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Sample records for gallium nitride materials

  1. Materials synthesis: Two-dimensional gallium nitride

    NASA Astrophysics Data System (ADS)

    Koratkar, Nikhil A.

    2016-11-01

    Graphene is used as a capping sheet to synthesize 2D gallium nitride by means of migration-enhanced encapsulation growth. This technique may allow the stabilization of 2D materials that are not amenable to synthesis by traditional methods.

  2. 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.

  3. 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.

  4. Ohmic contacts to Gallium Nitride materials

    NASA Astrophysics Data System (ADS)

    Greco, Giuseppe; Iucolano, Ferdinando; Roccaforte, Fabrizio

    2016-10-01

    In this review article, a comprehensive study of the mechanisms of Ohmic contact formation on GaN-based materials is presented. After a brief introduction on the physics of Ohmic contacts, a resume of the most important results obtained in literature is reported for each of the systems taken in consideration (n-type GaN, p-type GaN and AlGaN/GaN heterostructures). The optimal metallization schemes and processing conditions to obtain low resistance Ohmic contacts are presented, discussing the role of the single metals composing the stack and the modification induced by the thermal annealing, either on the metal layers or at the interface with GaN. Physical insights on the mechanism of Ohmic contact formation have been gained by correlating the temperature dependence of the electrical parameters with a morphological/structural analysis of the interface. In the case of the AlGaN/GaN systems, the influence of the heterostructure parameters on the Ohmic contacts has been taken into account adapting the classical thermionic field emission model to the presence of the two dimensional electron gas (2DEG). Finally, the state of the art of "Au-free" metallization to AlGaN/GaN heterostructures is also presented, being this latter a relevant topic for the integration of GaN technology on large scale Silicon devices fabs.

  5. 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.

  6. 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.

  7. 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.

  8. Bulk Cubic Gallium Nitride

    DTIC Science & Technology

    1999-02-09

    microcrysta. form at bottom of «he reaction vessel. The objective of the second step is the solvothermal transport of the gallium nitride residing in the...system using pressure pumps can be used to gain precise control of the pressure. High pressure is typically used for the solvothermal transport. The...takes place in the reaction vessel during heating is a solvothermal reaction that is conducted at or above the critical point of the solvent The

  9. Gallium nitride nanotube lasers

    DOE PAGES

    Li, Changyi; Liu, Sheng; Hurtado, Antonio; ...

    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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Salama, Islam Abdel Haleem

    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.

  15. 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

  16. 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.

  17. 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.

  18. Solar cell with a gallium nitride electrode

    DOEpatents

    Pankove, Jacques I.

    1979-01-01

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

  19. 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.

  20. Sodium Flux Growth of Bulk Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Von Dollen, Paul Martin

    This dissertation focused on development of a novel apparatus and techniques for crystal growth of bulk gallium nitride (GaN) using the sodium flux method. Though several methods exist to produce bulk GaN, none have been commercialized on an industrial scale. The sodium flux method offers potentially lower cost production due to relatively mild process conditions while maintaining high crystal quality. But the current equipment and methods for sodium flux growth of bulk GaN are generally not amenable to large-scale crystal growth or in situ investigation of growth processes, which has hampered progress. A key task was to prevent sodium loss or migration from the sodium-gallium growth melt while permitting N2 gas to access the growing crystal, which was accomplished by implementing a reflux condensing stem along with a reusable sealed capsule. The reflux condensing stem also enabled direct monitoring and control of the melt temperature, which has not been previously reported for the sodium flux method. Molybdenum-based materials were identified from a corrosion study as candidates for direct containment of the corrosive sodium-gallium melt. Successful introduction of these materials allowed implementation of a crucible-free containment system, which improved process control and can potentially reduce crystal impurity levels. Using the new growth system, the (0001) Ga face (+c plane) growth rate was >50 mum/hr, which is the highest bulk GaN growth rate reported for the sodium flux method. Omega X-ray rocking curve (?-XRC) measurements indicated the presence of multiple grains, though full width at half maximum (FWHM) values for individual peaks were <100 arcseconds. Oxygen impurity concentrations as measured by secondary ion mass spectroscopy (SIMS) were >1020 atoms/cm3, possibly due to reactor cleaning and handling procedures. This dissertation also introduced an in situ technique to correlate changes in N2 pressure with dissolution of nitrogen and precipitation of

  1. Gallium Nitride (GaN) High Power Electronics (FY11)

    DTIC Science & Technology

    2012-01-01

    Gallium Nitride (GaN) High Power Electronics (FY11) by Kenneth A. Jones, Randy P. Tompkins, Michael A. Derenge, Kevin W. Kirchner, Iskander...Army Research Laboratory Adelphi, MD 20783-1197 ARL-TR-5903 January 2012 Gallium Nitride (GaN) High Power Electronics (FY11) Kenneth A...DSI 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Gallium Nitride (GaN) High Power Electronics (FY11) 5a. CONTRACT NUMBER 5b. GRANT

  2. Indium Gallium Nitride Multijunction Solar Cell Simulation Using Silvaco Atlas

    DTIC Science & Technology

    2007-06-01

    possibilities of InGaN tandem PV structures”, Solar Energy Materials & Solar Cells, Vol. 87, 595-603, 2004. [6] S. M. Sze, Semiconductor Devices, 2nd edition... ENERGY (EV) TO WAVELENGTH (UM) ..............................................86 D. IV CURVE PLOTS FOR INDIUM GALLIUM NITRIDE QUAD JUNCTION SOLAR... energy on different band gaps (From [15]).....................................19 Figure 13. Simple cubic lattice structure (From [16])......20 Figure

  3. Gallium nitride T-ray transmission characteristics

    NASA Astrophysics Data System (ADS)

    Ferguson, Bradley; Mickan, Samuel P.; Hubbard, Seth; Pavlidis, Dimitris; Abbott, Derek

    2001-11-01

    T-ray imaging and spectroscopy both exploit the terahertz (THz) region of the spectrum. This gives rise to very promising industrial and biomedical applications, where non-invasive and sensitive identification of a substance is achievable, through a material's distinct absorption features in the THz band. Present T-ray systems are limited by low output power, and the race is now on to find more efficient THz emitters. We discuss the feasibility of a novel high-power gallium nitride emitter for terahertz generation. This paper details the advantages of such an emitter, primarily by virtue of its high-voltage capability, and evaluates the benefits of sapphire and silicon carbide substrates. The far-infrared transmission spectra for thin samples of GaN, sapphire and SiC are reported. A high-power THz emitter, that operates at room temperature and is potentially low-cost will open up a host of new possibilities and applications. The central result in this paper demonstrates that sapphire is the better choice over SiC, for the GaN supporting substrate, as we show that it has superior THz transmission characteristics.

  4. 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.

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

    PubMed

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

    2013-01-08

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

  6. Thermal Plasma Synthesis of Crystalline Gallium Nitride Nanopowder from Gallium Nitrate Hydrate and Melamine

    PubMed Central

    Kim, Tae-Hee; Choi, Sooseok; Park, Dong-Wha

    2016-01-01

    Gallium nitride (GaN) nanopowder used as a blue fluorescent material was synthesized by using a direct current (DC) non-transferred arc plasma. Gallium nitrate hydrate (Ga(NO3)3∙xH2O) was used as a raw material and NH3 gas was used as a nitridation source. Additionally, melamine (C3H6N6) powder was injected into the plasma flame to prevent the oxidation of gallium to gallium oxide (Ga2O3). Argon thermal plasma was applied to synthesize GaN nanopowder. The synthesized GaN nanopowder by thermal plasma has low crystallinity and purity. It was improved to relatively high crystallinity and purity by annealing. The crystallinity is enhanced by the thermal treatment and the purity was increased by the elimination of residual C3H6N6. The combined process of thermal plasma and annealing was appropriate for synthesizing crystalline GaN nanopowder. The annealing process after the plasma synthesis of GaN nanopowder eliminated residual contamination and enhanced the crystallinity of GaN nanopowder. As a result, crystalline GaN nanopowder which has an average particle size of 30 nm was synthesized by the combination of thermal plasma treatment and annealing.

  7. Two-dimensional gallium nitride realized via graphene encapsulation

    NASA Astrophysics Data System (ADS)

    Al Balushi, Zakaria Y.; Wang, Ke; Ghosh, Ram Krishna; Vilá, Rafael A.; Eichfeld, Sarah M.; Caldwell, Joshua D.; Qin, Xiaoye; Lin, Yu-Chuan; Desario, Paul A.; Stone, Greg; Subramanian, Shruti; Paul, Dennis F.; Wallace, Robert M.; Datta, Suman; Redwing, Joan M.; Robinson, Joshua A.

    2016-11-01

    The spectrum of two-dimensional (2D) and layered materials `beyond graphene’ offers a remarkable platform to study new phenomena in condensed matter physics. Among these materials, layered hexagonal boron nitride (hBN), with its wide bandgap energy (~5.0-6.0 eV), has clearly established that 2D nitrides are key to advancing 2D devices. A gap, however, remains between the theoretical prediction of 2D nitrides `beyond hBN’ and experimental realization of such structures. Here we demonstrate the synthesis of 2D gallium nitride (GaN) via a migration-enhanced encapsulated growth (MEEG) technique utilizing epitaxial graphene. We theoretically predict and experimentally validate that the atomic structure of 2D GaN grown via MEEG is notably different from reported theory. Moreover, we establish that graphene plays a critical role in stabilizing the direct-bandgap (nearly 5.0 eV), 2D buckled structure. Our results provide a foundation for discovery and stabilization of 2D nitrides that are difficult to prepare via traditional synthesis.

  8. 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.

  9. Gallium Nitride Based Logpile Photonic Crystal

    SciTech Connect

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

    2011-11-09

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

  10. Gallium nitride based logpile photonic crystals.

    PubMed

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

    2011-11-09

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

  11. 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

  12. Ellipsometric study of silicon nitride on gallium arsenide

    NASA Technical Reports Server (NTRS)

    Alterovitz, S. A.; Bu-Abbud, G. H.; Woollam, J. A.; Liu, D.; Chung, Y.; Langer, D.

    1982-01-01

    A method for optimizing the sensitivity of ellipsometric measurements for thin dielectric films on semiconductors is described in simple physical terms. The technique is demonstrated for the case of sputtered silicon nitride films on gallium arsenide.

  13. Gallium nitride electro-acoustic devices and acoustic metamaterials

    NASA Astrophysics Data System (ADS)

    Rais-Zadeh, Mina

    2016-05-01

    Gallium nitride (GaN) being one of a few piezoelectric semiconductors with low acoustic loss is a perfect material for electro-acoustic applications. Interactions of electrons and phonons are facilitated by the piezoelectric effect in addition to the deformation coupling in GaN, a property that can be used to implement a variety of very interesting devices and metamaterials, such as resonant transistors, acoustic amplifiers, circulators, and couplers. This talk covers theoretical basis of such devices and overviews recent advances in this technology.

  14. Carrier localization in gallium nitride

    SciTech Connect

    Wetzel, C.; Walukiewicz, W.; Haller, E.E.

    1996-09-01

    In wide bandgap GaN, a large number of interesting and important scientific questions remain to be answered. For example, the large free electron concentration reaching 10{sup 19} to 10{sup 20} cm{sup - 3} in nominally undoped material are ascribed to intrinsic defects because no chemical impurity has been found at such high concentrations. According to theoretical models, a nitrogen vacancy acts as a donor but its formation energy is very large in n-type materials, making this suggestion controversial. We have investigated the nature of this yet unidentified donor at large hydrostatic pressure. Results from infrared reflection and Raman scattering indicate strong evidence for localization of free carriers by large pressures. The carrier density is drastically decreased by two orders of magnitude between 20 and 30 GPa. Several techniques provide independent evidence for results in earlier reports and present the first quantitative analysis. A possible interpretation of this effect in terms of the resonant donor level is presented.

  15. Cathodoluminescence spectra of gallium nitride nanorods

    PubMed Central

    2011-01-01

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

  16. Cathodoluminescence spectra of gallium nitride nanorods.

    PubMed

    Tsai, Chia-Chang; Li, Guan-Hua; Lin, Yuan-Ting; Chang, Ching-Wen; Wadekar, Paritosh; Chen, Quark Yung-Sung; Rigutti, Lorenzo; Tchernycheva, Maria; Julien, François Henri; Tu, Li-Wei

    2011-12-14

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

  17. Thickness dependent thermal conductivity of gallium nitride

    NASA Astrophysics Data System (ADS)

    Ziade, Elbara; Yang, Jia; Brummer, Gordie; Nothern, Denis; Moustakas, Theodore; Schmidt, Aaron J.

    2017-01-01

    As the size of gallium nitride (GaN) transistors is reduced in order to reach higher operating frequencies, heat dissipation becomes the critical bottleneck in device performance and longevity. Despite the importance of characterizing the physics governing the thermal transport in thin GaN films, the literature is far from conclusive. In this letter, we report measurements of thermal conductivity in a GaN film with thickness ranging from 15-1000 nm grown on 4H-SiC without a transition layer. Additionally, we measure the thermal conductivity in the GaN film when it is 1 μm-thick in the temperature range of 300 < T < 600 K and use a phonon transport model to explain the thermal conductivity in this film.

  18. Interfacing epitaxial oxides to gallium nitride

    NASA Astrophysics Data System (ADS)

    Losego, Mark Daniel

    Molecular beam epitaxy (MBE) is lauded for its ability to control thin film material structures at the atomic level. This precision of control can improve performance of microelectronic devices and cultivate the development of novel device structures. This thesis explores the utility of MBE for designing interfaces between oxide epilayers and the wide band gap semiconductor gallium nitride (GaN). The allure of wide gap semiconductor microelectronics (like GaN, 3.4 eV) is their ability to operate at higher frequencies, higher powers, and higher temperatures than current semiconductor platforms. Heterostructures between ferroelectric oxides and GaN are also of interest for studying the interaction between GaN's fixed polarization and the ferroelectric's switchable polarization. Two major obstacles to successful integration of oxides with GaN are: (1) interfacial trap states; and (2) small electronic band offsets across the oxide/nitride interface due to the semiconductor's large band gap. For this thesis, epitaxial rocksalt oxide interfacial layers (˜8 eV band gap) are investigated as possible solutions to overcoming the challenges facing oxide integration with GaN. The cubic close-packed structure of rocksalt oxides forms a suitable epitaxial interface with the hexagonal close-packed wurtzite lattice of GaN. Three rocksalt oxide compounds are investigated in this thesis: MgO, CaO, and YbO. All are found to have a (111) MO || (0001) GaN; <1 10> MO || <11 20> GaN epitaxial relationship. Development of the epilayer microstructure is dominated by the high-energy polar growth surface (drives 3D nucleation) and the interfacial symmetry, which permits the formation of twin boundaries. Using STEM, strain relief for these ionicly bonded epilayers is observed to occur through disorder within the initial monolayer of growth. All rocksalt oxides demonstrate chemical stability with GaN to >1000°C. Concurrent MBE deposition of MgO and CaO is known to form complete solid

  19. 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

  20. 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.

  1. Crystallographic alignment of high-density gallium nitride nanowire arrays.

    PubMed

    Kuykendall, Tevye; Pauzauskie, Peter J; Zhang, Yanfeng; Goldberger, Joshua; Sirbuly, Donald; Denlinger, Jonathan; Yang, Peidong

    2004-08-01

    Single-crystalline, one-dimensional semiconductor nanostructures are considered to be one of the critical building blocks for nanoscale optoelectronics. Elucidation of the vapour-liquid-solid growth mechanism has already enabled precise control over nanowire position and size, yet to date, no reports have demonstrated the ability to choose from different crystallographic growth directions of a nanowire array. Control over the nanowire growth direction is extremely desirable, in that anisotropic parameters such as thermal and electrical conductivity, index of refraction, piezoelectric polarization, and bandgap may be used to tune the physical properties of nanowires made from a given material. Here we demonstrate the use of metal-organic chemical vapour deposition (MOCVD) and appropriate substrate selection to control the crystallographic growth directions of high-density arrays of gallium nitride nanowires with distinct geometric and physical properties. Epitaxial growth of wurtzite gallium nitride on (100) gamma-LiAlO(2) and (111) MgO single-crystal substrates resulted in the selective growth of nanowires in the orthogonal [1\\[Evec]0] and [001] directions, exhibiting triangular and hexagonal cross-sections and drastically different optical emission. The MOCVD process is entirely compatible with the current GaN thin-film technology, which would lead to easy scale-up and device integration.

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

    SciTech Connect

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

    2012-07-27

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

  3. Dielectric response of wurtzite gallium nitride in the terahertz frequency range

    NASA Astrophysics Data System (ADS)

    Hibberd, M. T.; Frey, V.; Spencer, B. F.; Mitchell, P. W.; Dawson, P.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J.; Graham, D. M.

    2016-12-01

    We report on the characterization of the intrinsic, anisotropic, dielectric properties of wurtzite gallium nitride in the spectral range of 0.5-11 THz, using terahertz time-domain spectroscopy. The ordinary (ε˜⊥) and extraordinary (ε˜∥) components of the complex dielectric function were determined experimentally for a semi-insulating, m-plane gallium nitride single crystal, providing measurements of the refractive indices (n⊥,∥) and absorption coefficients (α⊥,∥) . These material parameters were successfully modeled by considering the contribution of the optical phonon modes, measured using Raman spectroscopy, to the dielectric function, giving values for the relative static dielectric constants of ε0⊥ = 9.22 ± 0.02 and ε0∥ = 10.32 ± 0.03 for wurtzite gallium nitride.

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

    PubMed

    Sarkar, Sujoy; Sampath, S

    2016-05-28

    Correction for 'Ambient temperature deposition of gallium nitride/gallium oxynitride from a deep eutectic electrolyte, under potential control' by Sujoy Sarkar et al., Chem. Commun., 2016, 52, 6407-6410.

  5. Gallium nitride photocathodes for imaging photon counters

    NASA Astrophysics Data System (ADS)

    Siegmund, Oswald H. W.; Hull, Jeffrey S.; Tremsin, Anton S.; McPhate, Jason B.; Dabiran, Amir M.

    2010-07-01

    Gallium nitride opaque and semitransparent photocathodes provide high ultraviolet quantum efficiencies from 100 nm to a long wavelength cutoff at ~380 nm. P (Mg) doped GaN photocathode layers ~100 nm thick with a barrier layer of AlN (22 nm) on sapphire substrates also have low out of band response, and are highly robust. Opaque GaN photocathodes are relatively easy to optimize, and consistently provide high quantum efficiency (70% at 120 nm) provided the surface cleaning and activation (Cs) processes are well established. We have used two dimensional photon counting imaging microchannel plate detectors, with an active area of 25 mm diameter, to investigate the imaging characteristics of semitransparent GaN photocathodes. These can be produced with high (20%) efficiency, but the thickness and conductivity of the GaN must be carefully optimized. High spatial resolution of ~50 μm with low intrinsic background (~7 events sec-1 cm-2) and good image uniformity have been achieved. Selectively patterned deposited GaN photocathodes have also been used to allow quick diagnostics of optimization parameters. GaN photocathodes of both types show great promise for future detector applications in ultraviolet Astrophysical instruments.

  6. Gallium nitride photocathode development for imaging detectors

    NASA Astrophysics Data System (ADS)

    Siegmund, Oswald H. W.; Tremsin, Anton S.; Vallerga, John V.; McPhate, Jason B.; Hull, Jeffrey S.; Malloy, James; Dabiran, Amir M.

    2008-07-01

    Recent progress in Gallium Nitride (GaN, AlGaN, InGaN) photocathodes show great promise for future detector applications in Astrophysical instruments. Efforts with opaque GaN photocathodes have yielded quantum efficiencies up to 70% at 120 nm and cutoffs at ~380 nm, with low out of band response, and high stability. Previous work with semitransparent GaN photocathodes produced relatively low quantum efficiencies in transmission mode (4%). We now have preliminary data showing that quantum efficiency improvements of a factor of 5 can be achieved. We have also performed two dimensional photon counting imaging with 25mm diameter semitransparent GaN photocathodes in close proximity to a microchannel plate stack and a cross delay line readout. The imaging performance achieves spatial resolution of ~50μm with low intrinsic background (below 1 event sec-1 cm-2) and reasonable image uniformity. GaN photocathodes with significant quantum efficiency have been fabricated on ceramic MCP substrates. In addition GaN has been deposited at low temperature onto quartz substrates, also achieving substantial quantum efficiency.

  7. Electrical characterization of magnesium implanted gallium nitride

    NASA Astrophysics Data System (ADS)

    Krtschil, A.; Kielburg, A.; Witte, H.; Christen, J.; Krost, A.; Wenzel, A.; Rauschenbach, B.

    2002-01-01

    Gallium nitride layers grown by molecular beam epitaxy on c axis oriented sapphire substrates were implanted with 180 keV magnesium ions with ion doses between 1×1014 and 1×1016cm-2. The implantation induced defect states were investigated by temperature dependent conductivity (TDC) as well as by thermal and optical admittance spectroscopy (TAS, OAS) measurements. Dominant carrier emissions having thermal activation energies between 360 and 800 meV were found in TAS and TDC. These states are assigned to implantation induced electron traps since they do not appear in the nonimplanted reference sample. Defect states with similar transition energies were also observed in OAS resulting in an enhancement of defect-to-band transitions in the near band-gap region around 3.45 eV, in the blue band around 3.0 eV, as well as in the midgap range for photon energies between 2.5 and 1.80 eV, respectively. In addition, new transitions were found at 2.1 and 1.95 eV. Furthermore, transitions from implantation induced shallow states were observed, i.e., the magnesium acceptor as well as a new donor level at about 70 meV, tentatively discussed as nitrogen vacancy. The critical ion dose for amorphization was determined to be between 5×1015 and 1×1016Mg+ cm-2 using x-ray diffraction.

  8. 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

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

    PubMed

    Ghazali, Norizzawati Mohd; Yasui, Kanji; Hashim, Abdul Manaf

    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/cm(2) 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.

  10. 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.

  11. Gallium nitride nanowires by maskless hot phosphoric wet etching

    NASA Astrophysics Data System (ADS)

    Bharrat, D.; Hosalli, A. M.; Van Den Broeck, D. M.; Samberg, J. P.; Bedair, S. M.; El-Masry, N. A.

    2013-08-01

    We demonstrate gallium nitride (GaN) nanowires formation by controlling the selective and anisotropic etching of N-polar GaN in hot phosphoric acid. Nanowires of ˜109/cm,2 total height of ˜400 nm, and diameters of 170-200 nm were obtained. These nanowires have both non-polar {11¯00}/ {112¯0} and semi-polar {1011¯} facets. X-Ray Diffraction characterization shows that screw dislocations are primarily responsible for preferential etching to create nanowires. Indium gallium nitride multi-quantum wells (MQWs) grown on these GaN nanowires showed a blue shift in peak emission wavelength of photoluminescence spectra, and full width at half maximum decreased relative to MQWs grown on planar N-polar GaN, respectively.

  12. Amorphous carbon buffer layers for separating free gallium nitride films

    NASA Astrophysics Data System (ADS)

    Altakhov, A. S.; Gorbunov, R. I.; Kasharina, L. A.; Latyshev, F. E.; Tarala, V. A.; Shreter, Yu. G.

    2016-11-01

    The possibility of using amorphous diamond-like carbon (DLC) films for self-separation of gallium nitride (GaN) layers grown by hydride vapor-phase epitaxy has been analyzed. DLC films have been synthesized by plasma-enhanced chemical vapor deposition under low pressure on sapphire (Al2O3) substrates with a (0001) crystallographic orientation. The samples have been studied by the methods of Raman scattering and X-ray diffraction analysis. It is shown that thin DLC films affect only slightly the processes of nucleation and growth of gallium nitride films. Notably, the strength of the "GaN film-Al2O3" substrate interface decreases, which facilitates separation of the GaN layers.

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

    PubMed

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

    2013-03-07

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

  14. Gallium nitride electrodes for membrane-based electrochemical biosensors

    NASA Astrophysics Data System (ADS)

    Schubert, T.; Steinhoff, G.; von Ribbeck, H.-G.; Stutzmannn, M.; Eickhoff, M.; Tanaka, M.

    2009-10-01

    We report on the deposition of planar lipid bilayers (supported membranes) on gallium nitride (GaN) electrodes for potential applications as membrane-based biosensors. The kinetics of the lipid membrane formation upon vesicle fusion were monitored by simultaneous measurements of resistance and capacitance of the membrane using AC impedance spectroscopy in the frequency range between 50mHz and 50kHz. We could identify a two-step process of membrane spreading and self-healing. Despite its relatively low resistance, the membrane can be modeled by a parallel combination of an ideal resistor and capacitor, indicating that the membrane efficiently blocks the diffusion of ions.

  15. Interdiffusion of magnesium and iron dopants in gallium nitride

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Tomonobu; Kitatani, Takeshi; Terano, Akihisa; Mochizuki, Kazuhiro

    2015-03-01

    The interdiffusion of magnesium and iron in gallium nitride (GaN), i.e., magnesium-iron interdiffusion, was investigated using magnesium-doped GaN layers on iron-doped GaN substrates. The investigation confirms that the magnesium-iron interdiffusion strongly depends on the concentrations of magnesium and iron, that is, it occurs when the iron and magnesium concentrations are high (magnesium: 2 × 1020 cm-3 iron: 2 × 1019 cm-3). It also confirms that diffused iron in the magnesium-doped GaN layer acts as a nonradiative recombination center in GaN.

  16. 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.

  17. Gallium nitride electrodes for membrane-based electrochemical biosensors.

    PubMed

    Schubert, T; Steinhoff, G; von Ribbeck, H-G; Stutzmannn, M; Eickhoff, M; Tanaka, M

    2009-10-01

    We report on the deposition of planar lipid bilayers (supported membranes) on gallium nitride (GaN) electrodes for potential applications as membrane-based biosensors. The kinetics of the lipid membrane formation upon vesicle fusion were monitored by simultaneous measurements of resistance and capacitance of the membrane using AC impedance spectroscopy in the frequency range between 50 mHz and 50 kHz. We could identify a two-step process of membrane spreading and self-healing. Despite its relatively low resistance, the membrane can be modeled by a parallel combination of an ideal resistor and capacitor, indicating that the membrane efficiently blocks the diffusion of ions.

  18. Lasing action in gallium nitride quasicrystal nanorod arrays.

    PubMed

    Chang, Shih-Pang; Sou, Kuok-Pan; Chen, Chieh-Han; Cheng, Yuh-Jen; Huang, Ji-Kai; Lin, Chung-Hsiang; Kuo, Hao-Chung; Chang, Chun-Yen; Hsieh, Wen-Feng

    2012-05-21

    We report the observation of lasing action from an optically pumped gallium nitride quasicrystal nanorod arrays. The nanorods were fabricated from a GaN substrate by patterned etching, followed by epitaxial regrowth. The nanorods were arranged in a 12-fold symmetric quasicrystal pattern. The regrowth grew hexagonal crystalline facets and core-shell multiple quantum wells (MQWs) on nanorods. Under optical pumping, multiple lasing peaks resembling random lasing were observed. The lasing was identified to be from the emission of MQWs on the nanorod sidewalls. The resonant spectrum and mode field of the 12-fold symmetric photonic quasicrystal nanorod arrays is discussed.

  19. 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.

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

    DOE PAGES

    Jacobs, Benjamin W.; Ayres, Virginia M.; Stallcup, Richard E.; ...

    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.

  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. Two-dimensional gallium nitride realized via graphene encapsulation.

    PubMed

    Al Balushi, Zakaria Y; Wang, Ke; Ghosh, Ram Krishna; Vilá, Rafael A; Eichfeld, Sarah M; Caldwell, Joshua D; Qin, Xiaoye; Lin, Yu-Chuan; DeSario, Paul A; Stone, Greg; Subramanian, Shruti; Paul, Dennis F; Wallace, Robert M; Datta, Suman; Redwing, Joan M; Robinson, Joshua A

    2016-11-01

    The spectrum of two-dimensional (2D) and layered materials 'beyond graphene' offers a remarkable platform to study new phenomena in condensed matter physics. Among these materials, layered hexagonal boron nitride (hBN), with its wide bandgap energy (∼5.0-6.0 eV), has clearly established that 2D nitrides are key to advancing 2D devices. A gap, however, remains between the theoretical prediction of 2D nitrides 'beyond hBN' and experimental realization of such structures. Here we demonstrate the synthesis of 2D gallium nitride (GaN) via a migration-enhanced encapsulated growth (MEEG) technique utilizing epitaxial graphene. We theoretically predict and experimentally validate that the atomic structure of 2D GaN grown via MEEG is notably different from reported theory. Moreover, we establish that graphene plays a critical role in stabilizing the direct-bandgap (nearly 5.0 eV), 2D buckled structure. Our results provide a foundation for discovery and stabilization of 2D nitrides that are difficult to prepare via traditional synthesis.

  3. Oligonuclear gallium nitrogen cage compounds: molecular intermediates on the way from gallium hydrazides to gallium nitride.

    PubMed

    Uhl, Werner; Abel, Thomas; Hagemeier, Elke; Hepp, Alexander; Layh, Marcus; Rezaeirad, Babak; Luftmann, Heinrich

    2011-01-03

    Gallium hydrazides are potentially applicable as facile starting compounds for the generation of GaN by thermolysis. The decomposition pathways are, however, complicated and depend strongly on the substituents attached to the gallium atoms and the hydrazido groups. This paper describes some systematic investigations into the thermolysis of the gallium hydrazine adduct Bu(t)(3)Ga←NH(2)-NHMe (1a) and the dimeric gallium hydrazides [R(2)Ga(N(2)H(2)R')](2) (2b, R = Bu(t), R' = Bu(t); 2c, R = Pr(i), R' = Ph; 2d, R = Me, R' = Bu(t)) which have four- or five-membered heterocycles in their molecular cores. Heating of the adduct 1a to 170 °C gave the heterocyclic compound Bu(t)(2)Ga(μ-NH(2))[μ-N(Me)-N(=CH(2))]GaBu(t)(2) (3) by cleavage of N-N bonds and rearrangement. 3 was further converted at 400 °C into the tetrameric gallium cyanide (Bu(t)(2)GaCN)(4) (4). The thermolysis of the hydrazide (Bu(t)(2)Ga)(2)(NH-NHBu(t))(2) (2b) at temperatures between 270 and 420 °C resulted in cleavage of all N-N bonds and the formation of an octanuclear gallium imide, (Bu(t)GaNH)(8) (6). The trimeric dialkylgallium amide (Bu(t)(2)GaNH(2))(3) (5) was isolated as an intermediate. Thermolysis of the hydrazides (Pr(i)(2)Ga)(2)(NH-NHPh)(NH(2)-NPh) (2c) and (Me(2)Ga)(2)(NH-NHBu(t))(2) (2d) proceeded in contrast with retention of the N-N bonds and afforded a variety of novel gallium hydrazido cage compounds with four gallium atoms and up to four hydrazido groups in a single molecule: (Pr(i)Ga)(4)(NH-NPh)(3)NH (7), (MeGa)(4)(NH-NBu(t))(4) (8), (MeGa)(4)(NH-NBu(t))(3)NBu(t) (9), and (MeGa)(4)(NHNBu(t))(3)NH (10). Partial hydrolysis gave reproducibly the unique octanuclear mixed hydrazido oxo compound (MeGa)(8)(NHNBu(t))(4)O(4) (11).

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

    PubMed

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

    2015-03-11

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

  5. Modeling and Simulation of a Gallium Nitride (GaN) Betavoltaic Energy Converter

    DTIC Science & Technology

    2016-06-01

    ARL-TR-7675 ● JUNE 2016 US Army Research Laboratory Modeling and Simulation of a Gallium Nitride (GaN) Betavoltaic Energy ...Laboratory Modeling and Simulation of a Gallium Nitride (GaN) Betavoltaic Energy Converter by Marc S Litz and Johnny A Russo Sensors and Electron...GaN) Betavoltaic Energy Converter 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) William B Ray II, Marc S

  6. 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.

  7. Fabrication and characterization of gallium nitride electronic devices

    NASA Astrophysics Data System (ADS)

    Johnson, Jerry Wayne

    Gallium nitride (GaN)-based high electron mobility transistors (HEMTs), metal oxide semiconductor field effect transistors (MOSFETs), and Schottky rectifiers were fabricated and characterized. Novel dielectric materials Gd 2O3 and ScO were evaluated as potential gate dielectrics for GaN MOS applications. The devices presented herein show tremendous potential for elevated temperature, high frequency, and/or high voltage operation. AlGaN/GaN HEMTs were grown by MOCVD on sapphire and SiC substrates and by RF-MBE on sapphire substrates. Devices were fabricated with gate lengths from 100 nm to 1.2 mum. Drain current density approached 1 A/mm and extrinsic transconductance exceeded 200 mS/mm for small gate periphery devices. For the shortest gate length, a unity-gain cutoff frequency (fT) of 59 GHz and a maximum frequency of oscillation (fmax) of 90 GHz were extracted from measured scattering parameters. The experimental s-parameters were in excellent agreement with simulated results from small-signal linear modeling. Large signal characterization of 0.25 x 150 mum2 devices produced 2.75 W/mm at 3 GHz and 1.7 W/mm at 10 GHz. Devices fabricated on high thermal conductivity SiC substrates exhibited superior high temperature performance and a reduced density of threading dislocations. Novel gate dielectrics Gd2O3 and ScO were grown by gas source molecular beam epitaxy (GSMBE). Current-voltage (I-V) and capacitance-voltage (C-V) data were collected from MOS capacitors to evaluate the bulk and interfacial electrical properties of the insulators. Single crystal Gd2O 3 was demonstrated on GaN, but the resultant MOSFET exhibited a large gate leakage attributed to defects and dislocations in the oxide. MOSFETs with a stacked gate dielectric of Gd2O3/SiO2 were operational at a drain source bias of 80 V and a gate bias of +7 V. Bulk GaN templates grown by hydride vapor phase epitaxy (HYPE) were used to fabricate vertical geometry Schottky rectifiers. Size- and temperature

  8. 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.

  9. 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.

  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.

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

    PubMed

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

    2015-03-24

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

  12. A gallium nitride single-photon source operating at 200 K.

    PubMed

    Kako, Satoshi; Santori, Charles; Hoshino, Katsuyuki; Götzinger, Stephan; Yamamoto, Yoshihisa; Arakawa, Yasuhiko

    2006-11-01

    Fundamentally secure quantum cryptography has still not seen widespread application owing to the difficulty of generating single photons on demand. Semiconductor quantum-dot structures have recently shown great promise as practical single-photon sources, and devices with integrated optical cavities and electrical-carrier injection have already been demonstrated. However, a significant obstacle for the application of commonly used III-V quantum dots to quantum-information-processing schemes is the requirement of liquid-helium cryogenic temperatures. Epitaxially grown gallium nitride quantum dots embedded in aluminium nitride have the potential for operation at much higher temperatures. Here, we report triggered single-photon emission from gallium nitride quantum dots at temperatures up to 200 K, a temperature easily reachable with thermo-electric cooling. Gallium nitride quantum dots also open a new wavelength region in the blue and near-ultraviolet portions of the spectrum for single-photon sources.

  13. Studies on the reliability of ni-gate aluminum gallium nitride / gallium nitride high electron mobility transistors using chemical deprocessing

    NASA Astrophysics Data System (ADS)

    Whiting, Patrick Guzek

    Aluminum Gallium Nitride / Gallium Nitride High Electron Mobility Transistors are becoming the technology of choice for applications where hundreds of volts need to be applied in a circuit at frequencies in the hundreds of gigahertz, such as microwave communications. However, because these devices are very new, their reliability in the field is not well understood, partly because of the stochastic nature of the defects which form as a result of their operation. Many analytical techniques are not well suited to the analysis of these defects because they sample regions of the device which are either too small or too large for accurate observation. The use of chemical deprocessing in addition to surface-sensitive analysis techniques such as Scanning Electron Microscopy and Scanning Probe Microscopy can be utilized in the analysis of defect formation in devices formed with nickel gates. Hydrofluoric acid is used to etch the passivation nitride which covers the semiconducting layer of the transistor. A metal etch utilizing FeCN/KI is used to etch the ohmic and gate contacts of the device and a long exposure in various solvent solutions is used to remove organic contaminants, exposing the surface of the semiconducting layer for analysis. Deprocessing was used in conjunction with a variety of metrology techniques to analyze three different defects. One of these defects is a nanoscale crack which emanates from metal inclusions formed during alloying of the ohmic contacts of the device prior to use in the field, could impact the yield of production-level manufacturing of these devices. This defect also appears to grow, in some cases, during electrostatic stressing. Another defect, a native oxide at the surface of the semiconducting layer which appears to react in the presence of an electric field, has not been observed before during post-mortem analysis of degraded devices. It could play a major part in the degredation of the gate contact during high-field, off

  14. Growth and characterization aluminum gallium nitride/gallium nitride heterostructures on silicon(111) wafers using various buffer layers

    NASA Astrophysics Data System (ADS)

    Venugopal, Rajesh

    Devices based on nitride wide bandgap semiconductors are suitable for several promising applications such as blue lasers, LEDs, HEMTs etc. Due to the absence of bulk nitride crystals, nitride films are grown on lattice mismatched substrates like Al2O3 and 6H-SiC. However from a cost and integration standpoint silicon would be the substrate of choice for the growth of these materials. Nitride heterostructure growth on large area Si(111) is hence attempted by Metal Organic Chemical Vapor Deposition (MOCVD) in an modified AIX 200/4 system. The large lattice and thermal mismatch prevents the direct deposition of GaN on Si and also causes GaN layers grown on Si to crack severely. It is hence necessary to use buffer layers to alleviate this lattice and thermal mismatch. Several buffer layer schemes are used for this purpose. The crystal quality of the AlGaN/GaN heterostructures grown under various conditions on these buffers are studied using several methods like Photoluminescence, X-ray diffraction, Electron Microscopy etc. The quality of heterostructures grown on these buffers is compared in order to identify the strengths and weaknesses of each buffer and to also map the effects of process parameters on nitride layers deposited on each buffer.

  15. Distinctive signature of indium gallium nitride quantum dot lasing in microdisk cavities.

    PubMed

    Woolf, Alexander; Puchtler, Tim; Aharonovich, Igor; Zhu, Tongtong; Niu, Nan; Wang, Danqing; Oliver, Rachel; Hu, Evelyn L

    2014-09-30

    Low-threshold lasers realized within compact, high-quality optical cavities enable a variety of nanophotonics applications. Gallium nitride materials containing indium gallium nitride (InGaN) quantum dots and quantum wells offer an outstanding platform to study light-matter interactions and realize practical devices such as efficient light-emitting diodes and nanolasers. Despite progress in the growth and characterization of InGaN quantum dots, their advantages as the gain medium in low-threshold lasers have not been clearly demonstrated. This work seeks to better understand the reasons for these limitations by focusing on the simpler, limited-mode microdisk cavities, and by carrying out comparisons of lasing dynamics in those cavities using varying gain media including InGaN quantum wells, fragmented quantum wells, and a combination of fragmented quantum wells with quantum dots. For each gain medium, we use the distinctive, high-quality (Q ∼ 5,500) modes of the cavities, and the change in the highest-intensity mode as a function of pump power to better understand the dominant radiative processes. The variations of threshold power and lasing wavelength as a function of gain medium help us identify the possible limitations to lower-threshold lasing with quantum dot active medium. In addition, we have identified a distinctive lasing signature for quantum dot materials, which consistently lase at wavelengths shorter than the peak of the room temperature gain emission. These findings not only provide better understanding of lasing in nitride-based quantum dot cavity systems but also shed insight into the more fundamental issues of light-matter coupling in such systems.

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

    PubMed

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

    2013-07-02

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

  17. 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.

  18. Exploiting the Negative Polarization Properties of Indium Gallium Nitride (InGaN)/Gallium Nitride (GaN) Heterostructures to Achieve Frequency Doubled Blue-green Lasers with Deep UV (250 nm) Emission (Year 2)

    DTIC Science & Technology

    2011-05-01

    100 A/cm 2 , well beyond the current density 10–25 A/cm 2 at which conventional p-up, Ga-polar InGaN /GaN multi-quantum well LEDs exhibit significant...nitride ICP inductively coupled plasma InGaN indium gallium nitride KDP potassium di-hydrogen phosphate LBO lithium triborate LEDs light...Exploiting the Negative Polarization Properties of Indium Gallium Nitride ( InGaN )/Gallium Nitride (GaN) Heterostructures to Achieve Frequency

  19. Damage development of gallium nitride under plasma exposure

    NASA Astrophysics Data System (ADS)

    Ogawa, Daisuke; Banno, Yoshitsugu; Nakano, Yoshitaka; Nakamura, Keiji

    2016-09-01

    Plasma damage has been focused on since 1990s. In this era, this issue was manly targeted onto silicon-based semiconductors. However, since the gallium nitride (GaN) was paid attentions to after blue LEDs, they start to consider the damages given to GaN as well. We have so far utilized photoluminescence (PL) emission from the surface of GaN film to monitor the evolution of damage given by plasma exposure. This measurement gives us clues how plasma exposure changed intermediate electronical states in the film without taking the film out of the chamber. First of all, we analyzed the development of damage given by argon plasma, which is one of the most fundamental plasma to analyze. Argon plasma is responsible to give only physical damages over a GaN film. Our PL measurements showed a significant decrease within approximately 10 seconds after the plasma exposure started. This means that ions and radiations created from the plasma gives significant damages to the GaN film even short period of time. Chlorine-related gas is normally utilized for chemical etching. Chlorine species realize continuous damage layer removals, but some reports already mentioned that the processed device has difference electrical properties after the plasma exposure. In this presentation, we will show what happens to GaN film after the plasma exposure in terms of crystal structure and impurities of GaN, by connecting PL emission and ex-situ measurements.

  20. Photoelectrochemical etching of gallium nitride surface by complexation dissolution mechanism

    NASA Astrophysics Data System (ADS)

    Zhang, Miao-Rong; Hou, Fei; Wang, Zu-Gang; Zhang, Shao-Hui; Pan, Ge-Bo

    2017-07-01

    Gallium nitride (GaN) surface was etched by 0.3 M ethylenediamine tetraacetic acid disodium (EDTA-2Na) via photoelectrochemical etching technique. SEM images reveal the etched GaN surface becomes rough and irregular. The pore density is up to 1.9 × 109 per square centimeter after simple acid post-treatment. The difference of XPS spectra of Ga 3d, N 1s and O 1s between the non-etched and freshly etched GaN surfaces can be attributed to the formation of Ga-EDTA complex at the etching interface between GaN and EDTA-2Na. The proposed complexation dissolution mechanism can be broadly applicable to almost all neutral etchants under the prerequisite of strong light and electric field. From the point of view of environment, safety and energy, EDTA-2Na has obvious advantages over conventionally corrosive etchants. Moreover, as the further and deeper study of such nearly neutral etchants, GaN etching technology has better application prospect in photoelectric micro-device fabrication.

  1. Low-frequency noise in gallium nitride nanowire mechanical resonators

    NASA Astrophysics Data System (ADS)

    Gray, Jason M.; Bertness, Kris A.; Sanford, Norman A.; Rogers, Charles T.

    2012-12-01

    We report on the low-frequency 1/f (flicker) parameter noise displayed by the resonance frequency of doubly clamped c-axis gallium nitride nanowire (NW) mechanical resonators. The resonators are electrostatically driven and their mechanical response is electronically detected via NW piezoresistance. With an applied dc voltage bias, a NW driven near its mechanical resonance generates a dc and Lorentzian rf current that both display 1/f noise. The rf current noise is proportional to the square of the derivative of the Lorentzian lineshape with a magnitude highly dependent on NW dc bias voltage conditions, consistent with a model wherein noise in the NW's electrical impedance leads to temperature noise from local Joule heating, which in turn generates resonance frequency noise via thermal expansion and the temperature-dependent Young's modulus. An example device with a 27.8 MHz resonance frequency experiences an approximate resonance frequency shift of -1.4 Hz/nW. The resonance frequency noise increases as the square of the bias voltage, indicating specific operating conditions that optimize the signal-to-noise ratio in proposed NW sensors.

  2. Low-frequency noise in gallium nitride nanowire mechanical resonators

    NASA Astrophysics Data System (ADS)

    Gray, Jason; Bertness, Kris; Sanford, Norman; Rogers, Charles

    2012-02-01

    We report on the low-frequency 1/f (flicker) parameter noise displayed by the resonance frequency and resistance of doubly clamped c-axis gallium nitride nanowire (NW) mechanical resonators. The resonators are electrostatically driven and their mechanical response is electronically detected via NW piezoresistance. With an applied dc voltage bias, an NW driven near its mechanical resonance generates a dc and Lorentzian rf current that both display 1/f noise. The rf current noise is proportional to the square of the derivative of the Lorentzian lineshape with a magnitude highly dependent on NW dc bias voltage conditions, consistent with noise in the NW's resistance leading to temperature noise from local Joule heating, which in turn generates resonance frequency noise. An example device with a 27.8 MHz resonance frequency and 220 kφ resistance experiences an approximate resonance frequency shift of -5.8 Hz/nW. In terms of NW resistance change, this corresponds with shifts of 0.1 Hz/φ and 2.6 Hz/φ at 1 V bias and 4 V bias, respectively, with an average resistance fluctuation of 1 kφ in a 1-second bandwidth.

  3. 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.

  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. 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.

  6. Synthesis of aluminium nitride/boron nitride composite materials

    SciTech Connect

    Xiao, T.D. . Polymer Science Program and Dept. of Chemistry); Gonsalves, K.E. . Polymer Science Program and Dept. of Chemistry Univ. of Connecticut, Storrs, CT . Dept. of Chemistry); Strutt, P.R. . Dept. of Metallurgy)

    1993-04-01

    Aluminum nitride/boron nitride composite was synthesized by using boric acid, urea, and aluminum chloride (or aluminum lactate) as the starting compounds. The starting materials were dissolved in water and mixed homogeneously. Ammonolysis of this aqueous solution resulted in the formation of a precomposite gel, which converted into the aluminum nitride/boron nitride composite on further heat treatment. Characterization of both the precomposite and the composite powders included powder X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Analysis of the composite revealed that the aluminum nitride phase had a hexagonal structure, and the boron nitride phase a turbostratic structure.

  7. Localized surface plasmon resonances in gold nano-patches on a gallium nitride substrate.

    PubMed

    D'Antonio, Palma; Inchingolo, Alessio Vincenzo; Perna, Giuseppe; Capozzi, Vito; Stomeo, Tiziana; De Vittorio, Massimo; Magno, Giovanni; Grande, Marco; Petruzzelli, Vincenzo; D'Orazio, Antonella

    2012-11-16

    In this paper we describe the design, fabrication and characterization of gold nano-patches, deposited on gallium nitride substrate, acting as optical nanoantennas able to efficiently localize the electric field at the metal-dielectric interface. We analyse the performance of the proposed device, evaluating the transmission and the electric field localization by means of a three-dimensional finite difference time domain (FDTD) method. We detail the fabrication protocol and show the morphological characterization. We also investigate the near-field optical transmission by means of scanning near-field optical microscope measurements, which reveal the excitation of a localized surface plasmon resonance at a wavelength of 633 nm, as expected by the FDTD calculations. Such results highlight how the final device can pave the way for the realization of a single optical platform where the active material and the metal nanostructures are integrated together on the same chip.

  8. Bright Room-Temperature Single-Photon Emission from Defects in Gallium Nitride.

    PubMed

    Berhane, Amanuel M; Jeong, Kwang-Yong; Bodrog, Zoltán; Fiedler, Saskia; Schröder, Tim; Triviño, Noelia Vico; Palacios, Tomás; Gali, Adam; Toth, Milos; Englund, Dirk; Aharonovich, Igor

    2017-02-09

    Room-temperature quantum emitters in gallium nitride (GaN) are reported. The emitters originate from cubic inclusions in hexagonal lattice and exhibit narrowband luminescence in the red spectral range. The sources are found in different GaN substrates, and therefore are promising for scalable quantum technologies.

