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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

High-efficiency broad-area single-quantum-well lasers with narrow single-lobed far-field patterns prepared by molecular beam epitaxy

Broad-area single-quantum-well graded-index waveguide separate-confinement heterostructure lasers were fabricated by molecular beam epitaxy. A high external quantum efficiency of 79 percent and stable, single-lobed far-field patterns with a beam divergence as narrow as 0.8 deg (1.9 times diffraction limit) for a 100 micron-wide laser were obtained under pulsed conditions.

Larsson, A.↗
NASA NTRS1990

Photovoltaic characteristics of n(+)pp(+) InP solar cells grown by OMVPE

The photovoltaic characteristics of n(+)/p/p(+) homojunction InP solar cells fabricated by organometallic vapor-phase epitaxy (OMVPE) are described. The cells are characterized by I-V, C-V and quantum efficiency measurements, and simulations are used to obtain various device and material parameters. The I-V characteristics show a high recombination rate in the depletion region; this is shown to be independent of the impurity used. It is shown that cadmium is easier to use as an acceptor for the p base and p(+) buffer and is therefore beneficial. The high quantum efficiency of 98 percent at long wavelengths measured in these cells indicates a very good collection efficiency in the base. The short-wavelength quantum efficiency is poor, indicating a high surface recombination.

Tyagi, S.↗
NASA NTRS2017

Unipolar Barrier Dual-Band Infrared Detectors

Dual-band barrier infrared detectors having structures configured to reduce spectral crosstalk between spectral bands and/or enhance quantum efficiency, and methods of their manufacture are provided. In particular, dual-band device structures are provided for constructing high-performance barrier infrared detectors having reduced crosstalk and/or enhance quantum efficiency using novel multi-segmented absorber regions. The novel absorber regions may comprise both p-type and n-type absorber sections. Utilizing such multi-segmented absorbers it is possible to construct any suitable barrier infrared detector having reduced crosstalk, including npBPN, nBPN, pBPN, npBN, npBP, pBN and nBP structures. The pBPN and pBN detector structures have high quantum efficiency and suppresses dark current, but has a smaller etch depth than conventional detectors and does not require a thick bottom contact layer.

Ting, David Z.↗
NASA NTRS1996

Diffusion lengths in irradiated N/P InP-on-Si solar cells

Indium phosphide (InP) solar cells were made on silicon (Si) wafers (InP/Si) by to take advantage of both the radiation-hardness properties of the InP solar cell and the light weight and low cost of Si wafers. The InP/Si cell application is for long duration and/or high radiation orbit space missions. Spire has made N/P InP/Si cells of sizes up to 2 cm by 4 cm with beginning-of-life (BOL) AM0 efficiencies over 13% (one-sun, 28C). These InP/Si cells have higher absolute efficiency and power density after a high radiation dose than gallium arsenide (GaAs) or silicon (Si) solar cells after a fluence of about 2e15 1 MeV electrons/sq. cm. In this work, we investigate the minority carrier (electron) base diffusion lengths in the N/P InP/Si cells. A quantum efficiency model was constructed for a 12% BOL AM0 N/P InP/Si cell which agreed well with the absolutely measured quantum efficiency and the sun-simulator measured AM0 photocurrent (30.1 mA/sq. cm). This model was then used to generate a table of AM0 photocurrents for a range of base diffusion lengths. AM0 photocurrents were then measured for irradiations up to 7.7e16 1 MeV electrons/sq. cm (the 12% BOL cell was 8% after the final irradiation). By comparing the measured photocurrents with the predicted photocurrents, base diffusion lengths were assigned at each fluence level. A damage coefficient K of 4e-8 and a starting (unirradiated) base electron diffusion length of 0.8 microns fits the data well. The quantum efficiency was measured again at the end of the experiment to verify that the photocurrent predicted by the model (25.5 mA/sq. cm) agreed with the simulator-measured photocurrent after irradiation (25.7 mA/sq. cm).

