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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Multidimensional Coherent Spectroscopy of Semiconductors

Abstract Optical multidimensional coherent spectroscopy (MDCS) is a nonlinear spectroscopy technique where a material is excited by a series of laser pulses to produce a spectrum as a function of multiple frequencies. The technique's ability to elucidate excited‐state structure and interactions has made MDCS a valuable tool in the study of excitons in semiconductors. This review introduces the method and describes progress it has fostered establishing a better understanding of dephasing rates, coherent coupling mechanisms, and many‐body interactions pertaining to optically generated electronic excitations in a variety of semiconductor material systems. Emphasis is placed on nanostructured gallium arsenide quantum wells and quantum dots, on quantum dots in other III–V and II–VI semiconductors, and on atomically thin transition metal dichalcogenides. Recent technical advances and potential future directions in the field are also discussed.

Smallwood, Christopher L.↗
DOE OSTI2018

High-efficiency flexible III-V photovoltaic solar cells based on single-crystal-like thin films directly grown on metallic tapes

This study demonstrates the first flexible single-junction III-V photovoltaic solar cells (SCs) based on single-crystal-like gallium arsenide (GaAs) thin films on a low-cost metal substrate by direct and continuous deposition, which can bypass expensive single crystal wafer fabrication. The two-dimensional modeling of the GaAs SC is developed and used to study feasibility of single-crystal-like GaAs thin films for high performance SC devices. A promising SC device performance characteristic with an open-circuit voltage of 560 mV and short circuit current of 19.4 mA/cm 2 , resulting in a conversion efficiency of ~7.6%, is demonstrated.

36 MATERIALS SCIENCE↗
DOE OSTI2019

GaAs/silicon PVMirror tandem photovoltaic mini‐module with 29.6% efficiency with respect to the outdoor global irradiance

Abstract Balance‐of‐system costs now dominate the installed cost of photovoltaic systems, causing the annually averaged module efficiency to become a primary system cost driver. The resulting continued push towards higher module efficiencies, coupled with the dominance of single‐axis tracking in the utility‐scale PV market, may create an opportunity for a low‐concentration tandem module technology. Here, we demonstrate such a tandem, using the “PVMirror” concept, on the mini‐module scale. The tandem couples a (concentrating) silicon PVMirror having an aperture area of 156.25 cm 2 with a gallium arsenide receiver to achieve 29.6% efficiency with respect to the outdoor global irradiance. Unlike most concentrating technologies, the silicon PVMirror collects some of the diffuse light, but the tandem would nevertheless achieve 31% efficiency in the absence of diffuse light, as in a laboratory measurement. The same tandem technology can be implemented with a wide‐bandgap thin‐film PVMirror and silicon receiver—a potentially cost‐competitive combination—when efficient wide‐bandgap cells have been developed.

Yu, Zhengshan J.↗
DOE OSTI2026

Demonstration of GaAs-Based Photovoltaics on Acoustically Spalled Surfaces Grown by MOCVD

This study demonstrates the potential of sonic lift-off (SLO) technology for repeatable substrate reuse in gallium arsenide (GaAs)–based photovoltaics (PVs), offering a pathway toward cost effective production for terrestrial PV applications. Single-junction GaAs solar cells fabricated on acoustically spalled substrates achieved performance metrics comparable with those grown on standard commercial substrates, exhibiting short-circuit current densities (J sc ) of approximately 26.2–26.4 mA/cm 2 , open-circuit voltages (V oc ) around 1001 mV, fill factors (FFs) of 84%, and AM1.5G efficiencies near 22%. These results confirm that one reuse cycle can be realized without a performance penalty, offering a direct pathway to reducing substrate cost in fabrication. Furthermore, subsequent reuse of the substrates highlighted critical challenges, as devices fabricated from reused substrates showed significant degradation in performance (J sc of 15.5 mA/cm 2 , V oc of 748 mV, FF of 72%, and efficiency of 8%), primarily due to degradation of the epitaxial structure resulting from repeated spalling cycles.

