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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1966

Piezoelectroreflectance in GaAs.

Static uniaxial compression effect measurement along /100/, /110/ and /111/ on electroreflectance spectrum of gallium arsenide, using electrolyte technique

PIEZOELECTRICITY↗
DOE OSTI2012

Anisotropic Energy Gaps of Iron-Based Superconductivity from Intraband Quasiparticle Interference in LiFeAs

If strong electron-electron interactions between neighboring Fe atoms mediate the Cooper pairing in iron-pnictide superconductors, then specific and distinct anisotropic superconducting energy gaps {Delta}{sub i}(k) should appear on the different electronic bands i. Here, we introduce intraband Bogoliubov quasiparticle scattering interference (QPI) techniques for determination of {Delta}{sub i}(k) in such materials, focusing on lithium iron arsenide (LiFeAs). We identify the three hole-like bands assigned previously as {gamma}, {alpha}{sub 2}, and {alpha}{sub 1}, and we determine the anisotropy, magnitude, and relative orientations of their {Delta}{sub i}(k). These measurements will advance quantitative theoretical analysis of the mechanism of Cooper pairing in iron-based superconductivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Fast Near-Infrared Photodetection Using III–V Colloidal Quantum Dots

Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II–VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III–Vs—if their surface chemistry can be mastered—offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm 2 V -1 s -1 ) with a 4× reduction in permittivity compared to PbS CQDs. Finally, the resulting photodiodes achieve a response time faster than 2 ns—the fastest photodiode among previously reported CQD photodiodes—combined with an external quantum efficiency (EQE) of 30% at 940 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2022

From Salt to Electronics: Heteroepitaxy and GaAs Solar Cells

This paper presents work on the heteroepitaxy of salts, specifically fluorides, on semiconductor and heteroepitaxy of semiconductor on salts. Fluorides layers are deposited on commercial Gallium Arsenide (GaAs) wafers followed by the heteroepitaxial growth of GaAs using metal organic chemical vapor deposition (MOCVD). The fluoride layers consist of 2 lattice-engineered layers of alkaline-earth compounds to match with GaAs, and are used to sandwich another alkaline-earth compound with higher water-solubility as sacrificial layer. The triple fluoride layers enable liftoff of free-standing semiconductor films which can be further transferred to desirable substrates. 2D-X-ray Diffraction (2D-XRD) measurements confirm epitaxial growth of both the fluorides and the subsequently grown GaAs films. Single junction (SJ) solar cell devices based on thus prepared films show a power conversion efficiency (PCE) of 10.3% under 1 sun illumination. After the completion of device fabrications, the GaAs film is lifted off from the substrate by a novel water-assisted epitaxial liftoff (H 2 O-ELO) technique and transferred to a cheaper substrate. The original GaAs wafer is recycled and reused twice. Devices based on reused substrates show no significant degradation in performance. Lastly, the semiconductor-salt-semiconductor scheme has great implications in high performance, flexible, and large area electronics.

14 SOLAR ENERGY↗
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.↗