Wojtczuk, Steven↗
NASA NTRS1989

InSb DRO array characteristics

Researchers tested 58 x 62 low-doped InSb diode arrays bonded to MOSFET readouts for their performance potential in a low background space environment. Of primary concern were the quantum efficiency, dark current and read noise. The quantum efficiency (45 percent at 3.3 microns) and dark current (less than 2.4e(-)/s) were found to be adequate for the Space Infrared Telescope Facility (SIRTF) experiments, while the read noise (200 e(-) RMS) was found to be wanting. More subtle concerns, such as image quality, linearity/calibratibility and flat fielding were also investigated. In these respects the arrays appear to be well suited for the high sensitivity, photometric accuracy, and image clarity demanded by the SIRTF experiments.

Forrest, W. J.↗
NASA NTRS1989

Improved Si:As BIBIB (Back-Illuminated Blocked-Impurity-Band) hybrid arrays

Results of a program to increase the short wavelength (less than 10 microns) detective quantum efficiency, eta/beta, of Si:As Impurity Band Conduction arrays are presented. The arrays are epitaxially grown Back-Illuminated Blocked (BIB) Impurity-Band (BIBIB) 10x50 detectors bonded to switched-FET multiplexers. It is shown that the 4.7 microns detective quantum efficiency increases proportionately with the thickness of the infrared active layer. A BIB array with a thick active layer, designed for low dark current, exhibits eta/beta = 7 to 9 percent at 4.7 microns for applied bias voltages between 3 and 5 V. The product of quantum efficiency and photoelectric gain, etaG, increases from 0.3 to 2.5 as the voltage increases from 3 to 5 V. Over this voltage range, the dark current increases from 8 to 120 e(-)s(-1) at a device temperature of 4.2 K and is under 70 e(-)s(-1) for all voltages at 2 K. Because of device gain, the effective dark current (equivalent photon rate) is less than 3 e(-)s(-1) under all operating conditions. The effective read noise (equivalent photon noise) is found to be less than 12 electrons under all operating conditions and for integration times between 0.05 and 100 seconds.

Herter, T.↗
NASA NTRS2016

Low Frequency 1/f Noise on QWIPs, nBn, and Superlattice Focal Plane Array

Noise Equivalent Difference Temperature (NE△T) is a standard performance metric for most infrared focal plane array (FPA) systems. The frequency bandwidth and range associated with NE△T is at high frequency and it does not describe the long time noise behavior or the very low frequency noise of the FPA. Very low frequency noise measurement requires data capture that takes longer time duration and sampling interval. This study investigates low frequency noise in QWIP, nBn and LWIR n-type Complementary Barrier Infrared Detector (CBIRD) FPAs. The corner frequencies are extracted from the power spectral density (PSD) as function of frequency. The peak wavelength, quantum efficiency of QWIP detector are 6.2 µm and 2 %, respectively. QWIP FPA has a mean NE△T ~ 25 mK at an operating temperature of 65 K and an integration time of 16 msec. The mean QWIP PSD plot shows a corner frequency of < 0.5 mHz. The nBn FPA with 4 µm cut off and quantum efficiency of 67 % has NE△T ~ 15.6 mK at an integration time ~ 7.52 msec and an operating temperature of 120 K. The nBn has corner frequency of > 50 mHz. Lastly the n-type CBIRD FPA with a 50% cutoff at 8.8 µm and quantum efficiency of ~ 50 % has an NE△T ~ 18.6 mK at an integration time of 1.86 msec and operating temperature 120 K. The superlattice FPA has a corner frequency ~ 10 mHz. The investigation of the tail on the NE△T histogram reveals that its origin is not accounted for entirely by the high noise current, but also it needs the inclusion of lower responsivity for some pixels.

Pepper, B.↗
NASA NTRS1985

Enhancement of X-ray performance with new GEC charged coupled devices (CCD)

Samples of two GEC charge coupled devices with enhanced X-ray performance have been tested. The P8607, fabricated with reduced linear dimensions, gives the lowest detector noise reported for Fe-55 with a CCD. The deep depletion device P8600-HR gives the best combination of energy resolution and quantum efficiency at 6 keV. The energy resolution vs quantum efficiency trade-off curve are discussed.