  9. Gallium Nitride Light Emitter on a Patterned Sapphire Substrate for Improved Defectivity and Light Extraction Efficiency

    DTIC Science & Technology

    2010-01-01

    Gallium nitride light emitter on a patterned sapphire substrate for improved defectivity and light extraction efficiency Michael A. Mastro a,*, Byung ...Phys. 47 (2008) 7827. [6] B.J. Kim, H. Jung, J. Shin , M.A. Mastro, C.R. Eddy Jr., J.K. Hite, S.H. Kim, J. Bang, J. Kim, Thin Solid Films 517 (2009

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 1997 IEEE/LEOS Summer Topical Meeting on Gallium Nitride Materials, Processing and Devices Held in Montreal, Quebec, Canada on 11-15 August 1997

    DTIC Science & Technology

    1998-01-01

    papers in this book make up the digest of the meeting mentioned on the cover and title page. They reflect the authors’ opinions and are published as...have been exhibiting CW operation up to 64 °C[3] Further development may be necessary to compete with edge emitters employing DFB and spotsize...temperature (RT) cw operation[4]. The highest operation is up to 34 °C[5]. The introduction of GalnNAs/GaAs and AlGalnAs/InP may be a solution to material

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. Homoepitaxial n-core: p-shell gallium nitride nanowires: HVPE overgrowth on MBE nanowires.

    PubMed

    Sanders, Aric; Blanchard, Paul; Bertness, Kris; Brubaker, Matthew; Dodson, Christopher; Harvey, Todd; Herrero, Andrew; Rourke, Devin; Schlager, John; Sanford, Norman; Chiaramonti, Ann N; Davydov, Albert; Motayed, Abhishek; Tsvetkov, Denis

    2011-11-18

    We present the homoepitaxial growth of p-type, magnesium doped gallium nitride shells by use of halide vapor phase epitaxy (HVPE) on n-type gallium nitride nanowires grown by plasma-assisted molecular beam epitaxy (MBE). Scanning electron microscopy shows clear dopant contrast between the core and shell of the nanowire. The growth of magnesium doped nanowire shells shows little or no effect on the lattice parameters of the underlying nanowires, as measured by x-ray diffraction (XRD). Photoluminescence measurements of the nanowires show the appearance of sub-bandgap features in the blue and the ultraviolet, indicating the presence of acceptors. Finally, electrical measurements confirm the presence of electrically active holes in the nanowires.

  20. 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

  1. 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

  2. Real-time in-situ chemical sensing in aluminum gallium nitride/gallium nitride metal-organic chemical vapor deposition processes for advanced process control

    NASA Astrophysics Data System (ADS)

    Cho, Soon

    Gallium nitride and its alloys promise to be key materials for future semiconductor devices aimed at high frequency, high power electronic applications. However, manufacturing for such high performance products is challenged by reproducibility and material quality constraints that are notably more stringent than those required for optoelectronic applications. To meet this challenge, in-situ mass spectrometry was implemented as a real-time process- and wafer-state metrology tool in AlGaN/GaN/AlN metal-organic chemical vapor deposition processes on semi-insulating SiC substrate wafers. Dynamic chemical sensing through the process cycle, carried out downstream from the wafer, revealed generation of methane and ethane reaction byproducts, as well as other residual gas species. Real-time metrics were derived based on the chemical signals to predict/control material quality and thickness of critical layers within the heterostructure in real time during growth, and corresponding metrologies were used for real-time advanced process control. Using the methane/ethane ratio, GaN epilayer crystal quality was predicted in real time to 2--5% precision, which was verified by post-process x-ray diffraction. Moreover, the same real-time metric predicted material quality as indicated by post-process photoluminescence band-edge intensities to ˜5% precision. The methane/ethane ratio has a fundamental significance in terms of the intrinsic chemistry in that the two byproducts are believed to reflect two parallel reaction pathways leading to GaN-based material growth, namely the gas phase adduct formation route and the surface route for direct precursor decomposition, respectively. The fact that lower methane/ethane ratios consistently yield better material quality suggests that the surface pathway is preferred for high quality GaN growth. In addition, a metric based on methane and ethane signals integrated through the AlGaN growth period (˜1 min or less) enabled prediction of the cap

  3. 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.

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

    PubMed

    Agrawal, Ravi; Espinosa, Horacio D

    2011-02-09

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

  5. Growth of Gallium Nitride Nanorods and Their Coalescence Overgrowth

    DTIC Science & Technology

    2012-09-07

    absorption enhancements of amorphous silicon solar cells with periodical metal nanowall and nanopillar structures,” Optics Express, Vol. 20, No. S1, p...constituent atoms ( gallium , indium , which are formed through the decomposition of metalorganic precursors TEGa and TMIn, and nitrogen) projected onto the...found that the QW widths are narrower and the indium contents are higher in the sidewall m-plane QWs, when compared with the top-face c-plane QWs. Also

  6. 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.

  7. 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.

  8. Optical dielectric response of gallium nitride studied by variable angle spectroscopy ellipsometry

    SciTech Connect

    Yao, H.; Yan, C.H.; Jenkinson, H.A.; Zavada, J.M.; Speck, J.S.; Denbaars, S.P.

    1997-12-31

    Variable angle spectroscopic ellipsometry (VASE) and transmission measurements have been employed to study the dielectric response of gallium nitride (GaN) thin films -- an important material for light emitting diodes (LEDs) and laser diodes applications. The GaN films were grown by atmosphere pressure metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates ({alpha}-Al{sub 2}O{sub 3}). Room temperature VASE measurements were made, in the range of 0.75 to 5.5eV, at the angle of incidence of 73, 75, and 77 degree, respectively. Evidence of anisotropy is observed especially in the spectral range under the band gap ({approximately}3.4 eV), reflecting the nature of wurtzite crystal structure of GaN. The ordinary dielectric function {var_epsilon}{sub {perpendicular}}({omega}) of GaN were obtained through the analysis of transmission and VASE data in the range below and above the band gap. The thickness of these GaN films is also determined via the analysis.

  9. 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.

  10. Design and analysis of vertical-channel gallium nitride (GaN) junctionless nanowire transistors (JNT).

    PubMed

    Seo, Jae Hwa; Yoon, Young Jun; Lee, Hwan Gi; Yoo, Gwan Min; Jo, Young-Woo; Son, Dong-Hyeok; Lee, Jung-Hee; Cho, Eou-Sik; Cho, Seongjae; Kang, In Man

    2014-11-01

    Vertical-channel gallium nitride (GaN) junctionless nanowire transistor (JNT) has been designed and characterized by technology computer-aided design (TCAD) simulations. Various characteristics such as wide bandgap, strong polariztion field, and high electron velocity make GaN one of the attractive materials in advanced electronics in recent times. Nanowire-structured GaN can be applicable to various transistors for enhanced electrical performances by its geometrical feature. In this paper, we analyze the direct-current (DC) characteristics depending on various channel doping concentrations (N(ch)) and nanowire radii (R(NW)). Furthermore, the radio-frequency (RF) characteristics under optimized conditions are extracted by small-signal equivalent circuit modeling. For the optimally designed vertical GaN JNT demonstrated on-state current (I(on)) of 345 μA/μm and off-state current (I(off)) of 3.7 x 10(-18) A/μm with a threshold voltage (V(t)) of 0.22 V, and subthreshold swing (S) of 68 mV/dec. Besides, f(T) and f(max) under different operating conditions (gate voltage, V(GS)) have been obtained.

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

    PubMed

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

    2011-06-21

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

  12. Strategies to indium nitride and gallium nitride nanoparticles: Low-temperature, solution-phase and precursor routes

    NASA Astrophysics Data System (ADS)

    Dingman, Sean Douglas

    I present new strategies to low-temperature solution-phase synthesis of indium and gallium nitride (InN and GaN) ceramic materials. The strategies include: direct conversion of precursor molecules to InN by pyrolysis, solution-phase synthesis of nanostructured InN fibers via molecular precursors and co-reactants, and synthesis of powders through reactions derived from molten-salt chemistry. Indium nitride powders are prepared by pyrolysis of the precursors R 2InN3 (R = t-Bu (1), i-Amyl(2), Et(3), i-Pr( 4)). The precursors are synthesized via azide-alkoxide exchange of R2InOMe with Me3SiN3. The precursors are coordination polymers containing five-coordinate indium centers. Pyrolysis of 1 and 2 under N2 at 400°C yields powders consisting primarily of InN with average crystal sizes of 15--35 nm. 1 yields nanocrystalline InN with average particle sizes of 7 nm at 250°C. 3 and 4 yield primarily In metal from pyrolysis. Refluxing 1 in diisopropylbenzene (203°C) in the presence of primary amines yields InN nanofibers 10--100 nm in length. InN nanofibers of up to 1 mum can be synthesized by treating 1 with 1,1-dimethylhydrazine (DMHy) The DMHy appears to control the fiber length by acting as a secondary source of active nitrogen in order to sustain fiber growth. The resulting fibers are attached to droplets of indium metal implying a solution-liquid-solid growth mechanism. Precursor 4 yields crystalline InN whiskers when reacted with DMHy. Reactions of 4 with reducing agents such as HSnBu3, yield InN nanoparticles with an average crystallite size of 16 nm. Gallium precursors R2GaN3 (R = t-Bu( 5), Me3SiCH2(6) and i-Pr( 7)), synthesized by azide-alkoxide exchange, are found to be inert toward solution decomposition and do not yield GaN. These compounds are molecular dimers and trimers unlike the indium analogs. Compound 6 displays a monomer-dimer equilibrium in benzene solution, but exists as a solid-state trimer. InN powders are also synthesized by reactions of InCl3 and

  13. Synthesis and characterization of electrospun gallium nitride nanofibers

    NASA Astrophysics Data System (ADS)

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

    2009-08-01

    The simple and inexpensive technique of electrospinning was used for the production of long GaN nanofibers. The fibers were made using a precursor solution composed of pure Gallium Nitrate dissolved in dimethylacetamide (DMA) and a viscous solution of Cellulose acetate dissolved in a mixture of DMA and acetone. Using a tube furnace, they were sintered under a Nitrogen atmosphere to decompose the polymer and to reduce Oxygen contamination. This process was followed by sintering under a NH3 flow to complete the synthesis of wurtzite GaN. XRD, ESEM, and FTIR analysis were used to verify the chemical and structural composition of the samples. The I-V characteristics of a device constructed using a single GaN nanofiber showed the formation of ohmic contacts.

  14. 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.

  15. 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

  16. 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

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

    PubMed

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

    2015-02-14

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

  18. 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

  19. Optical polarization based logic functions (XOR or XNOR) with nonlinear Gallium nitride nanoslab.

    PubMed

    Bovino, F A; Larciprete, M C; Giardina, M; Belardini, A; Centini, M; Sibilia, C; Bertolotti, M; Passaseo, A; Tasco, V

    2009-10-26

    We present a scheme of XOR/XNOR logic gate, based on non phase-matched noncollinear second harmonic generation from a medium of suitable crystalline symmetry, Gallium nitride. The polarization of the noncollinear generated beam is a function of the polarization of both pump beams, thus we experimentally investigated all possible polarization combinations, evidencing that only some of them are allowed and that the nonlinear interaction of optical signals behaves as a polarization based XOR. The experimental results show the peculiarity of the nonlinear optical response associated with noncollinear excitation, and are explained using the expression for the effective second order optical nonlinearity in noncollinear scheme.

  20. Near-infrared characterization of gallium nitride photonic-crystal waveguides and cavities.

    PubMed

    Dharanipathy, U; Vico Triviño, N; Yan, C; Diao, Z; Carlin, J-F; Grandjean, N; Houdré, R

    2012-11-15

    We report the design and optical characterization of fully suspended wire waveguides and photonic crystal (PhC) membranes fabricated on a gallium nitride layer grown on silicon substrate operating at 1.5 μm. W1-type PhC waveguides are coupled with suspended wires and are investigated using a standard end-fire setup. The experimental and theoretical dispersion properties of the propagating modes in the wires and photonic-crystal waveguides are shown. Modified L3 cavities with quality factors of up to 2200 and heterostructure cavities with quality factors of up to 5400 are experimentally demonstrated.

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

    PubMed

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

    2013-01-01

    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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Compatibility of ITER candidate structural materials with static gallium

    SciTech Connect

    Luebbers, P.R.; Michaud, W.F.; Chopra, O.K.

    1993-12-01

    Tests were conducted on the compatibility of gallium with candidate structural materials for the International Thermonuclear Experimental Reactor, e.g., Type 316 SS, Inconel 625, and Nb-5 Mo-1 Zr alloy, as well as Armco iron, Nickel 270, and pure chromium. Type 316 stainless steel is least resistant to corrosion in static gallium and Nb-5 Mo-1 Zr alloy is most resistant. At 400{degrees}C, corrosion rates are {approx}4.0, 0.5, and 0.03 mm/yr for type 316 SS, Inconel 625, and Nb-5 Mo- 1 Zr alloy, respectively. The pure metals react rapidly with gallium. In contrast to findings in earlier studies, pure iron shows greater corrosion than nickel. The corrosion rates at 400{degrees}C are {ge}88 and 18 mm/yr, respectively, for Armco iron and Nickel 270. The results indicate that at temperatures up to 400{degrees}C, corrosion occurs primarily by dissolution and is accompanied by formation of metal/gallium intermetallic compounds. The solubility data for pure metals and oxygen in gallium are reviewed. The physical, chemical, and radioactive properties of gallium are also presented. The supply and availability of gallium, as well as price predictions through the year 2020, are summarized.

  8. Gallium nitride heterostructures on 3D structured silicon.

    PubMed

    Fündling, Sönke; Sökmen, Unsal; Peiner, Erwin; Weimann, Thomas; Hinze, Peter; Jahn, Uwe; Trampert, Achim; Riechert, Henning; Bakin, Andrey; Wehmann, Hergo-Heinrich; Waag, Andreas

    2008-10-08

    We investigated GaN-based heterostructures grown on three-dimensionally patterned Si(111) substrates by metal organic vapour phase epitaxy, with the goal of fabricating well controlled high quality, defect reduced GaN-based nanoLEDs. The high aspect ratios of such pillars minimize the influence of the lattice mismatched substrate and improve the material quality. In contrast to other approaches, we employed deep etched silicon substrates to achieve a controlled pillar growth. For that a special low temperature inductively coupled plasma etching process has been developed. InGaN/GaN multi-quantum-well structures have been incorporated into the pillars. We found a pronounced dependence of the morphology of the GaN structures on the size and pitch of the pillars. Spatially resolved optical properties of the structures are analysed by cathodoluminescence.

  9. Prospective for Gallium Nitride-Based Optical Waveguide Modulators

    NASA Astrophysics Data System (ADS)

    Stolz, Arnaud; Considine, Laurence; Dogheche, Elhadj; Decoster, Didier; Pavlidis, Dimitris

    A complete analysis of GaN-based structures with very promising characteristics for future optical waveguide devices, such as modulators, is presented. First the material growth was optimized for low dislocation density and surface roughness. Optical measurements demonstrate excellent waveguide properties in terms of index and temperature dependence while planar propagation losses are below 1dB/cm. Bias was applied on both sides of the epitaxially grown films to evaluate the refractive index dependence on reverse voltage and a variation of 2.10-3 was found for 30V. These results support the possibility of using structures of this type for the fabrication of modulator devices such as Mach-Zehnder interferometers.

  10. 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

  11. 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.

  12. 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.

  13. Maximizing cubic phase gallium nitride surface coverage on nano-patterned silicon (100)

    NASA Astrophysics Data System (ADS)

    Liu, R.; Bayram, C.

    2016-07-01

    Here we investigate the hexagonal-to-cubic phase transition in metalorganic-chemical-vapor-deposition-grown gallium nitride enabled via silicon (100) nano-patterning. Electron backscatter diffraction and depth-resolved cathodoluminescence experiments show complete cubic phase GaN surface coverage when GaN deposition thickness ( hc ), etch depth ( td ), and opening width ( p ) obey hc≈1.06 p -0.75 td ; in line with a geometrical model based on crystallography. Cubic GaN uniformity is studied via electron backscatter diffraction and cathodoluminescence measurements. Atomic force microscopy reveals a smooth cubic GaN surface. Phase-transition cubic GaN shows promising optical and structural quality for integrated photonic devices.

  14. A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications

    NASA Astrophysics Data System (ADS)

    Rajbhandari, Sujan; McKendry, Jonathan J. D.; Herrnsdorf, Johannes; Chun, Hyunchae; Faulkner, Grahame; Haas, Harald; Watson, Ian M.; O'Brien, Dominic; Dawson, Martin D.

    2017-02-01

    The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost polymer optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb s-1 are also outlined.

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

    NASA Astrophysics Data System (ADS)

    He, Shumin; Wang, Zhenhai; Liu, Qifa

    2016-09-01

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

  16. 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.

  17. 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.

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

    PubMed

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

    2015-10-14

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

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Khan, Muhammad Raziuddin A.

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    PubMed

    Gillen, Roland; Robertson, John

    2013-10-09

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

  3. Studies on the effect of ammonia flow rate induced defects in gallium nitride grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Suresh, S.; Lourdudoss, S.; Landgren, G.; Baskar, K.

    2010-10-01

    Gallium nitride (GaN) epitaxial layers were grown with different V/III ratios by varying the ammonia (NH 3) flow rate, keeping the flow rate of the other precursor, trimethylgallium (TMG), constant, in an MOCVD system. X-ray rocking curve widths of a (1 0 2) reflection increase with an increase in V/III ratio while the (0 0 2) rocking curve widths decrease. The dislocation density was found to increase with an increase in ammonia flow rate, as determined by hot-wet chemical etching and atomic force microscopy. 77 K photoluminescence studies show near band emission at 3.49 eV and yellow luminescence peaking at 2.2 eV. The yellow luminescence (YL) intensity decreases with an increase in V/III ratio. Positron annihilation spectroscopy studies show that the concentration of Ga-like vacancies increases with an increase in ammonia flow rate. This study confirms that the yellow luminescence in the GaN arises due to deep levels formed by gallium vacancies decorated with oxygen atoms.

  4. Magnetic properties of gadolinium and carbon co-doped gallium nitride

    NASA Astrophysics Data System (ADS)

    Syed Kaleemullah, N.; Ramsubramanian, S.; Mohankumar, R.; Munawar Basha, S.; Rajagopalan, M.; Kumar, J.

    2017-01-01

    Investigations have been carried out to study the ferromagnetic properties of Gadolinium (Gd) Carbon (C) co-doped wurtzite Gallium Nitride (GaN) using full-potential linear augmented plane wave (FP-LAPW) method within the density functional theory. The system shows half-metallic nature when single Gd is substituted in Ga36N36 supercell. The presence of carbon in GaN supercell is found to generate weak magnetic moment (Ms) in the neighbouring atoms. When Carbon is codoped in the Gd-GaN, it increased the total magnetic moment of the system (Mtot). The cause of ferromagnetism in the Gd and C co-doped GaN has been explained by Zener's p-d exchange mechanism. The role of defects in the magnetic property of this system is also investigated. The results indicate the gallium vacancy influences the magnetic moment of the Gd and C codoped GaN more than the nitrogen vacancy. The presence of holes is effective than electrons in achieving the ferromagnetism in the considered system.

  5. Microwave power aluminum gallium nitride/gallium nitride heterojunction field effect transistor for X-band applications

    NASA Astrophysics Data System (ADS)

    Cai, Shujun

    GaN material has been considered in recent years an attractive candidate for microwave power applications owing to its strong piezo-electric (PZ) and spontaneous polarization (SP) effects, high saturation velocity and wideband gap. AlGaN/GaN Heterojunction Field Effect Transistor (HFET) is chosen to overcome the disadvantages of low mobility in wide bandgap materials so that both high power and high speed are feasible. Analysis and simulation are performed to understand the enhancement of sheet charge density due to the PZ and SP effects in the AlGaN/GaN material system. Major factors affecting the sheet channel charge density are discussed. To verify the PZ and SP charge effects, testing structures of AlGaN/GaN with various Al contents for Hall measurement are then fabricated. Results support our analysis. GaN-based HFET devices with 25% Al content are fabricated after solving process issues. An external transconductance of 200 mS/mm, a saturation current density of 800 mA/mm and a breakdown voltage of 40 V to 50 V are achieved. A CW power amplifier with the output of 8 W at 9 GHz is achieved from a single 5 mm AlGaN/GaN HFET device. A novel process, referred to as Gamma gate process, is developed to realize high breakdown performance as well as small gate length. As a result, a 0.3 mum gate length device with an integrated field plate is fabricated using 1 mum conventional optical lithograph techniques. Improvements of breakdown voltage and RF performance by a factor of over 2 have been achieved. High temperature storage and measurement show that the AlGaN/GaN HFET devices can survive at an environment temperature as high as 592°C. The devices also survive after exposing to proton irradiation at a dosage of 1 x 1014 cm-2, indicating its intrinsic resistance to radiation.

  6. 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.

  7. Application of gallium nitride nanostructures and nitrogen doped carbon spheres as supports for the hydrogenation of cinnamaldehyde.

    PubMed

    Kente, Thobeka; Dube, Sibongile M A; Coville, Neil J; Mhlanga, Sabelo D

    2013-07-01

    This paper reports on the synthesis and use of nanostructures of gallium nitride (GaN NSs) and nitrogen doped carbon spheres (NCSs) as support materials for the hydrogenation of cinnamaldehyde. This study provides the first investigation of GaN as a catalyst support in hydrogenation reactions. The GaN NSs were synthesized via chemical vapour deposition (CVD) in a double stage furnace (750 degrees C) while NCSs were made by CVD in a single stage furnace (950 degrees C) respectively. TEM analysis revealed that the GaN NSs were rod-like with average diameters of 200 nm, while the NCSs were solid with smoother surfaces, and with diameters of 450 nm. Pd nanoparticles (1 and 3% loadings) were uniformly dispersed on acid functionalized GaN NSs and NCS. The Pd nanoparticles had average diameters that were influenced by the type of support material used. The GaN NSs and NCSs were tested for the selective hydrogenation of cinnamaldehyde in isopropanol at 40 and 60 degrees C under atmospheric pressure. A comparative study of the activity of the nanostructured materials revealed that the order of catalyst activity was 3% Pd/GaN > 3% Pd/NCSs > 1% Pd/NCSs > 1% Pd/GaN. However, 100% selectivity to hydrocinnamaldehyde (HCALD) was obtained with 1% Pd/GaN at reasonable conversion rates.

  8. Efficient continuous-wave nonlinear frequency conversion in high-Q gallium nitride photonic crystal cavities on silicon

    NASA Astrophysics Data System (ADS)

    Mohamed, Mohamed Sabry; Simbula, Angelica; Carlin, Jean-François; Minkov, Momchil; Gerace, Dario; Savona, Vincenzo; Grandjean, Nicolas; Galli, Matteo; Houdré, Romuald

    2017-03-01

    We report on nonlinear frequency conversion from the telecom range via second harmonic generation (SHG) and third harmonic generation (THG) in suspended gallium nitride slab photonic crystal (PhC) cavities on silicon, under continuous-wave resonant excitation. Optimized two-dimensional PhC cavities with augmented far-field coupling have been characterized with quality factors as high as 4.4 × 104, approaching the computed theoretical values. The strong enhancement in light confinement has enabled efficient SHG, achieving a normalized conversion efficiency of 2.4 × 10-3 W-1, as well as simultaneous THG. SHG emission power of up to 0.74 nW has been detected without saturation. The results herein validate the suitability of gallium nitride for integrated nonlinear optical processing.

  9. Gallium scan

    MedlinePlus

    ... material called gallium and is a type of nuclear medicine exam. A related test is gallium scan ... Brown ML, Forstrom LA, et al. Society of nuclear medicine procedure guideline for gallium scintigraphy in inflammation. ...

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

    PubMed

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

    2014-03-04

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

  11. On the solubility of gallium nitride in supercritical ammonia-sodium solutions

    NASA Astrophysics Data System (ADS)

    Griffiths, Steven; Pimputkar, Siddha; Speck, James S.; Nakamura, Shuji

    2016-12-01

    Due to the disparity between observed gallium nitride (GaN) growth under conditions for which literature reports normal solubility, GaN solubility in supercritical NH3-Na containing solutions was re-evaluated. Isothermal gravimetric experiments on polycrystalline GaN were performed in the temperature range (T =415-650 °C) for which retrograde growth of GaN routinely occurs (P ≈ 200 MPa, molar NH3:Na fill ratio =20:1). Two previously-unreported error contributions to the gravimetric determination of GaN solubility were identified: Ga-alloying of exposed Ni-containing components, and the presence of a dense, Ga-absorbing Na-rich, second phase under these conditions. Due to the inability to measure Ga-alloying of the exposed autoclave wall for each experiment, considerable scatter was introduced in the refined GaN solubility curve. No clear dependence of GaN solubility on temperature was resolvable, while most solubility values were determined to be within a band of 0.03-0.10 mol% GaN, normalized by fill NH3.

  12. 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).

  13. Nanoporous Gallium Nitride Through Anisotropic Metal-Assisted Electroless Photochemical Wet Etching Technique

    NASA Astrophysics Data System (ADS)

    Perumal, R.; Hassan, Z.

    2016-12-01

    Nanoporous gallium nitride (GaN) has many potential applications in light-emitting diodes (LEDs), photovoltaics, templates and chemical sensors. This article reports the porosification of GaN through UV enhanced metal-assisted electroless photochemical wet etching technique using three different acid-based etchants and platinum served as catalyst for porosification. The etching process was conducted at room temperature for a duration of 90min. The morphological, structural, spectral and optical features of the developed porous GaN were studied with appropriate characterization techniques and the obtained results were presented. Field emission scanning electron micrographs exhibited the porosity nature along with excellent porous network of the etched samples. Structural studies confirmed the mono crystalline quality of the porous nanostructures. Raman spectral analyzes inferred the presenting phonon modes such as E2 (TO) and A1 (LO) in fabricated nanoporous structures. The resulted porous nanostructures hold the substantially enhanced photoluminescence intensity compared with the pristine GaN epitaxial film that is interesting and desirable for several advances in the applications of Nano-optoelectronic devices.

  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. 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.

  16. Two single-layer porous gallium nitride nanosheets: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zhang, Hui; Meng, Fan-Sun; Wu, Yan-Bin

    2017-01-01

    The gallium nitride (GaN) is a novel wide-gap semiconductor for photoelectric devices. In this paper, two 2D single-layer GaN crystal structures, called H-GaN and T-GaN, are discovered by the density functional theory calculations. The phase stability is confirmed by phonon dispersions. The sole-atom-thick crystals of H-GaN and T-GaN, has possess enlarged specific surface area than the graphene-like allotrope (g-GaN) due to the porous structures. In addition, they have indirect band gaps of 1.85-1.89 eV and the electronic structures can be further modulated by applied strains. For example, T-GaN transforms from an indirect semiconductor to a direct one due to compressed strains. Both the combination of high specific surface area and moderate band gaps make these 2D crystals potential high-efficiency photocatalysts. Our results will also stimulate the investigations on 2D GaN nano crystals with rich electronic structures for wide applications.

  17. 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).

  18. Optical waveguide loss minimized into gallium nitride based structures grown by metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Stolz, A.; Cho, E.; Dogheche, E.; Androussi, Y.; Troadec, D.; Pavlidis, D.; Decoster, D.

    2011-04-01

    The waveguide properties are reported for wide bandgap gallium nitride (GaN) structures grown by metal organic vapor phase epitaxy on sapphire using a AlN/GaN short period-superlattice (SPS) buffer layer system. A detailed optical characterization of GaN structures has been performed using the prism coupling technique in order to evaluate its properties and, in particular, the refractive index dispersion and the propagation loss. In order to identify the structural defects in the samples, we performed transmission electron microscopy analysis. The results suggest that AlN/GaN SPS plays a role in acting as a barrier to the propagation of threading dislocations in the active GaN epilayer; above this defective region, the dislocations density is remarkably reduced. The waveguide losses were reduced to a value around 0.65dB/cm at 1.55 μm, corresponding to the best value reported so far for a GaN-based waveguide.

  19. Observation of surface plasmon polariton pumping of optical eigenmodes of gold-decorated gallium nitride nanowires.

    PubMed

    Sundararajan, Jency Pricilla; Bakharev, Pavel; Niraula, Ishwar; Kengne, Blaise Alexis Fouetio; MacPherson, Quinn; Sargent, Meredith; Hare, Brian; McIlroy, David N

    2012-10-10

    The photocurrent of individual gallium nitride (GaN) nanowires decorated with Au nanoparticles as function of the wavelength of light (405 nm (blue), 532 nm (green), and 632.8 nm (red)) and nanowire diameter (80 to 400 nm) is reported. The photocurrent scales with photon energy but oscillates with nanowire diameter. The oscillations are described in terms of the scattering of surface plasmon polaritons into allowed transverse magnetic electromagnetic modes of the nanowire that have maximum intensities in the undepleted region of the nanowire. These oscillations do not occur below a nanowire diameter of ~200 nm due to the depletion layer formed at the Au-GaN interface, which completely depletes the nanowire, that is, there is an insufficient density of carriers that can be excited into the conduction band. On the basis of estimations of the depletion depth and solutions of the Helmholtz equation, the maxima in the photocurrent for d > 200 nm are assigned to the two lowest azimuthally symmetric transverse magnetic eigenmodes: (m = 0, n = 1) and (m = 0, n = 2), which have maximum electric field intensities within the undepleted region of the GaN nanowire. The outcome of this work could have far reaching implications on the development of nanophotonics.

  20. Congruent melting of gallium nitride at 6 GPa and its application to single-crystal growth.

    PubMed

    Utsumi, Wataru; Saitoh, Hiroyuki; Kaneko, Hiroshi; Watanuki, Tetsu; Aoki, Katsutoshi; Shimomura, Osamu

    2003-11-01

    The synthesis of large single crystals of GaN (gallium nitride) is a matter of great importance in optoelectronic devices for blue-light-emitting diodes and lasers. Although high-quality bulk single crystals of GaN suitable for substrates are desired, the standard method of cooling its stoichiometric melt has been unsuccessful for GaN because it decomposes into Ga and N(2) at high temperatures before its melting point. Here we report that applying high pressure completely prevents the decomposition and allows the stoichiometric melting of GaN. At pressures above 6.0 GPa, congruent melting of GaN occurred at about 2,220 degrees C, and decreasing the temperature allowed the GaN melt to crystallize to the original structure, which was confirmed by in situ X-ray diffraction. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions.

  1. Photochemical functionalization of gallium nitride thin films with molecular and biomolecular layers.

    PubMed

    Kim, Heesuk; Colavita, Paula E; Metz, Kevin M; Nichols, Beth M; Sun, Bin; Uhlrich, John; Wang, Xiaoyu; Kuech, Thomas F; Hamers, Robert J

    2006-09-12

    We demonstrate that photochemical functionalization can be used to functionalize and photopattern the surface of gallium nitride crystalline thin films with well-defined molecular and biomolecular layers. GaN(0001) surfaces exposed to a hydrogen plasma will react with organic molecules bearing an alkene (C=C) group when illuminated with 254 nm light. Using a bifunctional molecule with an alkene group at one end and a protected amine group at the other, this process can be used to link the alkene group to the surface, leaving the protected amine exposed. Using a simple contact mask, we demonstrate the ability to directly pattern the spatial distribution of these protected amine groups on the surface with a lateral resolution of <12 mum. After deprotection of the amines, single-stranded DNA oligonucleotides were linked to the surface using a bifunctional cross-linker. Measurements using fluorescently labeled complementary and noncomplementary sequences show that the DNA-modified GaN surfaces exhibit excellent selectivity, while repeated cycles of hybridization and denaturation in urea show good stability. These results demonstrate that photochemical functionalization can be used as an attractive starting point for interfacing molecular and biomolecular systems with GaN and other compound semiconductors.

  2. 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.

  3. Improved performance of dye-sensitized solar cells using gallium nitride-titanium dioxide composite photoelectrodes.

    PubMed

    Huang, Yin-Rou; Huang, Tzu-Wei; Wang, Tzu-Hui; Tsai, Yu-Chen

    2014-08-15

    Dye-sensitized solar cells (DSSCs) are fabricated with gallium nitride-titanium dioxide (GaN-TiO2) composite photoelectrodes to enhance the power conversion efficiency. The value of power conversion efficiency increases with the incorporation of GaN in TiO2 matrix and reaches a maximum at 0.05 wt% GaN. Internal resistance in the DSSC is characterized by electrochemical impedance spectroscopy (EIS). From the EIS of electrolyte/dye/GaN-TiO2 interface resistances under illumination and in the dark, a decrease in the charge transfer resistance and an increase in the charge recombination resistance of the DSSCs are obtained after the inclusion of GaN (0.01-0.05 wt%) in the TiO2 matrix. The power conversion efficiency of the DSSC based on the GaN (0.05 wt%)-TiO2 composite photoelectrode is enhanced by ∼61% in comparison with a pristine TiO2 photoelectrode.

  4. 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.

  5. Wavelength-multiplexed pumping with 478- and 520-nm indium gallium nitride laser diodes for Ti:sapphire laser.

    PubMed

    Sawada, Ryota; Tanaka, Hiroki; Sugiyama, Naoto; Kannari, Fumihiko

    2017-02-20

    We experimentally reveal the pump-induced loss in a Ti:sapphire laser crystal with 451-nm indium gallium nitride (InGaN) laser diode pumping and show that 478-nm pumping can reduce such loss. The influence of the pump-induced loss at 451-nm pumping is significant even for a crystal that exhibits higher effective figure-of-merit and excellent laser performance at 520-nm pumping. We demonstrate the power scaling of a Ti:sapphire laser by combining 478- and 520-nm InGaN laser diodes and obtain CW output power of 593 mW.

  6. 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 %).

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

    PubMed

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

    2016-03-22

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

  8. 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

  9. The effect of gallium nitride on long-term culture induced aging of neuritic function in cerebellar granule cells.

    PubMed

    Chen, Chi-Ruei; Young, Tai-Horng

    2008-04-01

    Gallium nitride (GaN) has been developed for a variety of microelectronic and optical applications due to its unique electric property and chemical stability. In the present study, n-type and p-type GaN were used as substrates to culture cerebellar granule neurons to examine the effect of GaN on cell response for a long-term culture period. It was found that GaN could rapidly induce cultured neurons to exhibit a high phosphorylated Akt level after 20h of incubation. It was assumed that the anti-apoptotic effect of Akt phosphorylation could be correlated with cell survival, neurite growth and neuronal function for up to 35 days of incubation. Morphological studies showed GaN induced larger neuronal aggregates and neurite fasciculation to exhibit a dense fiber network after 8 days of incubation. Western blot analysis and immunocytochemical characterization showed that GaN still exhibited the expression of neurite growth and function, such as high levels of GAP-43, synapsin I and synaptophysin even after 35 days of incubation. In addition, survival of cerebellar granule neurons on GaN was improved by the analysis of lactate dehydrogenase (LDH) release from damaged cells. These results indicated that neuronal connections were formed on GaN by a gradual process from Akt activation and cell aggregation to develop neurite growth, fasciculation and function. Therefore, GaN offers a good model system to identify a well-characterized pattern of neuronal behavior for a long-term culture period, consistent with the development of a neurochip requiring the integration of biological system and semiconductor material.

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

    PubMed

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

    2014-04-30

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

  11. Epitaxial growth of III-V nitrides and phase separation and ordering in indium gallium nitride alloys

    NASA Astrophysics Data System (ADS)

    Doppalapudi, Dharanipal

    The family of III-V nitrides are wide band-gap semiconductors with a broad range of opto-electronic applications in LEDs, laser diodes, UV detectors as well as high temperature/high frequency devices. Due to the lack of good quality native substrates, GaN is grown on foreign substrates that have a lattice and thermal mismatch with GaN. This results in a material with a high density of defects, which in turn adversely affects the opto-electronic properties of the epilayer. In this study, GaN films were epitaxially grown on various substrates (C-plane sapphire, A-plane sapphire, SiC and ZnO) by molecular beam epitaxy. Additionally, GaN homoepitaxy onto laterally overgrown thick GaN substrates was investigated. It was demonstrated that the polarity of the GaN film plays a major role in determining the properties of the films. The growth parameters were optimized to eliminate inversion domain boundaries, which result in domains of opposite polarity in the GaN lattice. For growth on A-plane sapphire, it was found that substrate nitridation and low temperature buffer deposition are critical in order to obtain good epitaxial growth, in spite of the relatively small mismatch between the film and substrate. A crystallographic model was developed to explain this observation. By optimizing growth parameters, GaN films with excellent structural, transport, optical and device properties were grown. The second part of this research involves growth of ternary alloys and superlattice structures, which are essential in the fabrication of many devices. It was found that the InN-GaN pseudo-binary system is not homogeneous over the entire composition range. Due to the mismatch between the tetrahedral radii of GaN and InN, InGaN alloys exhibited phase separation and long-range atomic ordering. Investigations of InxGa1-xN films grown over a wide range of compositions by XRD and TEM showed that the predominant strain relieving mechanism was phase separation in films with x > 0.2, and

  12. Computational study on the growth of gallium nitride and a possible source of oxygen impurity.

    PubMed

    Mondal, Bhaskar; Mandal, Debasish; Ghosh, Deepanwita; Das, Abhijit K

    2010-04-15

    The reaction pathways for the gallium nitride GaN growth by gas phase reaction of trimethylgallium (TMG) with ammonia is studied theoretically. Water is the most important impurity in ammonia, therefore its reaction with TMG is investigated as a possible source of oxygen impurity in GaN. Gallium oxide (GaO) formed by the reaction between TMG and H(2)O is predicted to be one of the possible source of oxygen impurity in GaN. The mechanisms and energetics of these reactions in the gas phase have been investigated by density functional B3LYP/[LANL2DZ-ECP + 6-31G(d,p)] method and ab initio MP2/[LANL2DZ-ECP + 6-31G(d,p)], CCSD(T)/[LANL2DZ-ECP + 6-31G(d,p)]//B3LYP/[LANL2DZ-ECP + 6-31G(d,p)], CCSD(T)/[LANL2DZ-ECP + 6-31G(d,p)]//MP2/[LANL2DZ-ECP + 6-31G(d,p)], and CCSD(T)/[LANL2DZ-ECP + Ahlrichs-VTZP]//MP2/[LANL2DZ-ECP + Ahlrichs-VTZP] methods. Both the reactions of TMG with NH(3) and H(2)O are modeled using pre-equilibrium charge-transfer complexes (CH(3))(3)Ga:NH(3) (C1) and (CH(3))(3)Ga:OH(2) (C2) having binding energies of 18.8 and 12.4 kcal/mol, respectively. The first step of the methane elimination reaction from the complexes proceeds through the saddle points TS1 and TS1a having activation barriers 37.0 and 22.6 kcal/mol for C1 and C2, respectively. The first CH(4) elimination step is exothermic for both the cases, but the exothermicity is 15.0 kcal/mol greater for CH(4) elimination from C2. The next step of methane elimination from the stable reaction intermediates (CH(3))(2)GaNH(2) and (CH(3))(3)GaOH has a very high activation barrier of 76.0 and 67.8 kcal/mol via saddle points TS2 and TS2a, respectively. The calculated reaction rates at 298.15 K for both the reactions are low but are comparable to each other. The total rate constant k(tot) for GaN formation is 2.07 x 10(-60) cm(3) molecule(-1) s(-1), and that for GaO formation is 6.85 x 10(-62) cm(3) molecule(-1) s(-1).

  13. 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

  14. 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

  15. Design of gas inlets for the growth of gallium nitride by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Theodoropoulos, C.; Mountziaris, T. J.; Moffat, H. K.; Han, J.

    2000-07-01

    The problem of gas inlet design for metalorganic vapor phase epitaxy (MOVPE) of group III nitrides from metal alkyls and ammonia is addressed. The focus is on GaN growth from trimethyl-gallium and ammonia. In traditional reactors with well-mixed inlet streams, parasitic gas-phase reactions between the two precursors may lead to the formation of stable adducts that can condense on cool inlet walls, thus reducing the film growth efficiency. Such reactions may also lead to the formation of particulates through gas-phase condensation reactions (e.g. during AlN growth). A fundamentally-based model was developed to describe the MOVPE of GaN and was used to study the effect of inlet design and reactor operating conditions on film thickness uniformity in vertical stagnation-flow and rotating-disk reactors. The model includes a description of gas-phase kinetics and a simple gas-surface reaction mechanism. The kinetic model was coupled to a two-dimensional transport model describing flow, heat and mass transfer in a vertical MOVPE reactor. Predictions of growth rate compare well to experimental observations from a vertical rotating-disk reactor, without any adjustable parameters. The model was also used to study the distribution of gaseous species in the reactor and their role in film growth. Finite element simulations using a massively parallel computer code (MPSalsa) indicate that the species responsible for film growth are Ga-alkyls and not their adducts with ammonia. Sensitivity analysis was also performed to assess the relative importance of each reaction in determining the growth rate. The model was subsequently employed in the design of axisymmetric, multi-aperture gas inlets feeding precursors into the reactor in an alternating (not well-mixed) fashion. Simulations were performed to study the effect of key design parameters, such as inlet velocities, susceptor rotating speed, inlet to susceptor distance as well as the number and distribution of inlets, on GaN film

  16. Acidic ammonothermal growth of gallium nitride in a liner-free molybdenum alloy autoclave

    NASA Astrophysics Data System (ADS)

    Malkowski, Thomas F.; Pimputkar, Siddha; Speck, James S.; DenBaars, Steven P.; Nakamura, Shuji

    2016-12-01

    This paper discusses promising materials for use as internal, non-load bearing components as well as molybdenum-based alloys for autoclave structural components for an ammonothermal autoclave. An autoclave was constructed from the commercial titanium-zirconium-molybdenum (TZM) alloy and was found to be chemically inert and mechanically stable under acidic ammonothermal conditions. Preliminary seeded growth of GaN was demonstrated with negligible incorporation of transition metals (including molybdenum) into the grown material (<1017 cm-3). Molybdenum and TZM were exposed to a basic ammonothermal environment, leading to slight degradation through formation of molybdenum nitride powders on their surface at elevated temperatures (T>560 °C). The possibility of a 'universal', inexpensive, liner-free ammonothermal autoclave capable of exposure to basic and acidic chemistry is demonstrated.

  17. Growth and characterization of gallium nitride nanowire LEDs for application as on-chip optical interconnects

    NASA Astrophysics Data System (ADS)

    Brubaker, Matt

    Gallium nitride (GaN) nanowires have potential as nanoscale optoelectronic building blocks that can be functionally integrated with silicon MEMS and IC devices. This dissertation presents an overview of the synthesis, characterization, and application of GaN nanowire light-emitting-diodes (LEDs) grown by plasma-assisted molecular beam epitaxy (MBE). Specifically, this research demonstrates discrete axial p-n junction nanowires that produce ultra-violet (UV) electroluminescence at ˜40 nW optical power. It further demonstrates that a two-nanowire optical interconnect device can be fabricated from axial p-n junction nanowires with light-emitting and photoconductive capabilities. The nanowire structures obtained from MBE growth were found to depend sensitively on the morphology and crystallographic polarity of the underlying Aluminum Nitride (AlN) nucleation layer. These observations were enabled by piezoresponse force microscopy, which was developed and validated against polarity sensitive etching using uniform and mixed polarity AlN layers. The polarity and overall morphology of the AlN layers could be controlled by the V/III flux ratio and substrate temperature during MBE growth. GaN nanowires were observed to propagate the structural characteristics and crystallographic polarity of the underlying AlN layer, and in some cases a differential growth rate with respect to polarity was observed. Band-edge electroluminescence was obtained in axial p-n junction nanowires that incorporated a thin AlGaN electron blocking layer in the p-region of the device. Electroluminescence was below detection limits for p-n junction nanowires with no blocking layer, despite diode-like I-V characteristics and optically measured internal quantum efficiencies (IQEs) of ˜1 %. I-V measurements of the p-regions in p-n junction nanowires, as well as nanowires doped with Mg only, indicate low p-type conductivity and asymmetric Schottky-like p-contacts. These observations, in conjunction with

  18. Orbitally driven low thermal conductivity of monolayer gallium nitride (GaN) with planar honeycomb structure: a comparative study.

    PubMed

    Qin, Zhenzhen; Qin, Guangzhao; Zuo, Xu; Xiong, Zhihua; Hu, Ming

    2017-03-23

    Two-dimensional (2D) materials with graphene as a representative have been intensively studied for a long time. Recently, monolayer gallium nitride (ML GaN) with honeycomb structure was successfully fabricated in experiments, generating enormous research interest for its promising applications in nano- and opto-electronics. Considering all these applications are inevitably involved with thermal transport, systematic investigation of the phonon transport properties of 2D GaN is in demand. In this paper, by solving the Boltzmann transport equation (BTE) based on first-principles calculations, we performed a comprehensive study of the phonon transport properties of ML GaN, with detailed comparison to bulk GaN, 2D graphene, silicene and ML BN with similar honeycomb structure. Considering the similar planar structure of ML GaN to graphene, it is quite intriguing to find that the thermal conductivity (κ) of ML GaN (14.93 W mK(-1)) is more than two orders of magnitude lower than that of graphene and is even lower than that of silicene with a buckled structure. Systematic analysis is performed based on the study of the contribution from phonon branches, comparison among the mode level phonon group velocity and lifetime, the detailed process and channels of phonon-phonon scattering, and phonon anharmonicity with potential energy well. We found that, different from graphene and ML BN, the phonon-phonon scattering selection rule in 2D GaN is slightly broken by the lowered symmetry due to the large difference in the atomic radius and mass between Ga and N atoms. Further deep insight is gained from the electronic structure. Resulting from the special sp orbital hybridization mediated by the Ga-d orbital in ML GaN, the strongly polarized Ga-N bond, localized charge density, and its inhomogeneous distribution induce large phonon anharmonicity and lead to the intrinsic low κ of ML GaN. The orbitally driven low κ of ML GaN unraveled in this work would make 2D GaN prospective for

  19. The sensitivity of the electron transport within bulk zinc-blende gallium nitride to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley

    NASA Astrophysics Data System (ADS)

    Siddiqua, Poppy; O'Leary, Stephen K.

    2016-09-01

    Within the framework of a semi-classical three-valley Monte Carlo simulation approach, we analyze the steady-state and transient electron transport that occurs within bulk zinc-blende gallium nitride. In particular, we examine how the steady-state and transient electron transport that occurs within this material changes in response to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley. These results are then contrasted with those corresponding to a number of other compound semiconductors of interest.

  20. Development of wide-band gap indium gallium nitride solar cells for high-efficiency photovoltaics

    NASA Astrophysics Data System (ADS)

    Jani, Omkar K.

