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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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41 records · Page 3

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NASA NTRS2012

High Operating Temperature Midwave Quantum Dot Barrier Infrared Detector (QD-BIRD)

The nBn or XBn barrier infrared detector has the advantage of reduced dark current resulting from suppressed Shockley-Read-Hall (SRH) recombination and surface leakage. High performance detectors and focal plane arrays (FPAs) based on InAsSb absorber lattice matched to GaSb substrate, with a matching AlAsSb unipolar electron barrier, have been demonstrated. The band gap of lattice-matched InAsSb yields a detector cutoff wavelength of approximately 4.2 ??m when operating at ~150K. We report results on extending the cutoff wavelength of midwave barrier infrared detectors by incorporating self-assembled InSb quantum dots into the active area of the detector. Using this approach, we were able to extend the detector cutoff wavelength to ~6 ?m, allowing the coverage of the full midwave infrared (MWIR) transmission window. The quantum dot barrier infrared detector (QD-BIRD) shows infrared response at temperatures up to 225 K.

quantum dot↗

NASA NTRS2015

Superlattice Infrared Photodetector Research at the Jet Propulsion Laboratory

III-V semiconductors offer a highly effective platform for the development of sophisticated heterostructure-based MWIR and LWIR detectors, as exemplified by the high-performance double heterostructure (DH) nBn, XBn, and type- II superlattice infrared detectors. A key enabling design element is the unipolar barrier, which is used to implement the complementary barrier infra-red detector (CBIRD) design for increasing the collection efficiency of photo-generated carriers, and reducing dark current generation without impeding photocurrent flow. Heterostructure superlattice detectors that make effective use of unipolar barriers have demonstrated strong reduction of generation-recombination (G-R) dark current due to Shockley-Read-Hall (SRH) processes. In the last several years we solely focused on the development of antimonide based IR detectors. Recently, we demonstrated RoA values over 14,000 Ohm sq cm for a 9.9 micron cutoff device by incorporating electron-blocking and hole-blocking unipolar barriers. This device has shown 300K BLIP operation with f/2 optics at 87 K with blackbody D* of 1.1x10(exp 11) cm Hz1/2/W.

focal planes↗

NASA NTRSDate not supplied

Comparing 3D and 2D CFD for Mars Helicopter Ingenuity Rotor Performance Prediction

Single and coaxial rotor performance simulations for the Mars Helicopter Ingenuity rotor are performed for representative Mars atmospheric conditions. Analyses are presented using both a high-fidelity 3D CFD model of the rotor and 2D CFD models of the airfoil sections for comprehensive analyses that use CAMRADII (Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics). When available, the airfoil performance calculations are generated using a numerical approach identical to that used in the high-fidelity 3D model, allowing for a direct comparison between the approaches. Experimental data from a validation campaign to explore higher thrust from an Ingenuity rotor is provided to substantiate a discussion on the simulation fidelity required for both coaxial and single rotor performance predictions. The data is in support of the Sample Recovery Helicopter (SRH) element that serves as the primary backup for tube retrieval as part of the Mars Sample Return (MSR) Campaign. Insights on modeling turbulence at low Reynolds numbers and its influence on the rotor figure of merit are discussed. Key rotor performance metrics are compared. A detailed investigation into differences between 2D and 3D rotor performance predictions, spanwise loading, and rotor stall behavior is included.

Mars Helicopter↗

DOE OSTI2024

Coupled Process/Device Modeling and Point Defect Engineering of Cu(In,Ga)Se 2 Solar Cells

Point defects directly impact solar cell device performance by limiting the carrier lifetime. In this work, density functional theory calculations are first used to determine the formation energy and diffusion energy barriers of dominant defects in Cu(In,Ga)Se 2 . Next, continuum reaction–diffusion models are developed to analyze the redistribution of defects during manufacturing processes. We estimate defect capture cross sections using a first-principles-based approach. Here, these cross sections are combined with our calculated defect profiles and trap energy levels to parameterize a Shockley–Read–Hall recombination model, which we implement into a device simulator to predict carrier lifetimes and device performance. In that way, a predictive technology computer aided design model is built to predict and optimize the performance of Cu(In,Ga)Se 2 solar cells.

14 SOLAR ENERGY↗

DOE OSTI2020

Field Effect in CdSeTe/CdTe Solar Cells with Biased Spectroscopy

Steady-state and time-resolved photoluminescence measurements were performed under external electrical bias on thin polycrystalline CdSeTe/CdTe solar cells. The results indicate that internal field effects which can go unnoticed during traditional, unbiased spectroscopy measurements may be more consequential than generally realized. In addition, probing the field behavior with bias may allow investigation of defect states and the determination of transport characteristics, such as mobility.

14 SOLAR ENERGY↗