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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Development of a high capacity bubble domain memory element and related epitaxial garnet materials for application in spacecraft data recorders. Item 2: The optimization of material-device parameters for application in bubble domain memory elements for spacecraft data recorders

Bubble domain materials and devices are discussed. One of the materials development goals was a materials system suitable for operation of 16 micrometer period bubble domain devices at 150 kHz over the temperature range -10 C to +60 C. Several material compositions and hard bubble suppression techniques were characterized and the most promising candidates were evaluated in device structures. The technique of pulsed laser stroboscopic microscopy was used to characterize bubble dynamic properties and device performance at 150 kHz. Techniques for large area LPE film growth were developed as a separate task. Device studies included detector optimization, passive replicator design and test and on-chip bridge evaluation. As a technology demonstration an 8 chip memory cell was designed, tested and delivered. The memory elements used in the cell were 10 kilobit serial registers.

Besser, P. J.↗
NASA NTRS1977

Development of a high capacity bubble domain memory element and related epitaxial garnet materials for application in spacecraft data recorders. Item 1: Development of a high capacity memory element

Several versions of the 100K bit chip, which is configured as a single serial loop, were designed, fabricated and evaluated. Design and process modifications were introduced into each succeeding version to increase device performance and yield. At an intrinsic field rate of 150 KHz the final design operates from -10 C to +60 C with typical bias margins of 12 and 8 percent, respectively, for continuous operation. Asynchronous operation with first bit detection on start-up produces essentially the same margins over the temperature range. Cost projections made from fabrication yield runs on the 100K bit devices indicate that the memory element cost will be less than 10 millicents/bit in volume production.

Besser, P. J.↗
NASA NTRS1978

Epitaxial silicon growth for solar cells

Growth and fabrication procedures for the baseline solar cells are described along with measured cell parameters, and the results. Reproducibility of these results was established and the direction to be taken for higher efficiency is identified.

Daiello, R. V.↗
NASA NTRS1984

Metal-support interactions during the adsorption of CO on thin layers and islands of epitaxial palladium

Islands and continuous layers of palladium were grown in an ultrahigh vacuum on substrates of Mo(110)c(14 x 7)-O, designated MoO(x), and of clean Mo(110). It was found that as-deposited islands and layers exhibited bulk palladium adsorption properties for CO when deposited at room temperature and for palladium thicknesses in excess of about 3 monolayers. CO adsorption was drastically reduced, however, on annealing. For islands, annealing temperatures of as low as 400 K led to some reduction in CO adsorption whereas more severe reductions were found to occur at 600 K for islands and at 800 K for continuous multilayers. The deactivation depended on the palladium thickness, the substrate species and the extent of thermal treatments. Auger electron spectroscopy, temperature-programmed desorption and Delta-Phi measurements were combined to interpret the deactivation behavior in terms of substrate-support interactions involving the diffusion of substrate species towards the palladium surface.

Park, C.↗
NASA NTRS1986

Low-loss optical waveguides made with molecular beam epitaxial In(0.012)Ga(0.988)As and In(0.2)Ga(0.8)As-GaAs superlattices

Low-loss optical guiding in In-doped GaAs is demonstrated for the first time. Ridge waveguides are made with single In(0.012)Ga(0.988)As ternary layers and In(0.2)Ga(0.8)As-GaAs superlattices. Attenuation constants of about 1.3 dB/cm are measured and the principal loss mechanism is identified to be scattering at the ridge walls. It is expected that improved fabrication techniques will lead to guides with attenuation less than or equal to 0.5 dB/cm.

Das, U.↗
NASA NTRS1987

Diffusion length measurements in bulk and epitaxially grown 3-5 semiconductors using charge collection microscopy

Diffusion lengths and surface recombination velocities were measured in GaAs diodes and InP finished solar cells. The basic techniques used was charge collection microscopy also known as electron beam induced current (EBIC). The normalized currents and distances from the pn junction were read directly from the calibrated curves obtained while using the line scan mode in an SEM. These values were then equated to integral and infinite series expressions resulting from the solution of the diffusion equation with both extended generation and point generation functions. This expands previous work by examining both thin and thick samples. The surface recombination velocity was either treated as an unknown in a system of two equations, or measured directly using low e(-) beam accelerating voltages. These techniques give accurate results by accounting for the effects of surface recombination and the finite size of the generation volume.

Leon, R. P.↗
NASA NTRS1986

Passivation of Si solar cells by hetero-epitaxial compound semiconductor coatings

A development status evaluation is made for high efficiency Si solar cells, with emphasis on the suppression of the deleterious effects of surface recombination. ZnS(0.9)Se(0.1) and GaP are identified as candidates for the reduction of surface recombination. Attention is given to methods developed for the deposition of heteroepitaxial compounds designed to block minority carrier transport to the Si solar cell surface without interfering with the majority carrier flow.

Vernon, S. M.↗
NASA NTRS1987

Effects of substrate misorientation and background impurities on electron transport in molecular-beam-epitaxial grown GaAs/AlGaAs modulation-doped quantum-well structures

The effects of substrate misorientation off the (001) plane and of background impurities on electron transport in MBE-grown GaAs/AlGaAs modulation-doped superlattice-buffered quantum-well structures were investigated. Low-field transport data were obtained on GaAs/AlGaAs structures grown on substrates oriented 0, 2, 4, and 6.5 deg off the (001) plane towards either (111)A or (111)B. It is shown that the low-field two-dimensional electron gas (2DEG) mobility is a function of the angle and direction of the substrate orientation, and that the 2DEG mobility is a function of the direction of the applied electric field in the GaAs quantum well. The anisotropy in the 2DEG mobility is also a function of the tilt angle and tilt azimuth direction of the substrate from the (001) plane. In addition, it is shown that the amount of interface scattering from the inverted interface is a sensitive function of the amount of background impurities in the MBE machine.

Radulescu, D. C.↗
NASA NTRS1987

Phase equilibria and liquid phase epitaxy growth of PbSnSeTe lattice matched to PbSe

The necessary phase diagram data for growing lattice-matched layers of PbSnSeTe on PbSe are presented. Solid compounds of Pb(1-x)Sn(x)Se(1-y)Te(y) lattice-matched to PbSe were grown from liquid melts consisting of (Pb/1-x/Sn/x/)(1-z)(Se/1-y/Te/y/)(z); phase equilibria data were determined together with liquidus data for values of x(liquid) from 0 to 40 percent and y(liquid) from 0 to 40 percent for temperatures between 450 and 540 C. It was found that relatively large amounts of Te must be added to the melt to achieve lattice matching because of its low segregation coefficient relative to Se. A significant lattice-pulling effect was discovered for the 5-percent Sn case, and a similar effect is expected for the 10- and 20-percent Sn cases.

Mccann, Patrick J.↗