    Main objective of the present work is to develop wide-band gap InGaN solar cells in the 2.4--2.9 eV range that can be an integral component of photovoltaic devices to achieve efficiencies greater than 50%. The III-nitride semiconductor material system, which consists of InN, GaN, AlN and their alloys, offers a substantial potential in developing ultra-high efficiency photovoltaics mainly due to its wide range of direct-band gap, and other electronic, optical and mechanical properties. However, this novel InGaN material system poses challenges from theoretical, as well as technological standpoints, which are further extended into the performance of InGaN devices. In the present work, these challenges are identified and overcome individually to build basic design blocks, and later, optimized comprehensively to develop high-performance InGaN solar cells. One of the major challenges from the theoretical aspect arises due to unavailability of a suitable modeling program for InGaN solar cells. As spontaneous and piezoelectric polarization can substantially influence transport of carriers in the III-nitrides, these phenomena are studied and incorporated at a source-code level in the PC1D simulation program to accurately model InGaN solar cells. On the technological front, InGaN with indium compositions up to 30% (2.5 eV band gap) are developed for photovoltaic applications by controlling defects and phase separation using metal-organic chemical vapor deposition. InGaN with band gap of 2.5 eV is also successfully doped to achieve acceptor carrier concentration of 1018 cm-3. A robust fabrication scheme for III-nitride solar cells is established to increase reliability and yield; various schemes including interdigitated grid contact and current spreading contacts are developed to yield low-resistance Ohmic contacts for InGaN solar cells. Preliminary solar cells are developed using a standard design to optimize the InGaN material, where the band gap of InGaN is progressively

  1. Novel gallium nitride based microwave noise and power heterostructure field effect transistors

    NASA Astrophysics Data System (ADS)

    Chumbes, Eduardo Martin

    With the pioneering efforts of Isamu Akasaki of Meiji University and Shuji Nakamura of Nichia Chemical Industries in the late 1980's and early 1990's, the first long-lived candela-class blue and ultraviolet light emitting devices have finally come to fruition. Their success in conquering this Holy Grail in opto-electronics is due to their development of a new technology based remarkably on a class of semiconductor materials that has been practically ignored and overlooked by almost everyone for the past twenty years---the nitrides of Al, Ga and In and their alloys. The breakthroughs made from this new technology in the last decade of the 20th century has revolutionized and revitalized worldwide research and development efforts to the point where it is feasible for other important technologies such as high-density information storage, high-resolution full-color displays and efficient white light lamps and UV sensors to come much closer to realization. Equally important is the potential that this new technology can bring toward the development of efficient ultra-high power and high-temperature electronics that will revolutionize the aerospace and high-speed communication industries. Specifically, the large bandgap and strong polar properties of the group III-nitrides has at present allowed for the realization of simple doped and remarkably undoped AlGaN/GaN transistor structures on sapphire and SiC substrates with two-dimensional electron gas sheet densities significantly greater than that of conventional transistor structures based on GaAs and InP. This dissertation will look specifically at extending undoped AlGaN/GaN heterostructure field-effect transistors or HFETs towards more advanced system applications involving the integration of these devices onto a more advanced Si technology and looking at the feasibility of this integration. It will also address important issues similar devices on semi-insulating SiC substrates have in robust microwave low noise and

  2. 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

  3. Nitride Fuel Modeling Recommendation for Nitride Fuel Material Property Measurement Priority

    SciTech Connect

    William Carmack; Richard Moore

    2005-09-01

    The purpose of this effort was to provide the basis for a model that effectively predicts nitride fuel behavior. Material property models developed for the uranium nitride fuel system have been used to approximate the general behavior of nitride fuels with specific property models for the transuranic nitride fuels utilized as they become available. The AFCI fuel development program now has the means for predicting the behavior of the transuranic nitride fuel compositions. The key data and models needed for input into this model include: Thermal conductivity with burnup Fuel expansion coefficient Fuel swelling with burnup Fission gas release with burnup. Although the fuel performance model is a fully functional FEA analysis tool, it is limited by the input data and models.

  4. 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.

  5. Epitaxial Overgrowth of Gallium Nitride Nano-Rods on Silicon (111) Substrates by RF-Plasma-Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Ku, Jui-Tai; Yang, Tsung-Hsi; Chang, Jet-Rung; Wong, Yuen-Yee; Chou, Wu-Ching; Chang, Chun-Yen; Chen, Chiang-Yao

    2010-04-01

    Strain-free gallium nitride (GaN) overgrowth on GaN nano-rods is realized by RF-plasma assisted molecular beam epitaxy (RF-MBE) on silicon (Si) substrate. The strain-free condition was identified by the strong free A exciton (FXA) photoluminescence (PL) peak at 3.478 eV and the E2 high phonon Raman shift of 567 cm-1. It is clearly demonstrated that the critical diameter of GaN nano-rods is around 80 nm for the overgrowth of strain-free GaN. The blue-shift of PL peak energy and phonon Raman energy with decreasing the diameter of nano-rod result from the strain relaxation of overgrowth GaN.

  6. Single-Crystalline, Nanoporous Gallium Nitride Films With Fine Tuning of Pore Size for Stem Cell Engineering.

    PubMed

    Han, Lin; Zhou, Jing; Sun, Yubing; Zhang, Yu; Han, Jung; Fu, Jianping; Fan, Rong

    2014-11-01

    Single-crystalline nanoporous gallium nitride (GaN) thin films were fabricated with the pore size readily tunable in 20-100 nm. Uniform adhesion and spreading of human mesenchymal stem cells (hMSCs) seeded on these thin films peak on the surface with pore size of 30 nm. Substantial cell elongation emerges as pore size increases to ∼80 nm. The osteogenic differentiation of hMSCs occurs preferentially on the films with 30 nm sized nanopores, which is correlated with the optimum condition for cell spreading, which suggests that adhesion, spreading, and stem cell differentiation are interlinked and might be coregulated by nanotopography.

  7. Gallium nitride nanorod arrays as low-refractive-index transparent media in the entire visible spectral region.

    PubMed

    Chen, Hung-Ying; Lin, Hon-Way; Wu, Chen-Ying; Chen, Wei-Chun; Chen, Jyh-Shin; Gwo, Shangjr

    2008-05-26

    Vertically aligned gallium nitride (GaN) nanorod arrays grown by the catalyst-free, self-organized method based on plasma-assisted molecular-beam epitaxy are shown to behave as subwavelength optical media with low effective refractive indices. In the reflection spectra measured in the entire visible spectral region, strong reflectivity modulations are observed for all nanorod arrays, which are attributed to the effects of Fabry-Pérot microcavities formed within the nanorod arrays by the optically flat air/nanorods and nanorods/substrate interfaces. By analyzing the reflectivity interference fringes, we can quantitatively determine the refractive indices of GaN nanorod arrays as functions of light wavelength. We also propose a model for understanding the optical properties of GaN nanorod arrays in the transparent region. Using this model, good numerical fitting can be achieved for the reflectivity spectra.

  8. Visible and near infrared emitting thin film electroluminescent gallium nitride doped with rare earths

    NASA Astrophysics Data System (ADS)

    Kim, Joo Han

    Visible and near-infrared (NIR) light-emitting thin-film electroluminescent gallium nitride (GaN) doped with rare earth (RE) elements was studied. The rare-earth-doped GaN thin films were prepared by radio frequency (RF) planar magnetron co-sputtering of separate targets consisting of a GaN compound target and a metallic rare earth target in a pure nitrogen atmosphere. The luminescence of rare-earth-doped GaN was shown to be a strong function of its structure and properties, and growth parameters affected the structure and properties of the GaN host films. A phase transition from the thermodynamically stable wurtzite to the metastable zinc-blende structure at room temperature in GaN host films was observed upon increasing the impact energy of the bombarding species, thereby increasing the compressive stress in the GaN film. The switch from wurtzite to zinc-blende GaN occurred at a compressive internal stress of ˜1 GPa. The internal compressive stress above this threshold value apparently stabilizes the zinc-blende GaN phase at room temperature. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) showed that the impact by hyperthermal species yielded a highly condensed fibrous GaN microstructure with a smooth surface morphology due to annihilation of porosity by knock-on and bombardment-induced adatom mobility. X-ray diffraction and texture analyses showed that the GaN films deposited at a low pressure had a predominant cubic phase with a preferred crystallographic orientation of the [111] direction perpendicular to the surface of the film. X-ray rocking curve data revealed that cubic GaN films grown with a lower growth rate exhibited a more highly [111]-textured structure. Alternating-current thin-film electroluminescent (ACTFEL) devices were fabricated based on GaN doped with rare earth (RE) elements. Visible electroluminescent light emission peaks at 475 (blue), 530 (green), and 614 nm (red) were demonstrated at room temperature

  9. Modulated optical properties of nonpolar gallium nitride via surface in-situ functionalization with cysteamine assisted phosphoric acid

    NASA Astrophysics Data System (ADS)

    Wilkins, Stewart J.; Paskova, Tania; Ivanisevic, Albena

    2014-03-01

    In-situ functionalization of nonpolar a-plane gallium nitride (GaN) surface was achieved by adding cysteamine to phosphoric acid, aiming to modulate its optical properties. The emission properties and oxide formation were explored through surface characterization with atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and water contact angle. Nonpolar a-plane bulk GaN sample sliced from a GaN boule and nonpolar a-plane GaN thin layer heteroepitaxially grown on r-plane sapphire were used to elucidate the effects of in-situ functionalization of identical surface orientation of GaN crystals with different defect ensembles. The addition of cysteamine to the phosphoric acid solution was found to result in: (i) increased surface roughness, (ii) no change to hydrophobicity, (iii) decreased oxygen content at high solution temperatures and increased gallium and nitrogen content versus phosphoric acid solutions at similar temperatures without cysteamine. The in-situ functionalization resulted in enhanced PL intensity from the nonpolar bulk GaN, while the PL intensity from the nonpolar heteroepitaxially grown GaN layer on sapphire was significantly reduced. The opposite PL modulation was explained by the effects of different defects present in the two samples on the nonradiative recombination.

  10. The Growth of Gallium Nitride Films via the Innovative Technique of Atomic Layer Epitaxy

    DTIC Science & Technology

    1989-06-01

    6 3.2 Aluminum Nitride and AIN/GaN Layered Structures ............ 8 3.3 Boron Nitride and BGaN Graded...of tearing in lower left region, indirectly indicating the presence of multiple layers of BGaN ............................... 14 12. Auger electron...electron spectroscopy sputtered depth profile of a BN/ BGaN /GaN/P-SiC film. Note peak in nitrogen trace as interface of BN is passed

  11. 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.

  12. Characterization of Defects on MOCVD Grown Gallium Nitride Using Transient Analysis Techniques

    NASA Astrophysics Data System (ADS)

    Kasani, Sujan Phani Kumar

    Since the invention of the first visible spectrum (red) LED by Holonyak in 1962, there has been a need for more efficient, more reliable and less expensive LEDs. The III-nitrides revolutionized semiconductor technology with their applications in the blue LED's. However the internal quantum efficiency of LED's are limited by the deep level traps in GaN substrate. Traps are defects in the crystal lattice, which depends on growth parameters. These traps act as non-radiative centers where non-radiative recombination occurs without conversion of available energy into light. Characterization of these traps in a material is necessary for better understanding of the material growth quality and resulting device performance. In this work Capacitance-Voltage (C-V) and Deep Level Transient Spectroscopy (DLTS) are conducted which provide electronic properties of trap centers like activation energy, doping concentration and capture cross-section. In n-GaN grown by Metalorganic Chemical Vapor Deposition (MOCVD) on Sapphire two defects types are detected and are characterized by Capacitance-Voltage and Deep Level Transient Spectroscopy. Two deep levels E1 and E2 are typically observed in n-GaN with the activation energies of 0.21eV and 0.53eV at 125°K and 325°K, respectively. The deep level E1 is caused by linear line defects along dislocation cores while deep level E2 is related to point defects. The characterization techniques, experimental systems and preliminary characterization results are discussed in detail.

  13. Preparation and Characterization of Superhard Materials of Crystalline Carbon Nitride

    DTIC Science & Technology

    1999-02-01

    J 2 2 FEB 19% F49620-95-1-0384 PREPARATION AND CHARACTERIZATION OF SUPERHARD MATERIALS OF CRYSTALLINE CARBON NITRIDE Final Technical Report...and Letters 3, 1597-1602 (1996). F49620-95-1-0384 4. Y. W. Chung, "Synthesis and properties of crystalline carbon nitride composite superhard ...TYPE AND DATES COVERED Final Technical Report 1 Aus 97 to 31 Jul 98 4. TITLE AND SUBTITLE Preparation and Characterization of Superhard Materials

  14. Challenges for critical raw material recovery from WEEE - The case study of gallium.

    PubMed

    Ueberschaar, Maximilian; Otto, Sarah Julie; Rotter, Vera Susanne

    2017-02-01

    Gallium and gallium compounds are more frequently used in future oriented technologies such as photovoltaics, light diodes and semiconductor technology. In the long term the supply risk is estimated to be critical. Germany is one of the major primary gallium producer, recycler of gallium from new scrap and GaAs wafer producer. Therefore, new concepts for a resource saving handling of gallium and appropriate recycling strategies have to be designed. This study focus on options for a possible recycling of gallium from waste electric and electronic equipment. To identify first starting points, a substance flow analysis was carried out for gallium applied in integrated circuits applied on printed circuit boards and for LEDs used for background lighting in Germany in 2012. Moreover, integrated circuits (radio amplifier chips) were investigated in detail to deduce first approaches for a recycling of such components. An analysis of recycling barriers was carried out in order to investigate general opportunities and risks for the recycling of gallium from chips and LEDs. Results show, that significant gallium losses arose in primary production and in waste management. 93±11%, equivalent to 43,000±4700kg of the total gallium potential was lost over the whole primary production process until applied in electronic goods. The largest share of 14,000±2300kggallium was lost in the production process of primary raw materials. The subsequent refining process was related to additional 6900±3700kg and the chip and wafer production to 21,700±3200kg lost gallium. Results for the waste management revealed only low collection rates for related end-of-life devices. Not collected devices held 300 ± 200 kg gallium. Due to the fact, that current waste management processes do not recover gallium, further 80 ± 10 kg gallium were lost. A thermal pre-treatment of the chips, followed by a manual separation allowed an isolation of gallium rich fractions, with gallium mass fractions up to

  15. 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)

  16. Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide

    NASA Astrophysics Data System (ADS)

    Kerr, A. J.; Chagarov, E.; Gu, S.; Kaufman-Osborn, T.; Madisetti, S.; Wu, J.; Asbeck, P. M.; Oktyabrsky, S.; Kummel, A. C.

    2014-09-01

    A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al2O3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001).

  17. Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide.

    PubMed

    Kerr, A J; Chagarov, E; Gu, S; Kaufman-Osborn, T; Madisetti, S; Wu, J; Asbeck, P M; Oktyabrsky, S; Kummel, A C

    2014-09-14

    A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al2O3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001).

  18. The electron affinity of gallium nitride (GaN) and digallium nitride (GaNGa): the importance of the basis set superposition error in strongly bound systems.

    PubMed

    Tzeli, Demeter; Tsekouras, Athanassios A

    2008-04-14

    The electron affinity of GaN and Ga2N as well as the geometries and the dissociation energies of the ground states of gallium nitrides GaN, GaN(-), Ga2N, and Ga2N(-) were systematically studied by employing the coupled cluster method, RCCSD(T), in conjunction with a series of basis sets, (aug-)cc-pVxZ(-PP), x=D, T, Q, and 5 and cc-pwCVxZ(-PP), x=D, T, and Q. The calculated dissociation energy and the electron affinity of GaN are 2.12 and 1.84 eV, respectively, and those of Ga2N are 6.31 and 2.53 eV. The last value is in excellent agreement with a recent experimental value for the electron affinity of Ga2N of 2.506+/-0.008 eV. For such quality in the results to be achieved, the Ga 3d electrons had to be included in the correlation space. Moreover, when a basis set is used, which has not been developed for the number of the electrons which are correlated in a calculation, the quantities calculated need to be corrected for the basis set superposition error.

  19. Progress in periodically oriented III-nitride materials

    NASA Astrophysics Data System (ADS)

    Hite, Jennifer

    2016-12-01

    The ability to grow III-nitride structures with alternating c-plane orientation has garnered interest in using these materials for new application spaces, such as frequency conversion. An overview of recent progress in growing periodically oriented (PO) III-nitrides is discussed, including AlN, AlGaN, and GaN. Successes in fabricating thick PO GaN structures (>500 mm) for uses in frequency conversion are highlighted.

  20. Improved understanding and control of magnesium-doped gallium nitride by plasma assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Burnham, Shawn D.

    By an improved understanding of Mg-doped GaN through an exhaustive review of current limitations, increased control over the material was achieved by addressing several of these issues. To address the issues of the memory effect, low sticking coefficient and high vapor pressure of Mg, a new Mg dopant source was implemented, characterized and modeled for p-type doping of GaN. The device enhanced the sticking coefficient of Mg by energizing the outgoing Mg flux, and also allowed the first reported demonstration of an abrupt junction between two non-zero Mg concentrations and a graded Mg-doped GaN film. The significant compensation of Mg acceptors at high dopant concentrations was used advantageously to develop a new ex situ resistivity analysis technique using the energy distributions of SIMS to characterize doping of buried layers. The new technique was used to identify the barrier between conductive and resistive Mg doping for increased Mg concentration, which was then used to optimize Mg-doped GaN. Because Mg doping exhibits a dependence upon the growth regime, a new growth and regime characterization technique was developed using specific RHEED intensity responses to repeat growth conditions. During the development of this technique, a new surface kinetics growth model for III-nitrides was discovered based on DMS observations, which suggests preferential buildup of the metal bilayer before growth begins with an unfamiliar cation-anion exchange process initially upon metal shutter opening. Using the new RHEED growth and regime characterization technique, a new growth technique called metal modulated epitaxy (MME) was developed to increase repeatability, uniformity and smoothness. The MME technique was enhanced with a closed-loop control using real-time feedback from RHEED transients to control shutter transitions. This enhancement, called "smart shuttering," led to improved growth rate and further improvement of surface roughness and grain size, which were

  1. Magnetostrictive iron gallium thin films grown onto antiferromagnetic manganese nitride: Structure and magnetism

    NASA Astrophysics Data System (ADS)

    Mandru, Andrada-Oana; Corbett, Joseph P.; Richard, Andrea L.; Gallagher, James; Meng, Keng-Yuan; Ingram, David C.; Yang, Fengyuan; Smith, Arthur R.

    2016-10-01

    We report structural and magnetic properties of magnetostrictive Fe100 -xGax (x ≈ 15) alloys when deposited onto antiferromagnetic manganese nitride and non-magnetic magnesium oxide substrates. From X-ray diffraction measurements, we find that the FeGa films are single crystalline. Scanning tunneling microscopy imaging reveals that the surface morphologies are dictated by the growth temperature, composition, and substrate. The magnetic properties can be tailored by the substrate, as found by magnetic force microscopy imaging and vibrating sample magnetometry measurements. In addition to pronounced tetragonal deformations, depositing FeGa onto manganese nitride leads to the formation of stripe-like magnetic domain patterns and to the appearance of perpendicular magnetic anisotropy.

  2. Indium gallium nitride-based ultraviolet, blue, and green light-emitting diodes functionalized with shallow periodic hole patterns

    PubMed Central

    Jeong, Hyun; Salas-Montiel, Rafael; Lerondel, Gilles; Jeong, Mun Seok

    2017-01-01

    In this study, we investigated the improvement in the light output power of indium gallium nitride (InGaN)-based ultraviolet (UV), blue, and green light-emitting diodes (LEDs) by fabricating shallow periodic hole patterns (PHPs) on the LED surface through laser interference lithography and inductively coupled plasma etching. Noticeably, different enhancements were observed in the light output powers of the UV, blue, and green LEDs with negligible changes in the electrical properties in the light output power versus current and current versus voltage curves. In addition, confocal scanning electroluminescence microscopy is employed to verify the correlation between the enhancement in the light output power of the LEDs with PHPs and carrier localization of InGaN/GaN multiple quantum wells. Light propagation through the PHPs on the UV, blue, and green LEDs is simulated using a three-dimensional finite-difference time-domain method to confirm the experimental results. Finally, we suggest optimal conditions of PHPs for improving the light output power of InGaN LEDs based on the experimental and theoretical results. PMID:28374856

  3. 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

  4. Indium gallium nitride-based ultraviolet, blue, and green light-emitting diodes functionalized with shallow periodic hole patterns.

    PubMed

    Jeong, Hyun; Salas-Montiel, Rafael; Lerondel, Gilles; Jeong, Mun Seok

    2017-04-04

    In this study, we investigated the improvement in the light output power of indium gallium nitride (InGaN)-based ultraviolet (UV), blue, and green light-emitting diodes (LEDs) by fabricating shallow periodic hole patterns (PHPs) on the LED surface through laser interference lithography and inductively coupled plasma etching. Noticeably, different enhancements were observed in the light output powers of the UV, blue, and green LEDs with negligible changes in the electrical properties in the light output power versus current and current versus voltage curves. In addition, confocal scanning electroluminescence microscopy is employed to verify the correlation between the enhancement in the light output power of the LEDs with PHPs and carrier localization of InGaN/GaN multiple quantum wells. Light propagation through the PHPs on the UV, blue, and green LEDs is simulated using a three-dimensional finite-difference time-domain method to confirm the experimental results. Finally, we suggest optimal conditions of PHPs for improving the light output power of InGaN LEDs based on the experimental and theoretical results.

  5. Gallium nitride induces neuronal differentiation markers in neural stem/precursor cells derived from rat cerebral cortex.

    PubMed

    Chen, Chi-Ruei; Li, Yi-Chen; Young, Tai-Horng

    2009-09-01

    In the present study, gallium nitride (GaN) was used as a substrate to culture neural stem/precursor cells (NSPCs), isolated from embryonic rat cerebral cortex, to examine the effect of GaN on the behavior of NSPCs in the presence of basic fibroblast growth factor (bFGF) in serum-free medium. Morphological studies showed that neurospheres maintained their initial shape and formed many long and thick processes with the fasciculate feature on GaN. Immunocytochemical characterization showed that GaN could induce the differentiation of NSPCs into neurons and astrocytes. Compared to poly-d-lysine (PDL), the most common substrate used for culturing neurons, there was considerable expression of synapsin I for differentiated neurons on GaN, suggesting GaN could induce the differentiation of NSPCs towards the mature differentiated neurons. Western blot analysis showed that the suppression of glycogen synthase kinase-3beta (GSK-3beta) activity was one of the effects of GaN-promoted NSPC differentiation into neurons. Finally, compared to PDL, GaN could significantly improve cell survival to reduce cell death after long-term culture. These results suggest that GaN potentially has a combination of electric characteristics suitable for developing neuron and/or NSPC chip systems.

  6. 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.

  7. 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

    2016-05-25

    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.

  8. Recent developments in nitride chemistry

    SciTech Connect

    Niewa, R.; DiSalvo, F.J.

    1998-10-01

    The chemistry of ternary nitrides is reviewed with special focus on developments of the last two years (1996 and 1997). In particular, structures and properties of ternary and higher transition metal nitrides, main group nitrides, subnitrides, and nitride halides are compared, and a section on thermodynamics of ternary nitrides is included. Finally, methods for the preparation of gallium nitride single crystals are summarized.

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

    PubMed

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

    2012-03-13

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

  10. 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.

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

    SciTech Connect

    Vasquez, M. R.; Wada, M.

    2016-02-15

    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.

  12. 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.

  13. 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.

  14. Theoretical study of gallium nitride molecules, GaN2 and GaN4.

    PubMed

    Tzeli, Demeter; Theodorakopoulos, Giannoula; Petsalakis, Ioannis D

    2008-09-18

    The electronic and geometric structures of gallium dinitride GaN 2, and gallium tetranitride molecules, GaN 4, were systematically studied by employing density functional theory and perturbation theory (MP2, MP4) in conjunction with the aug-cc-pVTZ basis set. In addition, for the ground-state of GaN 4( (2)B 1) a density functional theory study was carried out combining different functionals with different basis sets. A total of 7 minima have been identified for GaN 2, while 37 structures were identified for GaN 4 corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces and bonding mechanisms for some low-lying electronic states of GaN 4. The dissociation energy of the ground-state GaN 2 ( X (2)Pi) is 1.1 kcal/mol with respect to Ga( (2)P) + N 2( X (1)Sigma g (+)). The ground-state and the first two excited minima of GaN 4 are of (2)B 1( C 2 v ), (2)A 1( C 2 v , five member ring), and (4)Sigma g (-)( D infinityh ) symmetry, respectively. The dissociation energy ( D e) of the ground-state of GaN 4, X (2)B 1, with respect to Ga( (2)P) + 2 N 2( X (1)Sigma g (+)), is 2.4 kcal/mol, whereas the D e of (4)Sigma g (-) with respect to Ga( (4)P) + 2 N 2( X (1)Sigma g (+)) is 17.6 kcal/mol.

  15. Solid State Synthesis and Characterization of Carbo-Nitride Materials

    DTIC Science & Technology

    2007-11-02

    The preparation of stoichiometric sp(sup 2)-bonded amorphous carbon nitride a- C3N4 in gram quantities was successfully achieved by performing a solid...deg C. The densification of micronized powders by cold isothermal pressing has produced disk-shaped ceramics of C3N4 and B-C-N materials, being...to preparation of a previously unknown material - sphere-shaped nanoscale-size carbon nitride built by stacking of curved C3N4 layers. Preliminary

  16. 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.

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

    PubMed

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L; Roy, Ajit K; Luo, Tengfei

    2016-03-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN)--another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics.

  18. 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

  19. 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.

  20. High sensitivity hydrogen sensing with Pt-decorated porous gallium nitride prepared by metal-assisted electroless etching.

    PubMed

    Duan, Barrett K; Bohn, Paul W

    2010-05-01

    A unique hydrogen sensor structure based on Pt-decorated porous gallium nitride (PGaN) was fabricated by a two-step process consisting of metal-assisted electroless etching to produce PGaN with highly anisotropic pores followed by electroless deposition of Pt in the pores from an ammoniacal PtCl(6)(2-) solution. The Pt-decorated PGaN structure contains 50-100 nm diameter nanopores which are 400 nm to 1 microm deep and filled with Pt islands. Both electroless etching and deposition steps are done in solution and allow for large-scale production. An AC four-point probe conductivity measurement was implemented at f = 1 kHz, a frequency where the impedance of Pt-PGaN is nearly entirely resistive, and the change in conductance upon H(2) exposure was measured for three sample types: PGaN with a surface sputtered layer of Pt only; unetched GaN (CGaN) with both sputtered and electrolessly deposited Pt; and PGaN with both sputtered and electrolessly deposited Pt. The hydrogen sensing performance of the Pt-filled PGaN sensor was more than an order of magnitude better than either of the other two sample types under all experimental conditions, an observation attributed to the significant increase in Pt-GaN interfacial area in the electrolessly decorated PGaN samples, exhibiting a response to H2 concentrations as low as 1 ppm. The conductance changes are ascribed to adsorption-induced changes in interfacial polarization that produce changes in band bending and thus to the width of the space charge region near the Pt-GaN interface.

  1. Lateral electrochemical etching of III-nitride materials for microfabrication

    DOEpatents

    Han, Jung

    2017-02-28

    Conductivity-selective lateral etching of III-nitride materials is described. Methods and structures for making vertical cavity surface emitting lasers with distributed Bragg reflectors via electrochemical etching are described. Layer-selective, lateral electrochemical etching of multi-layer stacks is employed to form semiconductor/air DBR structures adjacent active multiple quantum well regions of the lasers. The electrochemical etching techniques are suitable for high-volume production of lasers and other III-nitride devices, such as lasers, HEMT transistors, power transistors, MEMs structures, and LEDs.

  2. 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.

  3. Q-Band (45 GHz) Microwave Integrated Circuit Power Amplifier Designs Submitted to TriQuint Semiconductor for Fabrication with 0.15-micron High-Electron-Mobility Transistors (HEMT) Using 2-mil Gallium Nitride (GaN) on Silicon Carbide (SiC)

    DTIC Science & Technology

    2013-09-01

    Electron-Mobility Transistors (HEMT) Using 2-mil Gallium Nitride (GaN) on Silicon Carbide (SiC) by John E. Penn ARL-TN-0574 September 2013...µm High-Electron-Mobility Transistors (HEMT) Using 2-mil Gallium Nitride (GaN) on Silicon Carbide (SiC) John E. Penn Sensors and Electron Devices...with 0.15-µm High- Electron-Mobility Transistors (HEMT) Using 2-mil Gallium Nitride (GaN) on Silicon Carbide (SiC) 5a. CONTRACT NUMBER 5b. GRANT

  4. The Effects of Atmospheric pH on the Transport Properties of Gallium Nitride

    NASA Astrophysics Data System (ADS)

    McElroy, Andrew; Dyck, Jeffrey S.; Kash, Kathleen

    2011-04-01

    It has been theorized that there exists a thin layer of water molecules on the surface of many materials when in air. This layer is predicted to have an effect on the electrochemical properties of the material. GaN is one of these materials. It has been demonstrated that the optical properties of GaN are affected by the pH of the atmosphere around the sample. In this study the effects of pH on transport properties are tested. A system was developed to test the Hall coefficient and resistivity of samples under different ambients to discover the effects of pH on carrier concentration and Hall mobility of GaN. Thus far, the results show that the pH of the ambient water vapor does not have an effect on the transport properties. This project was funded through the National Science Foundation (DMR-1006132) and the Huntington and Codrington Foundations.

  5. David Adler Lectureship Award in the Field of Materials Physics Talk: Novel Nitride and Oxide Electronics

    NASA Astrophysics Data System (ADS)

    Pearton, Stephen

    2011-03-01

    Recent progress in development of GaN-based transistors for gas and bio-sensing applications and amorphous IGZO layers for use thin film transistors (TFTs)on flexible substrates, including paper,will be presented. For the detection of gases such as hydrogen, the gateless GaN transistors are typically coated with a catalyst metal such as Pd or Pt to increase the detection sensitivity at room temperature. Functionalizing the surface with oxides, polymers and nitrides is also useful in enhancing the detection sensitivity for gases and ionic solutions.The use of enzymes or adsorbed antibody layers on the semiconductor surface leads to highly specific detection of a broad range of antigens of interest in the medical and security fields. We give examples of recent work showing sensitive detection of glucose, lactic acid, prostate cancer and breast cancer markers and the integration of the sensors with wireless data transmission systems to achieve robust, portable sensors. The amorphous transparent conducting oxide InZnGaO4 (IGZO) is attracting attention because of its high electron mobility (10-50 cm2.V-1.sec-1), high transparency in the visible region of the spectrum and its ability to be deposited with a wide range of conductivities.This raises the possibility of making low-cost electronics on a very wide range of arbitrary surfaces, including paper and plastics. N-type oxides such as zinc oxide, zinc tin oxide, indium gallium oxide, and indium gallium zinc tin oxide (IGZO) exhibit surprisingly high carrier mobilities even for amorphous films deposited at 300K. This has been explained by the fact that the conduction in these materials is predominantly through non-directional s orbitals which are less affected by disorder than the directional sp3 orbitals which control electron transport in Si. Examples of progress and discussion of remaining obstacles to use of IGZO TFTs will be presented Work performed in collaboration with Fan Ren.

  6. Development of Advanced Ill-Nitride Materials

    DTIC Science & Technology

    2008-09-24

    doping, p-n junctions, and InGaN/InN quantum well structures for terahertz emitters; and (iii) develop AlInN materials lattice-matched to GaN for... GaN and InN- based materials by molecular beam epitaxy (MBE). Work is focused on three areas: (i) extend on our pioneering work on high...temperature nitrogen-rich growth of GaN , where we have demonstrated a new growth space for realizing high quality GaN materials and devices including world

  7. Deep Level Defects in Electron-Irradiated Aluminum Gallium Nitride Grown by Molecular Beam Epitaxy

    DTIC Science & Technology

    2005-03-01

    To date, these energy levels have not been systematically measured (i.e. temperature dependent Hall ( TDH ) and deep level transient spectroscopy...Material I.D. Ref. Donors 0.06 0.018 0.06 0.06 e- (1 MeV) TDH undoped HVPE n≈1017 VN SiGa 33 Acceptors deep e- (1 MeV) TDH " NI 33...qualitative agreement with the linear carrier removal model of equation II-33. More recently, TDH measurements were reported for the same type of GaN sample

  8. Electrical Activation Studies of Silicon Implanted Aluminum Gallium Nitride with High Aluminum Mole Fraction

    DTIC Science & Technology

    2007-12-01

    functioned at room temperature. Numerous other electronic inventions followed, such as the microprocessor in 1971, the charged couple device (CCD...the yellow band in GaN and in AlxGa1-xN materials in the literature. Glaser et al. claim the band is the result of radiative recombination between...grown sample exhibits two phonon coupled replicas separated by 80 meV on the low energy side of the (Do,X) peak at 4.33 and 4.25 eV (49

  9. Fe-doping in hydride vapor-phase epitaxy for semi-insulating gallium nitride

    NASA Astrophysics Data System (ADS)

    Richter, E.; Gridneva, E.; Weyers, M.; Tränkle, G.

    2016-12-01

    Fe-doping of GaN layers of 3 in. in diameter and a thickness of 1 mm in a vertical AIX-HVPE reactor is studied. Ferrocen was used as Fe source. It is shown that a sufficient uniformity of growth conditions, a high purity of undoped GaN layers, and a moderate Fe incorporation of 2×1018 cm-3 allow for growth of semi-insulating GaN layers with a sufficiently high specific resistivity even at elevated temperature. This makes the material suitable as substrate for electronic power devices at high power or in harsh ambient.

  10. The equilibrium state of hydrogen in gallium nitride: Theory and experiment

    SciTech Connect

    MYERS JR.,SAMUEL M.; WRIGHT,ALAN F.; PETERSEN,GARY A.; SEAGER,CARLETON H.; WAMPLER,WILLIAM R.; CRAWFORD,MARY H.; HAN,JUNG

    2000-04-17

    Formation energies and vibrational frequencies for H in wurtzite GaN were calculated from density functional theory and used to predict equilibrium state occupancies and solid solubilities for p-type, intrinsic, and n-type material. The solubility of deuterium (D) was measured at 600--800 C as a function of D{sub 2} pressure and doping and compared with theory. Agreement was obtained by reducing the H formation energies 0.2 eV from ab-initio theoretical values. The predicted stretch-mode frequency for H bound to the Mg acceptor lies 5% above an observed infrared absorption attributed to this complex. It is concluded that currently recognized H states and physical processes account for the equilibrium behavior of H examined in this work.

  11. Increased light extraction and directional emission control in gallium nitride photonic crystal light emitting diodes

    NASA Astrophysics Data System (ADS)

    McGroddy, Kelly C.

    GaN has become the prominent material for blue-green light emitting diodes (LEDs) and efficient white light sources. Advancements in LED efficiency for lighting has the potential to dramatically impact energy consumption world wide. A limiting factor to achieving high efficiencies in GaN LEDs is the light extraction efficiency. This work addresses many key issues pertaining to the use of PhCs to increase the extraction efficiency and emission directionality of GaN LEDs. Limitations in extraction efficiency of GaN photonic crystal light emitting diodes (LEDs) are addressed by implementing an LED design using both 2D photonic crystals (PhCs) in-plane and index guiding layers (IGLs) in the vertical direction. The effects of PhCs on light extraction and emission directionality from GaN LEDs are studied experimentally. Angular resolved electroluminescence clearly shows the combined effect of controlling the vertical mode profile with the IGLs and tailoring the emission profile with the periodicity of the PhC lattice. Various materials are used to increase the index contrast of the IGL and the effects are measured. Increases in vertical emission as high as 3.5x are achieved for PhC LEDs with an Al0.12Ga0.88N IGL over non-PhC LEDs with a ˜30% improvement attributed to the incorporation of the AlGaN IGL. This enhancement is achieved by tailoring both the directionality and guided mode control. The impact of incorporating PhCs and IGLs on LED device design and performance are addressed. Effects of etching the PhCs near the QWs have been observed and explanations for this behavior will be discussed. It will be shown that an un-doped IGL can severely limit current spreading in the n-type side of the device and have a detrimental impact on device performance. Finally, a method of patterning PhCs with periodicities as small as 230nm by laser interference lithography and imprint lithography has been developed to provide a fast, inexpensive method of pattering PhCs over large

  12. Selective excitation of the yellow and blue luminescence in n- and p-doped Gallium Nitride

    SciTech Connect

    Colton, John Synder

    2000-12-01

    GaN is an interesting material: technologically very useful, but still having many unexplained features. Two such features are the broad defect-related luminescence bands: the YL of n-type GaN and the BL of Mg-doped p-type GaN. We have employed selective excitation to investigate these bands. In the case of the YL, most of the previous evidence has supported a recombination model between distant donors and acceptors, most likely a transition involving a shallow donor to a deep acceptor. Our selective excitation experiments have resolved finer structures within the YL. Our results indicate that the YL in bulk samples is related to the YL in film samples. We suggest that selectively excited YL involves recombination at DAP complexes, rather than between spatially distant DAPs (however other recombination channels, including that of distant DAPs may become significant under other excitation conditions). Characteristics of the DAP complexes within our YL model include (a) an electron localization energy of around 60-70 meV, (b) a localized phonon energy of around 40 meV, and (c) excited states of the complex at 200 and 370 meV above the ground state. In the case of the BL, the deep defect responsible for the BL is unknown, and there may not even be a deep defect involved. Also in dispute is the role of potential fluctuations in the properties of the BL. Our results have been explain in a model whereby emission is from DAPs, and significant effects are produced by doping-related potential fluctuations and disorder. Characteristics of the our model for the BL include (a) an Urbach tail, having width E{sub 0} = 33 meV, (b) a strong electron-LO phonon coupling occurring with a Frank-Condon shift of {approx} 180 meV between excitation and emission, (c) a mobility gap at 2.8 eV, separating highly mobile states and highly localized states, and (d) PL-like behavior for excitation energies larger than 2.8 eV, having a blue-shift with increasing excitation energy caused by the

  13. Gallium nitride based power switches for next generation of power conversion

    SciTech Connect

    Chowdhury, S

    2015-03-17

    Power conversion impacts all areas of electricity consumption, including motion control, lighting, air conditioning, and information technology. Si, the workhorse of the industry, has served well so far but reached its material limits. To keep up with the advancement of technologies enabling new conveniences, power conversion techniques need to go through significant transformation that calls for the next generation semiconductor for power switching. SiC and GaN, which have the potential to push the envelope beyond Si providing solutions for the entire range of power conversion at higher efficiencies and reduced form factors. GaN HEMTs have an added advantage over SiC MOSFETs owing to the high-mobility electron channel formed at the AlGaN/GaN interface, which has been the basis of radio frequency amplifiers. GaN has enabled systems that can run with lesser cooling at frequencies at least ten times higher than current Si-based systems, significantly reducing the form factor both electrically (passive components) and mechanically (heat sinks). The high current and voltage required for high power conversion application make the chip area in a lateral topology uneconomical and difficult to manufacture. Vertical GaN devices on bulk GaN substrates complete the portfolio of power switches required to address the power conversion market.

  14. Effect of etching with cysteamine assisted phosphoric acid on gallium nitride surface oxide formation

    NASA Astrophysics Data System (ADS)

    Wilkins, S. J.; Paskova, T.; Ivanisevic, A.

    2013-08-01

    In-situ functionalization of polar GaN was performed by adding cysteamine to a phosphoric acid etchant in order to study its effect on photoluminescence and oxide formation on the surfaces. The functionalization was characterized by atomic force microscopy, x-ray photoelectron spectroscopy, photoluminescence (PL), and water contact angle measurements. Two sets of polar GaN samples with different dislocation densities were evaluated, thin GaN layers residing on sapphire and thick free-standing GaN separated from sapphire substrate aiming to reveal the effect of material quality on in-situ functionalization. The addition of cysteamine to the phosphoric acid solution was found to result in: (i) decreased surface roughness, (ii) no change to hydrophobicity, (iii) decreased oxygen content especially at high-temperature treatments. The effect of the in-situ functionalization on the PL efficiency was more pronounced in the free-standing sample than in the film residing on the sapphire, which was attributed to a higher crystal quality free from strain.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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, Pmax 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. 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.

  18. Design and fabrication of gallium nitride-based heterojunction bipolar transistors

    NASA Astrophysics Data System (ADS)

    Lee, Kyu-Pil

    A self-aligned fabrication process for small and large emitter contact area (2 x 4 mum2 and 1.96 x 103 mum 2 respectively) GaN-based heterojunction bipolar transistor and bipolar junction transistors is proposed. The process features dielectric-spacer sidewalls, low-damage dry etching and selected-area regrowth of GaAs(C) on the base contact, and self-aligned emitter base regrowth processes are provided. The junction current-voltage (I--V) characteristics were evaluated at various stages of the process sequence and provided an excellent diagnostic for monitoring the effect of plasma processes such as CVD or etching. A comparison is given with large emitter-area devices fabricated on the same material. The small-area devices are attractive for microwave power switching applications, provided that a high-yield process can be developed. Series resistance effects are still found to influence device performance. In the dc performance of small and large emitter contact area GaN-based heterojunction bipolar transistors, the do current gain of both types of device improves with temperature, which we ascribe to higher ionization efficiency of the Mg acceptor in the p-base region. The presence of a resistive base layer at room temperature forces base current to flow directly to the collector, reducing the current gain. However, to date, all of the reported GaN-based heterojunction bipolar transistors (HBTs) and bipolar junction transistors (BJTs) have had lots of problems to be solved even if there are many advantages to this technology. To predict the performance of GaN-based HBTs and BJTs, we simulated these structures with 2-dimensional device simulators. The effects of base doping and thickness on do current gain, collector-emitter saturation voltage, saturation current, collector-emitter breakdown voltage, rf characteristics (fT) and the effects of impurity ionization as a function of device operation temperature of GaN, AlGaN, InGaN-based heterojunction bipolar

  19. Electrical characterization of dislocations in gallium nitride using advanced scanning probe techniques

    NASA Astrophysics Data System (ADS)

    Simpkins, Blake Shelley Ginsberg

    GaN-based materials are promising for high speed and power applications such as amplifier and communications circuits. Ga, In, and AIN-based alloys span a wide optical range (2--6.1 eV) and exhibit strong polarizations making them useful in many devices; however, films are highly defective (˜10 8 dislocations cm-2) due to lack of suitable substrates. Thus, nanoscale electronic characterization of these dislocations is critical for device and growth optimization. Scanning probe techniques enable characterization at length-scales unattainable by conventional techniques. First, scanning Kelvin probe microscopy (SKPM) was used to image surface potential variations due to charged dislocations in HVPE-grown GaN. The film's structural evolution "with thickness was monitored showing a decrease in dislocation density, likely through dislocation reaction. Numerical simulations were used to investigate tip-size effects when imaging highly localized (tens of nm) potential variations indicating that measured dislocation induced potential features in GaN can be much smaller (˜80%) than true variations. Next, capacitance variations in MBE-grown HFETs, due to dislocations-induced carrier depletion, were imaged with scanning capacitance microscopy (SCM). The distribution of these charged centers was correlated with buffer schemes showing that an AIN buffer leads to pseudomorphic (2D) nucleation and randomly distributed misfit dislocations while deposition directly on SiC results in island (3D) nucleation and a domain structure with dislocations grouped at domain boundaries. Hall measurements and numerical simulations were also carried out to further study the implications of these microstructures. Numerical results indicated that randomly distributed dislocations deplete a larger fraction of free carriers than the same density of grouped dislocations and correlated favorably with Hall results. Correlated SKPM and conductive AFM (C-AFM) measurements were then used to study

  20. 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.

  1. Self-assembled Multilayers of Silica Nanospheres for Defect Reduction in Non- and Semipolar Gallium Nitride Epitaxial Layers

    PubMed Central

    2015-01-01

    Non- and semipolar GaN have great potential to improve the efficiency of light emitting devices due to much reduced internal electric fields. However, heteroepitaxial GaN growth in these crystal orientations suffers from very high dislocation and stacking faults densities. Here, we report a facile method to obtain low defect density non- and semipolar heteroepitaxial GaN via selective area epitaxy using self-assembled multilayers of silica nanospheres (MSN). Nonpolar (11–20) and semipolar (11–22) GaN layers with high crystal quality have been achieved by epitaxial integration of the MSN and a simple one-step overgrowth process, by which both dislocation and basal plane stacking fault densities can be significantly reduced. The underlying defect reduction mechanisms include epitaxial growth through the MSN covered template, island nucleation via nanogaps in the MSN, and lateral overgrowth and coalescence above the MSN. InGaN/GaN multiple quantum wells structures grown on a nonpolar GaN/MSN template show more than 30-fold increase in the luminescence intensity compared to a control sample without the MSN. This self-assembled MSN technique provides a new platform for epitaxial growth of nitride semiconductors and offers unique opportunities for improving the material quality of GaN grown on other orientations and foreign substrates or heteroepitaxial growth of other lattice-mismatched materials. PMID:27065755

  2. Self-assembled Multilayers of Silica Nanospheres for Defect Reduction in Non- and Semipolar Gallium Nitride Epitaxial Layers.

    PubMed

    Zhu, Tongtong; Ding, Tao; Tang, Fengzai; Han, Yisong; Ali, Muhammad; Badcock, Tom; Kappers, Menno J; Shields, Andrew J; Smoukov, Stoyan K; Oliver, Rachel A

    2016-02-03

    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.

  3. Graphitic Carbon Nitride Materials: Sensing, Imaging and Therapy.

    PubMed

    Dong, Yongqiang; Wang, Qian; Wu, Haishan; Chen, Yingmei; Lu, Chun-Hua; Chi, Yuwu; Yang, Huang-Hao

    2016-10-01

    Graphitic carbon nitrides (g-C3 N4 ) are a class of 2D polymeric materials mainly composed of carbon and nitrogen atoms. g-C3 N4 are attracting dramatically increasing interest in the areas of sensing, imaging, and therapy, due to their unique optical and electronic properties. Here, the luminescent properties (mainly includes photoluminescence and electrochemiluminescence), and catalytic and photoelectronic properties related to sensing and therapy applications of g-C3 N4 materials are reviewed. Furthermore, the fabrication and advantages of sensing, imaging and therapy systems based on g-C3 N4 materials are summarized. Finally, the future perspectives for developing the sensing, imaging and therapy applications of the g-C3 N4 materials are discussed.

  4. 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.

  5. Polarization Effects in Group III-Nitride Materials and Devices

    NASA Astrophysics Data System (ADS)

    Wei, Qiyuan

    Group III-nitride semiconductors have wide application in optoelectronic devices. Spontaneous and piezoelectric polarization effects have been found to be critical for electric and optical properties of group III-nitrides. In this dissertation, firstly, the crystal orientation dependence of the polarization is calculated and in-plane polarization is revealed. The in-plane polarization is sensitive to the lateral characteristic dimension determined by the microstructure. Specific semi-polar plane growth is suggested for reducing quantum-confined Stark effect. The macroscopic electrostatic field from the polarization discontinuity in the heterostructures is discussed, b ased on that, the band diagram of InGaN/GaN quantum well/barrier and AlGaN/GaN heterojunction is obtained from the self-consistent solution of Schrodinger and Poisson equations. New device design such as triangular quantum well with the quenched polarization field is proposed. Electron holography in the transmission electron microscopy is used to examine the electrostatic potential under polarization effects. The measured potential energy profiles of heterostructure are compared with the band simulation, and evidences of two-dimensional hole gas (2DHG) in a wurtzite AlGaN/ AlN/ GaN superlattice, as well as quasi two-dimensional electron gas (2DEG) in a zinc-blende AlGaN/GaN are found. The large polarization discontinuity of AlN/GaN is the main source of the 2DHG of wurtzite nitrides, while the impurity introduced during the growth of AlGaN layer provides the donor states that to a great extent balance the free electrons in zinc-blende nitrides. It is also found that the quasi-2DEG concentration in zinc-blende AlGaN/GaN is about one order of magnitude lower than the wurtzite AlGaN/GaN, due to the absence of polarization. Finally, the InAlN/GaN lattice-matched epitaxy, which ideally has a zero piezoelectric polarization and strong spontaneous polarization, is experimentally studied. The breakdown in

  6. Experimental and Theoretical Analysis of Strain Engineered Aluminium Nitride on Silicon for High Quality Aluminium(x)Indium(y)Gallium(1-x-y)Nitride Epitaxy

    NASA Astrophysics Data System (ADS)

    Tungare, Mihir

    III-Nitrides on Si are of great technological importance due to the availability of large area, epi ready Si substrates and the ability to heterointegrate with mature silicon micro and nanoelectronics. The major roadblock with realizing this is the large difference in thermal expansion coefficients and lattice constants between the two material systems. A novel technique developed in our research lab shows the potential of simultaneous and substantial reduction in dislocation and crack density in GaN on Si (111). Research undertaken in the current doctoral dissertation, validates the superior GaN quality on Si obtained using our technique and determines the factors responsible for its successful implementation. Detailed study of the stress evolution and dislocation reduction mechanism within overgrown GaN on as-grown and engineered AlN/Si substrates is carried out. Based on the conclusions obtained in this study, a pulsed metal-organic chemical vapor deposition (MOCVD) technique for the growth of AlN on Si (111) is developed to achieve a smoother AlN buffer with larger islands. A 14× reduction in surface pit density for overgrown GaN is attained on these AlN/Si substrates after substrate engineering. Deep green emission at 560 nm from InGaN/GaN MQWs with 10× increase in photoluminescence (PL) intensity is obtained on these templates. Molecular dynamics (MD) is used with an ultimate goal to theoretically understand the stress dilution mechanism and assist in improving the technique experimentally. Plausible models to accurately simulate wurtzite AlN (w-AlN) and AlN on Si (111) are developed. Motion of Si islands on Si (111) bulk substrate is examined to assess the required simulation conditions, their compliance with experimental set-up, and the limitations. Homoepitaxial growth of w-AlN is carried out to simulate epitaxial deposition as a starting point for heteroepitaxy of AlN on Si (111) and also to eventually build the entire complex film stack that closely

  7. Deposition of metallic gallium on re-crystallized ceramic material during focused ion beam milling

    SciTech Connect

    Muñoz-Tabares, J.A.; Reyes-Gasga, J.

