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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

The growth and characterization of Al(x)Ga(1-x)As/Ge heterostructures

The effects of the growth temperature and the Al(x)Ga(1-x)As layer thickness on the structural, optical, and electrical properties of Al(x)Ga(1-x)As/Ge heterostructures grown for photovoltaic applications were investigated using different-thickness (between 1 micron and 5 microns) Al(x)Ga(1-x)As layers grown by MOCVD in the temperature range between 660 and 780 C. Results obtained from double-crystal X-ray rocking curve measurements, electron beam induced current, cross-sectional TEM, Raman spectroscopy, SIMS, and steady-state and time-resolved photoluminescence measurements are presented. It was found that the highest minority carrier lifetime, 2.41 ns, was obtained for T(G) = 780 C, but the lowest interfacial recombination velocity, 1.6 x 10 exp 4, was obtained at 660 C.

Choi, S. W.↗
NASA NTRS1992

Reflection high-energy electron diffraction study of growth and interface formation of the Ga(1-x)In(x)Sb/InAs strained-layer superlattices

Reflection high-energy electron diffraction (RHEED) during molecular beam epitaxy is used to study the growth and interface formation of the Ga(1-x)In(x)Sb/InAs (x is not greater than 0.4) strained-layer superlattices (SLSs) on GaSb(100) substrates. A number of surface atomic structures were observed in the growth of the SLS: a (1 x 3) phase from the InAs epilayer surface, a (2 x 3) phase, a (2 x 4) phase, and diffuse (1 x 1)-like phases from the InAs epilayer surface. It is suggested that the long-range order quality of the interface of Ga(1-x)In(x)Sb on InAs may be better than that of the interface of InAs on Ga(1-x)In(x)Sb, but the abruptness of the interfaces would still be compatible. The RHEED intensity variations in the formation of the interfaces are discussed in terms of interface chemical reactions.

Fan, W. C.↗
NASA NTRS2001

Partial Pressures of Te2 and Thermodynamic Properties of Ga-Te System

The partial pressures of Te2 in equilibrium with Ga(1-x)Te(x) samples were measured by optical absorption technique from 450 to 1100 C for compositions, x, between 0.333 and 0.612. To establish the relationship between the partial pressure of Te, and the measured optical absorbance, the calibration runs of a pure Te sample were also conducted to determine the Beer's Law constants. The partial pressures of Te2 in equilibrium with the GaTe(s) and Ga2Te3(s)compounds, or the so-called three-phase curves, were established. These partial pressure data imply the existence of the Ga3Te4(s) compound. From the partial pressures of Te2 over the Ga-Te melts, partial molar enthalpy and entropy of mixing for Te were derived and they agree reasonable well with the published data. The activities of Te in the Ga-Te melts were also derived from the measured partial pressures of Te2. These data agree well with most of the previous results. The possible reason for the high activity of Te measured for x less than 0.60 is discussed.

Su, Ching-Hua↗
NASA NTRS2005

Hadean Crustal Processes Revealed from Oxygen Isotopes and U-Th-Pb Depth Profiling of Pre-4.0 Ga Detrital Zircons from Western Australia

Because physical and chemical processes of the past are determined from analysis of a preserved geologic record, little is known about terrestrial crustal processes of the first 500 Ma during the so-called Hadean Eon. What is known from direct measurements has been derived almost exclusively from the study of greater than 4.0 Ga detrital zircons from the Jack Hills, Western Australia. The geochemistry of these zircons has direct application to understanding the origin and evolution of the rocks during the Hadean because: (i) U-Th-Pb age determinations by ion microprobe suggests the presence of crust as early as 4.37 Ga, or shortly after lunar formation; (ii) high-resolution U-Th-Pb zircon depth profiles reported here reveal several episodes of zircon growth in the Hadean previously unrecognized; (iii) core regions of pre-4.0 Ga zircons with igneous compositions are enriched in O-18 and contain metaluminous and peraluminous mineral inclusions, both features indicative of S-type grainitod protoliths. Study of these ancient zircons provides a unique window into the first half billion years that permits assessment of the potential of the Hadean Earth to host an emergent biosphere.

