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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Methods for forming group III-arsenide-nitride semiconductor materials

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.

Major, Jo S.↗
NASA NTRS2016

Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approx.576-867 C. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Metallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120deg triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3+, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

Srinivasan, P.↗
NASA NTRS2016

Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approximately 576-867 degrees Centigrade. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Me-tallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120-degree triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3 plus, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

Srinivasan, P.↗
DOE OSTI2012

Bismuth in gallium arsenide: Structural and electronic properties of GaAs{sub 1-x}Bi{sub x} alloys

The structural and electronic properties of cubic GaAs{sub 1-x}Bi{sub x} alloys with bismuth concentration 0.0, 0.25, 0.50, 0.75 and 1.0 are studied using the 'special quasi-random structures' (SQS) approach of Zunger along with the generalized gradient approximation (GGA) and the Engel-Vosko generalized gradient approximation (EV-GGA). The lattice constant, bulk modulus, derivative of bulk modulus and energy gap vary with bismuth concentration nonlinearly. The present calculations show that the band gap decreases substantially with increasing bismuth concentration and that spin-orbit coupling influences the nature of bonding at high Bi concentrations. - Graphical abstract: Bowing effect of spin-orbit split-off band values versus Bi content with and without spin-orbit coupling for GaAs{sub 1-x}Bi{sub x} (at x=0.25, 0.50 and 0.75). Calculations are done with GGA. Highlights: Black-Right-Pointing-Pointer Structural and electronic properties of GaAs{sub 1-x}Bi{sub x} alloys were studied. Black-Right-Pointing-Pointer We present results of lattice constant, energy gap, bulk modulus and derivative. Black-Right-Pointing-Pointer The band gap decreases substantially with increasing Bi concentration. Black-Right-Pointing-Pointer Calculations of the density of states and charge densities are also presented. Black-Right-Pointing-Pointer We have performed calculations without and with spin-orbit coupling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

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

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

36 MATERIALS SCIENCE↗
DOE OSTI2016

Size-effects in indium gallium arsenide nanowire field-effect transistors

We fabricate and analyze InGaAs nanowire MOSFETs with channel widths down to 18 nm. Low-temperature measurements reveal quantized conductance due to subband splitting, a characteristic of 1D systems. We relate these features to device performance at room-temperature. In particular, the threshold voltage versus nanowire width is explained by direct observation of quantization of the first sub-band, i.e., band gap widening. An analytical effective mass quantum well model is able to describe the observed band structure. The results reveal a compromise between reliability, i.e., V{sub T} variability, and on-current, through the mean free path, in the choice of the channel material.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Distribution of elastic strains appearing in gallium arsenide as a result of doping with isovalent impurities of phosphorus and indium

The distribution of elastic strains in a system consisting of a quantum-dot layer and a buried GaAs{sub x}P{sub 1−x} layer is studied using geometric phase analysis. A hypothesis is offered concerning the possibility of controlling the process of the formation of InAs quantum dots in a GaAs matrix using a local isovalent phosphorus impurity.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Covalent surface modification of gallium arsenide photocathodes for water splitting in highly acidic electrolyte

Efficient water splitting using light as the only energy input requires stable semiconductor electrodes with favorable energetics for the water-oxidation and proton-reduction reactions. Strategies to tune electrode potentials using molecular dipoles adsorbed to the semiconductor surface have been pursued for decades but are often based on weak interactions and quickly react to desorb the molecule under conditions relevant to sustained photoelectrolysis. Here, we show that covalent attachment of fluorinated, aromatic molecules to p-GaAs(1 0 0) surfaces can be employed to tune the photocurrent onset potentials of p-GaAs(1 0 0) photocathodes and reduce the external energy required for water splitting. Results indicate that initial photocurrent onset potentials can be shifted by nearly 150 mV in pH -0.5 electrolyte under 1 Sun (1000 W m -2 ) illumination resulting from the covalently bound surface dipole. Furthermore, X-ray photoelectron spectroscopy analysis reveals that the covalent molecular dipole attachment is not robust under extended 50 h photoelectrolysis, the modified surface delays arsenic oxide formation that results in a p-GaAs(1 0 0) photoelectrode operating at a sustained photocurrent density of -20.5 mA cm -2 within -0.5 V of the reversible hydrogen electrode.