    2013-12-15

    We report a new kind of artifact observed in the preparation of a TEM sample of zirconia by FIB, which consists in the deposition of metallic gallium nano-dots on the TEM sample surface. High resolution TEM images showed a microstructure of fine equiaxed grains of ∼ 5 nm, with some of them possessing two particular characteristics: high contrast and well-defined fast Fourier transform. These grains could not be identified as any phase of zirconia but it was possible to identify them as gallium crystals in the zone axis [110]. Based on HRTEM simulations, the possible orientations between zirconia substrate and deposited gallium are discussed in terms of lattice mismatch and oxygen affinity. - Highlights: • We show a new type of artifact induced during preparation of TEM samples by FIB. • Deposition of Ga occurs due to its high affinity for oxygen. • Materials with small grain size (∼ 5 nm) could promote Ga deposition. • Small grain size permits the elastic accommodation of deposited Ga.

  8. ACCURATE QUANTIFICATION OF RADIOACTIVE MATERIALS BY X-RAY FLUORESCENCE: GALLIUM IN PLUTONIUM METAL.

    SciTech Connect

    WORLEY, CHRISTOPHER GORDON

    2002-09-04

    Determining the concentration of gallium in plutonium metal is imperative in manufacturing nuclear weapons. X-ray fluorescence (XRF) is an effective method used to quantify the gallium content in plutonium; however, the sample and specimen preparation methods currently employed could be improved from a time and safety standpoint. Recently, a dried residue specimen preparation method was developed as an alternative to the established aqueous approach. The method currently certified to prepare plutonium for gallium analysis by XRF involves dissolving the sample and removing the plutonium with ion exchange chromatography. The gallium remaining in solution is then analyzed. This method has been thoroughly developed, and relative accuracy and precision values less than 1% can be achieved. However, this process is time consuming, and the specimen solution is radioactive due to the presence of residual plutonium and trace americium. Thus, an alternate process was developed to avoid these issues in which the plutonium solution is cast in {mu}L spots on Mylar XRF film, dried, and sealed inside a sample cell for analysis. This specimen preparation method is considerably faster and also safer than the solution process. Previous studies have demonstrated that a very linear calibration can be obtained from dried residue standards. In the present work, accuracy and precision results will be compared from using the aqueous and dried residue specimen preparation methods. The strengths and limitations of each method will also be discussed. In summary, this work will illustrate both the challenges faced with analyzing radioactive materials by XRF and the high accuracy and precision achievable with proper sample and specimen preparation.

  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. Effect of nitrogen doping on the structural, optical and electrical properties of indium tin oxide films prepared by magnetron sputtering for gallium nitride light emitting diodes

    NASA Astrophysics Data System (ADS)

    Tian, Lifei; Cheng, Guoan; Wang, Hougong; Wu, Yulong; Zheng, Ruiting; Ding, Peijun

    2017-01-01

    The indium tin oxide (ITO) films are prepared by the direct current magnetron sputtering technology with an ITO target in a mixture of argon and nitrogen gas at room temperature. The blue transmittance at 455 nm rises from 63% to 83% after nitrogen doping. The resistivity of the ITO film reduces from 4.6 × 10-3 (undoped film) to 5.7 × 10-4 Ω cm (N-doped film). The X-ray photoelectron spectroscopy data imply that the binding energy of the In3d5/2 peak is declined 0.05 eV after nitrogen doping. The high resolution transmission electron microscope images show that the nitrogen loss density of the GaN/ITO interface with N-doped ITO film is smaller than that of the GaN/ITO interface with undoped ITO film. The forward turn-on voltage of gallium nitride light emitting diode reduces by 0.5 V after nitrogen doping. The fabrication of the N-doped ITO film is conducive to modify the N component of the interface between GaN and ITO layer.

  11. Fabrication of conducting-filament-embedded indium tin oxide electrodes: application to lateral-type gallium nitride light-emitting diodes.

    PubMed

    Kim, Hee-Dong; Kim, Kyeong Heon; Kim, Su Jin; Kim, Tae Geun

    2015-11-02

    A novel conducting filament (CF)-embedded indium tin oxide (ITO) film is fabricated using an electrical breakdown method. To assess the performance of this layer as an ohmic contact, it is applied to GaN (gallium nitride) light-emitting diodes (LEDs) as a p-type electrode for comparison with typical GaN LEDs using metallic ITO. The operating voltage and output power of the LED with the CF embedded ITO are 3.93 V and 8.49 mW, respectively, at an injection current of 100 mA. This is comparable to the operating voltage and output power of the conventionally fabricated LEDs using metallic ITO (3.93 V and 8.43 mW). Moreover, the CF-ITO LED displays uniform and bright light emission indicating excellent current injection and spreading. These results suggest that the proposed method of forming ohmic contacts is at least as effective as the conventional method.

  12. Effects of post-deposition annealing ambient on band alignment of RF magnetron-sputtered Y2O3 film on gallium nitride.

    PubMed

    Quah, Hock Jin; Cheong, Kuan Yew

    2013-01-29

    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).

  13. III-V aresenide-nitride semiconductor materials and devices

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    III-V arsenide-nitride semiconductor crystals, methods for producing such crystals and devices employing such crystals. 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.

  14. 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.

  15. 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.

  16. Evaluation of the indium gallium nitride/silicon broken-gap heterojunction and its potential application for solar cells

    NASA Astrophysics Data System (ADS)

    Yao, Yuan

    InGaN (especially In-rich alloy) has been actively studied for decades since the band gap of InN was revised downward from ˜2.0 eV to 0.64 eV. The potential applications for alloys of In-rich InGaN hence became apparent. Despite the promising potential, photovoltaic devices based on InGaN have struggled due to a number of key limitations and fundamental physical problems. Firstly, due to the deep excursion of the InN conduction band at the gamma point, defects in InN are almost universally n-type leading to unintentional degenerate doping. This also leads to the problem of electron accumulation at all surfaces and interfaces of InN. Secondly, p-type doping is problematic, partially due to the degenerate doping effect of defects, but it has also been observed that Mg-doping, while leading to a p-type layer, dramatically reduces the quantum efficiency. This thesis explores an alternative approach using n-type InGaN to form a heterojunction with a p-type Si substrate. One potential benefit to using p-type Si as a substrate material for InGaN is that the valence band of Si possibly lines up with the conduction band of InGaN for a specific mole fraction of indium. Such a band alignment is known as a broken gap heterojunction, an example of which is the interface between InAs and AlxGa 1--xSb. The benefits of this broken-gap junction include a low series resistance, high electron mobility, and mobility only weakly dependent on temperature. These properties enable new approach to photovoltaic devices. The InGaN/Si heterojunctions were fabricated by plasma-assisted molecular beam epitaxy under stoichiometric flux conditions. An ultra-thin SiN interface layer was introduced, by Si nitridation process, to passivate the substrate surface and prevent In-Si and Ga-Si eutectic problems. InGaN films with a variety of indium mole fractions were grown by calibrating the In/Ga flux ratio during the deposition. The chemical composition of as-grown films was characterized by x

  17. 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

  18. Resonant and nonresonant vibrational excitation of ammonia molecules in the growth of gallium nitride using laser-assisted metal organic chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Golgir, Hossein Rabiee; Zhou, Yun Shen; Li, Dawei; Keramatnejad, Kamran; Xiong, Wei; Wang, Mengmeng; Jiang, Li Jia; Huang, Xi; Jiang, Lan; Silvain, Jean Francois; Lu, Yong Feng

    2016-09-01

    The influence of exciting ammonia (NH3) molecular vibration in the growth of gallium nitride (GaN) was investigated by using an infrared laser-assisted metal organic chemical vapor deposition method. A wavelength tunable CO2 laser was used to selectively excite the individual vibrational modes. Resonantly exciting the NH-wagging mode (v2) of NH3 molecules at 9.219 μm led to a GaN growth rate of 84 μm/h, which is much higher than the reported results. The difference between the resonantly excited and conventional thermally populated vibrational states was studied via resonant and nonresonant vibrational excitations of NH3 molecules. Resonant excitation of various vibrational modes was achieved at 9.219, 10.35, and 10.719 μm, respectively. Nonresonant excitation was conducted at 9.201 and 10.591 μm, similar to conventional thermal heating. Compared to nonresonant excitation, resonant excitation noticeably promotes the GaN growth rate and crystalline quality. The full width at half maximum value of the XRD rocking curves of the GaN (0002) and GaN (10-12) diffraction peaks decreased at resonant depositions and reached its minimum value of 45 and 53 arcmin, respectively, at the laser wavelength of 9.219 μm. According to the optical emission spectroscopic studies, resonantly exciting the NH3 v2 mode leads to NH3 decomposition at room temperature, reduces the formation of the TMGa:NH3 adduct, promotes the supply of active species in GaN formation, and, therefore, results in the increased GaN growth rate.

  19. Enhanced current transport and injection in thin-film gallium-nitride light-emitting diodes by laser-based doping.

    PubMed

    Kim, Su Jin; Kim, Kyeong Heon; Chung, Ho Young; Shin, Hee Woong; Lee, Byeong Ryong; Jeong, Tak; Park, Hyung Jo; Kim, Tae Geun

    2014-10-08

    This paper reports improvements in the electrical and optical properties of blue-emission gallium nitride (GaN)-based thin-film light-emitting diodes (TFLEDs) after laser-based Si doping (LBSD) of a nitrogen-face n-GaN (denoted as hereafter n-GaN) layer. Experimental results show that the light-output powers of the flat- and rough-surface TFLEDs after LBSD are 52.1 and 11.35% higher than those before LBSD, respectively, at a current of 350 mA, while the corresponding operating voltages are decreased by 0.22 and 0.28 V for the flat- and rough-surface TFLEDs after LBSD, respectively. The reduced operating voltage after LBSD of the top n-GaN layer may result from the remarkably decreased specific contact resistance at the metal/n-GaN interface and the low series resistance of the TFLED device. The LBSD of n-GaN increases the number of nitrogen vacancies, and Si substitutes for Ga (SiGa) at the metal/n-GaN interface to produce highly Si-doped regions in n-GaN, leading to a decrease in the Schottky barrier height and width. As a result, the specific contact resistances are significantly decreased to 1.56 × 10(-5) and 2.86 × 10(-5) Ω cm(2) for the flat- and rough-surface samples after LBSD, respectively. On the other hand, the increased light-output power after LBSD can be explained by the uniform current spreading, efficient current injection, and enhanced light scattering resulting from the low contact resistivity, low lateral current resistance, and additional textured surface, respectively. Furthermore, LBSD did not degrade the electrical properties of the TFLEDs owing to low reverse leakage currents. The results indicate that our approach could potentially enable high-efficiency and high-power capabilities for optoelectronic devices.

  20. Impurity-induced disorder in III-nitride materials and devices

    DOEpatents

    Wierer, Jr., Jonathan J; Allerman, Andrew A

    2014-11-25

    A method for impurity-induced disordering in III-nitride materials comprises growing a III-nitride heterostructure at a growth temperature and doping the heterostructure layers with a dopant during or after the growth of the heterostructure and post-growth annealing of the heterostructure. The post-growth annealing temperature can be sufficiently high to induce disorder of the heterostructure layer interfaces.

  1. Rational design of metal nitride redox materials for solar-driven ammonia synthesis.

    PubMed

    Michalsky, Ronald; Pfromm, Peter H; Steinfeld, Aldo

    2015-06-06

    Fixed nitrogen is an essential chemical building block for plant and animal protein, which makes ammonia (NH3) a central component of synthetic fertilizer for the global production of food and biofuels. A global project on artificial photosynthesis may foster the development of production technologies for renewable NH3 fertilizer, hydrogen carrier and combustion fuel. This article presents an alternative path for the production of NH3 from nitrogen, water and solar energy. The process is based on a thermochemical redox cycle driven by concentrated solar process heat at 700-1200°C that yields NH3 via the oxidation of a metal nitride with water. The metal nitride is recycled via solar-driven reduction of the oxidized redox material with nitrogen at atmospheric pressure. We employ electronic structure theory for the rational high-throughput design of novel metal nitride redox materials and to show how transition-metal doping controls the formation and consumption of nitrogen vacancies in metal nitrides. We confirm experimentally that iron doping of manganese nitride increases the concentration of nitrogen vacancies compared with no doping. The experiments are rationalized through the average energy of the dopant d-states, a descriptor for the theory-based design of advanced metal nitride redox materials to produce sustainable solar thermochemical ammonia.

  2. Characterization and electrochemical activities of nanostructured transition metal nitrides as cathode materials for lithium sulfur batteries

    NASA Astrophysics Data System (ADS)

    Mosavati, Negar; Salley, Steven O.; Ng, K. Y. Simon

    2017-02-01

    The Lithium Sulfur (Li-S) battery system is one of the most promising candidates for electric vehicle applications due to its higher energy density when compared to conventional lithium ion batteries. However, there are some challenges facing Li-S battery commercialization, such as: low active material utilization, high self-discharge rate, and high rate of capacity fade. In this work, a series of transition metal nitrides: Tungsten nitride (WN), Molybdenum Nitride (Mo2N), and Vanadium Nitride (VN) was investigated as cathode materials for lithium polysulfide conversion reactions. Capacities of 697, 569, and 264 mAh g-1 were observed for WN, Mo2N, VN, respectively, with 8 mg cm-2 loading, after 100 cycles at a 0.1 C rate. WN higher electrochemical performance may be attributed to a strong reversible reaction between nitrides and polysulfide, which retains the sulfur species on the electrode surface, and minimizes the active material and surface area loss. X-ray photoelectron spectroscopy (XPS) analysis was performed to gain a better understanding of the mechanism underlying each metal nitride redox reactions.

  3. Rational design of metal nitride redox materials for solar-driven ammonia synthesis

    PubMed Central

    Michalsky, Ronald; Pfromm, Peter H.; Steinfeld, Aldo

    2015-01-01

    Fixed nitrogen is an essential chemical building block for plant and animal protein, which makes ammonia (NH3) a central component of synthetic fertilizer for the global production of food and biofuels. A global project on artificial photosynthesis may foster the development of production technologies for renewable NH3 fertilizer, hydrogen carrier and combustion fuel. This article presents an alternative path for the production of NH3 from nitrogen, water and solar energy. The process is based on a thermochemical redox cycle driven by concentrated solar process heat at 700–1200°C that yields NH3 via the oxidation of a metal nitride with water. The metal nitride is recycled via solar-driven reduction of the oxidized redox material with nitrogen at atmospheric pressure. We employ electronic structure theory for the rational high-throughput design of novel metal nitride redox materials and to show how transition-metal doping controls the formation and consumption of nitrogen vacancies in metal nitrides. We confirm experimentally that iron doping of manganese nitride increases the concentration of nitrogen vacancies compared with no doping. The experiments are rationalized through the average energy of the dopant d-states, a descriptor for the theory-based design of advanced metal nitride redox materials to produce sustainable solar thermochemical ammonia. PMID:26052421

  4. Designing of TJ VCSEL based on nitride materials

    NASA Astrophysics Data System (ADS)

    Sarzała, R. P.; Pijanowski, K.; Gebski, M.; Marciniak, M.; Nakwaski, W.

    2016-12-01

    Different structures of nitride Vertical-Cavity Surface-Emitting Lasers (VCSELs) have been developed in recent years. However there is still many problems with such constructions, especially with electrical and optical confinement, current injection and construction and fabrication of mirrors. In this paper we present novel approach to nitride VCSEL designing. We investigated structure with tunnel junction (TJ) and top and bottom dielectric distributed Bragg reflectors (DBRs). Using our three-dimensional self-consistent model we investigated thermal and electrical properties of such laser. We also proposed replacing bottom DBR by monolithic high contrast grating mirror (MHCG) and presented optical properties of VCSEL with such mirrors.

  5. Nanopipe formation as a result of boron impurity segregation in gallium nitride grown by halogen-free vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Kimura, Taishi; Aoki, Yuko; Horibuchi, Kayo; Nakamura, Daisuke

    2016-12-01

    The work reported herein demonstrated that nanopipes can be formed via a surfactant effect, in which boron impurities preferentially migrate to semipolar and nonpolar facets. Approximately 3 μm-thick GaN layers were grown using halogen-free vapor phase epitaxy. All layers grown in pyrolytic boron nitride (pBN) crucibles were found to contain a high density of nanopipes in the range of 1010 to 1011 cm-2. The structural properties of these nanopipes were analyzed by X-ray rocking curve measurements, transmission electron microscopy, and three-dimensional atom probe (3DAP) tomography. The resulting 3DAP maps showed nanopipe-sized regions of boron segregation, and these nanopipes were not associated with the presence of dislocations. A mechanism for nanopipe formation was developed based on the role of boron as a surfactant and considering energy minima. A drastic reduction in the nanopipe density was achieved upon replacing the pBN crucibles with tantalum carbide-coated carbon crucibles. Consequently, we have confirmed that nanopipes can be formed solely due to surface energy changes induced by boron impurity surface segregation. For this reason, these results also indicate that nanopipes should be formed by other surfactant impurities such as Mg and Si.

  6. 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

  7. Three-dimensional tungsten nitride nanowires as high performance anode material for lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Qiu, Yongfu; Han, Yi; Guo, Yan; Cheng, Faliang

    2016-08-01

    Nanostructure materials often achieve low capacity when the active material mass loading is high. In this communication, high mass-loading tungsten nitride nanowires (WNNWs) were fabricated on a flexible carbon cloth by hydrothermal method and post annealing. The prepared electrode exhibited remarkable cyclic stability and attractive rate capability for lithium storage. It delivers at a current density of 200 mA g-1, a high capacity of 418 mAh g-1, which is higher than that of conventional graphite. This research opens more opportunity for the fabrication of three-dimensional metal nitrides as negative electrode material for flexible lithium ion batteries.

  8. Potential use of gallium-doped phosphate-based glass material for periodontitis treatment.

    PubMed

    Sahdev, Rohan; Ansari, Tahera I; Higham, Susan M; Valappil, Sabeel P

    2015-07-01

    This study aimed at evaluating the potential effect of gallium-incorporated phosphate-based glasses towards periodontitis-associated bacteria, Porphyromonas gingivalis, and matrix metalloproteinase-13. Periodontitis describes a group of inflammatory diseases of the gingiva and supporting structures of the periodontium. They are initiated by the accumulation of plaque bacteria, such as the putative periodontal pathogen Porphyromonas gingivalis, but the host immune response such as elevated matrix metalloproteinases are the major contributing factor for destruction of periodontal tissues. Antibacterial assays of gallium-incorporated phosphate-based glasses were conducted on Porphyromonas gingivalis ATCC 33277 using disc diffusion assay on fastidious anaerobe agar and liquid broth assay in a modified tryptic soy broth. In vitro study investigated the effect of gallium on purified recombinant human matrix metalloproteinase-13 activity using matrix metalloproteinase assay kit. In vivo biocompatibility of gallium-incorporated phosphate-based glass was evaluated in rats as subcutaneous implants. Antibacterial assay of gallium displayed activity against Porphyromonas gingivalis (inhibition zone of 22 ± 0.5 mm compared with 0 mm for control glass, c-PBG). Gallium in the glass contributed to growth inhibitory effect on Porphyromonas gingivalis (up to 1.30 reductions in log 10 values of the viable counts compared with control) in a modified tryptic soy broth. In vitro study showed gallium-incorporated phosphate-based glasses inhibited matrix metalloproteinase activity significantly (p ≤ 0.01) compared with c-PBG. Evaluation of in vivo biocompatibility of gallium-incorporated phosphate-based glasses in rats showed a non-toxic and foreign body response after 2 weeks of implantation. The results indicate that gallium ions might act on multiple targets of biological mechanisms underlying periodontal disease. Moreover, gallium-incorporated phosphate-based glasses

  9. Compositional Control of the Mixed Anion Alloys in Gallium-Free InAs/InAsSb Superlattice Materials for Infrared Sensing (Postprint)

    DTIC Science & Technology

    2015-08-28

    AFRL-RX-WP-JA-2016-0251 COMPOSITIONAL CONTROL OF THE MIXED ANION ALLOYS IN GALLIUM- FREE InAs/InAsSb SUPERLATTICE MATERIALS FOR...ANION ALLOYS IN GALLIUM- FREE InAs/InAsSb SUPERLATTICE MATERIALS FOR INFRARED SENSING (POSTPRINT) 5a. CONTRACT NUMBER FA8650-07-D-5800-0006 5b...proceedings.spiedigitallibrary.org doi: 10.1117/12.2186188 14. ABSTRACT (Maximum 200 words) Gallium (Ga)- free InAs/InAsSb superlattices (SLs) are being actively explored for

  10. 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)

  11. Investigation of an Electrochemical Method for Separation of Copper, Indium, and Gallium from Pretreated CIGS Solar Cell Waste Materials.

    PubMed

    Gustafsson, Anna M K; Björefors, Fredrik; Steenari, Britt-Marie; Ekberg, Christian

    2015-01-01

    Recycling of the semiconductor material copper indium gallium diselenide (CIGS) is important to ensure a future supply of indium and gallium, which are relatively rare and therefore expensive elements. As a continuation of our previous work, where we recycled high purity selenium from CIGS waste materials, we now show that copper and indium can be recycled by electrodeposition from hydrochloric acid solutions of dissolved selenium-depleted material. Suitable potentials for the reduction of copper and indium were determined to be -0.5 V and -0.9 V (versus the Ag/AgCl reference electrode), respectively, using cyclic voltammetry. Electrodeposition of first copper and then indium from a solution containing the dissolved residue from the selenium separation and ammonium chloride in 1 M HCl gave a copper yield of 100.1 ± 0.5% and an indium yield of 98.1 ± 2.5%. The separated copper and indium fractions contained no significant contamination of the other elements. Gallium remained in solution together with a small amount of indium after the separation of copper and indium and has to be recovered by an alternative method since electrowinning from the chloride-rich acid solution was not effective.

  12. Planar Homojunction Gallium Nitride (GaN) P-i-N Device Evaluated for Betavoltaic Energy Conversion: Measurement and Analysis

    DTIC Science & Technology

    2016-09-01

    power sources are measured in decades, not years. The energy density of isotopes (J/kg) is 106 greater than that of chemical batteries. The energy...Device fabrication, structure design, and packaging with strict quality requirements are needed to improve the ability of the betavoltaic to produce...material, reducing their efficiency. It is not until recently that wafer quality of SiC has been improved due to wider use in power components

  13. Boron nitride composites

    DOEpatents

    Kuntz, Joshua D.; Ellsworth, German F.; Swenson, Fritz J.; Allen, Patrick G.

    2017-02-21

    According to one embodiment, a composite product includes: a matrix material including hexagonal boron nitride and one or more borate binders; and a plurality of cubic boron nitride particles dispersed in the matrix material. According to another embodiment, a composite product includes: a matrix material including hexagonal boron nitride and amorphous boron nitride; and a plurality of cubic boron nitride particles dispersed in the matrix material.

  14. Investigation of Nitrogen-Rich Carbon Nitride Networks as Redox-Active Metal Catalyst Support Materials

    DTIC Science & Technology

    2004-10-29

    Equation 1),1 although for mass balance there may be trace amounts of chloramines or chlorine gas also produced. (C3N3)(NHCl)3 C3N4+x(H)y + (3-y...It is significant to realize that the carbon nitride (C3N4+x) materials are formed under very hot and corrosive acidic conditions, facts that bode

  15. GaN@ZIF-8: selective formation of gallium nitride quantum dots inside a zinc methylimidazolate framework.

    PubMed

    Esken, Daniel; Turner, Stuart; Wiktor, Christian; Kalidindi, Suresh Babu; Van Tendeloo, Gustaaf; Fischer, Roland A

    2011-10-19

    The microporous zeolitic imidazolate framework [Zn(MeIM)(2); ZIF-8; MeIM = imidazolate-2-methyl] was quantitatively loaded with trimethylamine gallane [(CH(3))(3)NGaH(3)]. The obtained inclusion compound [(CH(3))(3)NGaH(3)]@ZIF-8 reveals three precursor molecules per host cavity. Treatment with ammonia selectively yields the caged cyclotrigallazane intermediate (H(2)GaNH(2))(3)@ZIF-8, and further annealing gives GaN@ZIF-8. This new composite material was characterized with FT-IR spectroscopy, solid-state NMR spectroscopy, powder X-ray diffraction, elemental analysis, (scanning) transmission electron microscopy combined with electron energy-loss spectroscopy, photoluminescence (PL) spectroscopy, and N(2) sorption measurements. The data give evidence for the presence of GaN nanoparticles (1-3 nm) embedded in the cavities of ZIF-8, including a blue-shift of the PL emission band caused by the quantum size effect.

  16. Crystalline boron nitride aerogels

    DOEpatents

    Zettl, Alexander K.; Rousseas, Michael; Goldstein, Anna P.; Mickelson, William; Worsley, Marcus A.; Woo, Leta

    2017-04-04

    This disclosure provides methods and materials related to boron nitride aerogels. In one aspect, a material comprises an aerogel comprising boron nitride. The boron nitride has an ordered crystalline structure. The ordered crystalline structure may include atomic layers of hexagonal boron nitride lying on top of one another, with atoms contained in a first layer being superimposed on atoms contained in a second layer.

  17. GALLIUM ARSENIDE DENDRITE SINGLE CRYSTAL PROGRAM

    DTIC Science & Technology

    ARSENIDES, *GALLIUM COMPOUNDS, *LABORATORY FURNACES, * SOLAR CELLS , CRUCIBLES, DESIGN, DIFFUSION, EXPLOSIONS, INTERMETALLIC COMPOUNDS, MATERIALS, PHOSPHORUS, SINGLE CRYSTALS, TEMPERATURE CONTROL, ZINC

  18. 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.

  19. UV-Assisted Alcohol Sensors using Gallium Nitride Nanowires Functionalized with Zinc Oxide and Tin Dioxide Nanoparticles

    NASA Astrophysics Data System (ADS)

    Bajpai, Ritu

    The motivation behind this work has been to address two of the most challenging issues posed to semiconductor gas sensors--- tuning the device selectivity and sensitivity to a wide variety of gases. In a chemiresistor type nanowire sensor, the sensitivity and selectivity depend on the interaction of different chemical analytes with the nanowire surface. Constrained by the surface properties of the nanowire material, most nanowire sensors can detect only specific type of analytes. In order to make a nano-sensor array for a wide range of analytes, there is a need to tune the device sensitivity and selectivity towards different chemicals. Employing the inherent advantages of nanostructure based sensing such as large surface area, miniature size, low power consumption, and nmol/mol (ppb) sensitivity, an attempt has been made to propose a device with tunable selectivity and sensitivity. The idea proposed in this work is to functionalize GaN nanowires which have relatively inactive surface properties (i.e., with no chemiresistive sensitivity to different classes of organic vapors), with analyte dependent active metal oxides. The selectivity of the sensor devices is controlled independent of the surface properties of the nanowire itself. It is the surface properties of the functionalizing metal oxides which determine the selectivity of these sensors. Further facilitated by the proposed fabrication technique, these sensors can be easily tuned to detect different gases. The prototype developed in this work is that of a UV assisted alcohol sensor using GaN nanowires functionalized with ZnO and SnO2 nanoparticles. As opposed to the widely demonstrated metal oxide based sensors assisted by elevated temperature, the operation of photoconductive semiconductor sensor devices such as those fabricated in this work, can also be assisted by UV illumination at room temperature. Temperature assisted sensing requires an integrated on-chip heater, which could impose constraints on the

  20. Hexagonal boron nitride epitaxial layers as neutron detector materials

    NASA Astrophysics Data System (ADS)

    Li, J.; Dahal, R.; Majety, S.; Lin, J. Y.; Jiang, H. X.

    2011-10-01

    Micro-strip metal-semiconductor-metal detectors for thermal neutron sensing were fabricated from hexagonal boron nitride (hBN) epilayers synthesized by metal organic chemical vapor deposition. Experimental measurements indicated that the thermal neutron absorption coefficient and length of natural hBN epilayers are about 0.00361 μm -1 and 277 μm, respectively. A continuous irradiation with a thermal neutron beam generated an appreciable current response in hBN detectors, corresponding to an effective conversion efficiency approaching ˜80% for absorbed neutrons. Our results indicate that hBN semiconductors would enable the development of essentially ideal solid-state thermal neutron detectors in which both neutron capture and carrier collection are accomplished in the same hBN semiconductor. These solid-state detectors have the potential to replace 3He gas detectors, which faces the very serious issue of 3He gas shortage.

  1. Nitride semiconductors for ultraviolet detection

    NASA Astrophysics Data System (ADS)

    Davis, R. F.; Bremser, M. D.; Gruss, K.; Linthicum, K.; Ferry, B.

    1995-06-01

    Continued development and commercialization of optoelectronic devices, including light emitting diodes and semiconductor lasers produced from 3-5 gallium arsenide-based materials, has also generated interest in the much wider bandgap semiconductor mononitride materials containing aluminum, gallium, and indium. The majority of the studies have been conducted on pure gallium nitride thin films having the wurtzite structure, and this emphasis continues to the present day. The program objectives achieved in this reporting period have been (1) the growth of undoped, high resistivity and n- and p-type doped monocrystalline, GaN thin films on alpha(6H)-SiC(000l) wafers via organometallic vapor phase epitaxy (OMVPE), and their characterization via photoluminescence; (2) the growth and cathodoluminescence characterization of Al(x)Ga(1-x)N alloys and abrupt heterojunctions of these alloys; (3) the development and application of a novel NH3 cracker cell for gas source MBE to reduce film damage; and (4) the reactive ion etching of undoped GaN films via use of Cl-containing compounds.

  2. Materials processing and in-vivo animal studies of nitrided hydroxyapatite bioceramics

    NASA Astrophysics Data System (ADS)

    Rashid, Nancy Elizabeth

    2000-10-01

    Calcium phosphate bioceramics are currently being used in medicine and dentistry, for reconstruction or repair of diseased or injured bone, but with limited success. Incorporating nitrogen into phosphate glasses has resulted in improved properties, and it is proposed that similar benefits may be gained from nitriding calcium phosphate bioceramics for bone implants as well. This work focuses on processing of hydroxyapatite and tricalcium phosphate bioceramics nitrided by using solid, liquid, gas and ion sources. These materials were characterized by chemical, structural, mechanical, and biological methods to determine both the material structure and their suitability as implant materials. Calcium nitride and NaPON glass were unsatisfactory sources of nitrogen for hydroxyapatite (HA) and/or tricalcium phosphate (TCP) ceramics. Calcium nitride, Ca3N2, is reacts with water vapor in the air, releasing ammonia, and leaving behind crystals of calcium oxide, CaO. The calcium oxide byproduct decreases the chemical stability of hydroxyapatite and HA/TCP composites in simulated body fluid. Sodium phosphorus oxynitride (NaPON) glass, in the form of a liquid sintering aid for HA, produces an inhomogeneous, composite as well. Hydroxyapatite heated at 800C in an ammonia atmosphere produces a homogeneous material with up to 2 wt% N. Infrared spectroscopy indicates cyanamide ions, CN22-, are formed by the incorporated nitrogen and impurity carbon. The use of 15N-doped ammonia results in an 15N NMR peak at 83.2 ppm, indicating P--N bonding. Raman spectroscopy may also indicate P--N bonding, but it is inconclusive. In a limited study, nitrogen may decrease the hardness and fracture toughness of the phosphate ceramic, hydroxyapatite, contrary to results expected for nitrogen in phosphate glasses. Nitrogen ions are incorporated in hydroxyapatite by ion implantation, with lower energies producing higher nitrogen contents. The highest concentration achieved was 3.55 wt% N, as determined

  3. Silicon nitride: A ceramic material with outstanding resistance to thermal shock and corrosion

    NASA Technical Reports Server (NTRS)

    Huebner, K. H.; Saure, F.

    1983-01-01

    The known physical, mechanical and chemical properties of reaction-sintered silicon nitride are summarized. This material deserves interest especially because of its unusually good resistance to thermal shock and corrosion at high temperatures. Two types are distinguished: reaction-sintered (porous) and hot-pressed (dense) Si3N4. Only the reaction-sintered material which is being produced today in large scale as crucibles, pipes, nozzles and tiles is considered.

  4. Bioactive silicon nitride: A new therapeutic material for osteoarthropathy.

    PubMed

    Pezzotti, Giuseppe; Marin, Elia; Adachi, Tetsuya; Rondinella, Alfredo; Boschetto, Francesco; Zhu, Wenliang; Sugano, Nobuhiko; Bock, Ryan M; McEntire, Bryan; Bal, Sonny B

    2017-03-22

    While the reciprocity between bioceramics and living cells is complex, it is principally governed by the implant's surface chemistry. Consequently, a deeper understanding of the chemical interactions of bioceramics with living tissue could ultimately lead to new therapeutic strategies. However, the physical and chemical principles that govern these interactions remain unclear. The intricacies of this biological synergy are explored within this paper by examining the peculiar surface chemistry of a relatively new bioceramic, silicon nitride (Si3N4). Building upon prior research, this paper aims at obtaining new insights into the biological interactions between Si3N4 and living cells, as a consequence of the off-stoichiometric chemical nature of its surface at the nanometer scale. We show here yet unveiled details of surface chemistry and, based on these new data, formulate a model on how, ultimately, Si3N4 influences cellular signal transduction functions and differentiation mechanisms. In other words, we interpret its reciprocity with living cells in chemical terms. These new findings suggest that Si3N4 might provide unique new medicinal therapies and effective remedies for various bone or joint maladies and diseases.

  5. Bioactive silicon nitride: A new therapeutic material for osteoarthropathy

    PubMed Central

    Pezzotti, Giuseppe; Marin, Elia; Adachi, Tetsuya; Rondinella, Alfredo; Boschetto, Francesco; Zhu, Wenliang; Sugano, Nobuhiko; Bock, Ryan M.; McEntire, Bryan; Bal, Sonny B.

    2017-01-01

    While the reciprocity between bioceramics and living cells is complex, it is principally governed by the implant’s surface chemistry. Consequently, a deeper understanding of the chemical interactions of bioceramics with living tissue could ultimately lead to new therapeutic strategies. However, the physical and chemical principles that govern these interactions remain unclear. The intricacies of this biological synergy are explored within this paper by examining the peculiar surface chemistry of a relatively new bioceramic, silicon nitride (Si3N4). Building upon prior research, this paper aims at obtaining new insights into the biological interactions between Si3N4 and living cells, as a consequence of the off-stoichiometric chemical nature of its surface at the nanometer scale. We show here yet unveiled details of surface chemistry and, based on these new data, formulate a model on how, ultimately, Si3N4 influences cellular signal transduction functions and differentiation mechanisms. In other words, we interpret its reciprocity with living cells in chemical terms. These new findings suggest that Si3N4 might provide unique new medicinal therapies and effective remedies for various bone or joint maladies and diseases. PMID:28327664

  6. Bioactive silicon nitride: A new therapeutic material for osteoarthropathy

    NASA Astrophysics Data System (ADS)

    Pezzotti, Giuseppe; Marin, Elia; Adachi, Tetsuya; Rondinella, Alfredo; Boschetto, Francesco; Zhu, Wenliang; Sugano, Nobuhiko; Bock, Ryan M.; McEntire, Bryan; Bal, Sonny B.

    2017-03-01

    While the reciprocity between bioceramics and living cells is complex, it is principally governed by the implant’s surface chemistry. Consequently, a deeper understanding of the chemical interactions of bioceramics with living tissue could ultimately lead to new therapeutic strategies. However, the physical and chemical principles that govern these interactions remain unclear. The intricacies of this biological synergy are explored within this paper by examining the peculiar surface chemistry of a relatively new bioceramic, silicon nitride (Si3N4). Building upon prior research, this paper aims at obtaining new insights into the biological interactions between Si3N4 and living cells, as a consequence of the off-stoichiometric chemical nature of its surface at the nanometer scale. We show here yet unveiled details of surface chemistry and, based on these new data, formulate a model on how, ultimately, Si3N4 influences cellular signal transduction functions and differentiation mechanisms. In other words, we interpret its reciprocity with living cells in chemical terms. These new findings suggest that Si3N4 might provide unique new medicinal therapies and effective remedies for various bone or joint maladies and diseases.

  7. Molecular single source precursors for synthesis of nitrogen-rich carbon nitride materials

    NASA Astrophysics Data System (ADS)

    Miller, Dale R.

    This dissertation describes work on the synthesis, characterization and application of nitrogen-rich (CN1.0-1.6), graphite-like, carbon nitride (CNX) materials. Despite the focus of many recent efforts towards diamond-like carbon nitrides, graphite-like carbon nitrides are able to stand alone as interesting and challenging materials. The CNX powders and films studied here were synthesized using a single-source precursor approach. Focus was aimed at precursors containing an s-triazine (C3N3) aromatic ring with a variety of substituents, including -NHCl, -N3, pyridyl, hydrazino and alkyl amino. In contrast to past high temperature/high pressure studies, this work focused on precursors designed to decompose at low temperature (< 400 °C) and ambient pressure. Precursors containing reactive substituents (-N3, -NHNH 2, -NHCl) are particularly good for low temperature (< 300 °C) production of nitrogen-rich CNX powders and films, some of which exhibit blue photoluminescence. Specifically, the commercial molecule trichloromelamine, [TCM, C3N3(NHCl)3], was shown to decompose rapidly and energetically near 185 °C, using thermal methods to produce CN1.6H0.7 powders. Capitalizing on the electron rich nitrogen sites of the TCM derived CNX material, both hot filament decomposition and hydrogen reduction were used to incorporate transition metals. The hydrogen reduction method was used to examine a series of CNX/metal (Pt, Cu, Ni) samples for use as methanol fuel cell catalyst supports. Carbon paste electrodes made from CNX/Pt and CNX/Ni materials showed promising catalytic behavior. The success of the s-triazine precursor approach was successfully extended to the larger ring system, s-heptazine. Specifically, 2,5,8-triazido-s-heptazine, [TAH, C6N 7(N3)3], was shown to be even more successful than its smaller counterpart 2,4,6-triazido-s-triazine, [TAT, C3N3(N3)3), at producing nitrogen-rich carbon nitride powders. The structurally ambiguous CNX materials were characterized

  8. Optical and Electrical Properties of III-Nitrides and Related Materials

    SciTech Connect

    Jiang, Hongxing; Lin, Jingyu

    2016-01-22

    Among the members of the III-nitride material system, boron-nitride (BN) is the least studied and understood. Its extraordinary physical properties, such as ultra-high chemical stability, thermal conductivity, electrical resistivity, band gap (Eg ~ 6 eV), and optical absorption near the band gap make hexagonal BN (h-BN) the material of choice for emerging applications such as deep ultraviolet (DUV) optoelectronic devices. Moreover, h-BN has a close lattice match to graphene and is the most suitable substrate and dielectric/separation layer for graphene electronics and optoelectronics. Similar to graphene, low dimensional h-BN is expected to possess rich new physics. Other potential applications include super-capacitors and electron emitters. However, our knowledge concerning the semiconducting properties of h-BN is very scarce. The project aims to extend our studies to the “newest” family member of the III-nitride material system, h-BN, and to address issues that have not yet been explored but are expected to profoundly influence our understanding on its fundamental properties and device applications. During the supporting period, we have improved the growth processes of h-BN epilayers by metal organic chemical vapor deposition (MOCVD), investigated the fundamental material properties, and identified several unique features of h-BN as well as critical issues that remain to be addressed.

  9. Sol-gel preparation of low oxygen content, high surface area silicon nitride and imidonitride materials.

    PubMed

    Sardar, Kripasindhu; Bounds, Richard; Carravetta, Marina; Cutts, Geoffrey; Hargreaves, Justin S J; Hector, Andrew L; Hriljac, Joseph A; Levason, William; Wilson, Felix

    2016-04-07

    Reactions of Si(NHMe)4 with ammonia are effectively catalysed by small ammonium triflate concentrations, and can be used to produce free-standing silicon imide gels. Firing at various temperatures produces amorphous or partially crystallised silicon imidonitride/nitride samples with high surface areas and low oxygen contents. The crystalline phase is entirely α-Si3N4 and structural similarities are observed between the amorphous and crystallised materials.

  10. III-nitride integration on ferroelectric materials of lithium niobate by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Namkoong, Gon; Lee, Kyoung-Keun; Madison, Shannon M.; Henderson, Walter; Ralph, Stephen E.; Doolittle, W. Alan

    2005-10-01

    Integration of III-nitride electrical devices on the ferroelectric material lithium niobate (LiNbO3) has been demonstrated. As a ferroelectric material, lithium niobate has a polarization which may provide excellent control of the polarity of III-nitrides. However, while high temperature, 1000°C, thermal treatments produce atomically smooth surfaces, improving adhesion of GaN epitaxial layers on lithium niobate, repolarization of the substrate in local domains occurs. These effects result in multi domains of mixed polarization in LiNbO3, producing inversion domains in subsequent GaN epilayers. However, it is found that AlN buffer layers suppress inversion domains of III-nitrides. Therefore, two-dimensional electron gases in AlGaN /GaN heterojunction structures are obtained. Herein, the demonstration of the monolithic integration of high power devices with ferroelectric materials presents possibilities to control LiNbO3 modulators on compact optoelectronic/electronic chips.

  11. High Kinetic Energy Penetrator Shielding and High Wear Resistance Materials Fabricated with Boron Nitride Nanotubes (BNNTS) and BNNT Polymer Composites

    NASA Technical Reports Server (NTRS)

    Kang, Jin Ho (Inventor); Park, Cheol (Inventor); Sauti, Godfrey (Inventor); Smith, Michael W. (Inventor); Jordan, Kevin C. (Inventor); Lowther, Sharon E. (Inventor); Bryant, Robert George (Inventor)

    2015-01-01

    Boron nitride nanotubes (BNNTs), boron nitride nanoparticles (BNNPs), carbon nanotubes (CNTs), graphites, or combinations, are incorporated into matrices of polymer, ceramic or metals. Fibers, yarns, and woven or nonwoven mats of BNNTs are used as toughening layers in penetration resistant materials to maximize energy absorption and/or high hardness layers to rebound or deform penetrators. They can be also used as reinforcing inclusions combining with other polymer matrices to create composite layers like typical reinforcing fibers such as Kevlar.RTM., Spectra.RTM., ceramics and metals. Enhanced wear resistance and usage time are achieved by adding boron nitride nanomaterials, increasing hardness and toughness. Such materials can be used in high temperature environments since the oxidation temperature of BNNTs exceeds 800.degree. C. in air. Boron nitride based composites are useful as strong structural materials for anti-micrometeorite layers for spacecraft and space suits, ultra strong tethers, protective gear, vehicles, helmets, shields and safety suits/helmets for industry.

  12. Sub-diffractional volume-confined polaritons in the natural hyperbolic material hexagonal boron nitride.

    PubMed

    Caldwell, Joshua D; Kretinin, Andrey V; Chen, Yiguo; Giannini, Vincenzo; Fogler, Michael M; Francescato, Yan; Ellis, Chase T; Tischler, Joseph G; Woods, Colin R; Giles, Alexander J; Hong, Minghui; Watanabe, Kenji; Taniguchi, Takashi; Maier, Stefan A; Novoselov, Kostya S

    2014-10-17

    Strongly anisotropic media, where the principal components of the dielectric tensor have opposite signs, are called hyperbolic. Such materials exhibit unique nanophotonic properties enabled by the highly directional propagation of slow-light modes localized at deeply sub-diffractional length scales. While artificial hyperbolic metamaterials have been demonstrated, they suffer from high plasmonic losses and require complex nanofabrication, which in turn induces size-dependent limitations on optical confinement. The low-loss, mid-infrared, natural hyperbolic material hexagonal boron nitride is an attractive alternative. Here we report on three-dimensionally confined 'hyperbolic polaritons' in boron nitride nanocones that support four series (up to the seventh order) modes in two spectral bands. The resonant modes obey the predicted aspect ratio dependence and exhibit high-quality factors (Q up to 283) in the strong confinement regime (up to λ/86). These observations assert hexagonal boron nitride as a promising platform for studying novel regimes of light-matter interactions and nanophotonic device engineering.

  13. Niobium Nitride Nb4N5 as a New High‐Performance Electrode Material for Supercapacitors

    PubMed Central

    Cui, Houlei; Zhu, Guilian; Liu, Xiangye; Liu, Fengxin; Xie, Yian; Yang, Chongyin; Lin, Tianquan; Gu, Hui

    2015-01-01

    Supercapacitors suffer either from low capacitance for carbon or derivate electrodes or from poor electrical conductivity and electrochemical stability for metal oxide or conducting polymer electrodes. Transition metal nitrides possess fair electrical conductivity but superior chemical stability, which may be desirable candidates for supercapacitors. Herein, niobium nitride, Nb4N5, is explored to be an excellent capacitive material for the first time. An areal capacitance of 225.8 mF cm−2, with a reasonable rate capability (60.8% retention from 0.5 to 10 mA cm−2) and cycling stability (70.9% retention after 2000 cycles), is achieved in Nb4N5 nanochannels electrode with prominent electrical conductivity and electrochemical activity. Faradaic pseudocapacitance is confirmed by the mechanistic studies, deriving from the proton incorporation/chemisorption reaction owing to the copious +5 valence Nb ions in Nb4N5. Moreover, this Nb4N5 nanochannels electrode with an ultrathin carbon coating exhibits nearly 100% capacitance retention after 2000 CV cycles, which is an excellent cycling stability for metal nitride materials. Thus, the Nb4N5 nanochannels are qualified for a candidate for supercapacitors and other energy storage applications. PMID:27980920

  14. Sub-diffractional volume-confined polaritons in the natural hyperbolic material hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Caldwell, Joshua D.; Kretinin, Andrey V.; Chen, Yiguo; Giannini, Vincenzo; Fogler, Michael M.; Francescato, Yan; Ellis, Chase T.; Tischler, Joseph G.; Woods, Colin R.; Giles, Alexander J.; Hong, Minghui; Watanabe, Kenji; Taniguchi, Takashi; Maier, Stefan A.; Novoselov, Kostya S.

    2014-10-01

    Strongly anisotropic media, where the principal components of the dielectric tensor have opposite signs, are called hyperbolic. Such materials exhibit unique nanophotonic properties enabled by the highly directional propagation of slow-light modes localized at deeply sub-diffractional length scales. While artificial hyperbolic metamaterials have been demonstrated, they suffer from high plasmonic losses and require complex nanofabrication, which in turn induces size-dependent limitations on optical confinement. The low-loss, mid-infrared, natural hyperbolic material hexagonal boron nitride is an attractive alternative. Here we report on three-dimensionally confined ‘hyperbolic polaritons’ in boron nitride nanocones that support four series (up to the seventh order) modes in two spectral bands. The resonant modes obey the predicted aspect ratio dependence and exhibit high-quality factors (Q up to 283) in the strong confinement regime (up to λ/86). These observations assert hexagonal boron nitride as a promising platform for studying novel regimes of light-matter interactions and nanophotonic device engineering.

  15. Quantum cascade emission in the III-nitride material system designed with effective interface grading

    SciTech Connect

    Song, Alex Y. Huang, Tzu-Yung; Zah, Chung-En; Gmachl, Claire F.; Bhat, Rajaram; Wang, Jie; Allerman, Andrew A.