Acoustic Spalling↗
DOE OSTI2019

Series Resistance Measurements of Perovskite Solar Cells Using J sc – V oc Measurements

The fill factor (FF) of perovskite solar cells is considerably lower than that of gallium arsenide and silicon cells, though they have similar open–circuit voltage deficits. To probe the FF loss, which mainly comes from series resistance, the J sc –V oc characterization technique is applied to perovskite solar cells. A continuous–lamp solar simulator with an array of neutral density filters is used instead of the quasi–steady–state photoconductance technique commonly employed for silicon cells, which allows us to tune sweep parameters to accommodate the complex behavior of perovskites such as hysteresis. It is found that, for Cs 0.25 FA 0.75 Pb(Br 0.2 I 0.8 ) 3 (CsFA) perovskite cells, sweeping from positive to negative voltage yields the same series resistance regardless of sweep speed, whereas this is not the case if the sweep is reversed. However, for CH 3 NH 3 PbI 3 perovskite cells, the series resistance is independent of the sweep speed in both sweep directions. Furthermore, it is also found that, for a poly[bis(4–phenyl)(2,4,6–trimethylphenyl)amine] (PTAA) hole contact, increasing the PTAA thickness barely changes the recombination–limited pseudo–FF, but reduces the FF due to increased series resistance. A maximum FF of 80.9% was achieved with the PTAA hole contact on a CsFA perovskite absorber.

14 SOLAR ENERGY↗
DOE OSTI2023

Spectral Effects on the Energy Harvesting Efficiency of Two- and Four-Terminal Tandem Photovoltaics

In this work, the effect of a varying spectral irradiance and top cell bandgap on the energy harvesting efficiency of two-terminal (2T) and four-terminal (4T) perovskite//silicon tandem solar cells under outdoor operating conditions is investigated. For the comparison, an optoelectronic model employing a 1 year outdoor data set for a 4T mechanical stacked gallium arsenide (GaAs) on crystalline silicon (Si) tandem device is first validated. Then, the verified model is used to simulate perovskite//silicon tandem devices with a varying perovskite top cell bandgap for a location in Golden, Colorado, USA. Here, a spectral binning method to efficiently reduce and improve the visualization of the 1 min-resolved environmental data while maintaining the simulation accuracy is introduced. The findings reveal that, for a device that is current matched under standard testing conditions, the annual spectral deviation reduces the energy harvesting efficiency by only 2% rel . When additional realistic losses for the 4T are taken into account, 2T devices are shown to have an energy-harvesting efficiency that is at parity or higher. Deviations in the top cell bandgap are more than 0.1 eV from current matching result in a reduced energy harvesting efficiency of more than 5% rel for the 2T tandem device.

14 SOLAR ENERGY↗
DOE OSTI2025

Synthesis, Structures, and Transport Properties of Quaternary Ba–Ag– Tr –As Materials ( Tr = Ga, In)

The synthesis, structures, and properties of two quaternary barium–arsenide materials are presented. The first, Ba 4 Ag 2.3 In 1.7 As 8 , is a novel material with the monoclinic unit cell ( P 2 1 / m space group). The layered crystal structure of Ba 4 Ag 2.3 In 1.7 As 8 may be considered a lower‐symmetry, distorted analog of the LaCuSb 2 structure. The structure features a rare As fragment, cis‐trans As chains along the [010] direction. Large crystals of Ba 4 Ag 2.3 In 1.7 As 8 can be grown from Bi flux and are used for subsequent transport property measurements. Electrical resistivity and heat capacity properties are reported, establishing Ba 4 Ag 2.3 In 1.7 As 8 as a metallic phase. The second material, Ba 4 AgGa 5 As 8 , is a 3D material that crystallizes in the orthorhombic unit cell (noncentrosymmetric and polar Iba 2 space group). Expanding upon its original discovery, the optimized synthetic profile for single‐phase polycrystalline samples as well as transport properties relevant to thermoelectric applications are presented. Ba 4 AgGa 5 As 8 exhibits a high Seebeck coefficient of 290 μV K −1 at room temperature, indicative of lower carrier concentrations typical for nonmetallic phases. Electrical resistivity measurements also affirm conventional semiconducting behavior for Ba 4 AgGa 5 As 8 .

Kyveryga, Victoria [Department of Chemistry Iowa S↗
DOE OSTI2017

Method for Accurate Determination of the Electron Contribution: Specific Heat of Ba 0.59 K 0.41 Fe 2 As 2