Trail, D.↗
NASA NTRS1994

(abstract) Transmission Electron Microscopy of Al(sub x)Ga(sub 1-x)N/SiC Multilayer Structures

The potential of wide-band-gap III-V nitrides as solar-blind ultraviolet sensors and light emitters has prompted an increasing amount of work recently, including the fabrication of the first UV sensors from as-deposited single crystal GaN. We have used high resolution transmission electron microscopy (TEM) to study the microstructure of two novel developments of wide-band-gap III-V nitrides: the growth of ultra-short period GaN/AlN super lattices (digital alloys); and the incorporation of SiC layers into Al(sub x)Ga(sub 1-x)N structures. By varying the relative periods in a GaN/AlN superlattice, it should be possible to tailor the band gap of the composite to lie between the elemental values of 365 nm for GaN and 200 nm for AlN. The group IV semiconductor, SiC, has a close lattice match (< 3%) to Al(sub x)Ga(sub 1-x)N for growth on the basal plane. Demonstration of epitaxial growth for Al(sub x)Ga(sub 1-x)N/SiC multilayers could enable an extension of direct band-gap material towards the visible.

microscopy GaN AlN semiconductor SiC↗
NASA NTRS2010

An Approximately 4.35 Ga Ar-Ar Age for GRA 8 and the Complex Chronology of its Parent Body

GRA06128 and GRA06129 (hereafter GRA 8 and GRA 9) are partial melts of a parent body of approximately chondritic composition. We reported a conventional Sm-147-Nd-143 isochron age of 4.559+/-0.096 Ga and a 146 Sm-142Nd model age of 4.549+/-0.036 for combined data for the two rocks. Plagioclase plus whole rock and leachate (approx.phosphate) samples gave a secondary Sm-147-Nd-143 age of 3.4+/-0.4 Ga. An Ar-39-Ar-40 age of 4.460+/-0.028 Ga was interpreted as dating metamorphism in GRA 9. We report Ar-39-Ar-40 ages in the range approx.4344-4366 Ma for GRA 8, establishing similar but different Ar-39-Ar-40 ages for the two rocks, consistent with their different Sr-isotopic systematics, and discuss these ages in the context of the complex sequence of events that affected these samples.

Park, J.↗
NASA NTRS2010

An Approximately 4.35 Ga Ar-Ar Age for GRA 8 and the Complex Chronology of its Parent Body

GRA06128 and GRA06129 (hereafter GRA 8 and GRA 9) are partial melts of a parent body of approximately chondritic composition. We reported a conventional SM-147Sm-ND_143 isochron age of 4.559 +/-.096 Ga and a SM-146-142Nd model age of 4.549 +/- 0.036 for combined data for the two rocks. Plagioclase plus whole rock and leachate (approximately phosphate) samples gave a secondary SM-147-ND-143 age of 3.4 +/-0.4 Ga. An Ar-39-Ar-40 age of 4.460+/-0.028 Ga was interpreted by as dating metamorphism in GRA 9. We report Ar-39-Ar-40 ages in the range approximately 4344-4366 Ma for GRA 8, establishing similar but different Ar-39-Ar-40 ages for the two rocks, consistent with their different Sr-istopic systematics, and discuss these ages in the context of the complex sequence of events that affected these samples

Park, J.↗
DOE OSTI2020

Materials Data on Ga(Bi3O5)4 by Materials Project

Ga(Bi3O5)4 crystallizes in the cubic I23 space group. The structure is three-dimensional. Ga2+ is bonded to four equivalent O2- atoms to form GaO4 tetrahedra that share corners with twelve equivalent BiO5 square pyramids. All Ga–O bond lengths are 1.89 Å. Bi+3.17+ is bonded to five O2- atoms to form distorted BiO5 square pyramids that share corners with eight equivalent BiO5 square pyramids, a cornercorner with one GaO4 tetrahedra, and an edgeedge with one BiO5 square pyramid. There are a spread of Bi–O bond distances ranging from 2.11–2.59 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to three equivalent Bi+3.17+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three equivalent Bi+3.17+ atoms. In the third O2- site, O2- is bonded to one Ga2+ and three equivalent Bi+3.17+ atoms to form distorted corner-sharing OGaBi3 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga(MoSe2)4 by Materials Project