    2015-09-28

    We report the realization of quantum cascade (QC) light emission in the III-nitride material system, designed with effective interface grading (EIG). EIG induces a continuous transition between wells and barriers in the quantum confinement, which alters the eigenstate system and even delocalizes the states with higher energy. Fully transverse-magnetic spontaneous emission is observed from the fabricated III-nitride QC structure, with a center wavelength of ∼4.9 μm and a full width at half maximum of ∼110 meV, both in excellent agreement with theoretical predictions. A multi-peak photo-response spectrum is also measured from the QC structure, which again agrees well with theoretical calculations and verifies the effects of EIG.

  16. Chemisorption of Hydroxide on 2D Materials From DFT Calculations: Graphene Versus Hexagonal Boron Nitride

    PubMed Central

    Grosjean, Benoit; Pean, Clarisse; Siria, Alessandro; Bocquet, Lyderic; Vuilleumier, Rodolphe; Bocquet, Marie-Laure

    2017-01-01

    Recent nanofluidic measurements revealed strongly different surface charge measurements for boron-nitride and graphitic nanotubes when in contact with saline and alkaline water. 1,2 These observations contrast with the similar reactivity of a graphene layer and its boron nitride counterpart, using Density Functional Theory (DFT) framework, for intact and dissociative adsorption of gaseous water molecules. Here, we investigate, by DFT in implicit water, single and multiple adsorption of anionic hydroxide on single layers. A differential adsorption strength is found in vacuum for the first ionic adsorption on the two materials – chemisorbed on BN while physisorbed on graphene. The effect of implicit solvation reduces all adsorption values resulting in a favorable (non-favorable) adsorption on BN (graphene). We also calculate a pKa ≃ 6 for BN in water, in good agreement with experiments. Comparatively, the unfavorable results for graphene in water echoes the weaker surface charge measurements, but points to an alternative scenario. PMID:27809540

  17. 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...

  18. 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...

  19. 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...

  20. 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...

  1. Synthesis of ternary metal nitride nanoparticles using mesoporous carbon nitride as reactive template.

    PubMed

    Fischer, Anna; Müller, Jens Oliver; Antonietti, Markus; Thomas, Arne

    2008-12-23

    Mesoporous graphitic carbon nitride was used as both a nanoreactor and a reactant for the synthesis of ternary metal nitride nanoparticles. By infiltration of a mixture of two metal precursors into mesoporous carbon nitride, the pores act first as a nanoconfinement, generating amorphous mixed oxide nanoparticles. During heating and decomposition, the carbon nitride second acts as reactant or, more precisely, as a nitrogen source, which converts the preformed mixed oxide nanoparticles into the corresponding nitride (reactive templating). Using this approach, ternary metal nitride particles with diameters smaller 10 nm composed of aluminum gallium nitride (Al-Ga-N) and titanium vanadium nitride (Ti-V-N) were synthesized. Due to the confinement effect of the carbon nitride matrix, the composition of the resulting metal nitride can be easily adjusted by changing the concentration of the preceding precursor solution. Thus, ternary metal nitride nanoparticles with continuously adjustable metal composition can be produced.

  2. The rapid solid-state synthesis of group III and transition metal nitrides at ambient and high pressures

    NASA Astrophysics Data System (ADS)

    Wallace, Charles Henry

    The development and improvement of new and existing technologies requires the synthesis of ultra-pure, crystalline materials. To meet this need, new ways of synthesizing materials with specific properties that are difficult or impossible to produce using traditional methods must be developed. The research presented herein outlines various new techniques that can be effectively used to produce high quality, crystalline materials using a novel time and energy efficient process called solid-state metathesis. This process combines two or more solid, molecular precursors that react exothermically to rapidly produce crystalline refractory ceramic and electronic materials, such as binary and ternary metal carbides, nitrides, phosphides, sulfides and oxides. Several important materials, including graphite, gallium nitride, indium nitride, tantalum nitride, silicon nitride and cubic boron nitride, which had been difficult or impossible to synthesize using standard solid-state metathesis reactions, can now be synthesized using modified metathesis methods. One of the new techniques described in this thesis for the successful synthesis of materials, such as gallium nitride, is the use of high pressures (up to 80,000 atm) before initiating a solid-state reaction. New nitrogen precursors were investigated, such as lithium amide and ammonium chloride, which when combined in the proper ratios, aid in the formation of gallium and indium nitride at ambient pressures. The major focus of this work is on new synthetic techniques that rapidly produce pure, crystalline materials. Since gallium nitride is an important direct wide-bandgap semiconductor of interest for high brightness, blue light-emitting diodes, lasers and flat panel displays, a large majority of the research described has been devoted to developing more efficient methods for synthesizing and purifying high quality products. Also discussed is the importance of controlling the temperature by the addition of less reactive

  3. III-antimonide/nitride based semiconductors for optoelectronic materials and device studies : LDRD 26518 final report.

    SciTech Connect

    Kurtz, Steven Ross; Hargett, Terry W.; Serkland, Darwin Keith; Waldrip, Karen Elizabeth; Modine, Normand Arthur; Klem, John Frederick; Jones, Eric Daniel; Cich, Michael Joseph; Allerman, Andrew Alan; Peake, Gregory Merwin

    2003-12-01

    The goal of this LDRD was to investigate III-antimonide/nitride based materials for unique semiconductor properties and applications. Previous to this study, lack of basic information concerning these alloys restricted their use in semiconductor devices. Long wavelength emission on GaAs substrates is of critical importance to telecommunication applications for cost reduction and integration into microsystems. Currently InGaAsN, on a GaAs substrate, is being commercially pursued for the important 1.3 micrometer dispersion minima of silica-glass optical fiber; due, in large part, to previous research at Sandia National Laboratories. However, InGaAsN has not shown great promise for 1.55 micrometer emission which is the low-loss window of single mode optical fiber used in transatlantic fiber. Other important applications for the antimonide/nitride based materials include the base junction of an HBT to reduce the operating voltage which is important for wireless communication links, and for improving the efficiency of a multijunction solar cell. We have undertaken the first comprehensive theoretical, experimental and device study of this material with promising results. Theoretical modeling has identified GaAsSbN to be a similar or potentially superior candidate to InGaAsN for long wavelength emission on GaAs. We have confirmed these predictions by producing emission out to 1.66 micrometers and have achieved edge emitting and VCSEL electroluminescence at 1.3 micrometers. We have also done the first study of the transport properties of this material including mobility, electron/hole mass, and exciton reduced mass. This study has increased the understanding of the III-antimonide/nitride materials enough to warrant consideration for all of the target device applications.

  4. Improvements to III-nitride light-emitting diodes through characterization and material growth

    NASA Astrophysics Data System (ADS)

    Getty, Amorette Rose Klug

    A variety of experiments were conducted to improve or aid the improvement of the efficiency of III-nitride light-emitting diodes (LEDs), which are a critical area of research for multiple applications, including high-efficiency solid state lighting. To enhance the light extraction in ultraviolet LEDs grown on SiC substrates, a distributed Bragg reflector (DBR) optimized for operation in the range from 250 to 280 nm has been developed using MBE growth techniques. The best devices had a peak reflectivity of 80% with 19.5 periods, which is acceptable for the intended application. DBR surfaces were sufficiently smooth for subsequent epitaxy of the LED device. During the course of this work, pros and cons of AlGaN growth techniques, including analog versus digital alloying, were examined. This work highlighted a need for more accurate values of the refractive index of high-Al-content AlxGa1-xNin the UV wavelength range. We present refractive index results for a wide variety of materials pertinent to the fabrication of optical III-nitride devices. Characterization was done using Variable-Angle Spectroscopic Ellipsometry. The three binary nitrides, and all three ternaries, have been characterized to a greater or lesser extent depending on material compositions available. Semi-transparent p-contact materials and other thin metals for reflecting contacts have been examined to allow optimization of deposition conditions and to allow highly accurate modeling of the behavior of light within these devices. Standard substrate materials have also been characterized for completeness and as an indicator of the accuracy of our modeling technique. We have demonstrated a new technique for estimating the internal quantum efficiency (IQE) of nitride light-emitting diodes. This method is advantageous over the standard low-temperature photoluminescence-based method of estimating IQE, as the new method is conducted under the same conditions as normal device operation. We have developed

  5. Structural silicon nitride materials containing rare earth oxides

    DOEpatents

    Andersson, Clarence A.

    1980-01-01

    A ceramic composition suitable for use as a high-temperature structural material, particularly for use in apparatus exposed to oxidizing atmospheres at temperatures of 400 to 1600.degree. C., is found within the triangular area ABCA of the Si.sub.3 N.sub.4 --SiO.sub.2 --M.sub.2 O.sub.3 ternary diagram depicted in FIG. 1. M is selected from the group of Yb, Dy, Er, Sc, and alloys having Yb, Y, Er, or Dy as one component and Sc, Al, Cr, Ti, (Mg +Zr) or (Ni+Zr) as a second component, said alloy having an effective ionic radius less than 0.89 A.

  6. Rolling-element fatigue life of silicon nitride balls. [as compared to that of steel, ceramic, and cermet materials

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Zaretsky, E. V.

    1974-01-01

    The five-ball fatigue tester was used to evaluate silicon nitride as a rolling-element bearing material. Results indicate that hot-pressed silicon nitride running against steel may be expected to yield fatigue lives comparable to or greater than those of bearing quality steel running against steel at stress levels typical rolling-element bearing application. The fatigue life of hot-pressed silicon nitride is considerably greater than that of any ceramic or cermet tested. Computer analysis indicates that there is no improvement in the lives of 120-mm-bore angular--contact ball bearings of the same geometry operating at DN values from 2 to 4 million where hot-pressed silicon nitride balls are used in place of steel balls.

  7. Ab initio studies on the adsorption and implantation of Al and Fe to nitride materials

    SciTech Connect

    Riedl, H.; Zálešák, J.; Arndt, M.; Polcik, P.; Holec, D.; Mayrhofer, P. H.

    2015-09-28

    The formation of transfer material products on coated cutting and forming tools is a major failure mechanism leading to various sorts of wear. To describe the atomistic processes behind the formation of transfer materials, we use ab initio to study the adsorption energy as well as the implantation barrier of Al and Fe atoms for (001)-oriented surfaces of TiN, Ti{sub 0.50}Al{sub 0.50}N, Ti{sub 0.90}Si{sub 0.10}N, CrN, and Cr{sub 0.90}Si{sub 0.10}N. The interactions between additional atoms and nitride-surfaces are described for pure adhesion, considering no additional stresses, and for the implantation barrier. The latter, we simplified to the stress required to implant Al and Fe into sub-surface regions of the nitride material. The adsorption energies exhibit pronounced extrema at high-symmetry positions and are generally highest at nitrogen sites. Here, the binary nitrides are comparable to their ternary counterparts and the average adhesive energy is higher (more negative) on CrN than TiN based systems. Contrary, the implantation barrier for Al and Fe atoms is higher for the ternary systems Ti{sub 0.50}Al{sub 0.50}N, Ti{sub 0.90}Si{sub 0.10}N, and Cr{sub 0.90}Si{sub 0.10}N than for their binary counterparts TiN and CrN. Based on our results, we can conclude that TiN based systems outperform CrN based systems with respect to pure adhesion, while the Si-containing ternaries exhibit higher implantation barriers for Al and Fe atoms. The data obtained are important to understand the atomistic interaction of metal atoms with nitride-based materials, which is valid not just for machining operations but also for any combination such as interfaces between coatings and substrates or multilayer and phase arrangements themselves.

  8. Low-temperature synthesis of gallium nitride thin films using electron cyclotron resonance plasma assisted pulsed laser deposition from a GaAs target

    SciTech Connect

    Sun, J.; Wu, A.M.; Xu, N.; Ying, Z.F.; Shen, X.K.; Dong, Z.B.; Wu, J.D.; Shi, L.Q.

    2005-11-15

    Using reactive pulsed laser deposition assisted by electron cyclotron resonance (ECR) plasma, we have synthesized GaN thin films from a polycrystalline GaAs target at low temperatures. This was achieved by ablating the GaAs target in the reactive environment of a nitrogen plasma generated from ECR microwave discharge in pure nitrogen gas and depositing the films with concurrent bombardment by the low-energy nitrogen plasma stream. High-energy ion backscattering spectroscopy analysis shows that the synthesized films are gallium rich. Characterizations by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy confirm the presence of GaN bonds in the films. The recorded absorption spectrum also reveals GaN stretching mode characteristic of the hexagonal GaN phase. The synthesized GaN films are transparent in the visible region and have a band gap of 3.38 eV. Optical emission from the plume during film deposition reveals that the plume created by pulsed laser ablation of the GaAs target consists mainly of monoatomic atoms and ions of gallium and arsenic. Mechanisms responsible for the formation of GaN molecules and the growth of GaN films are also discussed.

  9. 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.

  10. Dyakonov surface waves at the interface between hexagonal-boron-nitride and isotropic material

    NASA Astrophysics Data System (ADS)

    Zhu, B.; Ren, G.; Gao, Y.; Wang, Q.; Wan, C.; Wang, J.; Jian, S.

    2016-12-01

    In this paper we analyze the propagation of Dyakonov surface waves (DSWs) at the interface between hexagonal-boron-nitride (h-BN) and isotropic dielectric material. Various properties of DSWs supported at the dielectric-elliptic and dielectric-hyperbolic types of interfaces have been theoretically investigated, including the real effective index, propagation length, the angular existence domain (AED) and the composition ratio of evanescent field components in an h-BN crystal and isotropic dielectric material, respectively. The analysis in this paper reveals that h-BN could be a promising anisotropic material to observe the propagation of DSWs and may have potential diverse applications, such as high sensitivity stress sensing or optical sensing of analytes infiltrating dielectric materials.

  11. Identification of new pillared-layered carbon nitride materials at high pressure

    PubMed Central

    Salamat, Ashkan; Deifallah, Malek; Cabrera, Raul Quesada; Corà, Furio; McMillan, Paul F.

    2013-01-01

    The compression of the layered carbon nitride C6N9H3·HCl was studied experimentally and with density functional theory (DFT) methods. This material has a polytriazine imide structure with Cl− ions contained within C12N12 voids in the layers. The data indicate the onset of layer buckling accompanied by movement of the Cl− ions out of the planes beginning above 10–20 GPa followed by an abrupt change in the diffraction pattern and c axis spacing associated with formation of a new interlayer bonded phase. The transition pressure is calculated to be 47 GPa for the ideal structures. The new material has mixed sp2–sp3 hybridization among the C and N atoms and it provides the first example of a pillared-layered carbon nitride material that combines the functional properties of the graphitic-like form with improved mechanical strength. Similar behavior is predicted to occur for Cl-free structures at lower pressures. PMID:23817211

  12. Influence of molybdenum silicide additions on high-temperature oxidation resistance of silicon nitride materials

    SciTech Connect

    Klemm, H.; Tangermann, K.; Schubert, C.; Hermel, W.

    1996-09-01

    The influence of additions of molybdenum disilicide (MoSi{sub 2}) on the microstructure and the mechanical properties of a silicon nitride (Si{sub 3}N{sub 4}) material, with neodymium oxide (Nd{sub 2}O{sub 3}) and aluminum nitride (AlN) as sintering aids, was studied. The composites, containing 5, 10, and 17.6 wt% MoSi{sub 2}, were fabricated by hot pressing. All materials exhibited a similar phase composition, detected by X-ray diffractometry. Up to MoSi{sub 2} additions of 10 wt%, mechanical properties such as strength, fracture toughness, or creep at 1,400 C were not affected significantly, in comparison to that of monolithic Si{sub 3}N{sub 4}. The oxidation resistance of the composites, in terms of weight gain, degraded. After 1,000 h of oxidation at 1,400 and 1,450 C in air, a greater weight gain (by a factor of approximately three) was obtained, in comparison to that of the material without MoSi{sub 2}. Nevertheless, after 1,000 h of oxidation, the degradation in strength of the composites was considerably less severe than that of the material without MoSi{sub 2}. An additional layer was formed, caused by processes at the surface of the Si{sub 3}N{sub 4} material, preventing the formation of pores, cracks, or glassy-phase-rich areas, which are common features of oxidation damage in Si{sub 3}N{sub 4} materials. This surface layer, containing Mo{sub 5}Si{sub 3} and silicon oxynitride (Si{sub 2}ON{sub 2}), was the result of reactions between MoSi{sub 2}, Si{sub 3}N{sub 4}, and the oxygen penetrating by diffusion into the material during the high-temperature treatment.

  13. Excitons in van der Waals materials: From monolayer to bulk hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Koskelo, Jaakko; Fugallo, Giorgia; Hakala, Mikko; Gatti, Matteo; Sottile, Francesco; Cudazzo, Pierluigi

    2017-01-01

    We present a general picture of the exciton properties of layered materials in terms of the excitations of their single-layer building blocks. To this end, we derive a model excitonic Hamiltonian by drawing an analogy with molecular crystals, which are other prototypical van der Waals materials. We employ this simplified model to analyze in detail the excitation spectrum of hexagonal boron nitride (hBN) that we have obtained from the ab initio solution of the many-body Bethe-Salpeter equation as a function of momentum. In this way, we identify the character of the lowest-energy excitons in hBN, discuss the effects of the interlayer hopping and the electron-hole exchange interaction on the exciton dispersion, and illustrate the relation between exciton and plasmon excitations in layered materials.

  14. Transition-metal-nitride-based thin films as novel energy harvesting materials

    PubMed Central

    Kerdsongpanya, Sit; Alling, Björn

    2016-01-01

    The last few years have seen a rise in the interest in early transition-metal and rare-earth nitrides, primarily based on ScN and CrN, for energy harvesting by thermoelectricity and piezoelectricity. This is because of a number of important advances, among those the discoveries of exceptionally high piezoelectric coupling coefficient in (Sc,Al)N alloys and of high thermoelectric power factors of ScN-based and CrN-based thin films. These materials also constitute well-defined model systems for investigating thermodynamics of mixing for alloying and nanostructural design for optimization of phase stability and band structure. These features have implications for and can be used for tailoring of thermoelectric and piezoelectric properties. In this highlight article, we review the ScN- and CrN-based transition-metal nitrides for thermoelectrics, and drawing parallels with piezoelectricity. We further discuss these materials as a models systems for general strategies for tailoring of thermoelectric properties by integrated theoretical–experimental approaches. PMID:27358737

  15. Transition-metal-nitride-based thin films as novel energy harvesting materials.

    PubMed

    Eklund, Per; Kerdsongpanya, Sit; Alling, Björn

    2016-05-14

    The last few years have seen a rise in the interest in early transition-metal and rare-earth nitrides, primarily based on ScN and CrN, for energy harvesting by thermoelectricity and piezoelectricity. This is because of a number of important advances, among those the discoveries of exceptionally high piezoelectric coupling coefficient in (Sc,Al)N alloys and of high thermoelectric power factors of ScN-based and CrN-based thin films. These materials also constitute well-defined model systems for investigating thermodynamics of mixing for alloying and nanostructural design for optimization of phase stability and band structure. These features have implications for and can be used for tailoring of thermoelectric and piezoelectric properties. In this highlight article, we review the ScN- and CrN-based transition-metal nitrides for thermoelectrics, and drawing parallels with piezoelectricity. We further discuss these materials as a models systems for general strategies for tailoring of thermoelectric properties by integrated theoretical-experimental approaches.

  16. Carbon Nitride Supramolecular Hybrid Material Enabled High-Efficiency Photocatalytic Water Treatments.

    PubMed

    Liu, Jinghai; Xie, Shuyuan; Geng, Zhibin; Huang, Keke; Fan, Long; Zhou, Weilei; Qiu, Lixin; Gao, Denglei; Ji, Lei; Duan, Limei; Lu, Luhua; Li, Wanfei; Bai, Suozhu; Liu, Zongrui; Chen, Wei; Feng, Shouhua; Zhang, Yuegang

    2016-10-12

    Surface defects in relation to surface compositions, morphology, and active sites play crucial roles in photocatalytic activity of graphitic carbon nitride (g-C3N4) material for highly reactive oxygen radicals production. Here, we report a high-efficiency carbon nitride supramolecular hybrid material prepared by patching the surface defects with inorganic clusters. Fe (III) {PO4[WO(O2)2]4} clusters have been noncovalently integrated on surface of g-C3N4, where the surface defects provide accommodation sites for these clusters and driving forces for self-assembly. During photocatalytic process, the activity of supramolecular hybrid is 1.53 times than pure g-C3N4 for the degradation of Rhodamine B (RhB) and 2.26 times for Methyl Orange (MO) under the simulated solar light. Under the mediation of H2O2 (50 mmol L(-1)), the activity increases to 6.52 times for RhB and 28.3 times for MO. The solid cluster active sites with high specific surface area (SSA) defect surface promoting the kinetics of hydroxide radicals production give rise to the extremely high photocatalytic activity. It exhibits recyclable capability and works in large-scale demonstration under the natural sunlight as well and interestingly the environmental temperature has little effects on the photocatalytic activity.

  17. Theoretical Study of Material and Device Properties of Group-III Nitrides

    NASA Astrophysics Data System (ADS)

    Yan, Qimin

    Group-III nitride semiconductors, including AlN, GaN, InN, and their alloys, are ideal materials for solid state lighting applications. Current research focuses on improving the efficiency by improvements in materials quality and novel device designs, for instance based on nonpolar and semipolar growth. The motivation for our work is to assist and guide the experimental development of high-performance solid state optoelectronic devices by performing computational studies. Our investigations range from basic structural and electronic properties of nitrides to the effects of device design on efficiency of light emission. In the area of fundamental properties, we performed a systematic study of strain effects on the electronic band structures of the group-III-nitrides (AlN, GaN and InN) using density-functional theory with an advanced hybrid functional as well as using the quasiparticle GW method. We present a complete set of deformation potentials that allows us to predict the band positions of group-III nitrides and their alloys (InGaN and AlGaN) under realistic strain conditions. We then employed the resulting first-principles deformation potentials to predict the effects of strain on transition energies and valence-band structures of c-plane, nonpolar, and semipolar InGaN alloy layers grown on GaN substrates, with particular attention to the role of strain in the polarized light emission. We also investigated the role of native defects in the optical properties of GaN and AlN, again using hybrid density-functional calculations. We established that complexes between Mg and nitrogen vacancies lead to the broad red luminescence that has often been observed in GaN. We find that isolated nitrogen vacancies can give rise to broad emission peaked at 2.18 eV. We show that isolated aluminum vacancies lead to an absorption peak at 3.43 eV and an emission peak at 2.73 eV. We also find that the complexes can give rise to absorption peaked at 3.97 eV and

  18. Silicon nitride/silicon carbide composite densified materials prepared using composite powders

    DOEpatents

    Dunmead, S.D.; Weimer, A.W.; Carroll, D.F.; Eisman, G.A.; Cochran, G.A.; Susnitzky, D.W.; Beaman, D.R.; Nilsen, K.J.

    1997-07-01

    Prepare silicon nitride-silicon carbide composite powders by carbothermal reduction of crystalline silica powder, carbon powder and, optionally, crystalline silicon nitride powder. The crystalline silicon carbide portion of the composite powders has a mean number diameter less than about 700 nanometers and contains nitrogen. The composite powders may be used to prepare sintered ceramic bodies and self-reinforced silicon nitride ceramic bodies.

  19. 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.

  20. 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

  1. 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.

  2. Nitridation Temperature Effects on Electronic and Chemical Properties of (Ga1-xZnx)(N1-xOx) Solid Solution Nanocrystals

    SciTech Connect

    Ward, Matthew James; Han, Wei-Qiang; Sham, Tsun-Kong

    2013-11-15

    Solid solution nanocrystals of gallium nitride–zinc oxide have been realized as potential photocatalysts for visible light driven overall water splitting. The band gap of these materials has been found to narrow further into the visible region as a function of increasing zinc oxide concentration, and thus, it is desirable to synthesize zinc oxide-rich gallium nitride–zinc oxide solid solutions. In this paper, we discuss the effects of using nitridation temperature to control zinc oxide content on the electronic and chemical properties of gallium nitride–zinc oxide solid solution nanostructures. The effect of nitridation temperature was studied using X-ray absorption fine structure (XAFS), including both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), and X-ray excited optical luminescence (XEOL). It was determined that using nitridation temperature as a method of controlling zinc oxide concentration results in solid solutions with poor crystallinity, phase separation, and mixed surface oxide formation. These findings suggest that many complications arise from using nitridation temperature to control zinc oxide concentration in gallium nitride–zinc oxide solid solutions, and thus, it is possible that the resultant materials would exhibit poor photocatalytic activity.

  3. Investigation of copper indium gallium selenide material growth by selenization of metallic precursors

    NASA Astrophysics Data System (ADS)

    Han, Junfeng; Liao, Cheng; Jiang, Tao; Xie, Huamu; Zhao, Kui; Besland, M.-P.

    2013-11-01

    We report a study of copper indium gallium selenide (CIGS) thin film growth in the annealing process at temperature range from 120 °C to 600 °C. Thin films were prepared by sputtering metal precursors and subsequent selenization process. Surface morphologies of thin films were observed by using high resolution field emission scanning electron microscopy (FESEM). Phases in quaternary systems Cu-In-Ga-Se were investigated by X-ray diffraction (XRD). Evolution of crystalline structure in the film surface was studied by Raman spectra. A possible reaction path from metallic precursors to a single CIGS phase was obtained by merging all results of SEM, XRD and Raman. Above 210 °C, selenium reacted with Cu and In to form binary selenide. CuSe crystalline platelets were observed clearly in the film surfaces. When temperature was reaching 380 °C, Cu2-xSe and InSe reacted with excess Se to form CuInSe2 (CIS) and contributed to the grain growth. Above 410 °C, Ga-rich phase was detected in the films. With increased temperature, Ga diffused into CIS crystalline lattices. Finally, at 600 °C, a single phase of Cu-In-Ga-Se quaternary system was formed. A large number of triangular and hexagonal structures were observed in the film due to a re-crystalline process at a high annealing temperature.

  4. Thermal transport in silicon nitride membranes and far infrared studies of novel materials

    NASA Astrophysics Data System (ADS)

    Holmes, Warren Albert

    The central theme of this thesis is the design and use of bolometers for detection of far infrared and submillimeter wavelength radiation. A new material, micrometer thick membranes of silicon nitride, is used in modern bolometer designs. An understanding of thermal transport in silicon nitride is critical to evaluate and optimize detector performance. We have measured the thermal conductance, G, of {≈}1μm thick low-stress silicon nitride membranes over the temperature range, 0.06 4K,\\ G is independent of surface morphology indicating that the thermal transport is determined by bulk scattering. For T < 4K, scattering from membrane surfaces becomes significant. We find that G is reduced by a factor as large as 5 for membranes which have sub-micron sized Ag particles glued to the surface or are micromachined into narrow strips as are required in many applications when compared with that of clean, solid membranes with the same ratio of cross section to length. We have used optimized bolometers for the study of two novel materials, single walled carbon nanotubes (SWNT) and single crystals of high temperature superconductors. We have measured the transmittance of several samples of bundles of SWNT over the frequency range 10 < nu < 300cmsp{-1} at temperatures 1.2 < T < 300K. The broadband shape of the transmittance has a temperature dependence similar to the DC transport measurements. We find a temperature dependent feature near nu≈ 30cmsp{-1} that is consistent with the prediction of a small energy gap Esb{g}≈ 4meV and also with a soft librational mode in SWNT bundles. We have directly measured the absorptivity of high quality single crystals of YBasb2Cusb3Osb{6.5} and Tlsb2Basb2Casb2Cusb3Osb{10-delta} over the frequency range 50 < nu < 800cmsp{-1} at a temperature of 1.2K. Direct absorptivity measurements are powerful for studying materials in the superconducting state since in conventional superconductors the loss at frequencies below the energy gap is zero

  5. Biopolymer-Activated Graphitic Carbon Nitride towards a Sustainable Photocathode Material

    PubMed Central

    Zhang, Yuanjian; Schnepp, Zoë; Cao, Junyu; Ouyang, Shuxin; Li, Ying; Ye, Jinhua; Liu, Songqin

    2013-01-01

    Photoelectrochemical (PEC) conversion of solar light into chemical fuels is one of the most promising solutions to the challenge of sustainable energy. Graphitic carbon (IV) nitride polymer (g-CN) is an interesting sustainable photocathode material due to low-cost, visible-light sensitivity, and chemical stability up to 500°C in air. However, grain boundary effects and limited active sites greatly hamper g-CN activity. Here, we demonstrate biopolymer-activation of g-CN through simultaneous soft-templating of a sponge-like structure and incorporation of active carbon-dopant sites. This facile approach results in an almost 300% increase in the cathodic PEC activity of g-CN under simulated solar-irradiation. PMID:23831846

  6. Sputtering Erosion Measurement on Boron Nitride as a Hall Thruster Material

    NASA Technical Reports Server (NTRS)

    Britton, Melissa; Waters, Deborah; Messer, Russell; Sechkar, Edward; Banks, Bruce

    2002-01-01

    The durability of a high-powered Hall thruster may be limited by the sputter erosion resistance of its components. During normal operation, a small fraction of the accelerated ions will impact the interior of the main discharge channel, causing its gradual erosion. A laboratory experiment was conducted to simulate the sputter erosion of a Hall thruster. Tests of sputter etch rate were carried out using 300 to 1000 eV Xenon ions impinging on boron nitride substrates with angles of attack ranging from 30 to 75 degrees from horizontal. The erosion rates varied from 3.41 to 14.37 Angstroms/[sec(mA/sq cm)] and were found to depend on the ion energy and angle of attack, which is consistent with the behavior of other materials.

  7. Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials

    PubMed Central

    Nikzad, Shouleh; Hoenk, Michael; Jewell, April D.; Hennessy, John J.; Carver, Alexander G.; Jones, Todd J.; Goodsall, Timothy M.; Hamden, Erika T.; Suvarna, Puneet; Bulmer, J.; Shahedipour-Sandvik, F.; Charbon, Edoardo; Padmanabhan, Preethi; Hancock, Bruce; Bell, L. Douglas

    2016-01-01

    Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100–300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness. PMID:27338399

  8. Moving Graphitic Carbon Nitride from Electrocatalysis and Photocatalysis to a Potential Electrode Material for Photoelectric Devices.

    PubMed

    Xu, Jingsan; Antonietti, Markus; Shalom, Menny

    2016-09-20

    Carbon nitride (g-CN) has attracted significant interest in the last years as a robust, low-cost alternative to metal-based materials in different fields due to its low price, environmentally benign character, simple synthesis and tunable properties. In particular, g-CN demonstrates promising activity in energy-related applications such as photo and heterogeneous catalysis, batteries and electrolysis. However, while g-CN is already well-established as a photocatalyst, its utilization in (opto)electronic devices is still at an early stage. This Focus Review concentrates on the utilization of g-CN in solar and photoelectrochemical cells, electrolyzers and light emitting diode alongside the recap of new synthetic approaches. This review is expected to provide useful insights into the design and fabrication of g-CN based photoelectronic devices as well as g-CN working principles, including the main challenges toward its integration in optoelectronic devices.

  9. Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials.

    PubMed

    Nikzad, Shouleh; Hoenk, Michael; Jewell, April D; Hennessy, John J; Carver, Alexander G; Jones, Todd J; Goodsall, Timothy M; Hamden, Erika T; Suvarna, Puneet; Bulmer, J; Shahedipour-Sandvik, F; Charbon, Edoardo; Padmanabhan, Preethi; Hancock, Bruce; Bell, L Douglas

    2016-06-21

    Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100-300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness.

  10. A color-tunable luminescent material with functionalized graphitic carbon nitride as multifunctional supports

    NASA Astrophysics Data System (ADS)

    Lu, Jiutian; Cao, Yudong; Fan, Hai; Hou, Juying; Ai, Shiyun

    2015-12-01

    A color-tunable luminescent material was prepared based on the composition of functionalized graphitic carbon nitride (g-C3N4) and europium (III). The functionalized g-C3N4 layers not only behave as multifunctional supports including ligand coordinated with europium (III) and a support structure for the formation of the luminescent material, but exhibit excitation wavelength-dependent luminescence, thus the energy transfer between the functionalized g-C3N4 and europium (III) can match very well by controlling the emission wavelength of functionalized g-C3N4. The as-prepared materials was comprehensively characterized via X-ray photoelectron spectroscopy, Fourier Transform Infrared spectroscopy, X-ray scattering techniques, Ultraviolet and Visible spectrophotometer, fluorescence spectrophotometer, thermogravimetric analysis, etc. The luminescent material exhibits multi-color emissions which are consistent with the characteristic emissions of europium (III) and functionalized g-C3N4, and the photoluminescence quality and density of the europium (III) can be greatly enhanced. The brilliant optical properties of the materials make them suiting for multipurpose applications in practical fields.

  11. Picosecond pulsed laser processing of polycrystalline diamond and cubic boron nitride composite materials

    NASA Astrophysics Data System (ADS)

    Warhanek, Maximilian G.; Pfaff, Josquin; Meier, Linus; Walter, Christian; Wegener, Konrad

    2016-03-01

    Capabilities and advantages of laser ablation processes utilizing ultrashort pulses have been demonstrated in various applications of scientific and industrial nature. Of particular interest are applications that require high geometrical accuracy, excellent surface integrity and thus tolerate only a negligible heat-affected zone in the processed area. In this context, this work presents a detailed study of the ablation characteristics of common ultrahard composite materials utilized in the cutting tool industry, namely polycrystalline diamond (PCD) and polycrystalline cubic boron nitride composite (PCBN). Due to the high hardness of these materials, conventional mechanical processing is time consuming and costly. Herein, laser ablation is an appealing solution, since no process forces and no wear have to be taken into consideration. However, an industrially viable process requires a detailed understanding of the ablation characteristics of each material. Therefore, the influence of various process parameters on material removal and processing quality at 10 ps pulse duration are investigated for several PCD and PCBN grades. The main focus of this study examines the effect of different laser energy input distributions, such as pulse frequency and burst pulses, on the processing conditions in deep cutting kerfs and the resulting processing speed. Based on these results, recommendations for efficient processing of such materials are derived.

  12. Survey of the market, supply, and availability of gallium

    SciTech Connect

    Rosi, F.D.

    1980-01-01

    The present and potential availability of gallium metal in connection with materials evaluation recommendations for satellite power systems is examined in the following areas: (1) market considerations - the present and emerging uses of gallium, as well as the consumption and price of gallium; (2) supply considerations - present sources of gallium, commercial and new methods for extracting gallium from bauxite, and summary comments; (3) methods for purifying gallium to satisfy market demands; (4) principal suppliers of gallium; and (5) gallium availability from bauxite on the basis of primary aluminum production; and bauxite production, reserves and resources. The study was based on published information as well as information derived from private communications with both major and potential suppliers and users of gallium, and with staff members at the Bureau of Mines. 16 references, 3 figures, 6 tables.

  13. Conductive Graphitic Carbon Nitride as an Ideal Material for Electrocatalytically Switchable CO2 Capture

    PubMed Central

    Tan, Xin; Kou, Liangzhi; Tahini, Hassan A.; Smith, Sean C.

    2015-01-01

    Good electrical conductivity and high electron mobility of the sorbent materials are prerequisite for electrocatalytically switchable CO2 capture. However, no conductive and easily synthetic sorbent materials are available until now. Here, we examined the possibility of conductive graphitic carbon nitride (g-C4N3) nanosheets as sorbent materials for electrocatalytically switchable CO2 capture. Using first-principle calculations, we found that the adsorption energy of CO2 molecules on g-C4N3 nanosheets can be dramatically enhanced by injecting extra electrons into the adsorbent. At saturation CO2 capture coverage, the negatively charged g-C4N3 nanosheets achieve CO2 capture capacities up to 73.9 × 1013 cm−2 or 42.3 wt%. In contrast to other CO2 capture approaches, the process of CO2 capture/release occurs spontaneously without any energy barriers once extra electrons are introduced or removed, and these processes can be simply controlled and reversed by switching on/off the charging voltage. In addition, these negatively charged g-C4N3 nanosheets are highly selective for separating CO2 from mixtures with CH4, H2 and/or N2. These predictions may prove to be instrumental in searching for a new class of experimentally feasible high-capacity CO2 capture materials with ideal thermodynamics and reversibility. PMID:26621618

  14. Conductive Graphitic Carbon Nitride as an Ideal Material for Electrocatalytically Switchable CO2 Capture

    NASA Astrophysics Data System (ADS)

    Tan, Xin; Kou, Liangzhi; Tahini, Hassan A.; Smith, Sean C.

    2015-12-01

    Good electrical conductivity and high electron mobility of the sorbent materials are prerequisite for electrocatalytically switchable CO2 capture. However, no conductive and easily synthetic sorbent materials are available until now. Here, we examined the possibility of conductive graphitic carbon nitride (g-C4N3) nanosheets as sorbent materials for electrocatalytically switchable CO2 capture. Using first-principle calculations, we found that the adsorption energy of CO2 molecules on g-C4N3 nanosheets can be dramatically enhanced by injecting extra electrons into the adsorbent. At saturation CO2 capture coverage, the negatively charged g-C4N3 nanosheets achieve CO2 capture capacities up to 73.9 × 1013 cm-2 or 42.3 wt%. In contrast to other CO2 capture approaches, the process of CO2 capture/release occurs spontaneously without any energy barriers once extra electrons are introduced or removed, and these processes can be simply controlled and reversed by switching on/off the charging voltage. In addition, these negatively charged g-C4N3 nanosheets are highly selective for separating CO2 from mixtures with CH4, H2 and/or N2. These predictions may prove to be instrumental in searching for a new class of experimentally feasible high-capacity CO2 capture materials with ideal thermodynamics and reversibility.

  15. Conductive Graphitic Carbon Nitride as an Ideal Material for Electrocatalytically Switchable CO2 Capture.

    PubMed

    Tan, Xin; Kou, Liangzhi; Tahini, Hassan A; Smith, Sean C

    2015-12-01

    Good electrical conductivity and high electron mobility of the sorbent materials are prerequisite for electrocatalytically switchable CO2 capture. However, no conductive and easily synthetic sorbent materials are available until now. Here, we examined the possibility of conductive graphitic carbon nitride (g-C4N3) nanosheets as sorbent materials for electrocatalytically switchable CO2 capture. Using first-principle calculations, we found that the adsorption energy of CO2 molecules on g-C4N3 nanosheets can be dramatically enhanced by injecting extra electrons into the adsorbent. At saturation CO2 capture coverage, the negatively charged g-C4N3 nanosheets achieve CO2 capture capacities up to 73.9 × 10(13) cm(-2) or 42.3 wt%. In contrast to other CO2 capture approaches, the process of CO2 capture/release occurs spontaneously without any energy barriers once extra electrons are introduced or removed, and these processes can be simply controlled and reversed by switching on/off the charging voltage. In addition, these negatively charged g-C4N3 nanosheets are highly selective for separating CO2 from mixtures with CH4, H2 and/or N2. These predictions may prove to be instrumental in searching for a new class of experimentally feasible high-capacity CO2 capture materials with ideal thermodynamics and reversibility.

  16. Ga[OSi(O(t)Bu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry.

    PubMed

    Dombrowski, James P; Johnson, Gregory R; Bell, Alexis T; Tilley, T Don

    2016-07-05

    The molecular precursor tris[(tri-tert-butoxy)siloxy]gallium, as the tetrahydrofuran adduct Ga[OSi(O(t)Bu)3]3·THF (), was synthesized via the salt metathesis reaction of gallium trichloride with NaOSi(O(t)Bu)3. This complex serves as a model for isolated gallium in a silica framework. Complex decomposes thermally in hydrocarbon solvent, eliminating isobutylene, water, and tert-butanol to generate high surface area gallium-containing silica at low temperatures. When thermal decomposition was performed in the presence of P-123 Pluronic as a templating agent the generated material displayed uniform vermicular pores. Textural mesoporosity was evident in untemplated material. Co-thermolysis of with HOSi(O(t)Bu)3 in the presence of P-123 Pluronic led to materials with Ga : Si ratios ranging from 1 : 3 to 1 : 50, denoted UCB1-GaSi3, UCB1-GaSi10, UCB1-GaSi20 and UCB1-GaSi50. After calcination at 500 °C these materials exhibited decreasing surface areas and broadening pore distributions with increasing silicon content, indicating a loss of template effects. The position and dispersion of the gallium in UCB1-GaSi materials was investigated using (71)Ga MAS-NMR, powder XRD, and STEM/EDS elemental mapping. The results indicate a high degree of gallium dispersion in all samples, with gallium oxide clusters or oligomers present at higher gallium content.

  17. Deposition and electrical, chemical, and microstructural characterization of the interface formed between platinum, gold and silver rectifying contacts on cleaned n-type gallium nitride (0001) surfaces

    NASA Astrophysics Data System (ADS)

    Tracy, Kieran Mark

    2000-10-01

    The characteristics of clean n-type GaN surfaces and the interface between this surface and Pt, Au and Ag, have been investigated. Gallium-terminated (0001) surfaces of GaN, free of carbon and oxygen within the detection limits of XPS have been achieved by annealing in ammonia at 860°C for 15 minutes. Additional, in-situ surface analysis indicated a flat, stoichometric, and unreconstructed surface free of other contaminants. The electron affinity of this surface was 3.1 +/- 0.2 eV. The valence band maximum was located 3.0 +/- 0.1 eV below the Fermi level, indicating the presence of a surface state near the valence band maximum. Individual layers of Pt, Au or Ag were deposited in-situ on the cleaned surface and the interfaces characterized using XPS, UPS, LEED and TEM. All as-deposited meta/GaN interfaces were abrupt and unreacted; the Pt and Au were deposited epitaxially. The Schottky barrier heights obtained from photoemission measurements were 1.2, 0.9 and 0.5 +/- 0.2 eV for Pt, Au and Ag, respectively. Values of the metal work function from UPS results were 5.7, 5.3 and 4.4 +/- 0.2 eV for Pt, Au and Ag, respectively. Schottky barrier heights determined via ex-situ current-voltage measurements were 1.15, 0.88 and 0.56 +/- 0.05 eV for Pt, Au and Ag, respectively. Capacitance-voltage measurements yielded barrier heights of 1.25 and 0.96 +/- 0.05 eV, for Pt and Au, respectively. These results indicate that the Fermi level of the cleaned surface is not pinned. Upon annealing the aforementioned contacts from 400 to 800°C for 3 minutes each. The rectifying behavior of the Pt and Au contacts degraded as a function of temperature during annealing at 400, 600 and 800°C for 3 minutes each until they became ohmic. This was correlated with TEM of the annealed interfaces, which displayed increased chemical reaction and roughening as a function of temperature.

  18. Formation of Mach angle profiles during wet etching of silica and silicon nitride materials

    NASA Astrophysics Data System (ADS)

    Ghulinyan, M.; Bernard, M.; Bartali, R.; Pucker, G.

    2015-12-01

    In integrated circuit technology peeling of masking photoresist films is a major drawback during the long-timed wet etching of materials. It causes an undesired film underetching, which is often accompanied by a formation of complex etch profiles. Here we report on a detailed study of wedge-shaped profile formation in a series of silicon oxide, silicon oxynitride and silicon nitride materials during wet etching in a buffered hydrofluoric acid (BHF) solution. The shape of etched profiles reflects the time-dependent adhesion properties of the photoresist to a particular material and can be perfectly circular, purely linear or a combination of both, separated by a knee feature. Starting from a formal analogy between the sonic boom propagation and the wet underetching process, we model the wedge formation mechanism analytically. This model predicts the final form of the profile as a function of time and fits the experimental data perfectly. We discuss how this knowledge can be extended to the design and the realization of optical components such as highly efficient etch-less vertical tapers for passive silicon photonics.

  19. Development of an aluminum nitride-silicon carbide material set for high-temperature sensor applications

    NASA Astrophysics Data System (ADS)

    Griffin, Benjamin A.; Habermehl, Scott D.; Clews, Peggy J.

    2014-06-01

    A number of important energy and defense-related applications would benefit from sensors capable of withstanding extreme temperatures (>300°C). Examples include sensors for automobile engines, gas turbines, nuclear and coal power plants, and petroleum and geothermal well drilling. Military applications, such as hypersonic flight research, would also benefit from sensors capable of 1000°C. Silicon carbide (SiC) has long been recognized as a promising material for harsh environment sensors and electronics because it has the highest mechanical strength of semiconductors with the exception of diamond and its upper temperature limit exceeds 2500°C, where it sublimates rather than melts. Yet today, many advanced SiC MEMS are limited to lower temperatures because they are made from SiC films deposited on silicon wafers. Other limitations arise from sensor transduction by measuring changes in capacitance or resistance, which require biasing or modulation schemes that can with- stand elevated temperatures. We are circumventing these issues by developing sensing structures directly on SiC wafers using SiC and piezoelectric aluminum nitride (AlN) thin films. SiC and AlN are a promising material combination due to their high thermal, electrical, and mechanical strength and closely matched coefficients of thermal expansion. AlN is also a non-ferroelectric piezoelectric material, enabling piezoelectric transduction at temperatures exceeding 1000°C. In this paper, the challenges of incorporating these two materials into a compatible MEMS fabrication process are presented. The current progress and initial measurements of the fabrication process are shown. The future direction and the need for further investigation of the material set are addressed.

  20. Europium (III) Organic Complexes in Porous Boron Nitride Microfibers: Efficient Hybrid Luminescent Material

    PubMed Central

    Lin, Jing; Feng, Congcong; He, Xin; Wang, Weijia; Fang, Yi; Liu, Zhenya; Li, Jie; Tang, Chengchun; Huang, Yang

    2016-01-01

    We report the design and synthesis of a novel kind of organic-inorganic hybrid material via the incorporation of europium (III) β-diketonate complexes (Eu(TTA)3, TTA = 2-thenoyltrifluoroacetone) into one-dimensional (1D) porous boron nitride (BN) microfibers. The developed Eu(TTA)3@BN hybrid composites with typical 1D fibrous morphology exhibit bright visible red-light emission on UV illumination. The confinement of Eu(TTA)3 within pores of BN microfibers not only decreases the aggregation-caused quenching in solid Eu(TTA)3, but also improves their thermal stabilities. Moreover, The strong interactions between Eu(TTA)3 and porous BN matrix result in an interesting energy transfer process from BN host to TTA ligand and TTA ligand to Eu3+ ions, leading to the remarkable increase of red emission. The synthetic approach should be a very promising strategy which can be easily expanded to other hybrid luminescent materials based on porous BN. PMID:27687246

  1. Measurement and mapping of materials parameters for gallium arsenide wafers by infrared transmission topography

    SciTech Connect

    Mier, M.G.; Look, D.C.; Walters, D.C.

    1996-12-01

    Polished wafers of semiinsulating (SI) undoped GaAs or of doped conducting GaAs are important for manufacture of monolithic microwave integrated circuits or of junction light emitters. For SI wafers, the EL2 defect causes the SI state, and variation in EL2 density can cause on-wafer variations in device isolation and other device properties. With conducting materials, crystalline dislocations cause dark-line defects and other recombination centers that limit carrier lifetime in fabricated lasers. High free carrier concentration leads to low series resistance ohmic contacts and is very desirable in semiconductor lasers. In the process of evaluating these materials, we have found that infrared transmission measurements can provide dense data on device-pertinent materials parameters for correlation to device parameters. Our custom color maps of these materials parameters keyed to color histograms of the measurement data can provide informative presentations of very large data sets for comparison to device measurements. For example, we discuss nondestructive neutral and total EL2 density measurements in SI GaAs and nondestructive dislocation density and free carrier concentration measurements in GaAs: Si, both by infrared topography. When test devices can be fabricated at known positions on the materials evaluation wafer (or on a nearby wafer from the same boule), sensitive comparison of materials evaluation data to measured device performance can be achieved. We show that topographic color maps allow meaningful comparisons of the materials measurements to device measurements at different spacings.

