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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Eutectic Processing of Semiconductor Colloidal Nanocrystals for Energy Applications

Colloidal semiconductor nanocrystals (NCs) offer a costeffective platform for light-energy conversion in X-ray scintillators, photovoltaics, lasers, and display technologies. Yet, device-relevant NCs often require complex heterostructured compositions, where lattice imperfections compromise the efficiency and stability of photoconversion processes. Here, we show that a simple synthetic detour through a eutectic state of II−VI semiconductor NCs (e.g., CdSe, ZnSe) with halide salts (e.g., CdCl 2 , ZnCl 2 ) overcomes this limitation by melting and reconstructing NC lattices into defect-free alloyed and core/shell architectures. Applied to ternary CdSeTe NCs, this process produces downconverters with record brightness and minimal line widths, delivering a 3-fold increase in film-side external quantum efficiency of commercial CdTe photovoltaic modules (First Solar Inc.). Meanwhile, eutectic processing of CdSe-based core/shell emitters yields an 8-fold enhancement in their photoluminescence stability under backlight operation, addressing the reliability bottleneck for display technologies. Together, these findings establish eutectic NC processing as a scalable route to efficient, durable photoconversion materials for energy applications.

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

Microfabricated Ion Traps on Sapphire for Larger Trap Areas and Higher Qubit Count

Surface ion traps are a promising platform for quantum computing due to their potential to store large numbers of ions that can be addressed by electrical and optical control signals in order to implement quantum algorithms. Increasing the power of the quantum computer requires increasing the number of ions, but this poses a significant challenge in that it leads to a non-linear increase in on-chip power dissipation. The primary contributor to this power scaling in current devices is the capacitance between the radio frequency (RF) electrode and the metal plane that shields the silicon substrate from the RF signals applied to it. Silicon has traditionally been chosen for the substrate material for compatibility with the processing required for multi-metal-level traps. In this work, we address these capacitance and fabrication challenges by replacing the commonly used silicon substrate with an insulating sapphire substrate to fabricate a multi-metal-level ion trap, while still employing common semiconductor manufacturing techniques. This change in substrate allows the design to remove the metal shielding from the device design, reducing the capacitance of the RF electrode. The electrical characteristics of these traps were measured, specifically trap impedance, capacitance, and voltage breakdown, and compared to nearly identical silicon trap devices. Finally, we used laser cutting techniques to shape a sapphire wafer into bowtie shapes matching silicon traps previously fabricated at Sandia National Labs to explore solutions for integrating sapphire substrates into non-rectangular ion trap designs.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Ultranarrow electroluminescence from magnetic excitons in the van der Waals antiferromagnetic semiconductor NiPS 3

Electrically driven light emission from two-dimensional (2D) semiconducting materials has enabled numerous optoelectronic technologies, including light-emitting diodes, solid-state lasers, and single-photon sources for quantum communication. Here we report ultranarrow electroluminescence from the magnetic excitonic state of the van der Waals antiferromagnetic semiconductor NiPS 3 . This electroluminescence is enabled by the fabrication of gate-tunable NiPS 3 devices that remain electrically conductive below the antiferromagnetic ordering temperature of 155 K, ultimately allowing field-effect mobilities of 1.3 cm 2 V –1 s –1 and 4.5 cm 2 V –1 s –1 to be directly measured at room temperature and 7 K, respectively. By applying a high-frequency square wave voltage to the gate electrode of the resulting field-effect transistors, electroluminescence is capacitively induced from the magnetic excitons of NiPS 3 . Due to the coupling of these excitons with the underlying NiPS 3 antiferromagnetic order, the electroluminescence has an ultranarrow linewidth of 1 meV and a high degree of linear polarization (ρ = 0.78). In addition to facilitating fundamental studies of the coupling between spin states and excitons in van der Waals magnetic semiconductors, this work will accelerate the development of emerging 2D opto-spintronic applications.

two-dimensional materials↗
DOE OSTI2025

Magnetic Switching in Monolayer 2D Diluted Magnetic Semiconductors via Spin‐to‐Spin Conversion