Ga(MoSe2)4 crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mo+3.25+ is bonded to six Se2- atoms to form distorted MoSe6 pentagonal pyramids that share corners with three equivalent GaSe4 tetrahedra and edges with six equivalent MoSe6 pentagonal pyramids. There are three shorter (2.48 Å) and three longer (2.76 Å) Mo–Se bond lengths. Ga3+ is bonded to four equivalent Se2- atoms to form GaSe4 tetrahedra that share corners with twelve equivalent MoSe6 pentagonal pyramids. All Ga–Se bond lengths are 2.45 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Mo+3.25+ and one Ga3+ atom to form a mixture of distorted corner and edge-sharing SeGaMo3 tetrahedra. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Mo+3.25+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga(IO3)3 by Materials Project

Ga(IO3)3 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. Ga3+ is bonded in an octahedral geometry to six O2- atoms. There are three shorter (2.00 Å) and three longer (2.01 Å) Ga–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one I5+ atom. The O–I bond length is 1.80 Å. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ga3+ and one I5+ atom. The O–I bond length is 1.89 Å. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Ga3+ and one I5+ atom. The O–I bond length is 1.86 Å. I5+ is bonded in a 3-coordinate geometry to three O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga(MoSe2)4 by Materials Project

Ga(MoSe2)4 crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are two inequivalent Mo+3.25+ sites. In the first Mo+3.25+ site, Mo+3.25+ is bonded to six Se2- atoms to form distorted MoSe6 pentagonal pyramids that share corners with three equivalent GaSe4 tetrahedra and edges with six MoSe6 pentagonal pyramids. There are a spread of Mo–Se bond distances ranging from 2.47–2.76 Å. In the second Mo+3.25+ site, Mo+3.25+ is bonded to six Se2- atoms to form distorted MoSe6 pentagonal pyramids that share corners with three equivalent GaSe4 tetrahedra and edges with six equivalent MoSe6 pentagonal pyramids. There are three shorter (2.49 Å) and three longer (2.79 Å) Mo–Se bond lengths. Ga3+ is bonded to four Se2- atoms to form GaSe4 tetrahedra that share corners with twelve MoSe6 pentagonal pyramids. All Ga–Se bond lengths are 2.45 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three Mo+3.25+ and one Ga3+ atom to form a mixture of distorted edge and corner-sharing SeGaMo3 tetrahedra. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three Mo+3.25+ atoms. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three equivalent Mo+3.25+ atoms. In the fourth Se2- site, Se2- is bonded to three equivalent Mo+3.25+ and one Ga3+ atom to form a mixture of distorted edge and corner-sharing SeGaMo3 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga(FeO2)2 by Materials Project

Ga(FeO2)2 is Spinel-like structured and crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. there are two inequivalent Fe+2.50+ sites. In the first Fe+2.50+ site, Fe+2.50+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six equivalent FeO4 tetrahedra, edges with two equivalent FeO6 octahedra, and edges with four equivalent GaO6 octahedra. There are four shorter (2.07 Å) and two longer (2.16 Å) Fe–O bond lengths. In the second Fe+2.50+ site, Fe+2.50+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with six equivalent FeO6 octahedra and corners with six equivalent GaO6 octahedra. The corner-sharing octahedra tilt angles range from 56–58°. There is two shorter (1.92 Å) and two longer (1.96 Å) Fe–O bond length. Ga3+ is bonded to six O2- atoms to form GaO6 octahedra that share corners with six equivalent FeO4 tetrahedra, edges with two equivalent GaO6 octahedra, and edges with four equivalent FeO6 octahedra. All Ga–O bond lengths are 2.03 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Fe+2.50+ and one Ga3+ atom. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Fe+2.50+ and two equivalent Ga3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ga(CuN)3 by Materials Project