  2. A color-tunable luminescent material with functionalized graphitic carbon nitride as multifunctional supports

    SciTech Connect

    Lu, Jiutian; Cao, Yudong; Fan, Hai; Hou, Juying; Ai, Shiyun

    2015-12-15

    A color-tunable luminescent material was prepared based on the composition of functionalized graphitic carbon nitride (g-C{sub 3}N{sub 4}) and europium (III). The functionalized g-C{sub 3}N{sub 4} layers not only behave as multifunctional supports including ligand coordinated with europium (III) and a support structure for the formation of the luminescent material, but exhibit excitation wavelength-dependent luminescence, thus the energy transfer between the functionalized g-C{sub 3}N{sub 4} and europium (III) can match very well by controlling the emission wavelength of functionalized g-C{sub 3}N{sub 4}. The as-prepared materials was comprehensively characterized via X-ray photoelectron spectroscopy, Fourier Transform Infrared spectroscopy, X-ray scattering techniques, Ultraviolet and Visible spectrophotometer, fluorescence spectrophotometer, thermogravimetric analysis, etc. The luminescent material exhibits multi-color emissions which are consistent with the characteristic emissions of europium (III) and functionalized g-C{sub 3}N{sub 4}, and the photoluminescence quality and density of the europium (III) can be greatly enhanced. The brilliant optical properties of the materials make them suiting for multipurpose applications in practical fields. - Graphical abstract: Schematic illustration of the synthesis and basic composition of the luminescent material. Inset figures were luminescence emission spectra of g-C{sub 3}N{sub 4} (A), europium (III) complex (a) and luminescent material (b) with the same concentration in (B) (K{sub ex}=350 nm) and photographs of (left) H{sub 2}O and (right) the H{sub 2}O dispersion of luminescence emission spectra under 350 nm UV radiation. The energy transfer in the luminescent material matchs very well and it exhibits multi-color emissions simultaneously. The enhanced photoluminescence quality and density of the europium (III) makes them suiting for multipurpose applications in practical fields. - Highlights: • Luminescent

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

    PubMed

    Tanaka, Akiyo

    2004-08-01

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

  4. Chemisorption of Hydroxide on 2D Materials from DFT Calculations: Graphene versus Hexagonal Boron Nitride.

    PubMed

    Grosjean, Benoit; Pean, Clarisse; Siria, Alessandro; Bocquet, Lydéric; Vuilleumier, Rodolphe; Bocquet, Marie-Laure

    2016-11-17

    Recent nanofluidic experiments revealed strongly different surface charge measurements for boron-nitride (BN) and graphitic nanotubes when in contact with saline and alkaline water (Nature 2013, 494, 455-458; Phys. Rev. Lett. 2016, 116, 154501). These observations contrast with the similar reactivity of a graphene layer and its BN counterpart, using density functional theory (DFT) framework, for intact and dissociative adsorption of gaseous water molecules. Here we investigate, by DFT in implicit water, single and multiple adsorption of anionic hydroxide on single layers. A differential adsorption strength is found in vacuum for the first ionic adsorption on the two materials-chemisorbed on BN while physisorbed on graphene. The effect of implicit solvation reduces all adsorption values, resulting in a favorable (nonfavorable) adsorption on BN (graphene). We also calculate a pKa ≃ 6 for BN in water, in good agreement with experiments. Comparatively, the unfavorable results for graphene in water echo the weaker surface charge measurements but point to an alternative scenario.

  5. Fabrication of Silicon Nitride Dental Core Ceramics with Borosilicate Veneering material

    NASA Astrophysics Data System (ADS)

    Wananuruksawong, R.; Jinawath, S.; Padipatvuthikul, P.; Wasanapiarnpong, T.

    2011-10-01

    Silicon nitride (Si3N4) ceramic is a great candidate for clinical applications due to its high fracture toughness, strength, hardness and bio-inertness. This study has focused on the Si3N4 ceramic as a dental core material. The white Si3N4 was prepared by pressureless sintering at relative low sintering temperature of 1650 °C in nitrogen atmosphere. The coefficient of thermal expansion (CTE) of Si3N4 ceramic is lower than that of Zirconia and Alumina ceramic which are popular in this field. The borosilicate glass veneering was employed due to its compatibility in thermal expansion. The sintered Si3N4 specimens represented the synthetic dental core were paintbrush coated by a veneer paste composed of borosilicate glass powder (<150 micrometer, Pyrex) with 5 wt% of zirconia powder (3 wt% Y2O3 - partial stabilized zirconia) and 30 wt% of polyvinyl alcohol (5 wt% solution). After coating the veneer on the Si3N4 specimens, the firing was performed in electric tube furnace between 1000-1200°C. The veneered specimens fired at 1100°C for 15 mins show good bonding, smooth and glossy without defect and crazing. The veneer has thermal expansion coefficient as 3.98×10-6 °C-1, rather white and semi opaque, due to zirconia addition, the Vickers hardness as 4.0 GPa which is closely to the human teeth.

  6. Synthesis of large-area multilayer hexagonal boron nitride for high material performance

    PubMed Central

    Kim, Soo Min; Hsu, Allen; Park, Min Ho; Chae, Sang Hoon; Yun, Seok Joon; Lee, Joo Song; Cho, Dae-Hyun; Fang, Wenjing; Lee, Changgu; Palacios, Tomás; Dresselhaus, Mildred; Kim, Ki Kang; Lee, Young Hee; Kong, Jing

    2015-01-01

    Although hexagonal boron nitride (h-BN) is a good candidate for gate-insulating materials by minimizing interaction from substrate, further applications to electronic devices with available two-dimensional semiconductors continue to be limited by flake size. While monolayer h-BN has been synthesized on Pt and Cu foil using chemical vapour deposition (CVD), multilayer h-BN is still absent. Here we use Fe foil and synthesize large-area multilayer h-BN film by CVD with a borazine precursor. These films reveal strong cathodoluminescence and high mechanical strength (Young's modulus: 1.16±0.1 TPa), reminiscent of formation of high-quality h-BN. The CVD-grown graphene on multilayer h-BN film yields a high carrier mobility of ∼24,000 cm2 V−1 s−1 at room temperature, higher than that (∼13,000 2 V−1 s−1) with exfoliated h-BN. By placing additional h-BN on a SiO2/Si substrate for a MoS2 (WSe2) field-effect transistor, the doping effect from gate oxide is minimized and furthermore the mobility is improved by four (150) times. PMID:26507400

  7. Synthesis of large-area multilayer hexagonal boron nitride for high material performance

    NASA Astrophysics Data System (ADS)

    Kim, Soo Min; Hsu, Allen; Park, Min Ho; Chae, Sang Hoon; Yun, Seok Joon; Lee, Joo Song; Cho, Dae-Hyun; Fang, Wenjing; Lee, Changgu; Palacios, Tomás; Dresselhaus, Mildred; Kim, Ki Kang; Lee, Young Hee; Kong, Jing

    2015-10-01

    Although hexagonal boron nitride (h-BN) is a good candidate for gate-insulating materials by minimizing interaction from substrate, further applications to electronic devices with available two-dimensional semiconductors continue to be limited by flake size. While monolayer h-BN has been synthesized on Pt and Cu foil using chemical vapour deposition (CVD), multilayer h-BN is still absent. Here we use Fe foil and synthesize large-area multilayer h-BN film by CVD with a borazine precursor. These films reveal strong cathodoluminescence and high mechanical strength (Young's modulus: 1.16+/-0.1 TPa), reminiscent of formation of high-quality h-BN. The CVD-grown graphene on multilayer h-BN film yields a high carrier mobility of ~24,000 cm2 V-1 s-1 at room temperature, higher than that (~13,000 2 V-1 s-1) with exfoliated h-BN. By placing additional h-BN on a SiO2/Si substrate for a MoS2 (WSe2) field-effect transistor, the doping effect from gate oxide is minimized and furthermore the mobility is improved by four (150) times.

  8. 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.

  9. 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.

  10. (-201) β-Gallium oxide substrate for high quality GaN materials

    NASA Astrophysics Data System (ADS)

    Roqan, I. S.; Muhammed, M. M.

    2014-03-01

    (-201) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. The key advantages of Ga2O3 are its small lattice mismatches (4.7%), appropriate structural, thermal and electrical properties and a competitive price compared to other substrates. Optical characterization show that GaN layers grown on (-201) oriented β-Ga2O3 are dominated by intense bandedge emission with a high luminescence efficiency. Atomic force microscopy studies show a modest threading dislocation density of ~108 cm-2, while complementary Raman spectroscopy indicates that the GaN epilayer is of high quality with slight compressive strain. Room temperature time-findings suggest that the limitation of the photoluminescence lifetime (~500 ps) is due to nonradiative recombination arising from threading dislocation. Therefore, by optimizing the growth conditions, high quality material with significant optical efficiency can be obtained.

  11. Indium Nitride: A New Material for High Efficiency, Compact, 1550NM Laser-Based Terahertz Sources in Explosives Detection and Concealed Weapons Imaging

    DTIC Science & Technology

    2006-11-01

    INDIUM NITRIDE: A NEW MATERIAL FOR HIGH EFFICIENCY, COMPACT, 1550NM LASER-BASED TERAHERTZ SOURCES IN EXPLOSIVES DETECTION AND CONCEALED WEAPONS...nitride (InN) is identified as a promising terahertz (THz) emitter based on the optical and electronic properties of high quality In- and N-face...significant improvements in THz emitters. 1. INTRODUCTION The terahertz region of the electromagnetic spectrum, lying between microwave frequencies

  12. Investigation of crucible materials in gradient freeze gallium arsenide crystal growth

    SciTech Connect

    Hurd, J.L.

    1987-12-01

    Undoped synthesized GaAs and crystals grown by the gradient freeze method were analyzed by room temperature Hall effect for net carrier density, secondary ion mass spectroscopy for Si and residual impurity concentrations, localized vibrational mode spectroscopy for C concentration, and optical absorption for neutral EL2 concentration. Impurity compensation was examined to determine limits for Si content in semi-insulating GaAs. Boules synthesized in various materials are used to determine the residual impurity densities contributing to compensation. Shallow donor densities below the residual acceptor concentration resulted in semi-insulating electronic properties for two synthesis boules. The Si incorporation rate in gradient freeze crystals is quantified through the deviation of net donor concentration from the normal freeze distribution. Crystals grown As-rich, Ga-rich and near-stoichiometric composition in SiO/sub 2/ crucibles show order-of-magnitude differences of Si incorporation rate. Crystals grown in Al/sub 2/O/sub 3/ and graphite crucibles have <10/sup -2/ and >3 times the incorporation rates of gradient freeze GaAs grown in SiO/sub 2/ crucibles. Crystals grown in a vertical gradient freeze configuration have <1/7 the incorporation rate of those grown horizontally. A vapor mechanism for incorporation of Si is indicated that contributes enough Si to preclude semi-insulating properties. At high values of net donor density, an acceptor density is seen that may be of native defect origin and is positively correlated with net donor density. 63 refs., 16 figs., 6 tabs.

  13. MBE growth and processing of III/V-nitride semiconductor thin film structures: Growth of gallium indium arsenic nitride and nano-machining with focused ion beam and electron beam

    NASA Astrophysics Data System (ADS)

    Park, Yeonjoon

    The advanced semiconductor material InGaAsN was grown with nitrogen plasma assisted Molecular Beam Epitaxy (MBE). The InGaAsN layers were characterized with High Resolution X-ray Diffraction (HRXDF), Atomic Fore Microscope (AFM), X-ray Photoemission Spectroscopy (XPS) and Photo-Luminescence (PL). The reduction of the band gap energy was observed with the incorporation of nitrogen and the lattice matched condition to the GaAs substrate was achieved with the additional incorporation of indium. A detailed investigation was made for the growth mode changes from planar layer-by-layer growth to 3D faceted growth with a higher concentration of nitrogen. A new X-ray diffraction analysis was developed and applied to the MBE growth on GaAs(111)B, which is one of the facet planes of InGaAsN. As an effort to enhance the processing tools for advanced semiconductor materials, gas assisted Focused Ion Beam (FIB) vertical milling was performed on GaN. The FIB processed area shows an atomically flat surface, which is good enough for the fabrication of Double Bragg Reflector (DBR) mirrors for the Blue GaN Vertical Cavity Surface Emitting Laser (VCSEL) Diodes. An in-situ electron beam system was developed to combine the enhanced lithographic processing capability with the atomic layer growth capability by MBE. The electron beam system has a compensation capability against substrate vibration and thermal drift. In-situ electron beam lithography was performed with the low pressure assisting gas. The advanced processing and characterization methods developed in this thesis will assist the development of superior semiconductor materials for the future.

  14. Energy Landscape of Fullerene Materials: A Comparison of Boron to Boron Nitride and Carbon

    NASA Astrophysics Data System (ADS)

    de, Sandip; Willand, Alexander; Amsler, Maximilian; Pochet, Pascal; Genovese, Luigi; Goedecker, Stefan

    2011-06-01

    Using the minima hopping global geometry optimization method on the density functional potential energy surface we show that the energy landscape of boron clusters is glasslike. Larger boron clusters have many structures which are lower in energy than the cages. This is in contrast to carbon and boron nitride systems which can be clearly identified as structure seekers. The differences in the potential energy landscape explain why carbon and boron nitride systems are found in nature whereas pure boron fullerenes have not been found. We thus present a methodology which can make predictions on the feasibility of the synthesis of new nanostructures.

  15. Progress in gallium arsenide semiconductors

    SciTech Connect

    Brodsky, M.H. )

    1990-02-01

    After almost 30 years as the technology of the future, gallium arsenide has begun to make a place for itself, not by supplanting silicon but by complementing it in new applications. The inherent advantages of the material lie in the speed with which electrons move through it, in weak-signal operations and in the generation and detection of light. These advantages suit it for roles in computing, television reception and the optoelectronic transmission of data through optical-fiber networks. Gallium arsenide light-emitting diodes and lasers used in visual-display technologies and audio-disk players already account for more than $1 billion in sales annually. Hundreds of thousands of satellite-receiving dishes that use gallium arsenide detectors are sold every year, and high-speed circuits using gallium arsenide transistors are projected to reach a similar turnover in a few years. In an economy and society that depend on the rapid exchange of information as well as on the processing of it, many silicon-dominated processors will require a considerable admixture of gallium arsenide components in order to do their jobs.

  16. Polymer/boron nitride nanocomposite materials for superior thermal transport performance.

    PubMed

    Song, Wei-Li; Wang, Ping; Cao, Li; Anderson, Ankoma; Meziani, Mohammed J; Farr, Andrew J; Sun, Ya-Ping

    2012-06-25

    Boron nitride nanosheets were dispersed in polymers to give composite films with excellent thermal transport performances approaching the record values found in polymer/graphene nanocomposites. Similarly high performance at lower BN loadings was achieved by aligning the nanosheets in poly(vinyl alcohol) matrix by simple mechanical stretching (see picture).

  17. Single-crystal gallium nitride nanotubes.

    PubMed

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

    2003-04-10

    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 30-200 nm and wall thicknesses of 5-50 nm. 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.

  18. Growth process for gallium nitride porous nanorods

    DOEpatents

    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.

  19. Growth of single-crystal gallium nitride

    NASA Technical Reports Server (NTRS)

    Clough, R.; Richman, D.; Tietjen, J.

    1970-01-01

    Use of ultrahigh purity ammonia prevents oxygen contamination of GaN during growth, making it possible to grow the GaN at temperatures as high as 825 degrees C, at which point single crystal wafers are deposited on /0001/-oriented sapphire surfaces.

  20. Synthesis and characterization of actinide nitrides

    SciTech Connect

    Jaques, Brian; Butt, Darryl P.; Marx, Brian M.; Hamdy, A.S.; Osterberg, Daniel; Balfour, Gordon

    2007-07-01

    A carbothermic reduction of the metal oxides in a hydrogen/nitrogen mixed gas stream prior to nitriding in a nitrogen gas stream was used to synthesize uranium nitride at 1500 deg. C, cerium nitride at 1400 deg. C, and dysprosium nitride at 1500 deg. C. Cerium nitride and dysprosium nitride were also synthesized via hydriding and nitriding the metal shavings at 900 deg. C and 1500 deg. C, respectively. Also, a novel ball-milling synthesis route was used to produce cerium nitride and dysprosium nitride from the metal shavings at room temperature. Dysprosium nitride was also produced by reacting the metal shavings in a high purity nitrogen gas stream at 1300 deg. C. All materials were characterized by phase analysis via X-ray diffraction. Only the high purity materials were further analyzed via chemical analysis to characterize the trace oxygen concentration. (authors)

  1. Foreign Object Damage in a Gas-Turbine Grade Silicon Nitride by Spherical Projectiles of Various Materials

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Racz, Zsolt; Bhatt, Ramakrishna T.; Brewer, David N.

    2006-01-01

    Assessments of foreign object damage (FOD) of a commercial, gas-turbine grade, in situ toughened silicon nitride ceramic (AS800, Honeywell Ceramics Components) were made using four different projectile materials at ambient temperature. AS800 flexure target specimens rigidly supported were impacted at their centers in a velocity range from 50 to 450 m/s by spherical projectiles with a diameter of 1.59 mm. Four different projectile materials were used including hardened steel, annealed steel, silicon nitride ceramic, and brass. Post-impact strength of each target specimen impacted was determined as a function of impact velocity to appraise the severity of local impact damage. For a given impact velocity, the degree of strength degradation was greatest for ceramic balls, least for brass balls, and intermediate for annealed and hardened steel balls. For steel balls, hardened projectiles yielded more significant impact damage than annealed counterparts. The most important material parameter affecting FOD was identified as hardness of projectiles. Impact load as a function of impact velocity was quasi-statically estimated based on both impact and static indentation associated data.

  2. Correction: Ga[OSi(O(t)Bu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry.

    PubMed

    Dombrowski, James P; Johnson, Gregory R; Bell, Alexis T; Tilley, T Don

    2016-11-22

    Correction for 'Ga[OSi(O(t)Bu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry' by James P. Dombrowski et al., Dalton Trans., 2016, 45, 11025-11034.

  3. A Graphene-like Oxygenated Carbon Nitride Material for Improved Cycle-Life Lithium/Sulfur Batteries.

    PubMed

    Liu, Jinghai; Li, Wanfei; Duan, Limei; Li, Xin; Ji, Lei; Geng, Zhibin; Huang, Keke; Lu, Luhua; Zhou, Lisha; Liu, Zongrui; Chen, Wei; Liu, Liwei; Feng, Shouhua; Zhang, Yuegang

    2015-08-12

    Novel sulfur (S) anchoring materials and the corresponding mechanisms for suppressing capacity fading are urgently needed to advance the performance of Li/S batteries. Here, we designed and synthesized a graphene-like oxygenated carbon nitride (OCN) host material that contains tens of micrometer scaled two-dimensional (2D) rippled sheets, micromesopores, and oxygen heteroatoms. N content can reach as high as 20.49 wt %. A sustainable approach of one-step self-supporting solid-state pyrolysis (OSSP) was developed for the low-cost and large-scale production of OCN. The urea in solid sources not only provides self-supporting atmospheres but also produces graphitic carbon nitride (g-C3N4) working as 2D layered templates. The S/OCN cathode can deliver a high specific capacity of 1407.6 mA h g(-1) at C/20 rate with 84% S utilization and retain improved reversible capacity during long-term cycles at high current density. The increasing micropores, graphitic N, ether, and carboxylic O at the large sized OCN sheet favor S utilization and trapping for polysulfides.

  4. Preparation and characterization of superhard materials of crystalline carbon nitride. Final technical report, 15 May 1995--14 November 1998

    SciTech Connect

    Chung, Y.

    1999-02-01

    Prompted by the prediction of Cohen and coworkers that beta carbon nitride may have properties similar to diamond, there have been many attempts to synthesize this hypothetical metastable material. The author successfully synthesized this material via epitaxial stabilization using TiN(111) and ZrN(111) as the growth template. The coatings were CN/TiN or CN/ZrN multilayers grown in a dual-magnetron system. The existence of beta carbon nitride in these multilayers has been confirmed with cross-section electron diffraction, Rutherford backscattering, Raman spectroscopy and near-edge x-ray diffraction. Most important, these multilayers exhibit hardness in the 50 GPa, in spite of the large volume fraction (60--70%) of the softer TiN or ZrN component. Attempts to improve the hardness by using TiB{sub 2} (which is harder than TiN and ZrN) as the growth template did not work as well because TiB{sub 2} was markedly softened by the presence of nitrogen.

  5. Methods for and products of processing nanostructure nitride, carbonitride and oxycarbonitride electrode power materials by utilizing sol gel technology for supercapacitor applications

    DOEpatents

    Huang, Yuhong; Wei, Oiang; Chu, Chung-tse; Zheng, Haixing

    2001-01-01

    Metal nitride, carbonitride, and oxycarbonitride powder with high surface area (up to 150 m.sup.2 /g) is prepared by using sol-gel process. The metal organic precursor, alkoxides or amides, is synthesized firstly. The metal organic precursor is modified by using unhydrolyzable organic ligands or templates. A wet gel is formed then by hydrolysis and condensation process. The solvent in the wet gel is then be removed supercritically to form porous amorphous hydroxide. This porous hydroxide materials is sintered to 725.degree. C. under the ammonia flow and porous nitride powder is formed. The other way to obtain high surface area nitride, carbonitride, and oxycarbonitride powder is to pyrolyze polymerized templated metal amides aerogel in an inert atmosphere. The electrochemical capacitors are prepared by using sol-gel prepared nitride, carbonitride, and oxycarbonitride powder. Two methods are used to assemble the capacitors. Electrode is formed either by pressing the mixture of nitride powder and binder to a foil, or by depositing electrode coating onto metal current collector. The binder or coating is converted into a continuous network of electrode material after thermal treatment to provide enhanced energy and power density. Liquid electrolyte is soaked into porous electrode. The electrochemical capacitor assembly further has a porous separator layer between two electrodes/electrolyte and forming a unit cell.

  6. Fabrication of GaN nanotubular material using MOCVD with aluminum oxide membrane

    NASA Astrophysics Data System (ADS)

    Jung, Woo-Gwang; Jung, Se-Hyuck; Kung, Patrick; Razeghi, Manijeh

    2006-02-01

    GaN nanotubular material is fabricated with aluminum oxide membrane in MOCVD. SEM, XRD, TEM and PL are employed to characterize the fabricated GaN nanotubular material. An aluminum oxide membrane with ordered nano holes is used as template. Gallium nitride is deposited at the inner wall of the nano holes in aluminum oxide template, and the nanotubular material with high aspect ratio is synthesized using the precursors of TMG and ammonia gas. Optimal synthesis condition in MOCVD is obtained successfully for the gallium nitride nanotubular material in this research. The diameter of GaN nanotube fabricated is approximately 200 ~ 250 nm and the wall thickness is about 40 ~ 50 nm. GaN nanotubular material consists of numerous fine GaN particulates with sizes ranging 15 to 30 nm. The composition of gallium nitride is confirmed to be stoichiometrically 1:1 for Ga and N by EDS. XRD and TEM analyses indicate that grains in GaN nanotubular material have nano-crystalline structure. No blue shift is found in the PL spectrum on the GaN nanotubular material fabricated in aluminum oxide template.

  7. Fabrication of GaN nanotubular material using MOCVD with an aluminium oxide membrane

    NASA Astrophysics Data System (ADS)

    Jung, Woo-Gwang; Jung, Se-Hyuck; Kung, Patrick; Razeghi, Manijeh

    2006-01-01

    GaN nanotubular material is fabricated with an aluminium oxide membrane in MOCVD. SEM, XRD, TEM and PL are employed to characterize the fabricated GaN nanotubular material. An aluminium oxide membrane with ordered nanoholes is used as a template. Gallium nitride is deposited at the inner wall of the nanoholes in the aluminium oxide template, and the nanotubular material with high aspect ratio is synthesized using the precursors of TMG and ammonia gas. Optimal synthesis conditions in MOCVD are obtained successfully for the gallium nitride nanotubular material in this research. The diameter of the GaN nanotube fabricated is approximately 200-250 nm and the wall thickness is about 40-50 nm. GaN nanotubular material consists of numerous fine GaN particulates with size range 15-30 nm. The composition of gallium nitride is confirmed to be stoichiometrically 1:1 for Ga and N by EDS. XRD and TEM analyses indicate that the grains in GaN nanotubular material have a nano-crystalline structure. No blue shift is found in the PL spectrum on the GaN nanotubular material fabricated in an aluminium oxide template.

  8. Integrated Optical Pumping of Cr & Ti-Doped Sapphire Substrates With III-V Nitride Materials

    DTIC Science & Technology

    2005-08-24

    the Cr in sapphire could also permit the construction of white light LEDs . Ultimately, an integrated III-V Nitride optical pump for Ti:Sapphire could...substrates by MOCVD. 2. Characterization of doped sapphire/ InGaN structures byPL to simulate electrical injection by laser or LED device structures Part 2 1...Cr:sapphire substrate. Solid line is the spectrum of blue and red light emitted by InGaN LED epitaxially grown on Cr:sapphire substrate. The light was collected

  9. A modern perspective on the history of semiconductor nitride blue light sources

    NASA Astrophysics Data System (ADS)

    Maruska, Herbert Paul; Rhines, Walden Clark

    2015-09-01

    In this paper we shall discuss the development of blue light-emitting (LED) and laser diodes (LD), starting early in the 20th century. Various materials systems were investigated, but in the end, the nitrides of aluminum, gallium and indium proved to be the most effective. Single crystal thin films of GaN first emerged in 1968. Blue light-emitting diodes were first reported in 1971. Devices grown in the 1970s were prepared by the halide transport method, and were never efficient enough for commercial products due to contamination. Devices created by metal-organic vapor-phase epitaxy gave far superior performance. Actual true blue LEDs based on direct band-to-band transitions, free of recombination through deep levels, were finally developed in 1994, leading to a breakthrough in LED performance, as well as nitride based laser diodes in 1996. In 2014, the scientists who achieved these critical results were awarded the Nobel Prize in Physics.

  10. Magnetostriction and Magnetic Heterogeneities in Iron-Gallium

    DTIC Science & Technology

    2010-07-08

    REPORT Magnetostriction and Magnetic Heterogeneities in Iron-Gallium 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: Iron-gallium alloys Fe1-xGax exhibit...an exceptional increase in magnetostriction with gallium content. We present small-angle neutron scattering investigations on a Fe0.81Ga0.19 single...magnetic heterogeneities in the mechanism for magnetostriction in this material. 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 13. SUPPLEMENTARY NOTES

  11. 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.

  12. Molecular beam epitaxy of 2D-layered gallium selenide on GaN substrates

    NASA Astrophysics Data System (ADS)

    Lee, Choong Hee; Krishnamoorthy, Sriram; O'Hara, Dante J.; Brenner, Mark R.; Johnson, Jared M.; Jamison, John S.; Myers, Roberto C.; Kawakami, Roland K.; Hwang, Jinwoo; Rajan, Siddharth

    2017-03-01

    Large area epitaxy of two-dimensional (2D) layered materials with high material quality is a crucial step in realizing novel device applications based on 2D materials. In this work, we report high-quality, crystalline, large-area gallium selenide (GaSe) films grown on bulk substrates such as c-plane sapphire and gallium nitride (GaN) using a valved cracker source for Se. (002)-Oriented GaSe with random in-plane orientation of domains was grown on sapphire and GaN substrates at a substrate temperature of 350-450 °C with complete surface coverage. Higher growth temperature (575 °C) resulted in the formation of single-crystalline ɛ-GaSe triangular domains with six-fold symmetry confirmed by in-situ reflection high electron energy diffraction and off-axis x-ray diffraction. A two-step growth method involving high temperature nucleation of single crystalline domains and low temperature growth to enhance coalescence was adopted to obtain continuous (002)-oriented GaSe with an epitaxial relationship with the substrate. While six-fold symmetry was maintained in the two step growth, β-GaSe phase was observed in addition to the dominant ɛ-GaSe in cross-sectional scanning transmission electron microscopy images. This work demonstrates the potential of growing high quality 2D-layered materials using molecular beam epitaxy and can be extended to the growth of other transition metal chalcogenides.

  13. Influence of Cooling Hole Geometry and Material Conductivity on the Thermal Response of Cooled Silicon Nitride Plate

    NASA Technical Reports Server (NTRS)

    Abdul-Aziz, Ali; Bhatt, Ramakrishna T.; Girgis, Morris

    2002-01-01

    To complement the effectiveness of ceramic materials and the applicability to turbine engine applications, a parametric study using the finite element method was carried out. This study conducted thorough analyses of a thermal-barrier-coated silicon nitride (Si3N4) plate specimen with cooling channels, where its thermal conductivity was verified in an attempt to minimize the thermal stresses and reach an optimal rate of stress. The thermal stress profile was generated for specimens with circular and square cooling channels. Lower stresses were reported for a higher magnitude of thermal conductivity and in particular for the circular cooling channel arrangement. Contour plots for the stresses and the temperature are presented and discussed.

  14. Molten-Salt-Based Growth of Group III Nitrides

    DOEpatents

    Waldrip, Karen E.; Tsao, Jeffrey Y.; Kerley, Thomas M.

    2008-10-14

    A method for growing Group III nitride materials using a molten halide salt as a solvent to solubilize the Group-III ions and nitride ions that react to form the Group III nitride material. The concentration of at least one of the nitride ion or Group III cation is determined by electrochemical generation of the ions.

  15. III-nitride nanowires: novel materials for solid-state lighting

    NASA Astrophysics Data System (ADS)

    Wang, George T.; Li, Qiming; Huang, Jianyu; Talin, A. Alec; Armstrong, Andrew; Upadhya, Prashanth C.; Prasankumar, Rohit P.

    2011-03-01

    Although planar heterostructures dominate current solid-state lighting architectures (SSL), 1D nanowires have distinct and advantageous properties that may eventually enable higher efficiency, longer wavelength, and cheaper devices. However, in order to fully realize the potential of nanowire-based SSL, several challenges exist in the areas of controlled nanowire synthesis, nanowire device integration, and understanding and controlling the nanowire electrical, optical, and thermal properties. Here recent results are reported regarding the aligned growth of GaN and III-nitride core-shell nanowires, along with extensive results providing insights into the nanowire properties obtained using cutting-edge structural, electrical, thermal, and optical nanocharacterization techniques. A new top-down fabrication method for fabricating periodic arrays of GaN nanorods and subsequent nanorod LED fabrication is also presented.

  16. Preparation, structure, and properties of aluminium nitride (AIN) reinforced polymer composites: alternative substrate materials for microelectronic packaging

    NASA Astrophysics Data System (ADS)

    Hu, Xiao; Koh, Juay S.; Hing, Peter

    1997-08-01

    A series of composite materials of varying compositions based on a high temperature resistance engineering thermotropic liquid crystalline polymer and particulate aluminium nitride (AlN) were compounded at relatively low temperature using a co-rotating twin screw extruder/compounder equipped with the segmented screws. The compounded composites are injection molded into different shapes, i.e., dumbbell, rectangular bar and cylindrical disk, for various physical and mechanical tests. In particular, detailed study was carried out to understand the effect of AlN on the dielectric constant, thermal conductivity and thermal expansion behavior of these materials. Results have shown that the thermal conductivity steadily increases with AlN filler concentration. An increase by about 80 percent in thermal conductivity of the composite materials is achieved as compared to the unfilled polymer. The dielectric constants of these composites were found to increase with filer content and range from 3.6 to 5.0 at 1 kHz and 3.0 to 4.2 at 10 MHz. Substantial reductio in thermal expansion coefficient was also achieved in the composite materials. Attempt has been made to correlate the experimental data with composite theories.

  17. Sub-diffractional, volume-confined polaritons in a natural hyperbolic material: hexagonal boron nitride (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Caldwell, Joshua D.; Kretinin, Andrey V.; Chen, Yiguo; Giannini, Vincenzo; Fogler, Michael M.; Francescato, Yan; Ellis, Chase T.; Tischler, Joseph G.; Woods, Colin R.; Giles, Alexander J.; Watanabe, Kenji; Taniguchi, Takashi; Maier, Stefan A.; Novoselov, Kostya S.

    2015-09-01

    Strongly anisotropic media where principal components of the dielectric tensor have opposite signs are called hyperbolic. These materials permit highly directional, volume-confined propagation of slow-light modes at deeply sub-diffractional size scales, leading to unique nanophotonic phenomena. The realization of hyperbolic materials within the optical spectral range has been achieved primarily through the use of artificial structures typically composed of plasmonic metals and dielectric constituents. However, while proof-of-principle experiments have been performed, the high plasmonic losses and inhomogeneity of the structures limit most advances to the laboratory. Recently, hexagonal boron nitride (hBN) was identified as a natural hyperbolic material (NHM), offering a low-loss, homogeneous medium that can operate in the mid-infrared. We have exploited the NHM response of hBN within periodic arrays of conical nanoresonators to demonstrate `hyperbolic polaritons,' deeply sub-diffractional guided waves that propagate through the volume rather than on the surface of a hyperbolic material. We have identified that the polaritons are manifested as a four series of resonances in two distinct spectral bands that have mutually exclusive dependencies upon incident light polarization, modal order, and aspect ratio. These observations represent the first foray into creating NHM building blocks for mid-infrared to terahertz nanophotonic and metamaterial devices. This talk will also discuss potential near-term applications stemming from these developments.

  18. Progress and prospects of group-III nitride semiconductors

    NASA Astrophysics Data System (ADS)

    Mohammad, S. N.; Morkoç, H.

    We review recent progress in the group-III nitride and related materials, and electronic and optical devices based on them. Blue and UV (e.g. ultra violet) emitters and detectors, and high temperature/high power electronics which has long been coveted are beginning to be realized either in the laboratory or in the commercial arena, due in part to the breathtaking progress made in the last few years in the art and science of GaN, InN, AlN and their salloys. With brief references to the historical aspect of the relevant developments, this review concerns itself primarily with the current status of wide bandgap gallium nitride and related semiconductors from both the materials and devices points of view. Following a discussion of the structural properties of these materials, their electrical and optical properties are described in detail. The available data on metal contacts, the properties of which are indeed very conducive for the devices mentioned, from the points of view of ohmic contacts and Schottky barriers, are elaborated on. Recent progress on processing issues such as etching are reviewed. The review then embarks on an indash;depth discussion and analysis of field effect transistors, bipolar transistors, light emitting diodes, laser and photo detectors.

  19. Oxide-cladding aluminum nitride photonic crystal slab: Design and investigation of material dispersion and fabrication induced disorder

    NASA Astrophysics Data System (ADS)

    Melo, E. G.; Carvalho, D. O.; Ferlauto, A. S.; Alvarado, M. A.; Carreño, M. N. P.; Alayo, M. I.

    2016-01-01

    Photonic crystal slabs with a lower-index material surrounding the core layer are an attractive choice to circumvent the drawbacks in the fabrication of membranes suspended in air. In this work we propose a photonic crystal (PhC) slab structure composed of a triangular pattern of air holes in a multilayer thin film of aluminum nitride embedded in silicon dioxide layers designed for operating around 450 nm wavelengths. We show the design of an ideal structure and analyze the effects of material dispersion based on a first-order correction perturbation theory approach using dielectric functions obtained by experimental measurements of the thin film materials. Numerical methods were used to investigate the effects of fabrication induced disorder of typical nanofabrication processes on the bandgap size and spectral response of the proposed device. Deviation in holes radii and positions were introduced in the proposed PhC slab model with a Gaussian distribution profile. Impacts of slope in holes sidewalls that might result from the dry etching of AlN were also evaluated. The results show that for operation at the midgap frequency, slope in holes sidewalls is more critical than displacements in holes sizes and positions.

  20. Oxide-cladding aluminum nitride photonic crystal slab: Design and investigation of material dispersion and fabrication induced disorder

    SciTech Connect

    Melo, E. G. Alvarado, M. A.; Carreño, M. N. P.; Alayo, M. I.; Carvalho, D. O.; Ferlauto, A. S.

    2016-01-14

    Photonic crystal slabs with a lower-index material surrounding the core layer are an attractive choice to circumvent the drawbacks in the fabrication of membranes suspended in air. In this work we propose a photonic crystal (PhC) slab structure composed of a triangular pattern of air holes in a multilayer thin film of aluminum nitride embedded in silicon dioxide layers designed for operating around 450 nm wavelengths. We show the design of an ideal structure and analyze the effects of material dispersion based on a first-order correction perturbation theory approach using dielectric functions obtained by experimental measurements of the thin film materials. Numerical methods were used to investigate the effects of fabrication induced disorder of typical nanofabrication processes on the bandgap size and spectral response of the proposed device. Deviation in holes radii and positions were introduced in the proposed PhC slab model with a Gaussian distribution profile. Impacts of slope in holes sidewalls that might result from the dry etching of AlN were also evaluated. The results show that for operation at the midgap frequency, slope in holes sidewalls is more critical than displacements in holes sizes and positions.

  1. Interactions of Zircaloy cladding with gallium: 1998 midyear status

    SciTech Connect

    Wilson, D.F.; DiStefano, J.R.; Strizak, J.P.; King, J.F.; Manneschmidt, E.T.

    1998-06-01

    A program has been implemented to evaluate the effect of gallium in mixed-oxide (MOX) fuel derived from weapons-grade (WG) plutonium on Zircaloy cladding performance. The objective is to demonstrate that low levels of gallium will not compromise the performance of the MOX fuel system in a light-water reactor. The graded, four-phase experimental program was designed to evaluate the performance of prototypic Zircaloy cladding materials against (1) liquid gallium (Phase 1), (2) various concentrations of Ga{sub 2}O{sub 3} (Phase 2), (3) centrally heated surrogate fuel pellets with expected levels of gallium (Phase 3), and (4) centrally heated prototypic MOX fuel pellets (Phase 4). This status report describes the results of a series of tests for Phases 1 and 2. Three types of tests are being performed: (1) corrosion, (2) liquid metal embrittlement, and (3) corrosion-mechanical. These tests will determine corrosion mechanisms, thresholds for temperature and concentration of gallium that may delineate behavioral regimes, and changes in the mechanical properties of Zircaloy. Initial results have generally been favorable for the use of WG-MOX fuel. The MOX fuel cladding, Zircaloy, does react with gallium to form intermetallic compounds at {ge}300 C; however, this reaction is limited by the mass of gallium and is therefore not expected to be significant with a low level (parts per million) of gallium in the MOX fuel. Although continued migration of gallium into the initially formed intermetallic compound can result in large stresses that may lead to distortion, this was shown to be extremely unlikely because of the low mass of gallium or gallium oxide present and expected clad temperatures below 400 C. Furthermore, no evidence for grain boundary penetration by gallium has been observed.

  2. Interactions of zircaloy cladding with gallium -- 1997 status

    SciTech Connect

    Wilson, D.F.; DiStefano, J.R.; King, J.F.; Manneschmidt, E.T.; Strizak, J.P.

    1997-11-01

    A four phase program has been implemented to evaluate the effect of gallium in mixed oxide (MOX) fuel derived from weapons grade (WG) plutonium on Zircaloy cladding performance. The objective is to demonstrate that low levels of gallium will not compromise the performance of the MOX fuel system in LWR. This graded, four phase experimental program will evaluate the performance of prototypic Zircaloy cladding materials against: (1) liquid gallium (Phase 1), (2) various concentrations of Ga{sub 2}O{sub 3} (Phase 2), (3) centrally heated surrogate fuel pellets with expected levels of gallium (Phase 3), and (4) centrally heated prototypic MOX fuel pellets (Phase 4). This status report describes the results of an initial series of tests for phases 1 and 2. Three types of tests are being performed: (1) corrosion, (2) liquid metal embrittlement (LME), and (3) corrosion mechanical. These tests are designed to determine the corrosion mechanisms, thresholds for temperature and concentration of gallium that may delineate behavioral regimes, and changes in mechanical properties of Zircaloy. Initial results have generally been favorable for the use of WG-MOX fuel. The MOX fuel cladding, Zircaloy, does react with gallium to form intermetallic compounds at {ge} 300 C; however, this reaction is limited by the mass of gallium and is therefore not expected to be significant with a low level (in parts per million) of gallium in the MOX fuel. While continued migration of gallium into the initially formed intermetallic compound results in large stresses that can lead to distortion, this is also highly unlikely because of the low mass of gallium or gallium oxide present and expected clad temperatures below 400 C. Furthermore, no evidence for grain boundary penetration by gallium has been observed.

  3. Indium Gallium Nitride/Gallium Nitride (InGaN/GaN) Nanorods Superlattice (SL)

    DTIC Science & Technology

    2006-03-29

    distinct dislocation network and side wall damage are observed as shown in the upper inset of Fig. 10 which indicates an image of transmission electron...Phys. 76, 304 (1994). [42] W. I. Lee, T. C. Huang, J. Guo, and M. S. Feng, Appl. Phys. Lett. 67, 1721 (1995). [43] D. G. Thomas, J. J. Hopfield , and W

  4. Indium Gallium Nitride/Gallium Nitride (InGaN/GaN) Nanorods Superlattice (SL)

    DTIC Science & Technology

    2006-03-10

    of high-brightness and high-efficiency LEDs using dislocation-free InGaN /GaN SL NRAs by hydride vapor phase epitaxy (HVPE). The benefits of the... InGaN /GaN SL NRA LEDs are examined in this work, and their characteristics are compared to those of conventional broad area(BA) LEDs . The NRs SL were...demonstrates realization of high-brightness and high-efficiency LEDs using dislocation-free InGaN /GaN SL Nano rods arrays (NRAs) by hydride vapor

  5. 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)

  6. The Effect of Radiation on the Electrical Properties of Aluminum Gallium Nitride/Gallium Nitride Heterostructures

    DTIC Science & Technology

    2008-06-01

    34 Applied Physics . Letters vol. 74, 3353, 1999. [12] W. Shan, J. W. Ager III, K. M. Yu, W. Walukiewicz, E. E. Haller, M. C. Martin, W. R. McKinney, and...heterostructure field effect transistors”, Applied Physics Letters , vol. 77, no. 2, pp. 250-252, July 2000. [21] R. Vetury, et al., “Polarization induced...28] D. C. Look, et al., “Defect Donor and Acceptor in GaN,” Physical Review Letters , vol. 79, no. 12, pp. 2273-2276, 1997. [29] D. C. Look

  7. Two chain gallium fluorodiphosphates: synthesis, structure solution, and their transient presence during the hydrothermal crystallisation of a microporous gallium fluorophosphate.

    PubMed

    Millange, Franck; Walton, Richard I; Guillou, Nathalie; Loiseau, Thierry; O'Hare, Dermot; Férey, Gérard

    2002-04-21

    Two novel gallium fluorodiphosphates have been isolated and their structures solved ab initio from powder X-ray diffraction data; the materials readily interconvert under hydrothermal conditions, and are metastable with respect to an open-framework zeolitic gallium fluorophosphate, during the synthesis of which they are present as transient intermediates.

  8. Surface toughness of silicon nitride bioceramics: II, Comparison with commercial oxide materials.

    PubMed

    McEntire, Bryan J; Enomoto, Yuto; Zhu, Wenliang; Boffelli, Marco; Marin, Elia; Pezzotti, Giuseppe

    2016-02-01

    Raman microprobe-assisted indentation, a micromechanics method validated in a companion paper, was used to compare the surface toughening behaviors of silicon nitride (Si3N4) and alumina-based bioceramics employed in joint arthroplasty (i.e., monolithic alumina, Al2O3, and yttria-stabilized zirconia (ZrO2)-toughened alumina, ZTA). Quantitative assessments of microscopic stress fields both ahead and behind the tip of Vickers indentation cracks propagated under increasing indentation loads were systematically made using a Raman microprobe with spatial resolution on the order of a single micrometer. Concurrently, crack opening displacement (COD) profiles were monitored on the same microcracks screened by Raman spectroscopy. The Raman eye clearly visualized different mechanisms operative in toughening Si3N4 and ZTA bioceramics (i.e., crack-face bridging and ZrO2 polymorphic transformation, respectively) as compared to the brittle behavior of monolithic Al2O3. Moreover, emphasis was placed on assessing not only the effectiveness but also the durability of such toughening effects when the biomaterials were aged in a hydrothermal environment. A significant degree of embrittlement at the biomaterial surface was recorded in the transformation-toughened ZTA, with the surface toughness reduced by exposure to the hydrothermal environment. Conversely, the Si3N4 biomaterial experienced a surface toughness value independent of hydrothermal attack. Crack-face bridging thus appears to be a durable surface toughening mechanism for biomaterials in joint arthroplasty.

  9. Structural study of growth, orientation and defects characteristics in the functional microelectromechanical system material aluminium nitride

    SciTech Connect

    Hrkac, Viktor Schürmann, Ulrich; Kienle, Lorenz; Kobler, Aaron; Kübel, Christian; Marauska, Stephan; Wagner, Bernhard; Petraru, Adrian; Kohlstedt, Hermann; Kiran Chakravadhanula, Venkata Sai; Duppel, Viola; Lotsch, Bettina Valeska

    2015-01-07

    The real structure and morphology of piezoelectric aluminum nitride (AlN) thin films as essential components of magnetoelectric sensors are investigated via advanced transmission electron microscopy methods. State of the art electron diffraction techniques, including precession electron diffraction and automated crystal orientation mapping (ACOM), indicate a columnar growth of the AlN grains optimized for piezoelectric application with a (0 0 0 1) texture. Comparing ACOM with piezoresponse force microscopy measurements, a visual correlation of the structure and the piezoelectric properties is enabled. With a quantitative analysis of the ACOM measurements, a statistical evaluation of grain rotations is performed, indicating the presence of coincidence site lattices with Σ7, Σ13a, Σ13b, Σ25. Using a geometric phase analysis on high resolution micrographs, the occurrence of strain is detected almost exclusively at the grain boundaries. Moreover, high resolution imaging was applied for solving the atomic structure at stacking mismatch boundaries with a displacement vector of 1/2 〈1 0 -1 1〉. All real structural features can be interpreted via simulations based on crystallographic computing in terms of a supercell approach.

  10. Gallium Zeolites for Light Paraffin Aromatization

    SciTech Connect

    Price, G.L.; Dooley, K.M.

    1999-02-10

    The primary original goal of this project was to investigate the active state of gallium-containing MFI catalysts for light paraffin aromatization, in particular the state of gallium in the active material. Our original hypothesis was that the most active and selective materials were those which contained gallium zeolitic cations, and that previously reported conditions for the activation of gallium-containing catalysts served to create these active centers. We believed that in high silica materials such as MFI, ion-exchange is most effectively accomplished with metals in their 1+ oxidation state, both because of the sparsity of the anionic ion-exchange sites associated with the zeolite, and because the large hydration shells associated with aqueous 3+ cations hinder transport. Metals such as Ga which commonly exist in higher oxidation states need to be reduced to promote ion-exchange and this is the reason that reduction of gallium-containing catalysts for light paraffin aromatization often yields a dramatic enhancement in catalytic activity. We have effectively combined reduction with ion-exchange and we term this combined process ''reductive solid-state ion-exchange''. Our hypothesis has largely been proven true, and a number of the papers we have published directly address this hypothesis.

  11. Technical Progress Report for "Optical and Electrical Properties of III-Nitrides and Related Materials"

    SciTech Connect

    Jiang, Hongxing

    2008-10-31

    Investigations have been conducted focused on the fundamental material properties of AIN and high AI-content AIGaN alloys and further developed MOCVD growth technologies for obtaining these materials with improved crystalline quality and conductivities.

  12. Nanometric studies of the structure and tribology of carbon nitride materials. Final technical report, 15 June 1995--14 June 1998

    SciTech Connect

    Lieber, C.M.

    1998-07-31

    Significant effort has been placed on several areas. First, the authors have carried out systematic studies of the growth of carbon nitride materials as a function of carbon reactant energetics, nitrogen flux and growth temperature and have quantitatively analyzed the structure and local bonding in these materials. The emphasis of these studies has been to determine unambiguously conditions that can produce sp3-bonding since this is required for a superhard coating. Significantly, they have shown recently that there is a nitrogen-driven sp3 to sp2 structural transformation in the carbon nitride materials as nitrogen content is increased about 15 atomic percent. With these limits worked out they have also prepared films with optimal C-N ratios for hardness, and investigated their nanotribological properties by force microscopy. In addition, they have carried out theoretical cluster calculations to understand the origin of this sp3 to sp2 transition. Significantly, these calculations demonstrate that the transition is an intrinsic property of carbon nitride system since (1) the sp2 bonded structure becomes thermodynamically favored for 15% nitrogen and (2) the barrier between sp3 and sp2 structures also reduces significantly for 15% nitrogen.