Abstract The integration of 2D van der Waals (vdW) magnets with topological insulators or heavy metals holds great potential for realizing next‐generation spintronic memory devices. However, achieving high‐efficiency spin–orbit torque (SOT) switching of monolayer vdW magnets at room temperature poses a significant challenge, particularly without an external magnetic field. Here, it is shown field‐free, deterministic, and nonvolatile SOT switching of perpendicular magnetization in the monolayer, diluted magnetic semiconductor (DMS), Fe‐doped MoS 2 (Fe:MoS 2 ) at up to 380 K with a current density of ≈7 × 10 4 A cm −2 . The in situ doping of Fe into monolayer MoS 2 via chemical vapor deposition and the geometry‐induced strain in the crystal break the rotational switching symmetry in Fe:MoS 2 , promoting field‐free SOT switching by generating out‐of‐plane spins via spin‐to‐spin conversion. An apparent anomalous Hall effect (AHE) loop shift at a zero in‐plane magnetic field verifies the existence of z spins in Fe:MoS 2 , inducing an antidamping‐like torque that facilitates field‐free SOT switching. This field‐free SOT application using a 2D ferromagnetic monolayer provides a new pathway for developing highly power‐efficient spintronic memory devices.

Chen, Siwei [Department of Mechanical Engineering ↗
DOE OSTI2026

Magnetic Response of Excitons and Excitonic Complexes in Defective Hexyl Ammonium Lead Iodide Self-Assembled Quantum Wells

Correlating the magnetic behavior of low-dimensional semiconductors with the chemistry used to form these excitonic materials remains crucial to the development of devices applied to quantum technologies. In this study, we apply large magnetic fields during the collection of low-temperature photoluminescence (PL) to assess the magnetic properties of excitons in hexyl ammonium lead iodide (HA 2 PbI 4 ) self-assembled quantum wells (SAQWs) formed at liquid−liquid interfaces. The effect of incident laser power and temperature was used to assign lower energy features in these samples’ PL spectra to both excitons trapped at defect sites and trions. Measured peaks shifts allow us to estimate coupling between the applied magnetic fields and the charged defect excitons. Our conclusions are supported by density functional theory calculations on supercells of the proposed defective HA 2 PbI 4 SAQW structure. Additionally, we find an anomalous magnetic response from trion states that resembles the behavior of interacting excitonic complexes in similar, quantum-confined materials at low temperatures. These results highlight the crucial role that chemical conditions can play in the magnetic response of 2D semiconductors applied in quantum technologies.

defect chemistry↗
DOE OSTI2025

Perspectives of active Si photonics devices for data communication and optical sensing

Si photonics has made rapid progress in research and commercialization in the past two decades. While it started with electronic–photonic integration on Si to overcome the interconnect bottleneck in data communications, Si photonics has now greatly expanded into optical sensing, light detection and ranging (LiDAR), optical computing, and microwave/RF photonics applications. From an applied physics point of view, this perspective discusses novel materials and integration schemes of active Si photonics devices for a broad range of applications in data communications, spectrally extended complementary metal–oxide–semiconductor (CMOS) image sensing, as well as 3D imaging for LiDAR systems. We also present a brief outlook of future synergy between Si photonic integrated circuits and Si CMOS image sensors toward ultrahigh capacity optical I/O, ultrafast imaging systems, and ultrahigh sensitivity lab-on-chip molecular biosensing.

electronic band structure↗
DOE OSTI2026

Nickel Interlayer for Improved Silver Complex Inks Metallization in GaAs Photovoltaic Devices

Large areas of III-V photovoltaic panels are essential to supplying operational energy for a growing demand of satellites of strategic importance to the United States military, covering a range of applications. High fabrication costs and low manufacturing throughput are key barriers to meeting the necessary supply, which can in turn jeopardize mission success. At the device level, metallization based on printing of complex metal inks has attracted significant research interest due to its potential to substantially reduce processing costs and increase throughput while achieving electrical performance comparable to those of conventional metallization schemes. For GaAs photovoltaic devices, however, reliable electrical contacting remains challenging due to the formation of an interfacial oxide layer at the metal-semiconductor interface. This oxide barrier severely limits current extraction from the PV absorber, resulting in unacceptably high contact resistance. In this study, we report the introduction of a reactive nickel (Ni) interfacial layer between the silver metal fingers and the GaAs substrate to suppress oxide formation while maintaining a low-resistance electrical interface, and show performance data from fully fabricated GaAs devices incorporating the Ni interlayer. These results demonstrate the potential of reactive Ni ink as an effective interfacial layer for improved electrical contacting in low-cost PV metallization schemes.

14 SOLAR ENERGY↗
DOE OSTI2024

Three dimensional vertically structured electronic devices

An apparatus includes at least one vertical transistor, where the at least one vertical transistor includes: a substrate including a first semiconductor material, an array of three dimensional (3D) structures above the substrate, a sidewall heterojunction layer positioned on at least one vertical sidewall of each 3D structure, and an isolation region positioned between the 3D structures. Each 3D structure includes the first semiconductor material. The sidewall heterojunction layer includes a second semiconductor material, where the first and second semiconductor material have different bandgaps.