Twenty two years after the opening of the field of high temperature superconductivity by Georg Bednorz and Alex Müller a new addition to this class of materials, namely the iron-pnictides and chalcogenides, perplexes the scientific community. Making use of the accumulated wisdom, a great deal of their physics has been “mapped” in record time using all available measurement techniques. Among these, specific-heat has been proven a powerful and unique technique in the study of physical properties of bulk materials, especially of superconductors. We report here specific-heat measurements on the nearly optimally doped iconic iron-arsenide superconductor Ba 0.59 K 0.41 Fe 2 As 2 . We use a new method, based on direct comparisons of α-model expressions for the electron contribution with the measured total specific heat, to extract the electron contribution. It circumvents the need in the conventional analyses for an independent, necessarily approximate, determination of the lattice contribution, which is subtracted from the total to obtain the electron contribution, and it eliminates the consequent uncertainties in the electron contribution. For Ba 0.59 K 0.41 Fe 2 As 2 the electron density of states is comprised of contributions from two electron bands with superconducting-state energy gaps differing by a factor 3.8, with 77% coming from the band with the larger gap. The vortex-state specific heat suggests nodeless gaps. Comparison of the normal-state density of states with band-structure calculations shows an extraordinarily large effective mass enhancement, for which there is no precedent in simple metals and no theoretical explanation.

Conventional Analysis↗
DOE OSTI2017

Searching for dark absorption with direct detection experiments

We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB for silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. However, projected sensitivities of the upcoming SuperCDMS SNOLAB using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. We find similar results for dark photons from the sun. For all cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Assessing epitaxial regrowth material quality on a micro-transfer printed GaAs substrate

Micro-transfer printing has demonstrated value for device- and array-level heterogeneous integration in a variety of applications. In this report it is used instead to assemble unique substrates with the potential to enable III–V growth templates that are both low-cost and specified at any desired lattice parameter within the range of III–V materials. Critical to this, epitaxial growth crystal quality must be established as comparable to that produced on conventional epi-ready substrates. We demonstrate epitaxial regrowth on gallium arsenide membranes that were transfer printed from their source substrate and onto a target handle. Both morphology and luminescence properties were characterized. Comparing the transfer printed membrane epitaxy with epitaxy on a conventional substrate, we found recombination rates and spatial uniformity from power-dependent photoluminescence and cathodoluminescence, respectively, to yield similar results, suggesting material quality was not adversely limited by the engineered substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Crystal structure, electrical resistivity, and X-ray photoelectron spectroscopy of BaAg{sub 2}As{sub 2}

The ternary arsenide BaAg{sub 2}As{sub 2} has been prepared by reaction of the elements at 850 Degree-Sign C. Single-crystal and powder X-ray diffraction analysis revealed that it adopts the ThCr{sub 2}Si{sub 2}-type structure (Pearson symbol tI10, space group I4/mmm, Z=2, a=4.6025(3) A, c=10.8672(6) A at 295 K) featuring [Ag{sub 2}As{sub 2}] layers interconnected by homoatomic As-As bonds along the c-direction. Band structure calculations indicate no gap at the Fermi level, and support the occurrence of strong As-As and weak Ag-Ag bonding. The asymmetric lineshape and the absence of a BE shift in the Ag 3d{sub 5/2} core-line peak relative to the element suggest delocalization of the Ag valence electrons. A significant negative BE shift (1.0 eV) in the As 3d{sub 5/2} core-line peak relative to the element confirms the presence of anionic As atoms. A reversible transition is observed at 175 K in the electrical resistivity, and is probably related to a structural phase transition. - Graphical abstract: BaAg{sub 2}As{sub 2} adopts a ThCr{sub 2}Si{sub 2}-type structure with As-As pairs and undergoes a transition at 175 K in its electrical resistivity. Highlights: Black-Right-Pointing-Pointer BaAg{sub 2}As{sub 2} fills the gap within the BaM{sub 2}As{sub 2} series containing 4d metals. Black-Right-Pointing-Pointer [Ag{sub 2}As{sub 2}] layers are linked by As-As pairs. Black-Right-Pointing-Pointer XPS studies support the assignment of monovalent Ag and anionic As atoms. Black-Right-Pointing-Pointer An anomaly is observed at 175 K in the electrical resistivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Synthesis and structural characterization of the Zintl phases Na{sub 3}Ca{sub 3}TrPn{sub 4}, Na{sub 3}Sr{sub 3}TrPn{sub 4}, and Na{sub 3}Eu{sub 3}TrPn{sub 4} (Tr=Al, Ga, In; Pn=P, As, Sb)