Schwartz, D. A.↗
NASA NTRS1990

Iridium Film For Charge-Coupled Device

Usability extended to different environments. Application of thin film of iridium to back surface of back-surface-illuminated charge-coupled device expected to increase and stabilize quantum efficiency at wavelengths less than 4,500 Angstrom. Enhances quantum efficiency according to principle discussed in "Metal Film Increases CCD Output" (NPO-16815). Does not react with hydrogen, so device need not be kept in oxygen: Advantage where high absorption of ultraviolet light by oxygen undesirable; for example, when device used to make astronomical observations from high altitudes.

Hecht, Michael H.↗
NASA NTRS1993

InGaAs concentrator cells for laser power converters and tandem cells

In(0.53)Ga(0.47)As N-on-P concentrator cells were made as part of an effort to develop 1.315 micron laser power converters. The 1.315 micron laser power conversion efficiency was estimated as 29.4 percent (at 5.57 W/cm(sup 2)) based on an 86 percent measured external quantum efficiency at 1.315 microns, and a measured open circuit voltage (484 mV), and fill-factor (67 percent) at the equivalent AM0 short-circuit photocurrent (5.07 A/cm(sup 2)). A 13.5 percent percent AMO efficiency was achieved at 89 suns and 25 C. Measured one-sun and 100-sun AMO efficiency, log I-V analysis, and quantum efficiency are presented for InGaAs cells with and without InP windows to passivate the front surface. Windowed cells performed better at concentration than windowless cells. Lattice mismatch between InGaAs epilayers and InP substrate was less than 800 ppm. Theoretical efficiency is estimated for 1.315 microns laser power converters versus the bandgap energy. Adding aluminum to InGaAs to form In(x)Al(y)Ga(1-x-y)As is presented as a way to achieve an optimal bandgap for 1.315 microns laser power conversion.

Wojtczuk, S.↗
NASA NTRS1973

Photoemission from cesium-oxide-activated InGaAsP.

Zinc-doped InGaAsP quaternary III-V material of the proper composition range shows superior photoemission properties to either InGaAs or InAsP ternary material. The minority-carrier diffusion length in the quaternary material is at least as long as that in InAsP and much longer than observed in InGaAs. The barrier height at the InGaAsP-Cs2O interface is lowered by cooling, giving increased electron escape probability and new highs in quantum efficiency over a wide wavelength range. For example, a 1.06-micron quantum efficiency of 7.5%/incident photon was observed at -90 C.

James, L. W.↗
NASA NTRS1977

Ultraviolet response of InGaAsP photocathodes

Three type VPM 164 photomultiplier tubes with III-IV compound InGaAsP reflective photocathodes were developed for use in ground-based and space-borne astronomical detectors. Although the achieved response of about 0.02% quantum efficiency at 1.083 microns fell short of the goal of 1% quantum efficiency, the broadband characteristics are still considerably better than those of the S-1 photocathode.

Feibelman, W. A.↗
NASA NTRS1994

Delta-Doped CCDs for Enhanced UV Performance

Thin, backside-illuminated CCds are modified by growing a delta-doped silicon layer on the back surface using molecular beam epitaxy. Delta-doped CCDs exhibit stable and uniform 100 percent internal quantum efficiency. The process consists of growth of an epitaxial silicon layer on a fully-processed commercial CCd die in which 30 percent of a monolayer of boron atoms are incorporated into the lattice nominally in a single atomic layer. Long term stability was tested and showed no degradation of the device quantum efficiency over sixteen months.

silicon↗
NASA NTRS1978

Infrared heterodyne spectroscopy for astronomical purposes

Heterodyne infrared astronomy was carried out using CO2 lasers and some solid state tunable lasers. The best available detectors are mercury cadmium telluride photodiodes. Their quantum efficiencies reach values near 0.5 and in an overall system an effective quantum efficiency, taking into account optical losses and amplifier noise, of about 0.25 was demonstrated. Initial uses of 10 micron heterodyne spectroscopy were for the study of planetary molecular spectra.

