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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Phase transitions in Group III-V and II-VI semiconductors at high pressure

The structures and transition pressures of Group III-V and II-VI semiconductors and of a pseudobinary system (Ga/x/In/1-x/Sb) have been investigated. Results indicate that GaP, InSb, GaSb, GaAs and possible AlP assume Metallic structures at high pressures; a tetragonal, beta-Sn-like structure is adopted by only InSb and GaSb. The rocksalt phase is preferred in InP, InAs, AlSb, ZnO and ZnS. The model of Van Vechten (1973) gives transition pressures which are in good agreement with measured values, but must be refined to account for the occurrence of the ionic rocksalt structure in some compounds. In addition, discrepancies between the theoretical scaling values for volume changes at the semiconductor-to-metal transitions are observed.

Yu, S. C.↗
NASA NTRS1980

Study of LPE methods for growth of InGaAsP/InP CW lasers

Two methods for liquid phase growth of InGaAsP/InP lasers were studied. Single phase growth, based on saturated melts and 5 C supercooling, was compared to two phase growth excess InP and 20 C nominal supercooling. Substrates cut on the (100) plane were used, and morphology in both cases was excellent and comparable to that obtainable in AlGaAs materials. A high degree of reproducibility was obtained in the materials grown by the two phased method, which is therefore presently preferred for the preparation of laser material. A refractive index step of 0.28 and an index n = 3.46 were obtained for In.81Ga.19As,5P5 lasing at 1.3 microns. Oxide-stripe lasers with typical room temperature cw threshold currents of 180 mA were obtained and some of them showed single mode behavior without lateral cavity modifications. COntinuous operation of 800 h at room temperature was obtained without noticeable degradation.

Ladany, I.↗
NASA NTRS1980

Estimating the chlorophyll content in the waters of Guanabara Bay from the LANDSAT multispectral scanning digital data

Detection of water quality in Guanabara Bay using multispectral scanning digital data taken from LANDSAT satellites was examined. To test these processes, an empirical (statistical) approach was choosen to observe the degree of relationship between LANDSAT data and the in situ data taken simultaneously. The linear and nonlinear regression analyses were taken from among those developed by INPE in 1978. Results indicate that the major regression was in the number six MSS band, atmospheric effects, which indicated a correction coefficient of 0.99 and an average error of 6.59 micrograms liter. This error was similar to that obtained in the laboratory. The chlorophyll content was between 0 and 100 micrograms/liter, as taken from the MSS of LANDSAT.

Dejesusparada, N.↗
NASA NTRS1981

Monolithically integrated active optical devices

Considerations relevant to the monolithic integration of optical detectors, lasers, and modulators with high speed amplifiers are discussed. Some design considerations for representative subsystems in the GaAs-AlGaAs and GaInAs-InP materials systems are described. Results of a detailed numerical design of an electro-optical birefringent filter for monolithic integration with a laser diode is described, and early experimental results on monolithic integration of broadband MESFET amplifiers with photoconductive detectors are reported.

Ballantyne, J.↗
NASA NTRS1983

Advanced 3-V semiconductor technology assessment

Components required for extensions of currently planned space communications systems are discussed for large antennas, crosslink systems, single sideband systems, Aerostat systems, and digital signal processing. Systems using advanced modulation concepts and new concepts in communications satellites are included. The current status and trends in materials technology are examined with emphasis on bulk growth of semi-insulating GaAs and InP, epitaxial growth, and ion implantation. Microwave solid state discrete active devices, multigigabit rate GaAs digital integrated circuits, microwave integrated circuits, and the exploratory development of GaInAs devices, heterojunction devices, and quasi-ballistic devices is considered. Competing technologies such as RF power generation, filter structures, and microwave circuit fabrication are discussed. The fundamental limits of semiconductor devices and problems in implementation are explored.

Nowogrodzki, M.↗
NASA NTRS1984

BRESEX: On board supervision, basic architecture and preliminary aspects for payload and space shuttle interface

Data relative to the on board supervision subsystem are presented which were considered in a conference between INPE and NASA personnel, with the purpose of initiating a joint effort leading to the implementation of the Brazilian remote sensing experiment - (BRESEX). The BRESEX should consist, basically, of a multispectral camera for Earth observation, to be tested in a future space shuttle flight.

Bergamini, E. W.↗
NASA NTRS1984

Water resources by orbital remote sensing: Examples of applications

Selected applications of orbital remote sensing to water resources undertaken by INPE are described. General specifications of Earth application satellites and technical characteristics of LANDSAT 1, 2, 3, and 4 subsystems are described. Spatial, temporal and spectral image attributes of water as well as methods of image analysis for applications to water resources are discussed. Selected examples are referred to flood monitoring, analysis of water suspended sediments, spatial distribution of pollutants, inventory of surface water bodies and mapping of alluvial aquifers.

Martini, P. R.↗
NASA NTRS1984

Basic principles, methodology, and applications of remote sensing in agriculture

The basic principles of remote sensing applied to agriculture and the methods used in data analysis are described. Emphasis is placed on the importance of developing a methodology that may help crop forecast, basic concepts of spectral signatures of vegetation, the methodology of the LANDSAT data utilization in agriculture, and the remote sensing program application of INPE (Institute for Space Research) in agriculture.

Moreira, M. A.↗
NASA NTRS1984

Specification and preliminary design of the CARTA system for satellite cartography

Digital imagery acquired by satellite have inherent geometrical distortion due to sensor characteristics and to platform variations. In INPE a software system for geometric correction of LANDSAT MSS imagery is under development. Such connected imagery will be useful for map generation. Important examples are the generation of LANDSAT image-charts for the Amazon region and the possibility of integrating digital satellite imagery into a Geographic Information System.