  13. Growth and characterization of III-nitrides materials system for photonic and electronic devices by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Yoo, Dongwon

    A wide variety of group III-Nitride-based photonic and electronic devices have opened a new era in the field of semiconductor research in the past ten years. The direct and large bandgap nature, intrinsic high carrier mobility, and the capability of forming heterostructures allow them to dominate photonic and electronic device market such as light emitters, photodiodes, or high-speed/high-power electronic devices. Avalanche photodiodes (APDs) based on group III-Nitrides materials are of interest due to potential capabilities for low dark current densities, high sensitivities and high optical gains in the ultraviolet (UV) spectral region. Wide-bandgap GaN-based APDs are excellent candidates for short-wavelength photodetectors because they have the capability for cut-off wavelengths in the UV spectral region (lambda < 290 nm). These intrinsically solar-blind UV APDs will not require filters to operate in the solar-blind spectral regime of lambda < 290 nm. For the growth of GaN-based heteroepitaxial layers on lattice-mismatched substrates, a high density of defects is usually introduced during the growth; thereby, causing a device failure by premature microplasma, which has been a major issue for GaN-based APDs. The extensive research on epitaxial growth and optimization of AlxGa 1-xN (0 ≤ x ≤ 1) grown on low dislocation density native bulk III-N substrates have brought UV APDs into realization. GaN and AlGaN UV p-i-n APDs demonstrated first and record-high true avalanche gain of > 10,000 and 50, respectively. The large stable optical gains are attributed to the improved crystalline quality of epitaxial layers grown on low dislocation density bulk substrates. GaN p-i-n rectifiers have brought much research interest due to its superior physical properties. The AIN-free full-vertical GaN p-i-n rectifiers on n-type 6H-SiC substrates by employing a conducting AIGaN:Si buffer layer provides the advantages of the reduction of sidewall damage from plasma etching and

  14. Novel nitrogen/gallium precursor [Ga(bdma)H2] for MOVPE

    NASA Astrophysics Data System (ADS)

    Sterzer, E.; Beyer, A.; Nattermann, L.; Schorn, W.; Schlechter, K.; Pulz, S.; Sundermeyer, J.; Stolz, W.; Volz, K.

    2016-11-01

    Dilute nitrogen (N) containing III/V semiconductors are promising candidates for solar cell and laser applications. The N incorporation efficiency of 1,1-dimethylhydrazine (UMDHy) in metal organic vapor phase epitaxy (MOVPE), however, happens to be only in the one percentage range and below. This leads to an extremely high offer of UDMHy in the MOVPE reactor and, therefore, a drastic change in the growth conditions. Furthermore, the device efficiency of dilute nitride materials is currently hampered by carbon (C) incorporation, which is believed to be incorporated either jointly with the N from the dimethylamine radical of the UMDHy or from short hydrocarbon radicals originating from the decomposition of the other metal organics. Therefore, this work presents a novel N precursor N,N'-Bis(dimethylamino)acetamidinato-galliumdihydride [Ga(bdma)H2], which provides not only N but also gallium (Ga) during MOVPE. The direct N-Ga bond in this molecule might facilitate the N incorporation and hence increase the efficiency. For a systematic N incorporation study Ga(NAs)/GaAs heterostructures were grown by MOVPE. The N content was determined via high resolution X-ray diffraction and photoluminescence (PL) studies. Good structural quality and as grown room temperature PL were obtained. It will be also shown that the N incorporation efficiency in GaAs using [Ga(bdma)H2] is significantly higher than for growths using UDMHy under comparable conditions, making this class of molecules promising candidates for the growth of dilute nitride materials.

  15. New SMU Gallium Fixed-Point Cells

    NASA Astrophysics Data System (ADS)

    Ranostaj, Juraj; Ďuriš, Stanislav; Knorová, Renáta; Kaskötö, Mariana; Vyskočilová, Irena

    2011-08-01

    In the framework of the European research project EURAMET 732, the Slovak Institute of Metrology (SMU) built three primary gallium fixed-point cells of different designs. The cells are designed for the calibration of the long-stem SPRT. In regard to the procedure commonly used at SMU when realizing the gallium point, the cells are designed for use in a stirred liquid bath. This article provides information about the cell designs, materials used, method of filling, and results of the performed experiments. The experiments were focused on the study of the cells' metrological characteristics, some effects that could influence the melting-point temperature and the effect of the melted metal fraction on the immersion profile. New cells were compared with the SMU reference gallium cell.

  16. Nitride quantum light sources

    NASA Astrophysics Data System (ADS)

    Zhu, T.; Oliver, R. A.

    2016-02-01

    Prototype nitride quantum light sources, particularly single-photon emitters, have been successfully demonstrated, despite the challenges inherent in this complex materials system. The large band offsets available between different nitride alloys have allowed device operation at easily accessible temperatures. A wide range of approaches has been explored: not only self-assembled quantum dot growth but also lithographic methods for site-controlled nanostructure formation. All these approaches face common challenges, particularly strong background signals which contaminate the single-photon stream and excessive spectral diffusion of the quantum dot emission wavelength. If these challenges can be successfully overcome, then ongoing rapid progress in the conventional III-V semiconductors provides a roadmap for future progress in the nitrides.

  17. Effect of Variation of Silicon Nitride Passivation Layer on Electron Irradiated Aluminum Gallium Nitride/Gallium Nitride HEMT Structures

    DTIC Science & Technology

    2014-06-19

    temperature measurements are often used to provide spatial PL maps of doping and trap densities. Laser excitation (quasi-monochromatic) is... excited with a laser as the energy source: hγ > EG (2.40) 43 where hγ is the...was accomplished using a HeCd laser (325 nm) as excitation source and with an emission detection range varying from 3550 to 7450 Å. The laser beam

  18. Electrodeposition of gallium for photovoltaics

    SciTech Connect

    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.

  19. Experimental and theoretical investigations of functionalized boron nitride as electrode materials for Li-ion batteries

    SciTech Connect

    Zhang, Fan; Nemeth, Karoly; Bareno, Javier; Dogan, Fulya; Bloom, Ira D.; Shaw, Leon L.

    2016-03-03

    The feasibility of synthesizing functionalized h-BN (FBN) via the reaction between molten LiOH and solid h-BN is studied for the first time and its first ever application as an electrode material in Li-ion batteries is evaluated. Density functional theory (DFT) calculations are performed to provide mechanistic understanding of the possible electrochemical reactions derived from the FBN. Various materials characterizations reveal that the melt-solid reaction can lead to exfoliation and functionalization of h-BN simultaneously, while electrochemical analysis proves that the FBN can reversibly store charges through surface redox reactions with good cycle stability and coulombic efficiency. As a result, the DFT calculations have provided physical insights into the observed electrochemical properties derived from the FBN.

  20. Experimental and theoretical investigations of functionalized boron nitride as electrode materials for Li-ion batteries

    DOE PAGES

    Zhang, Fan; Nemeth, Karoly; Bareno, Javier; ...

    2016-03-03

    The feasibility of synthesizing functionalized h-BN (FBN) via the reaction between molten LiOH and solid h-BN is studied for the first time and its first ever application as an electrode material in Li-ion batteries is evaluated. Density functional theory (DFT) calculations are performed to provide mechanistic understanding of the possible electrochemical reactions derived from the FBN. Various materials characterizations reveal that the melt-solid reaction can lead to exfoliation and functionalization of h-BN simultaneously, while electrochemical analysis proves that the FBN can reversibly store charges through surface redox reactions with good cycle stability and coulombic efficiency. As a result, the DFTmore » calculations have provided physical insights into the observed electrochemical properties derived from the FBN.« less

  1. Amorphous carbon nitride as an alternative electrode material in electroanalysis: simultaneous determination of dopamine and ascorbic acid.

    PubMed

    Medeiros, Roberta A; Matos, Roberto; Benchikh, Abdelkader; Saidani, Boualem; Debiemme-Chouvy, Catherine; Deslouis, Claude; Rocha-Filho, Romeu C; Fatibello-Filho, Orlando

    2013-10-03

    Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CNx) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CNx electrode. Thus, an a-CNx film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L(-1) KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CNx electrode were 0.0656 μmol L(-1) for DA and 1.05 μmol L(-1) for AA, whereas with the BDD electrode these values were 0.283 μmol L(-1) and 0.968 μmol L(-1), respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CNx electrode in electroanalysis.

  2. Ultra-small vanadium nitride quantum dots embedded in porous carbon as high performance electrode materials for capacitive energy storage

    NASA Astrophysics Data System (ADS)

    Yang, Yunlong; Zhao, Lei; Shen, Kuiwen; Liu, Ying; Zhao, Xiaoning; Wu, Yage; Wang, Yanqin; Ran, Fen

    2016-11-01

    Ultra-small vanadium nitride quantum dots embedded in porous carbon (VNQDs/PC) were fabricated by a thermal treatment process of NH4VO3/C3H6N6 under nitrogen atmosphere. The specific capacitance of VNQDs/PC was 1008 mF cm-2 at a current density of 0.004 A cm-2, whereas the VN/carbon hybrid material obtained by a solid-state blending of NH4VO3 and C3H6N6 just exhibited a capacitance of 432 mF cm-2 at the same current density. By mediating the ratio of NH4VO3 and C3H6N6, a maximum specific capacitance of 1124 mF cm-2 was achieved at a current density of 0.002 A cm-2 in aqueous 6 mol/L KOH electrolyte with the potential range from 0 to -1.15 V when it reached 1: 7 (wt./wt.). Additionally, symmetrical supercapacitor fabricated with synthesized VNQDs/PC presented a high specific capacitance of 215 mF cm-2 at 0.002 A cm-2 based on the entire cell, and exhibited a high capacitance retention of 86.6% with current density increased to 5 A g-1. The VNQDs/PC negative electrodes were combined with Ni(OH)2 positive electrodes for the fabrication of hybrid supercapacitors. Remarkably, at a power density of 828.7 W kg-1, the device delivered an ultrahigh energy density of 47.2 Wh kg-1.

  3. EDITORIAL: Non-polar and semipolar nitride semiconductors Non-polar and semipolar nitride semiconductors

    NASA Astrophysics Data System (ADS)

    Han, Jung; Kneissl, Michael

    2012-02-01

    topics including growth and heteroepitaxy, bulk GaN substrates, theory and modelling, optical properties, laser diodes and LEDs as well as transport properties and electronics. Farrell et al review materials and growth issues for high-performance non- and semipolar light-emitting devices, and Scholz provides an overview of heteroepitaxial growth of semipolar GaN. Okada et al review growth mechanisms of non- and semipolar GaN layers on patterned sapphire substrates, and Vennéguès discusses defect reduction methods for heteroepitaxially grown non- and semipolar III-nitride films. Leung et al explain how kinetic Wulff plots can be used to design and control non-polar and semipolar GaN heteroepitaxy, and a contribution by Sawaki et al explores the impurity incorporation in (1-101) GaN grown on Si substrates. In the area of bulk crystal growth Kucharski et al review non- and semipolar GaN substrates by ammonothermal growth, and Chichibu et al discuss the challenges for epitaxial growth of InGaN on free-standing m-plane GaN substrates. Calculation of semipolar orientations for wurtzitic semiconductor heterostructures and their application to nitrides and oxides are reviewed by Bigenwald et al, and Ito et al present an ab initio approach to reconstruction, adsorption, and incorporation on GaN surfaces. Finally, the theoretical description of non-polar and semipolar nitride semiconductor quantum-well structures is presented by Ahn et al. In a discussion of the optical properties, Kisin et al discuss the effect of the quantum well population on the optical characteristics of polar, semipolar and non-polar III-nitride light emitters, and Jönen et al investigate the indium incorporation and optical properties of non- and semipolar GaInN QW structures. Wernicke et al explore the emission wavelength of polar, non-polar, and semipolar InGaN quantum wells and the incorporation of indium. In a contribution by Melo et al, the gain in polar and non-polar/semipolar gallium-nitride

  4. Impurity-Induced Layer Disordering and Hydrogenation in the Indium Aluminum Gallium Phosphide Material System: Visible-Spectrum Semiconductor Lasers.

    NASA Astrophysics Data System (ADS)

    Dallesasse, John Michael

    1991-02-01

    The development of visible-spectrum semiconductor lasers is of immense economic and practical importance. Because of the extremely high efficiency of semiconductor lasers, coherent visible light sources can be made with extremely low power requirements. Applications for such sources include high-density optical storage units and optical communications. Additionally, the use of multiple-stripe arrays makes high-power (gg200 mW per facet) coherent semiconductor light sources a possibility. In this work, various aspects of the problems involved in constructing visible-spectrum semiconductor lazers are discussed. First, the difficulties in obtaining reliable devices near the direct-indirect crossover of the rm Al_{x}Ga_ {1-x}As-GaAs material system are discussed. Hydrolysis of high Al-content buried layers via interaction of water vapor in the air with the crystal at pinholes and cleaved edges is found to result in slow decomposition of QWH material. Next, the rm In_{1-y}(Al_ {x} Ga_{1-x})_{y }P material system is put forth as the material system of choice for the construction of visible-spectrum semiconductor lasers. Data are shown on the continuous -wave (cw) room-temperture operation of oxide-stripe lasers. Two important techniques for the realization of high performance device operation are next described. The first of these, impurity-induced layer disordering (IILD), is useful for the construction of low-threshold single -stripe lasers, high-power multistripe lasers, and high beam-quality devices. The disordering of rm In_{1-y} (Al_{x} Ga_ {1-x})_{y}P heterolayers via Si and Ge diffusion is first examined via shallow-angle slant cross-sectioning, transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS), and photoluminescence (PL) on as-grown and disordered InAlP-InGaP superlattice (SL) crystals. Disordering via Si diffusion is then applied to the fabrication of buried heterostructure visible-spectrum lasers. These devices operate at room

  5. Behavior of Zircaloy Cladding in the Presence of Gallium

    SciTech Connect

    DiStefano, J.R.; King, J.F.; Manneschmidt, E.T.; Strizak, J.P.; Wilson, D.F.

    1998-09-28

    The U.S. Department of Energy has established a dual-track approach to the disposition of plutonium arising from the dismantling of nuclear weapons. Both immobilization and reactor-based mixed-oxide (MOX) fuel technologies are being evaluated. The reactor-based MOX fuel option requires assessment of the potential impact of concentrations of gallium (on the order of 1 to 10 ppm), not present in conventional MOX fuel, on cladding material performance. An experimental program was designed to evaluate the performance of prototypic Zircaloy cladding materials against (1) liquid gallium, and (2) various concentrations of G~03. Three types of tests were performed: (1) corrosion, (2) liquid metal embrittlement, and (3) corrosion-mechanical. These tests were to determine corrosion mechanisms, thresholds for temperature and concentration of gallium that delineate behavioral regimes, and changes in the mechanical properties of Zircaloy. Results have generally been favorable for the use of weapons-grade (WG) MOX fhel. The Zircaloy cladding does react with gallium to form intermetallic compounds at >3000 C; however, this reaction is limited by the mass of gallium and is therefore not expected to be significant with a low level (parts per million) of gallium in the MOX fuel. Furthermore, no evidence for grain boundary penetration by gallium or liquid metal embrittlement was observed.

  6. Efficient water reduction with gallium phosphide nanowires

    NASA Astrophysics Data System (ADS)

    Standing, Anthony; Assali, Simone; Gao, Lu; Verheijen, Marcel A.; van Dam, Dick; Cui, Yingchao; Notten, Peter H. L.; Haverkort, Jos E. M.; Bakkers, Erik P. A. M.

    2015-07-01

    Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainable fuel option for the future. Planar III/V material systems have shown the highest efficiencies, but are expensive. By moving to the nanowire regime the demand on material quantity is reduced, and new materials can be uncovered, such as wurtzite gallium phosphide, featuring a direct bandgap. This is one of the few materials combining large solar light absorption and (close to) ideal band-edge positions for full water splitting. Here we report the photoelectrochemical reduction of water, on a p-type wurtzite gallium phosphide nanowire photocathode. By modifying geometry to reduce electrical resistance and enhance optical absorption, and modifying the surface with a multistep platinum deposition, high current densities and open circuit potentials were achieved. Our results demonstrate the capabilities of this material, even when used in such low quantities, as in nanowires.

  7. Efficient water reduction with gallium phosphide nanowires

    PubMed Central

    Standing, Anthony; Assali, Simone; Gao, Lu; Verheijen, Marcel A.; van Dam, Dick; Cui, Yingchao; Notten, Peter H. L.; Haverkort, Jos E. M.; Bakkers, Erik P. A. M.

    2015-01-01

    Photoelectrochemical hydrogen production from solar energy and water offers a clean and sustainable fuel option for the future. Planar III/V material systems have shown the highest efficiencies, but are expensive. By moving to the nanowire regime the demand on material quantity is reduced, and new materials can be uncovered, such as wurtzite gallium phosphide, featuring a direct bandgap. This is one of the few materials combining large solar light absorption and (close to) ideal band-edge positions for full water splitting. Here we report the photoelectrochemical reduction of water, on a p-type wurtzite gallium phosphide nanowire photocathode. By modifying geometry to reduce electrical resistance and enhance optical absorption, and modifying the surface with a multistep platinum deposition, high current densities and open circuit potentials were achieved. Our results demonstrate the capabilities of this material, even when used in such low quantities, as in nanowires. PMID:26183949

  8. Sources of Shockley-Read-Hall recombination in III-nitride light emitters

    NASA Astrophysics Data System (ADS)

    Dreyer, Cyrus E.; Alkauskas, Audrius; Lyons, John L.; Speck, James S.; van de Walle, Chris G.

    Group-III nitrides are the key materials for high efficiency light-emitting diodes in the blue part of the visible spectrum, and a large research effort is aimed at extending this success to the green and the yellow range, where nitride LEDs are significantly less efficient. Though it has been noted that the efficiency of III-nitride devices may be limited by Shockley-Read-Hall recombination at point defects, the microscopic mechanism and defects responsible are unknown. Based on first-principles calculations of defect formation energies, charge-state transition levels, and nonradiative capture coefficients, we describe a mechanism by which complexes between gallium vacancies and oxygen and/or hydrogen can act as efficient channels for nonradiative recombination in InGaN alloys. The dependence of these quantities on alloy composition is analyzed. We find that modest concentrations of the proposed defect complexes, around 1016cm-3, can give rise to Shockley-Read-Hall coefficients A = (107 -109) s-1. The resulting nonradiative recombination can significantly reduce the internal quantum efficiency of optoelectronic devices. This work was supported by DOE and by EU Marie Sklodowska-Curie Action.

  9. Efficiency Improvement of Nitride-Based Solid State Light Emitting Materials -- CRADA Final Report

    SciTech Connect

    Kisielowski, Christian; Weber, Eicke

    2010-05-13

    The development of In{sub x}Ga{sub 1-x} N/GaN thin film growth by Molecular Beam Epitaxy has opened a new route towards energy efficient solid-state lighting. Blue and green LED's became available that can be used to match the whole color spectrum of visible light with the potential to match the eye response curve. Moreover, the efficiency of such devices largely exceeds that of incandescent light sources (tungsten filaments) and even competes favorably with lighting by fluorescent lamps. It is, however, also seen in Figure 1 that it is essential to improve on the luminous performance of green LED's in order to mimic the eye response curve. This lack of sufficiently efficient green LED's relates to particularities of the In{sub x}Ga{sub 1-x}N materials system. This ternary alloy system is polar and large strain is generated during a lattice mismatched thin film growth because of the significantly different lattice parameters between GaN and InN and common substrates such as sapphire. Moreover, it is challenging to incorporate indium into GaN at typical growth temperatures because a miscibility gap exists that can be modified by strain effects. As a result a large parameter space needs exploration to optimize the growth of In{sub x}Ga{sub 1-x}N and to date it is unclear what the detailed physical processes are that affect device efficiencies. In particular, an inhomogeneous distribution indium in GaN modifies the device performance in an unpredictable manner. As a result technology is pushed forward on a trial and error basis in particular in Asian countries such as Japan and Korea, which dominate the market and it is desirable to strengthen the competitiveness of the US industry. This CRADA was initiated to help Lumileds Lighting/USA boosting the performance of their green LED's. The tasks address the distribution of the indium atoms in the active area of their blue and green LED's and its relation to internal and external quantum efficiencies. Procedures to

  10. 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.

  11. 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.

  12. Hard and low friction nitride coatings and methods for forming the same

    DOEpatents

    Erdemir, Ali; Urgen, Mustafa; Cakir, Ali Fuat; Eryilmaz, Osman Levent; Kazmanli, Kursat; Keles, Ozgul

    2007-05-01

    An improved coating material possessing super-hard and low friction properties and a method for forming the same. The improved coating material includes the use of a noble metal or soft metal homogeneously distributed within a hard nitride material. The addition of small amounts of such metals into nitrides such as molybdenum nitride, titanium nitride, and chromium nitride results in as much as increasing of the hardness of the material as well as decreasing the friction coefficient and increasing the oxidation resistance.

  13. Method of preparation of uranium nitride

    DOEpatents

    Kiplinger, Jaqueline Loetsch; Thomson, Robert Kenneth James

    2013-07-09

    Method for producing terminal uranium nitride complexes comprising providing a suitable starting material comprising uranium; oxidizing the starting material with a suitable oxidant to produce one or more uranium(IV)-azide complexes; and, sufficiently irradiating the uranium(IV)-azide complexes to produce the terminal uranium nitride complexes.

  14. Electrical characterization of germanium implanted gallium arsenide

    NASA Astrophysics Data System (ADS)

    Pedrotti, F. L.

    1980-06-01

    The amphoteric electrical properties of germanium single implants into gallium arsenide, and of dual implants of germanium with either gallium or arsenic into gallium arsenide, have been studied. Room temperature implantation was performed for all implanted ions at 120 keV, with doses ranging from 5E12 to 3E15 ions per square centimeter. Implanted samples were annealed with pyrolytic silicon nitride encapsulants at temperatures ranging from 700 to 1000 degrees Celsius. Both p- and n-type layers were observed. Type of conductivity, electrical activation, and carrier mobility were found to depend critically upon ion dose and anneal temperature. The general electrical behavior suggests that in samples of lower dose and anneal temperature, the implanted Ge ions go into As sites preferentially, producing p-type activity, whereas in samples of higher dose and anneal temperature, more Ge ions go into Ga sites, producing n-type activity. Conductivity was found to change from p- to n-type at an intermediate dose of 3E14 ions per square centimeter and at an anneal temperature between 900 and 950 degrees Celsius. It has been determined that additional implantation of As into GaAs Ge favors Ge occupancy of Ga sites and an enhancement of n-type activity, whereas the additional implantation of Ga encourages Ge occupancy of As sites and an enhancement of p-type activity. Enhancement factors of as much as 8 for p-type activations, and as much as 50 for n-type activations have been measured.

  15. Investigation of titanium nitride as catalyst support material and development of durable electrocatalysts for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Avasarala, Bharat K.

    The impending energy and climatic crisis makes it imperative for human society to seek non-fossil based alternative sources for our energy needs. Although many alternative energy technologies are currently being developed, fuel cell technology provides energy solutions, which satisfy a wide range of applications. But the current fuel cell technology is far from its target of large scale commercialization mainly because of its high cost and poor durability. Considerable work has been done in reducing the cost but its durability still needs significant improvement. Of the various materials in a PEM fuel cell, the degradation of electrocatalyst affects its durability the most, leading to performance loss. Carbon black (C) support corrosion plays a significant role in the electrocatalyst degradation and its severe affects due to potential cycling has been identified through my research. Through my resaerch, I introduce titanium nitride nanoparticles (TiN NP) as alternative catalyst supports replacing carbon black. TiN NP has higher electrical conductivity and corrosion resistance compared to that of C. The physical and electrochemical properties of TiN NP were studied and the Pt/TiN electrocatalyst was synthesized using polyol process. Upon optimizing using DOE, for desired catalyst particle size and activity, Pt/TiN is shown to have higher catalytic performance than conventional Pt/C. TiN NP are significantly influenced by the electrochemical conditions and show 'active' or 'passive' nature depending on the temperature and acidic concentration; and a temperature dependence model is proposed to understand the active/passive nature of TiN NP. A one-to-one comparison between TiN NP and C electrodes under similar electrochemical conditions show a superior performance of TiN NP as a catalyst support. The durability of the Pt/TiN electrocatalyst is also tested and it agrees well with the proposed model of active/passive nature of the TiN NP. Through theoretical calculation

  16. Antitumor effect of novel gallium compounds and efficacy of nanoparticle-mediated gallium delivery in lung cancer.

    PubMed

    Wehrung, Daniel; Oyewumi, Moses O

    2012-02-01

    The widespread application of gallium (Ga) in cancer therapy has been greatly hampered by lack of specificity resulting in poor tumor accumulation and retention. To address the challenge, two lipophilic gallium (III) compounds (gallium hexanedione; GaH and gallium acetylacetonate; GaAcAc) were synthesized and antitumor studies were conducted in human lung adenocarcinoma (A549) cells. Nanoparticles (NPs) containing various concentrations of the Ga compounds were prepared using a binary mixture of Gelucire 44/14 and cetyl alcohol as matrix materials. NPs were characterized based on size, morphology, stability and biocompatibility. Antitumor effects of free or NP-loaded Ga compounds were investigated based on cell viability, production of reactive oxygen species and reduction of mitochondrial potential. Compared to free Ga compounds, cytotoxicity of NP-loaded Ga (5-150 microg/ml) was less dependent on concentration and incubation time (exposure) with A549 cells. NP-mediated delivery (5-150 microg Ga/ml) enhanced antitumor effects of Ga compounds and the effect was pronounced at: (i) shorter incubation times; and (ii) at low concentrations of gallium (approximately 50 microg/ml) (p < 0.0006). Additional studies showed that NP-mediated Ga delivery was not dependent on transferrin receptor uptake mechanism (p > 0.13) suggesting the potential in overcoming gallium resistance in some tumors. In general, preparation of stable and biocompatible NPs that facilitated Ga tumor uptake and antitumor effects could be effective in gallium-based cancer therapy.

  17. Boron nitride insulating material

    DOEpatents

    Morgan, Jr., Chester S.; Cavin, O. Burl; McCulloch, Reginald W.; Clark, David L.

    1978-01-01

    High temperature BN-insulated heaters for use as fuel pin simulators in reactor thermal hydraulic test facility studies comprise a cylindrical housing and a concentric heating element disposed within the housing and spaced apart from the housing to define an annular region therebetween. The annular region contains BN for providing electrical resistance and thermal conductivity between the housing and the heating element. The fabrication method of this invention comprises the steps of cold pressing BN powder at a pressure of 20 to 80,000 psig and a dwell time of at least 0.1-3 seconds to provide hollow cylindrical preforms of suitable dimensions for insertion into the annular region, the BN powder having a tap density of about 0.6-1.1 g/cm.sup.3 and an orientation ratio of at least about 100/3.5. The preforms are inserted into the annular region and crushed in place.

  18. 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.

  19. III-nitride ultraviolet emitters produced by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Anirban

    In this dissertation, the growth of III-Nitride based ultraviolet (UV) emitters by molecular beam epitaxy has been addressed. These devices can find applications in optical data storage, solid-state lighting, and in biological detection. A significant part of the research involved materials development, as there are several major scientific and technological hurdles that must be overcome in order to produce commercially viable devices. For emission in the wavelength region 330 nm to 350 nm, the devices were designed as electrically-injected light emitting diodes (LEDs). Each layer of this structure was individually optimized to improve the materials properties. To overcome the difficulties in p-type doping, a new growth regime has been explored which led to films with hole concentrations of up to 2 x 10 18/cm3. Multiple quantum wells (MQWs) were grown along polar and non-polar directions to understand the effects of the presence of built-in polarization fields. It was found that these detrimental effects are minimized for ultra thin wells. Use of an Indium flux as a surfactant was found to substantially improve the luminescence properties of bulk Aluminum Gallium Nitride (AlGaN) alloys and MQWs. UV-LEDs grown under these optimized conditions show an optical power output of 0.75 mW at 340 nm and 4.5 mW at 350nm. For emission in the wavelength region below 270 nm, due to the difficulty of doping AlGaN alloys with high Aluminum Nitride (AlN) mole fraction, edge or vertical emitting electron beam-pumped laser structures have been developed. Since it is difficult to cleave III-Nitrides deposited onto C-plane sapphire, edge emitting laser structures using a Graded-Index Separate Confinement Heterostructure (GRINSCH) based geometry have been deposited onto A-plane sapphire using a novel AlN buffer layer. An AlGaN bulk film or a set of AlN/AlGaN MQWs is used as the active region. For use in these devices, the growth of high Al content AlGaN was optimized to reduce the deep

  20. Theoretical studies of impurity and hole subband states in nitride semiconductors

    NASA Astrophysics Data System (ADS)

    Mireles Higuera, Francisco

    We present a comprehensive theoretical study of the shallow donor and acceptor states and their binding energies in large bandgap bulk nitride semiconductors. An envelope function scheme within the effective mass theory in a multi-band formalism was used to obtain the impurity levels in a variational fashion. Suitable atomic pseudopotentials were employed to resemble the impurity potential of the different dopants. Numerical calculations are reported for the binding energies of several substitutional acceptor and donor impurities from groups IIA, IIB and IVA of the periodic table in gallium and aluminum nitride. It is found that both acceptors and donors have smaller binding energy in the cubic zincblende phase of these materials than in the normally grown hexagonal wurtzite phase. This finding would predict the more favorable p-type doping characteristics of the zincblende nitrides. A study of the first excited states for donor impurities was also performed under the influence of external magnetic fields. Among other interesting features, it is found that residual carbon in GaN may play an important role as a shallow donor, typically attributed to other species, and suggesting that the amphoteric behavior of carbon impurities has been overlooked in the interpretation of the experimental optical spectra. We have studied as well the problem of the eigenstates in nitride based quantum wells and superlattices. Through the use of the exact envelope function theory together with symmetry arguments, we have provided a systematic derivation for a valence band effective mass Hamiltonian suitable for wurtzite heterostructures. Correct analytical expressions for the boundary conditions at the heterointerfaces of these materials are also derived. By using numerical examples, we show that the conventional Hamiltonian and boundary conditions lead to overestimates of the subband dispersion energies of nitride quantum wells for in-plane wave numbers not at the zone center. This

  1. Gallium-containing anticancer compounds.

    PubMed

    Chitambar, Christopher R

    2012-06-01

    There is an ever pressing need to develop new drugs for the treatment of cancer. Gallium nitrate, a group IIIa metal salt, inhibits the proliferation of tumor cells in vitro and in vivo and has shown activity against non-Hodgkin's lymphoma and bladder cancer in clinical trials. Gallium can function as an iron mimetic and perturb iron-dependent proliferation and other iron-related processes in tumor cells. Gallium nitrate lacks crossresistance with conventional chemotherapeutic drugs and is not myelosuppressive; it can be used when other drugs have failed or when the blood count is low. Given the therapeutic potential of gallium, newer generations of gallium compounds are now in various phases of preclinical and clinical development. These compounds hold the promise of greater anti-tumor activity against a broader spectrum of cancers. The development of gallium compounds for cancer treatment and their mechanisms of action will be discussed.

  2. 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.

  3. Interactions of Zircaloy Cladding with Gallium: Final Report

    SciTech Connect

    D.F. Wilson; E.T. Manneschmidt; J.F. King; J.P. Strizak; J.R. DiStefano

    1998-09-01

    The U.S. Department of Energy has established a dual-track approach to the disposition of plutonium arising from the dismantling of nuclear weapons. Both immobilization and reactor-based mixed-oxide (MOX) fuel technologies are being evaluated. The reactor-based MOX fuel option requires assessment of the potential impact of concentrations of gallium (on the order of 1 to 10 ppm), not present in conventional MOX fhel, on cladding material performance. Three previous repmts"3 identified several compatibility issues relating to the presence of gallium in MOX fuel and its possible reaction with fiel cladding. Gallium initially present in weapons-grade (WG) plutonium is largely removed during processing to produce MOX fhel. After blending the plutonium with uranium, only 1 to 10 ppm gallium is expected in the sintered MOX fuel. Gallium present as gallium oxide (G~OJ could be evolved as the suboxide (G~O). Migration of the evolved G~O and diffusion of gallium in the MOX matrix along thermal gradients could lead to locally higher concentrations of G~03. Thus, while an extremely low concentration of gallium in MOX fiel almost ensures a lack of significant interaction of gallium whh Zircaloy fhel cladding, there remains a small probability that corrosion effects will not be negligible. General corrosion in the form of surface alloying resulting from formation of intermetallic compounds between Zircaloy and gallium should be ma& limited and, therefore, superficial because of the expected low ratio of gallium to the surface area or volume of the Zircaloy cladding. Although the expected concentration of gallium is low and there is very limited volubility of gallium in zirconium, especially at temperatures below 700 "C,4 grain boundary penetration and liquid metal embrittlement (LME) are forms of localized corrosion that were also considered. One fuel system darnage mechanism, pellet clad interaction, has led to some failure of the Zircaloy cladding in light-water reactors (LWRS

  4. Growth, Fabrication, and Characterization of Continuous-Wave Aluminum Gallium Nitride -Cladding-Free m-plane Indium Gallium Nitride / Gallium Nitride Laser Diodes

    NASA Astrophysics Data System (ADS)

    Farrell, Robert Michael

    Many applications exist for InGaN/GaN laser diodes (LDs), including high-density optical data storage, laser-based projection displays, high-resolution laser printing, solid-state lighting, medical diagnostics, and chemical sensing. Although device performance continues to improve, current commercially-available InGaN/GaN LDs are still grown on the (0001) c-plane of the wurtzite crystal structure and their performance is nonetheless affected by the presence of polarization-related electric fields. As an alternative to conventional c-plane technologies, growth of InGaN/GaN LDs on nonpolar or semipolar orientations presents a viable approach to reducing or eliminating the issues associated with polarization-related electric fields. Despite these potential advantages, though, the lowest reported threshold current densities for nonpolar and semipolar LDs are still about 2 to 3 times higher than those reported for c-plane LDs. In this thesis, we discuss the growth, fabrication, and characterization of continuous-wave AlGaN-cladding-free (ACF) m-plane LDs with performance that is comparable to the best state-of-the-art c-plane LDs. In the first part of this thesis, the characterization of low-defect-density m-plane thin films and devices grown by metalorganic chemical vapor deposition is presented. The physical origin of the four-sided pyramidal hillocks commonly observed on m-plane thin films is identified and an understanding of these mechanisms is used to explain the impact of carrier gas and substrate misorientation on the morphological, structural, and optical properties of m-plane thin films and devices. In the second part of this thesis, several aspects of the development of a quick, self-aligned LD fabrication process are discussed. These include the implementation of relatively conventional fabrication technologies for routine device processing as well as the development of innovative approaches for improving the accuracy and reproducibility of facet cleaving and ridge waveguide etching processes. Finally, in the third and last part of this thesis, the performance of ACF m-plane LDs with threshold current densities of 1.54 kA/cm2 and peak output powers of 1.6 W is discussed. The transparency carrier density of these devices is estimated to be 4.9 x 10 18 cm-3, which is lower than typical transparency carrier densities reported or even calculated for c-plane GaN-based LDs and comparable to typical transparency carrier densities reported for GaAs- and InP-based LDs.

  5. Low loss nitride ceramics for terahertz windows

    NASA Astrophysics Data System (ADS)

    Naftaly, M.; Greenslade, P. J.; Miles, R. E.; Evans, D.

    2009-09-01

    Terahertz frequency transmission measurements on ceramic boron nitride and aluminium nitride are described. The absorption coefficients and refractive indices of these materials show that they have high terahertz transparency, which together with their high melting temperatures and mechanical strength makes them particularly suitable for use as THz windows in high pressure and/or high temperature applications.

  6. Manual modification and plasma exposure of boron nitride ceramic to study Hall effect thruster plasma channel material erosion

    NASA Astrophysics Data System (ADS)

    Satonik, Alexander J.

    Worn Hall effect thrusters (HET) show a variety of unique microstructures and elemental compositions in the boron nitride thruster channel walls. Worn thruster channels are typically created by running test thrusters in vacuum chambers for hundreds of hours. Studies were undertaken to manually modify samples of boron nitride without the use of a hall effect thruster. Samples were manually abraded with an abrasive blaster and sandpaper, in addition to a vacuum heater. Some of these samples were further exposed to a xenon plasma in a magnetron sputter device. Sandpaper and abrasive blaster tests were used to modify surface roughness values of the samples from 10,000 A to 150,000 A, matching worn thruster values. Vacuum heat treatments were performed on samples. These treatments showed the ability to modify chemical compositions of boron nitride samples, but not in a manner matching changes seen in worn thruster channels. Plasma erosion rate was shown to depend on the grade of the BN ceramic and the preparation of the surface prior to plasma exposure. Abraded samples were shown to erode 43% more than their pristine counterparts. Unique surface features and elemental compositions on the worn thruster channel samples were overwritten by new surface features on the ceramic grains. The microscope images of the ceramic surface show that the magnetron plasma source rounded the edges of the ceramic grains to closely match the worn HET surface. This effect was not as pronounced in studies of ion beam bombardment of the surface and appears to be a result of the quasi-neutral plasma environment.

  7. Development of gallium compounds for treatment of lymphoma: gallium maltolate, a novel hydroxypyrone gallium compound, induces apoptosis and circumvents lymphoma cell resistance to gallium nitrate.

    PubMed

    Chitambar, Christopher R; Purpi, David P; Woodliff, Jeffrey; Yang, Meiying; Wereley, Janine P

    2007-09-01

    Clinical studies have shown gallium nitrate to have significant antitumor activity against non-Hodgkin's lymphoma and bladder cancer, thus indicating that gallium-based drugs have potential for further development as antineoplastic agents. In this study, we compared the cytotoxicity of gallium maltolate, a novel gallium compound, with gallium nitrate in lymphoma cell lines, including p53 variant and unique gallium nitrate-resistant cells. We found that gallium maltolate inhibited cell proliferation and induced apoptosis through the mitochondrial pathway at lower concentrations and more rapidly than gallium nitrate. Gallium maltolate produced an increase in intracellular reactive oxygen species (ROS) within 2 h of incubation with cells; this effect could be blocked by mitoquinone, a mitochondria-targeted antioxidant. The role of the transferrin receptor (TfR) in gallium maltolate's action was examined using monoclonal antibody (MoAb) 42/6 to block TfR function. However, although MoAb 42/6 reduced gallium maltolate-induced caspase-3 activity, it had only a minor effect on cell growth inhibition. Importantly, gallium maltolate induced apoptosis in cells resistant to gallium nitrate, and, unlike gallium nitrate, its cytotoxicity was not affected by cellular p53 status. Cellular gallium uptake was greater with gallium maltolate than with gallium nitrate. We conclude that gallium maltolate inhibits cell proliferation and induces apoptosis more efficiently than gallium nitrate. Gallium maltolate is incorporated into lymphoma cells to a greater extent than gallium nitrate via both TfR-independent and -dependent pathways; it has significant activity against gallium nitrate-resistant cells and acts independently of p53. Further studies to evaluate its antineoplastic activity in vivo are warranted.

  8. Method of fabricating germanium and gallium arsenide devices

    NASA Technical Reports Server (NTRS)

    Jhabvala, Murzban (Inventor)

    1990-01-01

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

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

    SciTech Connect

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

    1988-07-26

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

  10. Synthesis of transition metal nitride by nitridation of metastable oxide precursor

    SciTech Connect

    Wang, Huamin; Wu, Zijie; Kong, Jing; Wang, Zhiqiang; Zhang, Minghui

    2012-10-15

    Metastable transition metal oxides were used as precursors to synthesize transition metal nitrides at low temperature. Amorphous MoO{sub 2} was prepared by reduction of (NH{sub 4}){sub 6}Mo{sub 7}O{sub 24} solution with hydrazine. As-synthesized amorphous MoO{sub 2} was transformed into fcc {gamma}-Mo{sub 2}N at 400 Degree-Sign C and then into hexagonal {delta}-MoN by further increasing the temperature to 600 Degree-Sign C under a NH{sub 3} flow. The nitridation temperature employed here is much lower than that employed in nitridation of crystalline materials, and the amorphous materials underwent a unique nitridation process. Besides this, the bimetallic nitride Ni{sub 2}Mo{sub 3}N was also synthesized by nitridating amorphous bimetallic precursor. These results suggested that the nitridation of amorphous precursor possessed potential to be a general method for synthesizing many interstitial metallic compounds, such as nitrides and carbides at low temperature. - graphical abstract: Amorphous oxide was used as new precursor to prepare nitride at low temperature. Pure {gamma}-Mo{sub 2}N and {delta}-MoN were obtained at 400 Degree-Sign C and at 600 Degree-Sign C, respectively. Highlights: Black-Right-Pointing-Pointer We bring out a new method to synthesize transition metal nitrides at low temperature. Black-Right-Pointing-Pointer Both mono- and bimetallic molybdenum nitrides were synthesized at a mild condition. Black-Right-Pointing-Pointer The formation of two different molybdenum nitrides {gamma}-Mo{sub 2}N and {delta}-MoN can be controlled from the same metastable precursor. Black-Right-Pointing-Pointer The nitridation temperature was much lower than that reported from crystalline precursors. Black-Right-Pointing-Pointer The metastable precursor had different reaction process in comparison with crystalline precursor.

  11. Estimations of the spontaneous polarization of binary and ternary compounds of group III nitrides

    NASA Astrophysics Data System (ADS)

    Davydov, S. Yu.; Posrednik, O. V.

    2016-04-01

    The dependences of spontaneous polarizations P sp of solid solutions of aluminum, gallium, and indium nitrides on the compositions were estimated using the Harrison bond-orbital method. A simple formula was proposed to estimate P sp using only lengths of the interatomic bonds between the nearest neighbor atoms and the angles between these bonds.

  12. 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.

  13. Gallium--A smart metal

    USGS Publications Warehouse

    Foley, Nora; Jaskula, Brian W.

    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.

  14. Aluminum nitride grating couplers.

    PubMed

    Ghosh, Siddhartha; Doerr, Christopher R; Piazza, Gianluca

    2012-06-10

    Grating couplers in sputtered aluminum nitride, a piezoelectric material with low loss in the C band, are demonstrated. Gratings and a waveguide micromachined on a silicon wafer with 600 nm minimum feature size were defined in a single lithography step without partial etching. Silicon dioxide (SiO(2)) was used for cladding layers. Peak coupling efficiency of -6.6 dB and a 1 dB bandwidth of 60 nm have been measured. This demonstration of wire waveguides and wideband grating couplers in a material that also has piezoelectric and elasto-optic properties will enable new functions for integrated photonics and optomechanics.

  15. Characterization of Heavily Doped ALUMINUM(X)GALLIUM(1 -X)ARSENIDE:TELLURIUM Grown on Semi-Insulating Gallium-Arsenide

    NASA Astrophysics Data System (ADS)

    Malloy, Kevin John

    The ability to dope a semiconductor into near metallic conduction widens its usefulness as a material and thereby permits the construction of new devices. Aluminum Gallium Arsenide is no exception. Heavily doped n-type Aluminum Gallium Arsenide has important device applications in tandem junction solar cells and in high electron mobility transistors. Aluminum Gallium Arsenide heavily doped with Tellurium was grown on semi-insulating Gallium Arsenide using liquid phase epitaxy. It was found that the addition of 0.4 atomic percent Tellurium to the melt reduced the Aluminum content of solid Aluminum Gallium Arsenide by up to 20 percent. A model was offered for this behavior involving a differential in the degree of association between Aluminum-Tellurium and Gallium-Tellurium in the liquid phase epitaxial melt. The electrical properties of n-type Aluminum Gallium Arsenide grown on semi-insulating Gallium Arsenide were modeled as a two sheet conductor. The two conductors consisted of the epitaxial n-type Aluminum Gallium Arsenide layer and the induced two dimensional electron gas present at the n-type Aluminum Gallium Arsenide-Gallium Arsenide heterojunction. This model showed the two dimensional electron gas as responsible for the constant low temperature carrier concentration observed experimentally. It also successfully explained the observation of a slope equal to the donor ionization potential instead of the donor ionization potential divided by two in the plot of the log of the carrier concentration versus reciprocal temperature. Because of the chemically independent nature of the deep donor ionization potential in Aluminum Gallium Arsenide, a minima interaction model was introduced to describe the donor level. The major matrix elements were determined to be V(,LX) = 4mV (+OR-) 1mV and V(,LL) = 40mV (+OR-) 10mV. These minima interaction matrix elements were an order of magnitude larger than suggested by theory, thus indicating the possible non-coulombic nature of

  16. Application of a new composite cubic-boron nitride gasket assembly for high pressure inelastic x-ray scattering studies of carbon related materials

    SciTech Connect

    Wang, Lin; Yang, Wenge; Xiao, Yuming; Liu, Bingbing; Chow, Paul; Shen, Guoyin; Mao, Wendy L.; Mao, Ho-kwang

    2011-01-01

    We have developed a new composite cubic-boron nitride (c-BN) gasket assembly for high pressurediamond anvil cell studies, and applied it to inelastic x-ray scattering (IXS) studies of carbon related materials in order to maintain a larger sample thickness and avoid the interference from the diamond anvils. The gap size between the two diamond anvils remained ~80 μm at 48.0 GPa with this new composite c-BN gasket assembly. The sample can be located at the center of the gap, ~20 μm away from the surface of both diamond anvils, which provides ample distance to separate the sample signal from the diamond anvils. The high pressure IXS of a solvated C₆₀ sample was studied up to 48 GPa, and a pressure induced bonding transition from sp² to sp³ was observed at 27 GPa.

  17. 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.

  18. Compensation and Characterization of Gallium Arsenide

    NASA Astrophysics Data System (ADS)

    Roush, Randy Allen

    1995-01-01

    The properties of transition metals in gallium arsenide have been previously investigated extensively with respect to activation energies, but little effort has been made to correlate processing parameters with electronic characteristics. Diffusion of copper in gallium arsenide is of technological importance due to the development of GaAs:Cu bistable photoconductive devices. Several techniques are demonstrated in this work to develop and characterize compensated gallium arsenide wafers. The material is created by the thermal diffusion of copper into silicon-doped GaAs. Transition metals generally form deep and shallow acceptors in GaAs, and therefore compensation is possible by material processing such that the shallow silicon donors are compensated by deep acceptors. Copper is an example of a transition metal that forms deep acceptors in GaAs, and therefore this work will focus on the compensation and characterization of GaAs:Si:Cu. The compensation of the material has shown that the lower diffusion temperatures (500-600^ circC) form primarily the well-known Cu _{rm B} centers whereas the higher temperature anneals (>750 ^circC) result in the formation of CU_{rm A}. Using compensation curves, the copper density is found by comparing the compensation temperature with copper solubility curves given by others. These curves also show that the formation of CU_{rm B}, EL2, and CU_{rm A} can be manipulated by varying processing parameters such as annealing temperature and arsenic pressure. The compensation results are confirmed using Temperature-Dependent Hall (TDH) measurements to detect the copper levels. Also, the photoconductive properties of the material under illumination from 1.06 and 2.1 μm wavelength laser pulses have been used to demonstrate the effects of the different processing procedures. The persistent photoconductivity inherent to these devices under illumination from the 1.06 μm laser pulse is used to predict the concentration of the Cu_ {rm B

  19. Optical bistability in a silicon nitride microring resonator with azo dye-doped liquid crystal as cladding material.

    PubMed

    Wang, Chun-Ta; Tseng, Chih-Wei; Yu, Jui-Hao; Li, Yuan-Cheng; Lee, Chun-Hong; Jau, Hung-Chang; Lee, Ming-Chang; Chen, Yung-Jui; Lin, Tsung-Hsien

    2013-05-06

    This investigation reports observations of optical bistability in a silicon nitride (SiN) micro-ring resonator with azo dye-doped liquid crystal cladding. The refractive index of the cladding can be changed by switching the liquid crystal between nematic (NLC) and photo-induced isotropic (PHI) states by. Both the NLC and the PHI states can be maintained for many hours, and can be rapidly switched from one state to the other by photo-induced isomerization using 532 nm and 408 nm addressing light, respectively. The proposed device exhibits optical bistable switching of the resonance wavelength without sustained use of a power source. It has a 1.9 nm maximum spectral shift with a Q-factor of over 10000. The hybrid SiN- LC micro-ring resonator possesses easy switching, long memory, and low power consumption. It therefore has the potential to be used in signal processing elements and switching elements in optically integrated circuits.

