 45-degrees- incidence angles. A self-aligned etch technique is introduced using 4 separate photoresist selector-masks on top of a fixed SMAC master -mask on top of the AlGaAs/GaAs substrate to perform 4 separate CAIBE etches at 3 different angles and to 3 different depths to create self-aligned 3-dimensional microstructures of 1.3-μm deep ridge waveguides (RWG), 6-μm deep laser facets, and 11- μm long back-to-back 45-degree reflectors arranged in 3 by 100 arrays. Trenches on topside and underside of laser facets are introduced to deflect current away from laser facets. Silicon-rich nitro-oxide thin film is introduced as triple-use encapsulation to provide chemical passivation of AlGaAs/GaAs, optical anti-reflection coating by being refractive-index matched to AlGaAs/GaAs, and electrical insulation. A pincer-action sample-holder for CAIBE is introduced allowing samples to heat up by ion beam heating. Various surface preparations procedures are used to precede either deposition or etching of materials. Carbon thin film is used as adhesion mediator between photoresist and AlGaAs/GaAs. A complete fabrication process sequence is demonstrated. Operations are demonstrated of spontaneous emission output and of the surface-emitting function.

  19. Growth and Process-Induced Defects and Recombination Mechanisms in Aluminum Gallium Arsenide/gallium Arsenide and CADMIUM(1-X) Zinc(x) Tellurium/cadmium Sulfide Photovoltaic Device Structures

    NASA Astrophysics Data System (ADS)

    Ringel, Steven Adam

    The objective of this research was to provide guidelines to improve the performance of crystalline GaAs and polycrystallize CdTe and CdZnTe solar cells through an improved understanding of defects and recombination mechanisms within these structures. Three main issues were investigated: the role of bulk defects and interface recombination on GaAs cell performance and design; performance limiting defects in CdTe thin film cells; and processing of wide bandgap CdZnTe for use as the top cell of a two cell tandem arrangement. In the first part of the research an improved methodology to determine lifetime and recombination velocity within AlGaAs/GaAs heteroface cells was developed. The quantitative dependence of device performance on defect characteristics was demonstrated. A novel device structure was proposed which is shown to minimize the effects of defects while resulting in high efficiency. The second area of research investigated the effects of the commonly used but poorly understood CdCl_2 treatment on CdTe/CdS solar cells. The CdCl_2 treatment was found to improve cell performance via increased carrier collection from the bulk and across the interface, and by a change in the dominant current transport mechanism from interface-assisted tunneling to depletion region recombination. However, an E _{v} + 0.64 eV trap was detected in the CdCl_2-treated cells, resulting from the formation of cadmium vacancy-related defects during processing, that may limit CdTe cell performance. A preliminary correlation between the trap density and cell V_{oc} was established. In the third area, 1.7 eV bandgap CdZnTe was successfully grown on CdS substrates by molecular beam epitaxy. However, subsequent standard cell processing reduced photoresponse, decreased the CdZnTe bandgap, and caused high series resistance. The high series resistance resulted from the preferential oxidation of Zn during the anneal, which was removed by a dichromate etch. The reaction of Zn with CdCl_2 and formation of volatile ZnCl_2 was identified as the source of both the bandgap shift and reduced photoresponse. A physical model to explain this phenomenon was developed. It was shown that a closed -system anneal is a promising approach to overcome these effects and result in optimum CdZnTe cells.

  20. Performance of GaN-on-Si-based vertical light-emitting diodes using silicon nitride electrodes with conducting filaments: correlation between filament density and device reliability.

    PubMed

    Kim, Kyeong Heon; Kim, Su Jin; Lee, Tae Ho; Lee, Byeong Ryong; Kim, Tae Geun

    2016-08-01

    Transparent conductive electrodes with good conductivity and optical transmittance are an essential element for highly efficient light-emitting diodes. However, conventional indium tin oxide and its alternative transparent conductive electrodes have some trouble with a trade-off between electrical conductivity and optical transmittance, thus limiting their practical applications. Here, we present silicon nitride transparent conductive electrodes with conducting filaments embedded using the electrical breakdown process and investigate the dependence of the conducting filament density formed in the transparent conductive electrode on the device performance of gallium nitride-based vertical light-emitting diodes. Three gallium nitride-on-silicon-based vertical light-emitting diodes using silicon nitride transparent conductive electrodes with high, medium, and low conducting filament densities were prepared with a reference vertical light-emitting diode using metal electrodes. This was carried to determine the optimal density of the conducting filaments in the proposed silicon nitride transparent conductive electrodes. In comparison, the vertical light-emitting diodes with a medium conducting filament density exhibited the lowest optical loss, direct ohmic behavior, and the best current injection and distribution over the entire n-type gallium nitride surface, leading to highly reliable light-emitting diode performance. PMID:27505739