Machadoesilva, A. J. F.↗
NASA NTRS1985

Optical properties of hydrogenated amorphous carbon films grown from methane plasma

A 30 kHz ac glow discharge formed from methane gas was used to grow carbon films on InP substrates. Both the growth rate, and the realitive Ar ion sputtering rate at 3 keV varied monotonically with deposition power. Results from the N-15 nuclear reaction profile experiments indicated a slight drop in the hydrogen concentration as more energy was dissipated in the ac discharge. Values for the index of refraction and extinction coefficient ranged from 1.721 to 1.910 and 0 to -0.188, respectively. Optical bandgaps as high as 2.34 eV were determined.

Pouch, J. J.↗
NASA NTRS1985

Carbon films grown from plasma on III-V semiconductors

Dielectric carbon films were grown on n- and p-type GaAs and InP substrates using plasmas generated at 30 KHz from gaseous hydrocarbons. The effect of gas source, flow rate, and power on film growth were investigated. Methane and n-butane gases were utilized. The flow rate and power ranged from 30 to 50 sccm and 25 to 300 W, respectively. AES measurements show only carbon to be present in the films. The relative Ar ion sputtering rate (3 KeV) of carbon depends on the ratio power/pressure. In addition, the degree of asymmetry associated with the carbon-semiconductor interface is approximately power-independent. SIMS spectra indicate different H-C bonding configurations to be present in the films. Band gaps as high as 3.05 eV are obtained from optical absorption studies.

Pouch, J. J.↗
NASA NTRS1986

Potential high efficiency solar cells: Applications from space photovoltaic research

NASA involvement in photovoltaic energy conversion research development and applications spans over two decades of continuous progress. Solar cell research and development programs conducted by the Lewis Research Center's Photovoltaic Branch have produced a sound technology base not only for the space program, but for terrestrial applications as well. The fundamental goals which have guided the NASA photovoltaic program are to improve the efficiency and lifetime, and to reduce the mass and cost of photovoltaic energy conversion devices and arrays for use in space. The major efforts in the current Lewis program are on high efficiency, single crystal GaAs planar and concentrator cells, radiation hard InP cells, and superlattice solar cells. A brief historical perspective of accomplishments in high efficiency space solar cells will be given, and current work in all of the above categories will be described. The applicability of space cell research and technology to terrestrial photovoltaics will be discussed.

Flood, D. J.↗
NASA NTRS1986

Zone leveling and solution growth of complex compound semiconductors in space

A research program on complex semiconducting compounds and alloys was completed that addressed the growth of single crystals of CdSe(y)Te(1-y), Zn(x)Cd(1-x)Te, Mn(x)Cd(1-x)Te, InP(y)As(1-y) and CuInSe2 and the measurement of fundamental physico-chemical properties characterizing the above materials. The purpose of this ground based research program was to lay the foundations for further research concerning the growth of complex ternary compound semiconductors in a microgravity environment.

Bachmann, K. J.↗
NASA NTRS1987

ITO/InP solar cells: A comparison of devices fabricated by ion beam and RF sputtering of the ITO

This work was performed with the view of elucidating the behavior of indium tin oxide/indium phosphide (ITO/InP) solar cells prepared by RF and ion beam sputtering. It was found that using RF sputter deposition of the ITO always leads to more efficient devices than ion beam sputter deposition. An important aspect of the former technique is the exposure of the single crystal p-InP substrates to a very low plasma power prior to deposition. Substrates treated in this manner have also been used for ion beam deposition of ITO. In this case the cells behave very similarly to the RF deposited cells, thus suggesting that the lower power plasma exposure (LPPE) is the crucial process step.

Coutts, T. J.↗
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 NTRS1987

Material growth and characterization for solid state devices

During this period InGaAs and InGaAsP were grown on (100)InP by liquid phase electroepitaxy (LPEE). Results of the epitaxial growth of InGaAs on sputtered quartz masked substrates are presented. The resulting surface morphology can be related to the current density distribution near the edges of a masked pattern. The quaternary InGaAs was grown with compositions corresponding to 1.3 micron and 1.5 micron emission wavelengths. Growth rates were found to be linearly dependent upon current density, and a strong dependence upon composition was noted. These compositions lie in the miscibility gap region of the alloy phase diagram at the 645 C growth temperature. Growths were performed at 685 C to avoid the miscibility gap. Epilayers were characterized by photoluminescence, X-ray diffraction, secondary ion mass spectrometry, and Hall effect measurements. Aluminum oxide was deposited on silicon and InGaAs substrates for the characterization of this material as an insulator in a field effect transistor structure. It was determined that the results did not warrant further work with the deposition from an aluminum isopropoxide source. A metallographic vapor phase epitaxy system installation is nearing completion for use in hybrid III-V semiconductor epilayer growths.

Collis, Ward J.↗
NASA NTRS1986

Radiation damage in proton irradiated indium phosphide solar cells

Indium phosphide solar cells exposed to 10 MeV proton irradiations were found to have significantly greater radiation resistance than either GaAs or Si. Performance predictions were obtained for two proton dominated orbits and one in which both protons and electrons were significant cell degradation factors. Array specific power was calculated using lightweight blanket technology, a SEP array structure, and projected cell efficiencies. Results indicate that arrays using fully developed InP cells should out-perform those using GaAs or Si in orbits where radiation is a significant cell degradation factor.

Weinberg, I.↗