36 MATERIALS SCIENCE↗
DOE OSTI2013

New ternary phosphides and arsenides. Syntheses, crystal structures, physical properties of Eu{sub 2}ZnP{sub 2}, Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3}

Three new europium pnictides Eu{sub 2}ZnP{sub 2}, Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3} have been synthesized and their structures were determined by single-crystal X-ray diffraction. Eu{sub 2}ZnP{sub 2} is isotypic with Yb{sub 2}CdSb{sub 2} (Cmc2{sub 1} (No. 36); cell parameters a=4.1777(7) Å, b=15.925(3) Å, c=7.3008(12) Å), while the latter two compounds crystallize with the Ba{sub 2}Cd{sub 2}Sb{sub 3} structure type (C2/m (No. 12); cell parameters a=15.653(5)/16.402(1) Å, b=4.127(1)/4.445(4) Å, c=11.552(4)/12.311(1) Å and β=126.647(4)/126.515(7)° for Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3}, respectively). Magnetic susceptibility measurements in the interval 5–300 K confirm paramagnetic behavior and effective magnetic moments characteristic of Eu{sup 2+} ([Xe] 4f{sup 7}) ground states. Temperature-dependent electrical conductivity measurements also prove that Eu{sub 2}Cd{sub 2}As{sub 3} is a semiconducting compound with a narrow band gap of 0.059 eV below 100 K. According to TG/DSC analyses, Eu{sub 2}Cd{sub 2}As{sub 3} starts to decompose at about 950 K. - Graphical abstract: A polyhedral view of the crystal structure of new pnictides Eu{sub 2}T{sub 2}Pn{sub 3} (T=Zn or Cd; Pn=P or As). Display Omitted - Highlights: • Three new ternary pnictide Zintl compounds, Eu{sub 2}ZnP{sub 2}, Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3}, have been synthesized and characterized. • The europium cations are divalent and ferromagnetically coupled in both Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3}. • Eu{sub 2}Cd{sub 2}As{sub 3} has a very small band gap of 0.06 eV and starts to decompose over 950 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Five new ternary indium-arsenides discovered. Synthesis and structural characterization of the Zintl phases Sr 3 In 2 As 4 , Ba 3 In 2 As 4 , Eu 3 In 2 As 4 , Sr 5 In 2 As 6 and Eu 5 In 2 As 6

Five new ternary indium aresenides, AE 3 In 2 As 4 ( AE =Sr, Ba, Eu), and AE 5 In 2 As 6 ( AE =Sr, Eu), have been synthesized using molten metal In, Pb, and Sn fluxes. Structure elucidation was aided by powder X-ray and single crystal X-ray diffraction. This demonstrated Sr 3 In 2 As 4 and Eu 3 In 2 As 4 are orthorhombic and isostructural to Sr 3 In 2 P 4 (space group Pnnm , Z =2), while Ba 3 In 2 As 4 is monoclinic and isostructural to Ca 3 Al 2 As 4 (space group C 2/ c , Z =4). In addition, Sr 5 In 2 As 6 and Eu 5 In 2 As 6 crystallize orthorhombically and adopt the Ca 5 Ga 2 As 6 structure type (space group Pbam , Z =2). The valence electron count for all structures conform to the Zintl-Klemm concept, and as such can be rationalized as divalent Sr, Ba, Eu cations and polyanionic In–As fragments of different dimensionality. In Sr 3 In 2 As 4 and Eu 3 In 2 As 4 , one-dimensional chains [In 2 As 4 ] 6– running along the crystallographic c -axis exist, and they are made up of edge- and corner-shared tetrahedra InAs 4 . The [In 2 As 4 ] 6– two-dimensional sheets in the structure of Ba 3 In 2 As 4 are composed of a pair of edge-shared InAs 4 tetrahedra, that are further connected by corner-sharing. In Sr 5 In 2 As 6 and Eu 5 In 2 As 6 , the InAs 4 tetrahedra are only corner-shared to make infinite [InAs 2 As 2/2 ] 6– chains running along the a -axis, which are dimerized via As–As bonds into [In 2 As 6 ] 10- ribbons. Furthermore, electronic structure calculations affirm these assignments and suggest intrinsic, narrow-gap seminconducting behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Electrical characteristics of field-effect transistors based on indium arsenide nanowire thinner than 10 nm