  20. 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.

  1. 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.

  2. Graphitic Carbon Nitride Supported Catalysts for Polymer Electrolyte Fuel Cells.

    PubMed

    Mansor, Noramalina; Jorge, A Belen; Corà, Furio; Gibbs, Christopher; Jervis, Rhodri; McMillan, Paul F; Wang, Xiaochen; Brett, Daniel J L

    2014-04-03

    Graphitic carbon nitrides are investigated for developing highly durable Pt electrocatalyst supports for polymer electrolyte fuel cells (PEFCs). Three different graphitic carbon nitride materials were synthesized with the aim to address the effect of crystallinity, porosity, and composition on the catalyst support properties: polymeric carbon nitride (gCNM), poly(triazine) imide carbon nitride (PTI/Li(+)Cl(-)), and boron-doped graphitic carbon nitride (B-gCNM). Following accelerated corrosion testing, all graphitic carbon nitride materials are found to be more electrochemically stable compared to conventional carbon black (Vulcan XC-72R) with B-gCNM support showing the best stability. For the supported catalysts, Pt/PTI-Li(+)Cl(-) catalyst exhibits better durability with only 19% electrochemical surface area (ECSA) loss versus 36% for Pt/Vulcan after 2000 scans. Superior methanol oxidation activity is observed for all graphitic carbon nitride supported Pt catalysts on the basis of the catalyst ECSA.

  3. Graphitic Carbon Nitride Supported Catalysts for Polymer Electrolyte Fuel Cells

    PubMed Central

    2014-01-01

    Graphitic carbon nitrides are investigated for developing highly durable Pt electrocatalyst supports for polymer electrolyte fuel cells (PEFCs). Three different graphitic carbon nitride materials were synthesized with the aim to address the effect of crystallinity, porosity, and composition on the catalyst support properties: polymeric carbon nitride (gCNM), poly(triazine) imide carbon nitride (PTI/Li+Cl–), and boron-doped graphitic carbon nitride (B-gCNM). Following accelerated corrosion testing, all graphitic carbon nitride materials are found to be more electrochemically stable compared to conventional carbon black (Vulcan XC-72R) with B-gCNM support showing the best stability. For the supported catalysts, Pt/PTI-Li+Cl– catalyst exhibits better durability with only 19% electrochemical surface area (ECSA) loss versus 36% for Pt/Vulcan after 2000 scans. Superior methanol oxidation activity is observed for all graphitic carbon nitride supported Pt catalysts on the basis of the catalyst ECSA. PMID:24748912

  4. Fatigue life of silicon nitride balls

    SciTech Connect

    Galbato, A.T.; Cundill, R.T.; Harris, T.A. SKF Engineering and Research Center, Nieuwegein Pennsylvania State Univ., University Park )

    1992-11-01

    Because its specific weight is 40 percent that of steel, silicon nitride has been considered as a rolling element material in very high speed ball and roller bearings. Furthermore, similar to steel components, hot pressed silicon nitride rolling components, when properly manufactured, have demonstrated the capacity to fail in a non-catastrophic manner, i.e., fatigue of the rolling contact surfaces. In this investigation, hot isostatically-pressed silicon nitride balls were endurance-tested using a NASA 5-ball rig and the results were compared against similarly tested VIMVAR M50 balls. The silicon nitride balls demonstrated fatigue lives many times those obtained for the M50 balls. Therefore it is concluded that silicon nitride can be effectively employed in applications where steel rolling element life has previously proved to be a limiting factor. 12 refs.

  5. Nitride tuning of lanthanide chromites.

    PubMed

    Black, Ashley P; Johnston, Hannah E; Oró-Solé, Judith; Bozzo, Bernat; Ritter, Clemens; Frontera, Carlos; Attfield, J Paul; Fuertes, Amparo

    2016-03-21

    LnCrO(3-x)N(x) perovskites with Ln = La, Pr and Nd and nitrogen contents up to x = 0.59 have been synthesised through ammonolysis of LnCrO4 precursors. These new materials represent one of the few examples of chromium oxynitrides. Hole-doping through O(2-)/N(3-) anion substitution suppresses the magnetic transition far less drastically than Ln(3+)/M(2+) (M = Ca, Sr) cation substitutions because of the greater covalency of metal-nitride bonds. Hence, nitride-doping is a more benign method for doping metal oxides without suppressing electronic transitions.

  6. Functionalized boron nitride nanotubes

    DOEpatents

    Sainsbury, Toby; Ikuno, Takashi; Zettl, Alexander K

    2014-04-22

    A plasma treatment has been used to modify the surface of BNNTs. In one example, the surface of the BNNT has been modified using ammonia plasma to include amine functional groups. Amine functionalization allows BNNTs to be soluble in chloroform, which had not been possible previously. Further functionalization of amine-functionalized BNNTs with thiol-terminated organic molecules has also been demonstrated. Gold nanoparticles have been self-assembled at the surface of both amine- and thiol-functionalized boron nitride Nanotubes (BNNTs) in solution. This approach constitutes a basis for the preparation of highly functionalized BNNTs and for their utilization as nanoscale templates for assembly and integration with other nanoscale materials.

  7. III-Nitride nanowire optoelectronics

    NASA Astrophysics Data System (ADS)

    Zhao, Songrui; Nguyen, Hieu P. T.; Kibria, Md. G.; Mi, Zetian

    2015-11-01

    Group-III nitride nanowire structures, including GaN, InN, AlN and their alloys, have been intensively studied in the past decade. Unique to this material system is that its energy bandgap can be tuned from the deep ultraviolet (~6.2 eV for AlN) to the near infrared (~0.65 eV for InN). In this article, we provide an overview on the recent progress made in III-nitride nanowire optoelectronic devices, including light emitting diodes, lasers, photodetectors, single photon sources, intraband devices, solar cells, and artificial photosynthesis. The present challenges and future prospects of III-nitride nanowire optoelectronic devices are also discussed.

  8. Graphene on hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Yankowitz, Matthew; Xue, Jiamin; LeRoy, B. J.

    2014-07-01

    The field of graphene research has developed rapidly since its first isolation by mechanical exfoliation in 2004. Due to the relativistic Dirac nature of its charge carriers, graphene is both a promising material for next-generation electronic devices and a convenient low-energy testbed for intrinsically high-energy physical phenomena. Both of these research branches require the facile fabrication of clean graphene devices so as not to obscure its intrinsic physical properties. Hexagonal boron nitride has emerged as a promising substrate for graphene devices as it is insulating, atomically flat and provides a clean charge environment for the graphene. Additionally, the interaction between graphene and boron nitride provides a path for the study of new physical phenomena not present in bare graphene devices. This review focuses on recent advancements in the study of graphene on hexagonal boron nitride devices from the perspective of scanning tunneling microscopy with highlights of some important results from electrical transport measurements.

  9. Highly Flexible and Self-Healable Thermal Interface Material Based on Boron Nitride Nanosheets and a Dual Cross-Linked Hydrogel.

    PubMed

    Jiang, Hongbo; Wang, Zifeng; Geng, Huiyuan; Song, Xiufeng; Zeng, Haibo; Zhi, Chunyi

    2017-03-22

    The booming growth of flexible and stretchable electronic devices with increasing power and multifunctionalities calls for novel highly efficient thermal interface materials (TIMs) with versatile functions, such as high deformability and self-healing ability, whereas traditional metallic-based or grease-based ones could hardly provide. Herein, we report a highly flexible and self-healable dual-cross-linked hydrogel-based nanocomposite filled with hexagonal boron nitride (h-BN) nanosheets fabricated by in situ polymerization of acrylic acid (AA). The thermal conductivity of the composites can be tuned by adjusting both fraction of BNNSs and water content. Although a solid, the highly flexible characteristic of the developed TIMs enables a perfect ability to replicate the texture of a rough surface, which may greatly enhance thermal transfer between adjacent surfaces. By increasing the water content to soften the material, it can be recycled and reused for different kinds of rough surface. In addition, benefiting from the dual-cross-linked structure, the composites are capable of recovering both mechanical strength and thermal conductivity even from severe structural breakdowns, for example, three consecutive cutting and healing cycles. This study may pave the way to fabrication of multifunctional highly flexible TIMs, which may promote the development of heat dissipation materials.

  10. 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.

  11. 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

  12. Strongly localized donor level in oxygen doped gallium nitride

    SciTech Connect

    Wetzel, C.; Suski, T.; Ager, J.W. III; Fischer, S.; Meyer, B.K.; Grzegory, I.; Porowski, S.

    1996-08-01

    A classification in terms of localization of donor defects in GaN is performed by Raman spectroscopy under large hydrostatic pressure. We observe a significant decrease of free carrier concentration in highly O doped GaN epitaxial films at 22 GPa, indicating the presence of a strongly localized donor defect at large pressure. Monitoring the phonon plasmon coupled mode, we find similarities with results on highly n-type bulk crystals. We refine the model of localized defects in GaN and transfer it to the AlGaN system.

  13. 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.

  14. Formation mechanisms of spatially-directed zincblende gallium nitride nanocrystals

    SciTech Connect

    Wood, A. W.; Collino, R. R.; Cardozo, B. L.; Naab, F.; Wang, Y. Q.; Goldman, R. S.

    2011-12-15

    We report on the spatially selective formation of GaN nanocrystals embedded in GaAs. Broad-area N{sup +} implantation followed by rapid thermal annealing leads to the formation of nanocrystals at the depth of maximum ion damage. With additional irradiation using a Ga{sup +} focused ion beam, selective lateral positioning of the nanocrystals within the GaAs matrix is observed in isolated regions of increased vacancy concentration. Following rapid thermal annealing, the formation of zincblende GaN is observed in the regions of highest vacancy concentration. The nucleation of zincblende nanocrystals over the wurtzite phase of bulk GaN is consistent with the predictions of a thermodynamic model for the nanoscale size-dependence of GaN nucleation.

  15. Polarity Control and Doping in Aluminum Gallium Nitride

    DTIC Science & Technology

    2013-06-01

    intensity can also be observed. These observations are consistent with the observation of a decreased resistivity in FIG. 21 (a). In addition to the...Ladungsträger. Diese hohen Konzentrationen werden dadurch erklärt, dass im Bereich hoher Dotierungen die Formierungsenergien dieser Störstellen...elektrischen Widerstand führt. Des Weiteren wird im Rahmen dieser Arbeit gezeigt, dass das hier vorgestellte Modell zur Kontrolle des Einbaus von Defekten

  16. 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).

  17. Electrical and Thermal Analysis of Gallium Nitride HEMTs

    DTIC Science & Technology

    2009-06-01

    in Table 1. The DMT program will merge Polystrata and GaN technologies to eliminate the need for monolithic microwave integrated circuits (MMICs...Reliability and Microwave Performance within the WBGS-RF Program. The WBGS-RF program has three distinct performance tracks. The goals of these...The gate is constructed with 200 Å nickel and 3800 Å gold and has a 1000 Å SiN passivation layer. Because of the high thermal conductivity of the

  18. Gallium nitride nanowire based nanogenerators and light-emitting diodes.

    PubMed

    Chen, Chih-Yen; Zhu, Guang; Hu, Youfan; Yu, Jeng-Wei; Song, Jinghui; Cheng, Kai-Yuan; Peng, Lung-Han; Chou, Li-Jen; Wang, Zhong Lin

    2012-06-26

    Single-crystal n-type GaN nanowires have been grown epitaxially on a Mg-doped p-type GaN substrate. Piezoelectric nanognerators based on GaN nanowires are investigated by conductive AFM, and the results showed an output power density of nearly 12.5 mW/m(2). Luminous LED modules based on n-GaN nanowires/p-GaN substrate have been fabricated. CCD images of the lighted LED and the corresponding electroluminescence spectra are recorded at a forward bias. Moreover, the GaN nanowire LED can be lighted up by the power provided by a ZnO nanowire based nanogenerator, demonstrating a self-powered LED using wurtzite-structured nanomaterials.

  19. 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

    2015-11-16

    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.

  20. Neutron irradiation effects on metal-gallium nitride contacts

    SciTech Connect

    Katz, Evan J.; Lin, Chung-Han; Zhang, Zhichun; Qiu, Jie; Cao, Lei; Mishra, Umesh K.; Brillson, Leonard J.

    2014-03-28

    We have measured the effect of fast and thermal neutrons on GaN Schottky barriers and ohmic contacts using current–voltage and transmission line method electrical techniques, optical, atomic force and scanning electron microscopy morphological techniques, and X-ray photoemission spectroscopy chemical techniques. These studies reveal a 10{sup 15} n/cm{sup 2} neutron threshold for Schottky barrier ideality factor increases, a 10{sup 15} n/cm{sup 2} fast plus thermal neutron threshold for ohmic contact sheet and contact resistance increases, and 10{sup 16} n/cm{sup 2} neutron fluence threshold for major device degradation identified with thermally driven diffusion of Ga and N into the metal contacts and surface phase changes. These results demonstrate the need for protecting metal-GaN contacts in device applications subject to neutron radiation.

  1. Kinase detection with gallium nitride based high electron mobility transistors.

    PubMed

    Makowski, Matthew S; Bryan, Isaac; Sitar, Zlatko; Arellano, Consuelo; Xie, Jinqiao; Collazo, Ramon; Ivanisevic, Albena

    2013-07-01

    A label-free kinase detection system was fabricated by the adsorption of gold nanoparticles functionalized with kinase inhibitor onto AlGaN/GaN high electron mobility transistors (HEMTs). The HEMTs were operated near threshold voltage due to the greatest sensitivity in this operational region. The Au NP/HEMT biosensor system electrically detected 1 pM SRC kinase in ionic solutions. These results are pertinent to drug development applications associated with kinase sensing.

  2. Infrared Plasmonics with Conductive Ternary Nitrides.

    PubMed

    Metaxa, C; Kassavetis, S; Pierson, J F; Gall, D; Patsalas, P

    2017-03-29

    Conductive transition metal nitrides are emerging as promising alternative plasmonic materials that are refractory and CMOS-compatible. In this work, we show that ternary transition metal nitrides of the B1 structure and consisting of a combination of group-IVb transition metal, such as Ti or Zr, and group III (Sc, Y, Al) or group II (Mg, Ca) elements can have tunable plasmonic activity in the infrared range in contrast to Ta-based ternary nitrides, which exhibit plasmonic performance in the visible and UV ranges. We consider the intrinsic quality factors of surface plasmon polariton for the ternary nitrides, and we calculate the dispersion of surface plasmon polariton and the field enhancement at the vicinity of nitride/silica interfaces. Based on these calculations, it is shown that among these nitrides the most promising are TixSc1-xN and TixMg1-xN. In particular, TixSc1-xN can have plasmonic activity in the usual telecom bands at 850, 1300, and 1550 nm. Still, these nitrides exhibit substantial electronic losses mostly due to fine crystalline grains that deteriorate the plasmonic field enhancement. This unequivocally calls for improved growth processes that would enable the fabrication of such ternary nitrides of high crystallinity.

  3. Vanadium Nitride Nanowire Supported SnS2 Nanosheets with High Reversible Capacity as Anode Material for Lithium Ion Batteries.

    PubMed

    Balogun, Muhammad-Sadeeq; Qiu, Weitao; Jian, Junhua; Huang, Yongchao; Luo, Yang; Yang, Hao; Liang, Chaolun; Lu, Xihong; Tong, Yexiang

    2015-10-21

    The vulnerable restacking problem of tin disulfide (SnS2) usually leads to poor initial reversible capacity and poor cyclic stability, which hinders its practical application as lithium ion battery anode (LIB). In this work, we demonstrated an effective strategy to improve the first reversible capacity and lithium storage properties of SnS2 by growing SnS2 nanosheets on porous flexible vanadium nitride (VN) substrates. When evaluating lithium-storage properties, the three-dimensional (3D) porous VN coated SnS2 nanosheets (denoted as CC-VN@SnS2) yield a high reversible capacity of 75% with high specific capacity of about 819 mAh g(-1) at a current density of 0.65 A g(-1). Remarkable cyclic stability capacity of 791 mAh g(-1) after 100 cycles with excellent capacity retention of 97% was also achieved. Furthermore, discharge capacity as high as 349 mAh g(-1) is still retained after 70 cycles even at a elevated current density of 13 A g(-1). The excellent performance was due to the conductive flexible VN substrate support, which provides short Li-ion and electron pathways, accommodates large volume variation, contributes to the capacity, and provides mechanical stability, which allows the electrode to maintain its structural stability.

  4. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    SciTech Connect

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R.

    2014-04-15

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  5. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R.

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  6. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    PubMed

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  7. Novel surface molecularly imprinted material modified multi-walled carbon nanotubes as solid-phase extraction sorbent for selective extraction gallium ion from fly ash.

    PubMed

    Zhang, Zhaohui; Zhang, Huabin; Hu, Yufang; Yang, Xiao; Yao, Shouzhuo

    2010-06-30

    A new gallium (Ga(III)) ion-imprinted multi-walled carbon nanotubes (CNTs) composite sorbent was synthesized by a surface imprinting technique. The Ga(III) ion-imprinted/multi-walled carbon nanotubes (Ga(III)-imprinted/CNTs) sorbent was characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), nitrogen adsorption experiment, static adsorption experiment, and solid-phase extraction (SPE) experiment. The effects of sample volume, sample pH, washing and elution conditions on the extraction of Ga(III) ion from real sample were studied in detail. The imprinted sorbent offered a fast kinetics for the adsorption of Ga(III). The maximum static adsorption capacity of the imprinted sorbent towards was 58.8 micromol g(-1). The largest selectivity coefficient for Ga(III) in the presence of Al(III) was over 57.3. Compared with non-imprinted sorbent, the imprinted sorbent showed good imprinting effect for Ga(III) ion, the imprinting factor (alpha) was 2.6, the selectivity factor (beta) was 2.4 and 2.9 for Al(III) and Zn(II), respectively. The developed imprinted SPE method was applied successfully to the detection of trace Ga(III) ion in fly ash samples with satisfactory results.

  8. Low-loss binder for hot pressing boron nitride

    DOEpatents

    Maya, Leon

    1991-01-01

    Borazine derivatives used as low-loss binders and precursors for making ceramic boron nitride structures. The derivative forms the same composition as the boron nitride starting material, thereby filling the voids with the same boron nitride material upon forming and hot pressing. The derivatives have a further advantage of being low in carbon thus resulting in less volatile byproduct that can result in bubble formation during pressing.

  9. 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.

  10. 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.

  11. Magnetostriction and magnetic heterogeneities in iron-gallium.

    PubMed

    Laver, M; Mudivarthi, C; Cullen, J R; Flatau, A B; Chen, W-C; Watson, S M; Wuttig, M

    2010-07-09

    Iron-gallium alloys Fe(1-x)Ga(x) exhibit an exceptional increase in magnetostriction with gallium content. We present small-angle neutron scattering investigations on a Fe(0.81)Ga(0.19) single crystal. We uncover heterogeneities with an average spacing of 15 nm and with magnetizations distinct from the matrix. The moments in and around the heterogeneities are observed to reorient with an applied magnetic field or mechanical strain. We discuss the possible roles played by nanoscale magnetic heterogeneities in the mechanism for magnetostriction in this material.

  12. Magnetostriction and Magnetic Heterogeneities in Iron-Gallium

    SciTech Connect

    Laver, M.; Mudivarthi, C.; Cullen, J. R.; Wuttig, M.; Flatau, A. B.; Chen, W.-C.; Watson, S. M.

    2010-07-09

    Iron-gallium alloys Fe{sub 1-x}Ga{sub x} exhibit an exceptional increase in magnetostriction with gallium content. We present small-angle neutron scattering investigations on a Fe{sub 0.81}Ga{sub 0.19} single crystal. We uncover heterogeneities with an average spacing of 15 nm and with magnetizations distinct from the matrix. The moments in and around the heterogeneities are observed to reorient with an applied magnetic field or mechanical strain. We discuss the possible roles played by nanoscale magnetic heterogeneities in the mechanism for magnetostriction in this material.

  13. Titanium Nitride Cermets

    DTIC Science & Technology

    1952-07-01

    7696i ’-Brewer, L., et al. Thermodynamic and Physical Properties of Nitrides. Carbides, Sulfides, i1licides, and Phosphides, Chemistry and Metallurgy of...12 Referen eCs 0 . ...................... • • • 14 WADC TR 52-155 iv LIST OF TABLES I Properties of Titanium Nitride Bodies...15 II Properties of Titanium Nitride-Nickel Bodies............16 III Properties of Titanium Nitride Cermets with Nickel,..... 17 Cobalt, and

  14. Design of Integrated III-Nitride/Non-III-Nitride Tandem Photovoltaic Devices

    SciTech Connect

    Toledo, N. G.; Friedman, D..J.; Farrell, R. M.; Perl, E. E.; Lin, C. T.; Bowers, J. E.; Speck, J. S.; Mishra, U. K.

    2012-03-01

    The integration of III-nitride and non-III-nitride materials for tandem solar cell applications can improve the efficiency of the photovoltaic device due to the added power contributed by the III-nitride top cell to that of high-efficiency multi-junction non-III-nitride solar cells if the device components are properly designed and optimized. The proposed tandem solar cell is comprised of a III-nitride top cell bonded to a non-III-nitride, series-constrained, multi-junction subcell. The top cell is electrically isolated, but optically coupled to the underlying subcell. The use of a III-nitride top cell is potentially beneficial when the top junction of a stand-alone non-III-nitride subcell generates more photocurrent than the limiting current of the non-III-nitride subcell. Light producing this excess current can either be redirected to the III-nitride top cell through high energy photon absorption, redirected to the lower junctions through layer thickness optimization, or a combination of both, resulting in improved total efficiency. When the non-III-nitride cell's top junction is the limiting junction, the minimum power conversion efficiency that the III-nitride top cell must contribute should compensate for the spectrum filtered from the multi-junction subcell for this design to be useful. As the III-nitride absorption edge wavelength, {lambda}{sub N}, increases, the performance of the multi-junction subcell decreases due to spectral filtering. In the most common spectra of interest (AM1.5G, AM1.5 D, and AM0), the technology to grow InGaN cells with {lambda}{sub N}<520 nm is found to be sufficient for III-nitride top cell applications. The external quantum efficiency performance, however, of state-of-the-art InGaN solar cells still needs to be improved. The effects of surface/interface reflections are also presented. The management of these reflection issues determines the feasibility of the integrated III-nitride/non-III-nitride design to improve overall cell

  15. 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

  16. Surface photovoltage spectroscopy of carbon nitride powder

    SciTech Connect

    Dittrich, Th.; Fiechter, S.; Thomas, A.

    2011-08-22

    Powder of carbon nitride has been investigated by surface photovoltage spectroscopy at temperatures between 30 deg. C and 150 deg. C. Photo-generated holes were preferentially separated towards the external surface. Electronic states below the optical band gap from which charge separation may be possible have not been observed. The band gap of the investigated carbon nitride decreased from 2.93 to 2.80 eV with increasing temperature from 30 deg. C to 150 deg. C. The material exhibits a higher optical transition at E = 3.6 eV. Results are discussed from the point of view of photo-catalytic water splitting with carbon nitride.

  17. Patterned gallium surfaces as molecular mirrors.

    PubMed

    Bossi, Alessandra; Rivetti, Claudio; Mangiarotti, Laura; Whitcombe, Michael J; Turner, Anthony P F; Piletsky, Sergey A

    2007-09-30

    An entirely new means of printing molecular information on a planar film, involving casting nanoscale impressions of the template protein molecules in molten gallium, is presented here for the first time. The metallic imprints not only replicate the shape and size of the proteins used as template. They also show specific binding for the template species. Such a simple approach to the creation of antibody-like properties in metallic mirrors can lead to applications in separations, microfluidic devices, and the development of new optical and electronic sensors, and will be of interest to chemists, materials scientists, analytical specialists, and electronic engineers.

  18. 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.

  19. Electrochemical Solution Growth of Magnetic Nitrides

    SciTech Connect

    Monson, Todd C.; Pearce, Charles

    2014-10-01

    Magnetic nitrides, if manufactured in bulk form, would provide designers of transformers and inductors with a new class of better performing and affordable soft magnetic materials. According to experimental results from thin films and/or theoretical calculations, magnetic nitrides would have magnetic moments well in excess of current state of the art soft magnets. Furthermore, magnetic nitrides would have higher resistivities than current transformer core materials and therefore not require the use of laminates of inactive material to limit eddy current losses. However, almost all of the magnetic nitrides have been elusive except in difficult to reproduce thin films or as inclusions in another material. Now, through its ability to reduce atmospheric nitrogen, the electrochemical solution growth (ESG) technique can bring highly sought after (and previously inaccessible) new magnetic nitrides into existence in bulk form. This method utilizes a molten salt as a solvent to solubilize metal cations and nitrogen ions produced electrochemically and form nitrogen compounds. Unlike other growth methods, the scalable ESG process can sustain high growth rates (~mm/hr) even under reasonable operating conditions (atmospheric pressure and 500 °C). Ultimately, this translates into a high throughput, low cost, manufacturing process. The ESG process has already been used successfully to grow high quality GaN. Below, the experimental results of an exploratory express LDRD project to access the viability of the ESG technique to grow magnetic nitrides will be presented.

  20. Alkylamine-functionalized hexagonal boron nitride nanoplatelets as a novel material for the reduction of friction and wear.

    PubMed

    Kumari, Sangita; Sharma, Om P; Khatri, Om P

    2016-08-17

    Hexagonal boron nitride nanoplatelets (h-BNNPs), which are structurally analogous to graphene, were prepared via the ultrasound-assisted exfoliation of h-BN powder using N-methyl pyrrolidone as the solvent. The alkylamines with variable alkyl chains and electron-rich nitrogen atoms were grafted onto the boron sites of the h-BNNPs based on Lewis acid-base chemistry. The grafting of the alkylamines onto the h-BNNPs was confirmed using FTIR, XPS, TGA and (13)C SSNMR analyses. The crystalline and structural features of the alkylamine-functionalized h-BNNPs were studied using XRD and HRTEM analyses. The TGA and FTIR results revealed a higher grafting of octadecylamine (ODA) on the h-BNNPs compared to trioctylamine (TOA). The cohesive interaction between the alkyl chains grafted onto the h-BNNPs and the hydrocarbon chains of mineral lube base oil facilitates the dispersion of the alkylamine-functionalized h-BNNPs. The TOA-grafted h-BNNPs (h-BNNPs-TOA) exhibited long-term dispersion stability compared to the ODA-grafted h-BNNPs and this was attributed to a higher degree of van der Waals interactions between the octyl chains of the TOA molecules grafted onto the h-BNNPs and the hydrocarbon chains of the mineral lube base oil. The tribo-performance of the h-BNNPs-TOA as an additive to mineral lube base oil was evaluated in terms of the coefficient of friction and wear using ball-on-disc contact geometry. A minute dosing (0.02 mg mL(-1)) of h-BNNPs-TOA significantly improved the lubrication characteristics of the mineral lube base oil and showed a 35 and 25% reduction of friction and wear, respectively. The presence of boron and nitrogen on the worn scar of an aluminium disc, as deduced from elemental mapping, confirmed the formation of a tribo-chemical thin film of h-BN lamellae on the contact interfaces, which not only reduced the friction but also protected the contact interfaces against undesirable wear events.

  1. An investigation on corrosion protection of chromium nitride coated Fe-Cr alloy as a bipolar plate material for proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Pan, T. J.; Zhang, B.; Li, J.; He, Y. X.; Lin, F.

    2014-12-01

    The corrosion properties of chromium nitride (CrN) coating are investigated to assess the potential use of this material as a bipolar plate for proton exchange membrane fuel cells (PEMFCs). Conductive metallic ceramic CrN layers are firstly deposited onto Fe-Cr alloy using a multi-arc ion plating technique to increase the corrosion resistance of the base alloy. Electrochemical measurements indicate that the corrosion resistance of the substrate alloy is greatly enhanced by the CrN coating. The free corrosion potential of the substrate is increased by more than 50 mV. Furthermore, a decrease in three orders of magnitude of corrosive current density for the CrN-coated alloy is observed compared to the as-received Fe-Cr alloy. Long-term immersion tests show that the CrN layer is highly stable and effectively acts as a barrier to inhibit permeation of corrosive species. On the contrary, corrosion of the Fe-Cr alloy is rather severe without the protection of CrN coating due to the active dissolution. Finally, the corresponding electrochemical impedance models are proposed to elucidate the corrosion process of the CrN/Fe-Cr alloy submerged in a simulated PEMFCs environment.

  2. Boron Nitride Nanotube Mat as a Low- k Dielectric Material with Relative Dielectric Constant Ranging from 1.0 to 1.1

    NASA Astrophysics Data System (ADS)

    Hong, Xinghua; Wang, Daojun; Chung, D. D. L.

    2016-01-01

    This paper reports that a boron nitride nanotube (BNNT) mat containing air and 1.4 vol.% BNNTs is a low- k dielectric material for microelectronic packaging, exhibiting relative dielectric constant of 1.0 to 1.1 (50 Hz to 2 MHz) and elastic modulus of 10 MPa. The mat is prepared by compacting BNNTs at 5.8 kPa. This paper also presents measurements of the dielectric properties of BNNTs (mostly multiwalled). The relative dielectric constant of the BNNT solid in the mat decreases with increasing frequency, with attractively low values ranging from 3.0 to 6.2; the alternating-current (AC) electrical conductivity increases with increasing frequency, with attractively low values ranging from 10-10 S/m to 10-6 S/m and an approximately linear relationship between log conductivity and log frequency. The specific contact capacitance of the interface between BNNTs and the electrical contact decreases with increasing frequency, with attractively high values ranging from 1.6 μF/m2 to 2.3 μF/m2. The AC electrical resistivity of the BNNT-contact interface decreases with increasing frequency, with high values ranging from 0.14 MΩ cm2 to 440 MΩ cm2.

  3. High-surface Thermally Stable Mesoporous Gallium Phosphates Constituted by Nanoparticles as Primary Building Blocks

    SciTech Connect

    V Parvulescu; V Parvulescu; D Ciuparu; C Hardacre; H Garcia

    2011-12-31

    In constant, search for micro/mesoporous materials, gallium phosphates, have attracted continued interest due to the large pore size reported for some of these solids in comparison with analogous aluminum phosphates. However up to now, the porosity of gallium phosphates collapsed upon template removal or exposure to the ambient moisture. In the present work, we describe high-surface thermally stable mesoporous gallium phosphates synthesized from gallium propoxide and PCl{sub 3} and different templating agents such as amines (dipropylamine, piperidine and aminopiperidine) and quaternary ammonium salts (C{sub 16}H{sub 33}(CH{sub 3})3NBr and C{sub 16}PyCl). These highly reactive precursors have so far not been used as gallium and phosphate sources for the synthesis of gallophosphates. Conceptually, our present synthetic procedure is based on the fast formation of gallium phosphate nanoparticles via the reaction of gallium propoxide with PCl{sub 3} and subsequent construction of the porous material with nanoparticles as building blocks. The organization of the gallophosphate nanoparticles in stable porous structures is effected by the templates. Different experimental procedures varying the molar composition of the sol-gel, pH and the pretreatment of gallium precursor were assayed, most of them leading to satisfactory materials in terms of thermal stability and porosity. In this way, a series of gallium phosphates with surface are above 200 m{sup 2} g{sup -1}, and narrow pore size from 3 to 6 nm and remarkable thermal stability (up to 550 C) have been prepared. In some cases, the structure tends to show some periodicity and regularity as determined by XRD. The remarkable stability has allowed us to test the catalytic activity of gallophosphates for the aerobic oxidation of alkylaromatics with notable good results. Our report reopens the interest for gallophosphates in heterogeneous catalysis.

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

    PubMed

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

    2010-01-01

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

  5. Multimillion Atom Simulations of Nanostructured Materials on Parallel Computers ---Sintering and Consolidation, Fracture, and Oxidation---

    NASA Astrophysics Data System (ADS)

    Vashishta, P.; Bachlechner, M. E.; Campbell, T.; Kalia, R. K.; Kikuchi, H.; Kodiyalam, S.; Nakano, A.; Ogata, S.; Shimojo, F.; Walsh, P.

    Multiresolution molecular-dynamics approach for multimillion atom simulations has been used to investigate structural properties, mechanical failure in ceramic materials, and atomic-level stresses in nanoscale semiconductor/ceramic mesas (Si/Si3N4). Crack propagation and fracture in silicon nitride, silicon carbide, gallium arsenide, and nanophase ceramics are investigated. We observe a crossover from slow to rapid fracture and a correlation between the speed of crack propagation and morphology of fracture surface. A 100 million atom simulation is carried out to study crack propagation in GaAs. Mechanical failure in the Si/Si3N4 interface is studied by applying tensile strain parallel to the interface. Ten million atom molecular dynamics simulations are performed to determine atomic-level stress distributions in a 54 nm nanopixel on a 0.1 μm silicon substrate. Multimillion atom simulations of oxidation of aluminum nanoclusters and nanoindentation in silicon nitride are also discussed.

  6. Investigation into nitrided spur gears

    SciTech Connect

    Yilbas, B.S.; Coban, A.; Nickel, J.; Sunar, M.; Sami, M.; Abdul Aleem, B.J.

    1996-12-01

    The cold forging method has been widely used in industry to produce machine parts. In general, gears are produced by shaping or hobbing. One of the shaping techniques is precision forging, which has several advantages over hobbing. In the present study, cold forging of spur gears from Ti-6Al-4V material is introduced. To improve the surface properties of the resulting gears, plasma nitriding was carried out. Nuclear reaction analysis was carried out to obtain the nitrogen concentration, while the micro-PIXE technique was used to determine the elemental distribution in the matrix after forging and nitriding processes. Scanning electron microscopy and x-ray powder diffraction were used to investigate the metallurgical changes and formation of nitride components in the surface region. Microhardness and friction tests were carried out to measure the hardness depth profile and friction coefficient at the surface. Finally, scoring failure tests were conducted to determine the rotational speed at which the gears failed. Three distinct regions were obtained in the nitride region, and at the initial stages of the scoring tests, failure in surface roughness was observed in the vicinity of the tip of the gear tooth. This occurred at a particular rotational speed and work input.

  7. Request for assistance in reducing the potential risk of developing cancer from exposure to gallium arsenide in the microelectronics industry

    SciTech Connect

    Not Available

    1987-10-01

    Various methods through which exposure to gallium-arsenide might be reduced in the microelectronics industry were discussed. While there were no reported studies showing ill effects in workers from exposure to gallium arsenide or gallium particulates, three studies in animals indicated that gallium arsenide dissociates into gallium and arsenic in biological tissue, the latter being a carcinogen. NIOSH Recommended Exposure Limit (REL) for arsenic was 2 micrograms/cubic meter air (microg/cu m). NIOSH recommends control of worker exposure to gallium arsenide by observing NIOSH REL for inorganic arsenic, and that concentration of gallium arsenide in air be estimated by determining arsenic. Workers should be educated in possible hazards connected with gallium arsenide exposure. Proper engineering controls should be installed during production of microelectronic devices where exposure to gallium-arsenide is likely. Personal protective clothing and equipment should be available to workers, and proper procedures for washing, removal of wastes, transport, and disposal of contaminated materials should be explained and carried out. Specific safety recommendations are offered for use during crystal growth, crystal puller cleaning, crystal surface grinding and sawing, and wafer polishing, backlapping, and dicing.

  8. 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.

  9. Medical applications and toxicities of gallium compounds.

    PubMed

    Chitambar, Christopher R

    2010-05-01

    Over the past two to three decades, gallium compounds have gained importance in the fields of medicine and electronics. In clinical medicine, radioactive gallium and stable gallium nitrate are used as diagnostic and therapeutic agents in cancer and disorders of calcium and bone metabolism. In addition, gallium compounds have displayed anti-inflammatory and immunosuppressive activity in animal models of human disease while more recent studies have shown that gallium compounds may function as antimicrobial agents against certain pathogens. In a totally different realm, the chemical properties of gallium arsenide have led to its use in the semiconductor industry. Gallium compounds, whether used medically or in the electronics field, have toxicities. Patients receiving gallium nitrate for the treatment of various diseases may benefit from such therapy, but knowledge of the therapeutic index of this drug is necessary to avoid clinical toxicities. Animals exposed to gallium arsenide display toxicities in certain organ systems suggesting that environmental risks may exist for individuals exposed to this compound in the workplace. Although the arsenic moiety of gallium arsenide appears to be mainly responsible for its pulmonary toxicity, gallium may contribute to some of the detrimental effects in other organs. The use of older and newer gallium compounds in clinical medicine may be advanced by a better understanding of their mechanisms of action, drug resistance, pharmacology, and side-effects. This review will discuss the medical applications of gallium and its mechanisms of action, the newer gallium compounds and future directions for development, and the toxicities of gallium compounds in current use.

  10. Elastic properties of indium nitrides grown on sapphire substrates determined by nano-indentation: In comparison with other nitrides

    NASA Astrophysics Data System (ADS)

    Yonenaga, Ichiro; Ohkubo, Yasushi; Deura, Momoko; Kutsukake, Kentaro; Tokumoto, Yuki; Ohno, Yutaka; Yoshikawa, Akihiko; Wang, Xin Qiang

    2015-07-01

    The hardness of wurtzite indium nitride (α-InN) films of 0.5 to 4 μm in thickness was measured by the nano-indentation method at room temperature. After investigation of crystalline quality by x-ray diffraction, the hardness and Young's modulus were determined to be 8.8 ± 0.4 and 184 ± 5 GPa, respectively, for the In (0001)- and N ( 000 1 ¯ ) -growth faces of InN films. The bulk and shear moduli were then derived to be 99 ± 3 and 77 ± 2 GPa, respectively. The Poisson's ratio was evaluated to be 0.17 ± 0.03. The results were examined comprehensively in comparison with previously reported data of InN as well as those of other nitrides of aluminum nitride and gallium nitride. The underlying physical process determining the moduli and hardness was examined in terms of atomic bonding and dislocation energy of the nitrides and wurtzite zinc oxide.

  11. Gallium and Reactor Neutrino Anomalies

    NASA Astrophysics Data System (ADS)

    Acero, M. A.; Giunti, C.; Laveder, M.

    2009-03-01

    The observed deficit in the Gallium radioactive source experiments may be interpreted as a possible indication of active-sterile ν mixing. In the effective framework of two-neutrino mixing we obtain sin2ϑ≳0.03 and Δm≳0.1 eV. The compatibility of this result with the data of the Bugey reactor ν disappearance experiments is studied. It is found that the Bugey data present a hint of neutrino oscillations with 0.02≲sin2ϑ≲0.08 and Δm≈1.8 eV, which is compatible with the Gallium allowed region of the mixing parameters. This hint persists in the combined analysis of Gallium, Bugey, and Chooz data.

  12. Mineral resource of the month: gallium

    USGS Publications Warehouse

    Jaskula, Brian W.

    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.

  13. Dissolution of bulk specimens of silicon nitride

    NASA Technical Reports Server (NTRS)

    Davis, W. F.; Merkle, E. J.

    1981-01-01

    An accurate chemical characterization of silicon nitride has become important in connection with current efforts to incorporate components of this material into advanced heat engines. However, there are problems concerning a chemical analysis of bulk silicon nitride. Current analytical methods require the pulverization of bulk specimens. A pulverization procedure making use of grinding media, on the other hand, will introduce contaminants. A description is given of a dissolution procedure which overcomes these difficulties. It has been found that up to at least 0.6 g solid pieces of various samples of hot pressed and reaction bonded silicon nitride can be decomposed in a mixture of 3 mL hydrofluoric acid and 1 mL nitric acid overnight at 150 C in a Parr bomb. High-purity silicon nitride is completely soluble in nitric acid after treatment in the bomb. Following decomposition, silicon and hydrofluoric acid are volatilized and insoluble fluorides are converted to a soluble form.

  14. Corrosion behavior of mesoporous transition metal nitrides

    SciTech Connect

    Yang, Minghui; Allen, Amy J.; Nguyen, Minh T.; Ralston, Walter T.; MacLeod, Michelle J.; DiSalvo, Francis J.

    2013-09-15

    Transition metal nitrides (TMN) have many desirable characteristics such as high hardness and good thermal stability under reducing conditions. This work reports an initial survey of the chemical stability of mesoporous TMNs (TM=Nb, V, Cr and Ti) in water at 80 °C at neutral, acidic and alkaline pH. The mesoporous TMNs had specific surface areas of 25–60 m{sup 2}/g with average pore sizes ranging from 10 to 50 nm. The high surface areas of these materials enhance the rate of corrosion per unit mass over that of a bulk material, making detection of corrosion much easier. The products were characterized by Rietveld refinement of powder X-ray diffraction (PXRD) patterns and by scanning electron microscopy (SEM). Several nitrides have corrosion rates that are, within error, not distinguishable from zero (±1 Å/day). Of the nitrides examined, CrN appears to be the most corrosion resistant under acidic conditions. None of the nitrides studied are corrosion resistant under alkaline conditions. - Graphical abstract: Corrosion behavior of mesoporous transition metal nitrides (TM=Nb, V, Cr and Ti) in acidic and alkaline solutions at 80 °C for 2 weeks. Display Omitted - highlights: • Corrosion rates of mesoporous transition metal nitrides in aqueous solution is reported. • The mesoporous TMNs had surface areas of 25–60 m{sup 2}/g. • CrN is the most corrosion resistant under the conditions studied.

  15. Renal amyloidosis. Evaluation by gallium imaging

    SciTech Connect

    Lee, V.W.; Skinner, M.; Cohen, A.S.; Ngai, S.; Peng, T.T.

    1986-09-01

    A study has been performed to evaluate the efficacy of gallium imaging in the detection of renal amyloidosis. Ten of the 11 patients who had biopsy-proven renal amyloidosis demonstrated marked uptake in both kidneys. One patient revealed moderate gallium uptake in his kidneys. None of the patients had underlying renal or extrarenal pathology other than amyloidosis, which could account for renal gallium uptake (renal infection, neoplasm, hepatic failure or frequent blood transfusions). Four patients also had extrarenal foci of abnormal gallium uptake, suggesting other sites of amyloid deposits. Our data strongly suggest that gallium imaging has a high sensitivity for detection of renal amyloidosis. Its specificity is enhanced significantly by careful review of the clinical history to exclude other known causes of renal gallium uptake. Potentially, gallium imaging may be used to monitor the progress of patients under experimental therapy.

  16. Gallium-containing phospho-silicate glasses: synthesis and in vitro bioactivity.

    PubMed

    Franchini, Mirco; Lusvardi, Gigliola; Malavasi, Gianluca; Menabue, Ledi

    2012-08-01

    A series of Ga-containing phospho-silicate glasses based on Bioglass 45S5, having molar formula 46.2SiO2·24.3Na2O·26.9CaO·2.6P2O5·xGa2O3 (x=1.0, 1.6, 3.5), were prepared by fusion method. The reference Bioglass 45S5 without gallium was also prepared. The synthesized glasses were immersed in simulated body fluid (SBF) for 30 days in order to observe ion release and hydroxyapatite (HA) formation. All Ga-containing glasses maintain the ability of HA formation as indicated by main X-ray diffractometric peaks and/or electronic scanning microscopy results. HA layer was formed after 1 day of SBF soaking in 45S5 glass containing up to 1.6% Ga2O3 content. Moreover, gallium released by the glasses was found to be partially precipitated on the glass surface as gallium phosphate. Further increase in gallium content reduced the ion release in SBF. The maximum of Ga(3+) concentration measured in solution is ~6 ppm determined for 3.5% Ga2O3 content. This amount is about half of the toxic level (14 ppm) of gallium and the glasses release gallium till 30 days of immersion in SBF. Considering the above results, the studied materials can be proposed as bioactive glasses with additional antimicrobial effect of gallium having no toxic outcome.

  17. Strategies for gallium removal after focused ion beam patterning of ferroelectric oxide nanostructures

    NASA Astrophysics Data System (ADS)

    Schilling, A.; Adams, T.; Bowman, R. M.; Gregg, J. M.

    2007-01-01

    As part of a study into the properties of ferroelectric single crystals at nanoscale dimensions, the effects that focused ion beam (FIB) processing can have, in terms of structural damage and ion implantation, on perovskite oxide materials has been examined, and a post-processing procedure developed to remove such effects. Single crystal material of the perovskite ferroelectric barium titanate (BaTiO3) has been patterned into thin film lamellae structures using a FIB microscope. Previous work had shown that FIB patterning induced gallium impregnation and associated creation of amorphous layers in a surface region of the single crystal material some 20 nm thick, but that both recrystallization and expulsion of gallium could be achieved through thermal annealing in air. Here we confirm this observation, but find that thermally induced gallium expulsion is associated with the formation of gallium-rich platelets on the surface of the annealed material. These platelets are thought to be gallium oxide. Etching using nitric and hydrochloric acids had no effect on the gallium-rich platelets. Effective platelet removal involved thermal annealing at 700 °C for 1 h in a vacuum followed by 1 h in oxygen, and then a post-annealing low-power plasma clean in an Ar/O atmosphere. Similar processing is likely to be necessary for the full recovery of post FIB-milled nanostructures in oxide ceramic systems in general.

  18. Nano boron nitride flatland.

    PubMed

    Pakdel, Amir; Bando, Yoshio; Golberg, Dmitri

    2014-02-07

    Recent years have witnessed many breakthroughs in research on two-dimensional (2D) nanomaterials, among which is hexagonal boron nitride (h-BN), a layered material with a regular network of BN hexagons. This review provides an insight into the marvellous nano BN flatland, beginning with a concise introduction to BN and its low-dimensional nanostructures, followed by an overview of the past and current state of research on 2D BN nanostructures. A comprehensive review of the structural characteristics and synthetic routes of BN monolayers, multilayers, nanomeshes, nanowaves, nanoflakes, nanosheets and nanoribbons is presented. In addition, electronic, optical, thermal, mechanical, magnetic, piezoelectric, catalytic, ecological, biological and wetting properties, applications and research perspectives for these novel 2D nanomaterials are discussed.

  19. Hemocompatibility of titanium nitride.

    PubMed

    Dion, I; Baquey, C; Candelon, B; Monties, J R

    1992-10-01

    The left ventricular assist device is based on the principle of the Maillard-Wenkel rotative pump. The materials which make up the pump must present particular mechanical, tribological, thermal and chemical properties. Titanium nitride (TiN) because of its surface properties and graphite because of its bulk characteristics have been chosen. The present study evaluated the in vitro hemocompatibility of TiN coating deposited by the chemical vapor deposition process. Protein adsorption, platelet retention and hemolysis tests have been carried out. In spite of some disparities, the TiN behavior towards albumin and fibrinogen is interesting, compared with the one of a reference medical grade elastomer. The platelet retention test gives similar results as those achieved with the same elastomer. The hemolysis percentage is near to zero. TiN shows interesting characteristics, as far as mechanical and tribological problems are concerned, and presents very encouraging blood tolerability properties.

  20. Evaluation of silicon-nitride ceramic valves.

    SciTech Connect

    Sun, J. G.; Zhang, J. M.; Andrews, M. J.; Tretheway, J. S.; Phillips, N. S .L.; Jensen, J. A.; Nuclear Engineering Division; Univ. of Texas; Caterpillar, Inc.

    2008-01-01

    Silicon-nitride ceramic valves can improve the performance of both light- and heavy-duty automotive engines because of the superior material properties of silicon nitrides over current metal alloys. However, ceramics are brittle materials that may introduce uncertainties in the reliability and durability of ceramic valves. As a result, the lifetime of ceramic valves are difficult to predict theoretically due to wide variations in the type and distribution of microstructural flaws in the material. Nondestructive evaluation (NDE) methods are therefore required to assess the quality and reliability of these valves. Because ceramic materials are optically translucent and the strength-limiting flaws are normally located near the valve surface, a laser-scatter method can be used for NDE evaluation of ceramic valves. This paper reviews the progress in the development of this NDE method and its application to inspect silicon-nitride ceramic valves at various stages of manufacturing and bench and engine tests.