Conway, Adam↗
DOE OSTI2025

Gallium oxide (Ga2O3) as a radiation detector distinguishing neutrons and gammas

Gallium oxide (Ga2O3) is a promising ultrawide bandgap semiconductor for radiation detection with the potential of integrating electronic and scintillation functions within a single crystal device. This study establishes the scintillation response of β-Ga2O3 gamma irradiation from yttrium-88 (88Y). Then, californium-252 (252Cf) is used as a spontaneous fission source of mixed neutron and gamma radiation field to measure scintillation signals. Pulse shape discrimination and constant fraction discrimination techniques were used to separate neutron and gamma interaction events. Further investigation indicates that the prompt temporal responses of β-Ga2O3 for gammas and neutrons may enable discrimination of the two by prompt pulse fitting methods, focused around the initial peak. For gamma irradiation, we observed a rise time (τr) of 2.1 ns, decay time (τd) of 9.5 ns, and a full width at half maximum (FWHM) of 6.2 ns. For neutrons, it showed a τr of 2.3 ns, a τd of 12.1 ns, 9.4 ns FWHM, and reduced peak intensity. A diamond detector exhibited a more symmetrical τr and τd for both gamma and neutron signals and therefore is less effective at discriminating between the two by this method. This draws attention to β-Ga2O3’s ability to distinguish neutron and gamma particles. These findings showcase Ga2O3’s potential as a next-generation semiconductor for applications in nuclear safety and medical imaging, where precise discrimination between neutron and gamma interactions is essential.

Valdes, D. J. (ORCID:0000000304373720)↗
DOE OSTI2026

Finite-element-based simulations of electrodes for CO 2 cascade reduction reactions

The multielectron reduction of CO 2 to liquid fuels could be a path to scalable energy storage, but reaching this goal requires major advances in catalysis and systems engineering. Cascade catalysis, which couples sequential reactions without isolating intermediates, has emerged as a promising route to enhance selectivity and efficiency in CO 2 reduction (CO 2 R). In this review, we examine how finite-element-based simulations of continuum model [finite element method (FEM)] approaches are being used to analyze and guide CO 2 R cascade systems. We first outline the fundamentals of cascade catalysis and recent advances in catalytic materials (metallic, molecular, and hybrid architectures). We then focus on FEM developments at the electrode and device scales, emphasizing how these models capture transport phenomena, local microenvironments, and geometry-dependent effects. To clarify design principles, we present case studies of cascade electrodes organized in systems without and with integrated semiconductors. We further emphasize the integration of FEM with multiscale frameworks (density functional theory, molecular dynamics, kinetic Monte Carlo) and its role in bridging atomic-level insights with device-level performance. Finally, we identify current limitations and future prospects, including improved boundary conditions, coupling with operando experiments, and machine learning-accelerated model development. Together, these insights provide design principles for next-generation CO 2 R cascade systems for efficient solar fuel production.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Photovoltage behaviour of p-Sb 2 S 3 photocathodes for hydrogen evolution: effect of n-In 2 S 3 passivation layers

The 1.76 eV band gap of antimony(iii) sulphide (Sb 2 S 3 ) makes this semiconductor material a promising light absorber for photoelectrochemical water splitting, but scalable fabrication approaches to efficient devices are still lacking. Here we show that compact Sb 2 S 3 films on FTO can be obtained by electrochemical growth from aqueous colloidal sulphur and antimony trichloride solutions, followed by mild annealing. These films can be converted into hydrogen evolution photocathodes after coating with In 2 S 3 passivation layers and the addition of Pt proton reduction co-catalysts. For the first time, vibrating Kelvin probe surface photovoltage (VKP-SPV) spectroscopy is used to observe the carrier dynamics in such photoelectrodes. While the bare Sb 2 S 3 films suffer from high surface recombination rates and poor electron extraction, the In 2 S 3 overlayer is found to raise the photovoltage and cathodic photocurrent density, due to passivation of surface defects and formation of a p–n heterojunction. In thick In 2 S 3 films, these benefits are offset by shading and slow electron transfer. Also, we find that O 2 strongly affects the band bending in the Sb 2 S 3 –air and In 2 S 3 –air junctions and their photovoltage. The optimised devices evolve H 2 at 77.5% Faradaic efficiency and with 0.084% applied bias photon-to-current efficiency (ABPE) at 0.12 V vs. RHE. The low ABPE value is attributed to Sb 2 S 3 sub-bandgap defects visible in SPV spectra, the random orientation of Sb 2 S 3 crystallites in the films, which inhibits charge transport, the absence of crystal facets of Sb 2 S 3 , and a detrimental Schottky junction at the FTO|Sb 2 S 3 interface.