To suppress short channel effects, lower off-state leakage current and enhance gate coupling efficiency, InAs nanowires (NWs) with diameter smaller than 10 nm could be needed in field-effect transistors (FETs) as the channel length scales down to tens of nanometers to improve the performance and increase the integration. Here, we fabricate and study FETs based on ultrathin wurtzite-structured InAs NWs, with the smallest NW diameter being 7.2 nm. The FETs based on ultrathin NWs exhibit high I{sub on}/I{sub off} ratios of up to 2 × 10{sup 8}, small subthreshold swings of down to 120 mV/decade, and operate in enhancement-mode. The performance of the devices changes as a function of the diameter of the InAs NWs. The advantages and challenges of the FETs based on ultrathin NWs are discussed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

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

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

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Fabrication and characterisation of gallium arsenide ambipolar quantum point contacts

We show that ballistic one-dimensional channels can be formed in an ambipolar device fabricated on a high mobility Al{sub 0.34}Ga{sub 0.66}As/GaAs heterostructure. Both electron and hole quantised conductances can be measured in the same one-dimensional channel. We have used this device to compare directly the subband spacings of the two charge carriers in the same confining potential and used this to compare the electron and hole effective masses.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Temperature dependent characterization of gallium arsenide X-ray mesa p-i-n photodiodes

Electrical characterization of two GaAs p{sup +}-i-n{sup +} mesa X-ray photodiodes over the temperature range 0 °C to 120 °C together with characterization of one of the diodes as an X-ray detector over the temperature range 0 °C to 60 °C is reported as part of the development of photon counting X-ray spectroscopic systems for harsh environments. The randomly selected diodes were fully etched and unpassivated. The diodes were 200 μm in diameter and had 7 μm thick i layers. The leakage current density was found to increase from (3 ± 1) nA/cm{sup −2} at 0 °C to (24.36 ± 0.05) μA/cm{sup −2} at 120 °C for D1 and from a current density smaller than the uncertainty (0.2 ± 1.2) nA/cm{sup −2} at 0 °C to (9.39 ± 0.02) μA/cm{sup −2} at 120 °C for D2 at the maximum investigated reverse bias (15 V). The best energy resolution (FWHM at 5.9 keV) was achieved at 5 V reverse bias, at each temperature; 730 eV at 0 °C, 750 eV at 20 °C, 770 eV at 40 °C, and 840 eV at 60 °C. It was found that the parallel white noise was the main source of the photopeak broadening only when the detector operated at 60 °C, at 5 V, 10 V, and 15 V reverse bias and at long shaping times (>5 μs), whereas the sum of the dielectric noise and charge trapping noise was the dominant source of noise for all the other spectra.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Gallium arsenide (GaAs) (001) after sublimation of arsenic (As) thin-film cap, by XPS

Survey and high energy resolution spectra are reported for MBE grown GaAs (001) that had been capped with As. The As cap was removed by heating in situ prior to analysis. The current data expands upon the spectral regions previously reported in Surface Science Spectra. High energy resolution spectral features reported include: 2p, 3s, 3p, 3d, and L3M45M45 peaks for As; 2p, 3s, 3p, 3d, and L3M45M45 peaks for Ga; and the valance band region.

As-capped GaAs↗
DOE OSTI2011

Deformation of the surface of gallium arsenide during the deposition of gold

Deformation phenomena of near-surface GaAs layers are studied using surface acoustic waves during the deposition of Au and the irradiation of the semiconductor surface by the light of a heated evaporator. It is shown that, in the case of Au deposition, the near-surface layers are plasticized due to the phase transformations in the Au-Ga-As system, while upon irradiation of the GaAs surface with light, a coarse-grained layer with liquid-like interlayers is formed. As a result, the type of surface deformations and their relaxation time change. The integral temporal characteristics of the surface acoustic wave, such as the variation integrals of its rate and dissipated power, reflect the processes occurring on the surface in the real-time mode. In summary, they reflect the current magnitude of the resulting deformation. The parameters of occurring processes such as activation energy and relaxation time are determined.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Effect of pressure on the electronic spectrum of indium arsenide

Based on the dependences of the Hall coefficient and the resistivity of n- and p-InAs and p-InAs Left-Pointing-Angle-Bracket Mn Right-Pointing-Angle-Bracket bulk crystals on hydrostatic pressures up to 9 GPa at 77 and 300 K, the evolution of the energy spectrum of electrons upon isotropic contraction of a crystal lattice is studied. Intervals between the energy levels of shallow, deep, and deep resonance impurity centers and between the edges of intrinsic bands, and the pressure coefficients for these intervals, were determined.

36 MATERIALS SCIENCE↗