Townes, C. H.↗
NASA NTRS1987

Electro-optical characterization of the Tektronix TK512M-011 charge-coupled device

An electrooptical characterization encompassing linearity, blooming, dark-count rate, charge-transfer efficiency (CTE), and quantum efficiency, is presented for a front/side-illuminated CCD with 512x512 format and 27x27-micron pixels. The detailed noise characteristics of the CCD-output FET are reported. While very good low light level CTE is obtained in the parallel-shift direction, CTE problems arise in the serial direction. The output FET noise is equivalent to 5-12 electrons, depending on FET operating conditions and system bandwidth.

Epperson, Patrick M.↗
NASA NTRS1990

A 128 x 128 InGaAs detector array for 1.0 - 1.7 microns

A two-dimensional 128 x 128 detector array for the 1.0 - 1.7 micron spectral region has been demonstrated with indium gallium arsenide. The 30 micron square pixels had 60 micron spacing in both directions and were designed to be compatible with a 2D Reticon multiplexer. Dark currents below 100 pA, capacitance near 0.1 pF, and quantum efficiencies above 80 percent were measured. Probe maps of dark current and quantum efficiency are presented along with pixel dropout data and wafer yield which was as high as 99.89 percent (7 dropouts) in an area of 6528 pixels and 99.37 percent (103 dropouts) over an entire 128 x 128 pixel region.

Olsen, G.↗
NASA NTRS2002

CIGS2 Thin-Film Solar Cells on Flexible Foils for Space Power

CuIn(1-x)Ga(x)S2 (CIGS2) thin-film solar cells are of interest for space power applications because of the near optimum bandgap for AM0 solar radiation in space. CIGS2 thin film solar cells on flexible stainless steel (SS) may be able to increase the specific power by an order of magnitude from the current level of 65 Wkg(sup -1). CIGS solar cells are superior to the conventional silicon and gallium arsenide solar cells in the space radiation environment. This paper presents research efforts for the development of CIGS2 thin-film solar cells on 127 micrometers and 20 micrometers thick, bright-annealed flexible SS foil for space power. A large-area, dual-chamber, inline thin film deposition system has been fabricated. The system is expected to provide thickness uniformity of plus or minus 2% over the central 5" width and plus or minus 3% over the central 6" width. During the next phase, facilities for processing larger cells will be acquired for selenization and sulfurization of metallic precursors and for heterojunction CdS layer deposition both on large area. Small area CIGS2 thin film solar cells are being prepared routinely. Cu-rich Cu-Ga/In layers were sputter-deposited on unheated Mo-coated SS foils from CuGa (22%) and In targets. Well-adherent, large-grain Cu-rich CIGS2 films were obtained by sulfurization in a Ar: H2S 1:0.04 mixture and argon flow rate of 650 sccm, at the maximum temperature of 475 C for 60 minutes with intermediate 30 minutes annealing step at 120 C. Samples were annealed at 500 C for 10 minutes without H2S gas flow. The intermediate 30 minutes annealing step at 120 C was changed to 135 C. p-type CIGS2 thin films were obtained by etching the Cu-rich layer segregated at the surface using dilute KCN solution. Solar cells were completed by deposition of CdS heterojunction partner layer by chemical bath deposition, transparent-conducting ZnO/ZnO: Al window bilayer by RF sputtering, and vacuum deposition of Ni/Al contact fingers through metal mask. PV parameters of a CIGS2 solar cell on 127 micrometers thick SS flexible foil measured under AM 0 conditions at NASA GRC were: V(sub oc) = 802.9 mV, J(sub sc) = 25.07 mA per square centimeters, FF = 60.06%, and efficiency 0 = 8.84%. For this cell, AM 1.5 PV parameters measured at NREL were: V(sub oc) = 788 mV, J(sub sc) = 19.78 mA per square centimeter, FF = 59.44%, efficiency 0 = 9.26%. Quantum efficiency curve showed a sharp QE cutoff equivalent to CIGS2 bandgap of approximately 1.50 eV, fairly close to the optimum value for efficient AM0 PV conversion in the space.

Dhere, Neelkanth G.↗