de Araújo, Moisés A. [University of California, Da↗
DOE OSTI2026

World’s First Vertical GaN based High Power (200 kW) Multi-level Traction Electric Drive Design

Vertical GaN (vGaN) technology leverages a fully conductive 3D semiconductor structure, enabling superior power density compared to GaN-on-Si and other wide bandgap devices. It offers a pathway to surpass cost and efficiency limitations of Si and SiC devices in traction applications. However, scaling for high-voltage, high-power systems remains challenging. This paper presents the design of an 800V, 200kW traction inverter utilizing vertical GaN devices. The inverter achieves ultra-high efficiency (> 99.5%) through advanced power module integration and employs multilevel neutral-point-less X-type (NPL.X) inverter topology to ensure optimal traction drive system performance. These innovations demonstrate the potential of vGaN for next￾generation electric propulsion systems.

Alam, Khorshed [General Motors LLC, Detroit, MI (U↗
DOE OSTI2024

Advances in Molecular Beam Epitaxy Growth of Ultra-Wide Bandgap Ga2O3 Based Alloys

Gallium oxide (Ga2O3) is an emerging ultra-wide bandgap semiconductor material that has attracted attention for its potential to outperform existing SiC and GaN based devices operating at high breakdown voltages and high temperature. Isovalent alloying of In and Al in Ga2O3 provides the ability to engineer bandgap energy and strain of the material. Alloying with Al increases the bandgap energy and the theoretically achievable Baliga's figure of merit, a key measure of a material's ultimate performance limits for high power switching devices. Alloying with In introduces compressive strain and can be used to counteract the tensile strain of Al incorporation. The resulting (AlxGa1-x-yIny)2O3 alloy can be lattice-matched to commercially available Ga2O3 wafers and has a tunable bandgap energy greater than that of Ga2O3, 4.76 eV. Such lattice-matched material can be grown arbitrarily thick without the detrimental effects of elastic strain and relaxation, making it suitable for high voltage diodes and transistors. However, efforts to synthesize isovalent alloys are complicated by their tendency to phase separate into corundum Al2O3 or bixbyite In2O3. Literature reports of the quaternary (AlxGa1-x-yIny)2O3 are limited to <1% unintentional indium incorporation in In-catalyzed (AlxGa1-x)2O3. The primary limitation to quaternary growth is the limited incorporation of indium at elevated growth temperatures. This limited incorporation is due to both the volatility of indium oxide and Al and Ga cation exchange reactions which replace indium in In2O3. We report on the development of a novel high-throughput molecular beam epitaxy (MBE) technique to screen the growth conditions for the ternary alloy (InyGa1-y)2O3, and the application of these findings to the first successful synthesis of phase pure monoclinic (AlxGa1-x-yIny)2O3 by MBE. By leveraging the unique sub-oxide chemistry of Ga2O3 and in-situ monitoring of crystal properties by reflection high-energy electron diffraction (RHEED), a cyclical growth and etch-back method is developed and applied to rapidly characterize the (InyGa1-y)2O3 growth space. This cyclical method provides approximately 10x increase in experimental throughput and up to 46x improvement in Ga2O3 substrate utilization. Appropriate growth conditions for monoclinic (InyGa1- y)2O3 are identified by machine learning analysis of RHEED patterns and targeted growths are characterized ex-situ to confirm improved In incorporation. These growth conditions are then combined with established (AlxGa1-x)2O3 growth conditions to grow quaternary (AlxGa1-x-yIny)2O3 with Al mole fractions ranging from 1.4% - 24.4% and In mole fractions ranging from 3.1% to 15.5%. The chemical and optical properties of the alloys are investigated by XRD, XPS, and spectroscopic ellipsometry. A lattice-matched (AlxGa1-x-yIny)2O3 alloy is examined by 4D-STEM and the chemical and physical uniformity of Al and In incorporation are discussed.

alloy↗
DOE OSTI2025

MnSi 2 Te 4 : A van der Waals Antiferromagnetic Semiconductor with Large Negative Magnetoresistance

Magnetism in van der Waals semiconductors offers significant potential for fundamental research on low-dimensional magnetism and the development of high-performance two-dimensional spintronic devices. Here, we report the growth, physical properties, and first-principles calculations of a new dual-octahedral transition metal chalcogenide (DTMC) MnSi 2 Te 4 . MnSi 2 Te 4 features a layered structure with an intralayer heterostructure, where the metal octahedra and nonmetal dimeric octahedra form zigzag chains alternately. Property characterization reveals that MnSi 2 Te 4 is a collinear G-type antiferromagnetic semiconductor, with a Néel temperature T N of 18.6 K and a significant unsaturated negative magnetoresistance (NMR) reaching −42.5% at 9 T and 100 K. First-principles calculations on the electronic band structure demonstrate that the large NMR primarily originates from the spin splitting due to parity-time symmetry breaking. This study not only discovers a new member of DTMCs with a unique crystal structure and large NMR, but also establishes a promising platform for investigating next-generation spintronic devices.