Ga(CuN)3 crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Cu2+ is bonded in a square co-planar geometry to four equivalent N3- atoms. All Cu–N bond lengths are 2.07 Å. Ga3+ is bonded to six equivalent N3- atoms to form corner-sharing GaN6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ga–N bond lengths are 2.07 Å. N3- is bonded to four equivalent Cu2+ and two equivalent Ga3+ atoms to form a mixture of edge and corner-sharing NGa2Cu4 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Defect-mediated metastability and carrier lifetimes in polycrystalline (Ag,Cu)(In,Ga)Se 2 absorber materials

Using a combination of optical and electrical measurements, we develop a model for metastable defects in Ag-alloyed Cu(In,Ga)Se 2 , one of the leading thin film photovoltaic materials. By controlling the pre-selenization conditions of the back contact prior to the growth of polycrystalline (Ag,Cu)(In,Ga)Se 2 absorbers and subsequently exposing them to various stresses (light soaking and dark-heat), we explore in this paper the nature and role of metastable defects on the electro-optical and photovoltaic performance of high-efficiency solar cell materials and devices. Positron annihilation spectroscopy indicates that dark-heat exposure results in an increase in the concentration of the selenium–copper divacancy complex (V Se –V Cu ), attributed to depassivation of donor defects. Deep-level optical spectroscopy finds a corresponding increase of a defect at Ev+0.98 eV, and deep-level transient spectroscopy suggests that this increase is accompanied by a decrease in the concentration of mid-bandgap recombination centers. Time-resolved photoluminescence excitation spectroscopy data are consistent with the presence of the V Se –V Cu divacancy complex, which may act as a shallow trap for the minority carriers. Light-soaking experiments are consistent with the V Se –V Cu optical cycle proposed by Lany and Zunger, resulting in the conversion of shallow traps into recombination states that limit the effective minority carrier recombination time (and the associated carrier diffusion length) and an increase in the doping density that limits carrier extraction in photovoltaic devices.

14 SOLAR ENERGY↗
DOE OSTI2025

Synergistic effects of Al, Ga, and In doping on ZnO nanorod arrays grown via citrate-assisted hydrothermal technique for highly efficient and fast scintillator screens

To be used as efficient alpha particle scintillator in the fields of nuclear security, nuclear nonproliferation and high-energy physics, scintillator screens must have high light output and fast decay properties. While there has been a great deal of progress in scintillation efficiency, achieving fast decay time properties are still a challenge. In this work, the near band edge (NBE) UV luminescence and alpha particle induced scintillation properties of vertically aligned densely packed ZnO nanorods (NRs) doped with Al, Ga, and In have been thoroughly investigated. The high crystalline hexagonal wurtzite structure with a strong orientation through the c -axis plane (002) and aspect ratios in the range 13–22 have been observed for all ZnO NRs. Electron paramagnetic resonance (EPR) analysis exhibited paramagnetic signals at g ≈ 1.96 for all ZnO NRs. A cost effective green hydrothermal synthesis technique was employed to grow well-aligned NRs. Using citrate as an additive acting as a strong reducing agent in the solution during the crystal growth, defects on the surface are significantly suppressed, thereby enhancing the NBE UV emission. Significantly higher NBE UV emission was observed from the top surface of ZnO NRs in cathodoluminescence (CL) microscopy. Results show that citrate assisted donor doping of ZnO NRs not only reduces the defect emission and NBE self-absorption, but also induces fast decay time (~ 600–700 ps), which makes ZnO NRs a good candidate for fast alpha particle scintillator screens used in associated particle imaging for time and direction tagging of individual neutrons generated in D–T and D–D neutron generators.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Radiation Response of Ga 2 O 3 MOSFETs Probed via Focused Particle Beams