15 new quaternary Zintl phases have been synthesized by solid-state reactions from the respective elements, and their structures have been determined by single-crystal X-ray diffraction. Na{sub 3}E{sub 3}TrPn{sub 4} (E=Ca, Sr, Eu; Tr=Al, Ga, In; Pn=P, As, Sb) crystallize in the hexagonal crystal system with the non-centrosymmetric space group P6{sub 3}mc (No. 186). The structure represents a variant of the K{sub 6}HgS{sub 4} structure type (Pearson index hP22) and features [TrPn{sub 4}]{sup 9–} tetrahedral units, surrounded by Na{sup +} and Ca{sup 2+}, Sr{sup 2+}, Eu{sup 2+} cations. The nominal formula rationalization [Na{sup +}]{sub 3}[E{sup 2+}]{sub 3}[TrPn{sub 4}]{sup 9–} follows the octet rule, suggesting closed-shell configurations for all atoms and intrinsic semiconducting behavior. However, structure refinements for several members hint at disorder and mixing of cations that potentially counteract the optimal valence electron count. - Graphical abstract: The hexagonal, non-centrosymmetric structure of Na{sub 3}E{sub 3}TrPn{sub 4} (E=Ca, Sr, Eu; Tr=Al, Ga, In; Pn=P, As, Sb) features [TrPn{sub 4}]{sup 9–} tetrahedral units, surrounded by Na{sup +} and Ca{sup 2+}, Sr{sup 2+}, Eu{sup 2+} cations. - Highlights: • 15 quaternary phosphides, arsenides, and antimonides are synthesized and structurally characterized. • The structure is a variant of the hexagonal K{sub 6}HgS{sub 4}-type, with distinctive pattern for the cations. • Occupational and/or positional disorder of yet unknown origin exists for some members of the series.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Underlying mechanism of structural transformation between GaSb and GaAs response to intense electronic excitation

Ion irradiation of semiconductors has emerged as a promising approach for fabricating self-organized nanosystems with high atomic precision, despite often being accompanied by undesirable phenomena. Exploring the mechanisms underlying structural transformations is crucial for assessing nanostructure array types under complex irradiation environments. By quantitatively calculating the thermodynamically driven processes and analyzing the impact of intrinsic structural parameters, distinct structural transformations in response to intense electronic excitation are systematically investigated in gallium antimonide (GaSb) and gallium arsenide (GaAs) systems. In high-energy regimes, the nanofibers layer of GaSb exhibits intriguing structural discrepancy, characterized by partial nanofibers with coherent boundaries, interspersed nanopores accompanied by antisite defects and Ga precipitates, distinguishing to a series of discontinuous latent tracks that emerged within cylindrical trajectories in GaAs. Furthermore, significant diffusion behaviors of the nanohillocks are discovered in GaAs, with higher average roughness than GaSb, driven by the gradient stress distribution influenced by the free-surface effects. The deposition energy for melting phase formation, Gibbs free energy, and Ga diffusion coefficients contribute to the distinctive structural features, evidencing relatively stable morphological configurations and higher irradiation resistance in GaAs. Consequently, special optoelectronic properties associated with structural discrepancies facilitate the design and optimization of material functionalities by irradiation technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Material-dependent photon ionizing radiation effects in Si and GaAs PIN diodes: A numerical investigation

We present a finite-element drift-diffusion-Poisson model in the Multiphysics Object-Oriented Simulation Environment (MOOSE) framework to compare the radiation response of silicon (Si) and gallium arsenide (GaAs) PIN diodes under high-energy photon irradiation. The model solves coupled carrier continuity and Poisson’s equations with Shockley-Read-Hall recombination, and is verified against standard analytical J-V behavior. Using a simplified 1D geometry with ideal Ohmic contacts, we quantify device response under forward and reverse bias with a 100 MeV photon flux. Under forward bias, Si exhibits markedly greater radiation sensitivity than GaAs, including larger increases in current density, stronger local field and carrier-product perturbations, and higher recombination. Under reverse bias, GaAs shows larger radiation-induced photocurrent and broader current-density peaks near junctions, indicating an advantage for photodetection. Integrated steady-state recombination is consistently higher in Si across voltages. Under periodic photon pulses, GaAs produces higher-amplitude photoresponse and settles more rapidly than Si. These results highlight material-dependent trade-offs for radiation-tolerant, high-speed optoelectronics and provide guidance for selecting PIN architectures in aerospace, nuclear, and high-energy physics environments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Modeling athermal phonons in novel materials using the G4CMP simulation toolkit