Liao, Ke [Chinese Academy of Sciences (CAS), Beiji↗
DOE OSTI2024

A Bottom-Up Approach to Rational Design of Crystalline Materials: Investigation of Vibronic Coherences Underlying Exciton Dynamics in Semiconductors

In this project we uncovered structure-function relationships of donor-acceptor co-crystals used to develop next-generation optoelectronic devices. Unraveling the photodynamics of molecular crystalline materials poses many challenges for spectroscopy due to broad, overlapping features representing numerous underlying dynamical processes. This leads researchers to make many assumptions about the dynamics of a system in choosing an appropriate kinetic fitting model. Computationally, electronic structure methods are either prohibitively expensive or underdeveloped for computing the excited state structure of molecular materials, especially states that exhibit charge transfer. Researchers must therefore perform calculations of excited electronic states using truncated models of molecular materials. Here we present a joint experimental-theoretical approach to bridging the gap between the photodynamics of a molecular material and its constituent molecules. We focus our efforts on quantifying the timescales and mechanisms of photoexcitation in donor-acceptor co-crystals and donor-acceptor dimers where the lowest-lying excited state is characterized by charge transfer from the donor to the acceptor. We employ ultrafast UV pump, UV-Vis probe transient absorption spectroscopy to unravel the time-resolved spectroscopic signatures of the photodynamics in both the crystalline material and donor-acceptor dimers in solution. We perform electronic structure and excited state dynamics calculations of the dimers to inform kinetic fitting models and assign the spectral features. The photodynamics of the crystal vs. dimer systems have many similarities, enabling unprecedented insights into the formation and evolution of charge transfer excitons in the crystalline systems.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Epitaxial Growth of Ga2O3: A Review

Beta-phase gallium oxide (β-Ga2O3) is a cutting-edge ultrawide bandgap (UWBG) semiconductor, featuring a bandgap energy of around 4.8 eV and a highly critical electric field strength of about 8 MV/cm. These properties make it highly suitable for next-generation power electronics and deep ultraviolet optoelectronics. Key advantages of β-Ga2O3 include the availability of large-size single-crystal bulk native substrates produced from melt and the precise control of n-type doping during both bulk growth and thin-film epitaxy. A comprehensive understanding of the fundamental growth processes, control parameters, and underlying mechanisms is essential to enable scalable manufacturing of high-performance epitaxial structures. This review highlights recent advancements in the epitaxial growth of β-Ga2O3 through various techniques, including Molecular Beam Epitaxy (MBE), Metal-Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Epitaxy (HVPE), Mist Chemical Vapor Deposition (Mist CVD), Pulsed Laser Deposition (PLD), and Low-Pressure Chemical Vapor Deposition (LPCVD). This review concentrates on the progress of Ga2O3 growth in achieving high growth rates, low defect densities, excellent crystalline quality, and high carrier mobilities through different approaches. It aims to advance the development of device-grade epitaxial Ga2O3 thin films and serves as a crucial resource for researchers and engineers focused on UWBG semiconductors and the future of power electronics.

Chemistry↗
DOE OSTI2025

Coherent Spins in van der Waals Semiconductor GeS 2 at Ambient Conditions

Optically active spin defects in van der Waals (vdW) materials have emerged as versatile quantum sensors, enabling applications for a wide range of quantum phenomena in condensed matter systems. Their ease of exfoliation and compatibility with device integration make them promising candidates for future quantum technologies. Here we report the observation and room-temperature coherent control of ensemble spin defects in the high-temperature crystalline phase of germanium disulfide (β-GeS 2 ), a two-dimensional (2D) semiconductor with low nuclear spin density. The defects exhibit spin-1/2 behavior, and their dynamics can be explained by a weakly coupled spin-pair model. We implement dynamical decoupling techniques to extend the coherence time (T 2 ) by a factor of 20. Finally, we use density functional theory (DFT) calculations to estimate the structures and spin densities of two possible spin defect candidates. This work will help to expand the field of quantum sensing with spin defects in 2D materials.

2D materials↗