Gallium Oxide (Ga 2 O 3 ), particularly in its β-phase, is attracting lots of interest for high-power and high-voltage electronics due to its wide bandgap, high breakdown field, and thermal stability. This study investigates the radiation response of Ga 2 O 3 Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) under Total Ionizing Dose (TID) and Displacement Damage (DD) conditions, which are critical for applications in radiation environments. Utilizing a dual-beam Focused Ion Beam and Scanning Electron Microscope setup, microscale analysis of radiation effects on individual devices is performed. The findings reveal distinct behaviors under TID and DD + TID conditions, with TID leading to threshold voltage shifts due to trapped charges, while DD results in decreased drive current attributed to increased carrier scattering from lattice defects. Notably, it is demonstrated that the TID effect can be mitigated through dynamic threshold voltage adjustments and that the predicted TID from ions calculated by Monte Carlo simulations overestimates actual TID due to unaccounted charge yield effects. In conclusion, this research enhances the understanding of Ga2O3 MOSFETs' performance in harsh radiation environments, providing insights for the design of robust electronic devices for space and nuclear applications.

MOSFET↗
DOE OSTI2020

Behavior of Na and RbF-Treated CdS/Cu(In,Ga)Se 2 Solar Cells with Stress Testing under Heat, Light, and Junction Bias

In this work, the effects of Na and RbF alkali treatment on the metastability behavior of CdS/Cu(In,Ga)Se 2 solar cells are investigated with stress factors of heat, junction bias, and illumination. Four device types with and without Na or RbF treatments are subjected to heat- and light-soaking under open- and short-circuit (OC, SC) junction bias. Low-Na devices show a higher bandgap due to increased minimum Ga content, higher recombination current, and lower open-circuit voltage (V OC ). Devices with RbF post-deposition treatment (PDT) show an improvement in net doping density ≈10 16 cm –3 , V OC , and efficiency. Heat- and light-soaking under OC junction bias provokes an increase in net carrier concentration and V OC irrespective of the alkali treatments. After SC stress, a decrease in V OC and net carrier concentration is observed, which can be stabilized by RbF-PDT. An increase in Na and oxygen concentration in CIGS is observed for baseline and low-Na devices, respectively, after OC stress. The oxygen concentration in CdS decreases after heat- and light-soaking for devices without RbF-PDT, whereas it remains unchanged for devices with RbF-PDT. The atomic concentration profiles in CIGS significantly stabilize as a function of stress with the addition of RbF-PDT.

14 SOLAR ENERGY↗
DOE OSTI2024

Rigidity‐Driven Structural Isomers in the NaCl–Ga 2 S 3 System: Implications for Energy Storage

Alternative energy sources require the search for innovative materials with promising functionalities. Systems with unusual chemical properties represent an insufficiently explored domain, concealing unexpected features. Using diffraction and Raman spectroscopy over a wide temperature range, supported by first‐principles simulations, a rare phenomenon is unveiled: phase‐dependent chemical interactions between binary components in the NaCl–Ga 2 S 3 system. In this unique occurrence, previously intact binary crystalline species transform upon melting into mixed liquid structural isomers, forming bonds with new partners. The chemical combinatorics appears to be fully reversible for stable crystals and liquids. Despite this, rapidly frozen glasses out of thermodynamic equilibrium remain in a metastable isomeric state, offering remarkable properties, particularly a high room‐temperature Na + conductivity, comparable to the best sodium halide superionic conductors and therefore encouraging for sodium solid‐state batteries and energy applications. A rigidity paradigm is responsible for the observed phenomenon, as the extremely constrained Ga 2 S 3 crystal lattice does not survive viscous flow, breaking up at a short‐range level. The removal of rigidity constraints and dense packing leads to a significant increase in empty space, which is the origin of high sodium diffusivity. Broadly, the rigidity‐driven structural isomerism opens up an inspiring path to the discovery of atypical materials.

25 ENERGY STORAGE↗