Understanding phonon and charge propagation in superconducting devices plays an important role in both performing low-threshold dark matter searches and limiting correlated errors in superconducting qubits. The Geant4 Condensed Matter Physics (G4CMP) package, originally developed for the Cryogenic Dark Matter Search (CDMS) experiment, models charge and phonon transport within silicon and germanium detectors and has been validated by experimental measurements of phonon caustics, mean charge-carrier drift velocities, and heat pulse propagation times. Here, in this work, we present a concise framework for expanding the capabilities for phonon transport to a number of other novel substrate materials of interest to the dark matter and quantum computing communities, including sapphire (Al 2 O 3 ), gallium arsenide (GaAs), lithium fluoride (LiF), calcium tungstate (CaWO 4 ), and calcium fluoride (CaF 2 ). We demonstrate the use of this framework in generating phonon transport properties of these materials and compare these properties with experimentally-determined values where available.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Measurement of optically-pumped electron spin polarization in n-GaAs at high external electric fields

We use the technique of time-resolved Kerr rotation (TRKR) to measure the electron spin polarization generated by optical spin pumping in an n-type gallium arsenide (GaAs) epilayer when an external electric field is simultaneously applied on the sample. The drift of the electron spins under the influence of the external electric field is captured with spatial scans of the pump–probe separation. A significant decay in the magnitude of electron spin polarization with electric field is observed and is attributed to the increased inhomogeneous broadening caused by the field-induced drift and the hot electron effects. Here, we extend the electric field range to as high as the Gunn threshold field in the measurement and we do not observe a spin amplification effect due to the spin Gunn effect under our experimental scheme.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Near-field transport imaging applied to photovoltaic materials

We developed and applied a new analytical technique - near-field transport imaging (NF-TI or simply TI) - to photovoltaic materials. Charge-carrier transport is an important factor in solar cell performance, and TI is an innovative approach that integrates a scanning electron microscope with a near-field scanning optical microscope, providing the possibility to study luminescence associated with recombination and transport with high spatial resolution. In this paper, we describe in detail the technical barriers we had to overcome to develop the technique for routine application and the data-fitting procedure used to calculate minority-carrier diffusion length values. The diffusion length measured by TI agrees well with the results calculated by time-resolved photoluminescence on well-controlled gallium arsenide (GaAs) thin-film samples. We report for the first time on measurements on thin-film cadmium telluride using this technique, including the determination of effective carrier diffusion length, as well as the first near-field imaging of the effect of a single localized defect on carrier transport and recombination in a GaAs heterostructure. Furthermore, by changing the scanning setup, we were able to demonstrate near-field cathodoluminescence (CL), and correlated the results with standard CL measurements. In conclusion, the TI technique shows great potential for mapping transport properties in solar cell materials with high spatial resolution.

14 SOLAR ENERGY↗
DOE OSTI2022

On the Effects of Aliovalent Substitutions in Thermoelectric Zintl Pnictides. Varied Polyanionic Dimensionality and Complex Structural Transformations–The Case of Sr 3 ZnP 3 vs Sr 3 Al x Zn 1– x P 3

The structures and the transport properties of a novel family of Zintl phosphides and arsenides with the formula AE 3 ZnPn 3 and the solid solutions AE 3 Al x Zn 1–x Pn 3 , AE 3 ZnAs y P 1–y (AE = Sr, Eu; Pn = P, As) are reported. Crystals of nine new phases have been obtained via Pb-flux reactions and used for structural work by means of single-crystal X-ray diffraction methods. The derived orthorhombic structure is without a direct analog, and features unusual structural units, where the Zn atoms are in both distorted tetrahedral and trigonal-planar coordination of pnictogens. Electronic structure calculations reveal moderately wide bandgaps for Sr 3 ZnP 3 and Sr 3 ZnAs 3 , on the order of 0.70 and 0.63 eV, respectively. Electrical transport measurements above room temperature indicate relatively high resistivity values above 500 K (ρ ≈ 4.8 Ω cm and above), but some of the samples exhibit very high Seebeck coefficients, as large as 300 μV/K at 560 K for Sr 3 ZnAs 3 . Aliovalent substitutions in AE 3 ZnPn 3 , achieved by the partial replacement of Zn 2+ with Al 3+ cations promote occupational and positional disorder, which causes structural transformation towards the disordered variant of the Sr 5 Al 2 Sb 6 structure type. Such substitutions also change the dimensionality of the polyanionic sub-lattice in the resulting quaternary AE 3 Al x Zn 1–x Pn 3 phases. Furthermore, preliminary transport property data on the latter reveal nine times lower electrical resistivity (ρ 500 ≈ 0.5 Ω cm) together with a significantly enhanced Seebeck coefficient, αmax ≈ 430 μV/K at 560 K.

36 MATERIALS SCIENCE↗