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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Analysis of epitaxial drift field N on P silicon solar cells

The performance of epitaxial drift field silicon solar cell structures having a variety of impurity profiles was calculated. These structures consist of a uniformly doped P-type substrate layer, and a P-type epitaxial drift field layer with a variety of field strengths. Several N-layer structures were modeled. A four layer solar cell model was used to calculate efficiency, open circuit voltage and short circuit current. The effect on performance of layer thickness, doping level, and diffusion length was determined. The results show that peak initial efficiency of 18.1% occurs for a drift field thickness of about 30 micron with the doping rising from 10 to the 17th power atoms/cu cm at the edge of the depletion region to 10 to the 18th power atoms/cu cm in the substrate. Stronger drift fields (narrow field regions) allowed very high performance (17% efficiency) even after irradiation to 3x10 to the 14th power 1 MeV electrons/sq cm.

Baraona, C. R.↗
NASA NTRS1978

Epitaxial solar cells on low-cost silicon substrates

This work is directed toward a low-cost approach to the fabrication of silicon solar cells and combines the advantages and flexibility of the epitaxial technique with the use of potentially low-cost silicon substrates. Epitaxial graded base n/p/p+ solar cell structures were grown and evaluated on various forms of polycrystalline and metallurgical grade silicon as well as single crystal substrates. X-ray topographic techniques have shown improvements in the crystallographic quality of the layer grown on polycrystalline material.

Robinson, P. H.↗
NASA NTRS1981

Evaluation and verification of epitaxial process sequence for silicon solar cell production

The applicability of solar cell and module processing sequences, to be used on lower cost epitaxial silicon wafers was evaluated. The extent to which the process sequences perform effectively when applied to film solar cells formed by epitaxial deposition of Si on potentially inexpensive substrates of upgraded metallurgical grade Si is examined. It is concluded that these substrates are satisfactory in their cell performance.

Redfield, D.↗
NASA NTRS1980

Liquid-phase epitaxy grown PbSnTe distributed feedback laser diodes with broad continuous single-mode tuning range

Distributed feedback (DFB) pulsed laser operation has been demonstrated in stripe geometry Pb(1-x)Sn(x)Te double-heterostructures grown by liquid-phase epitaxy. The grating structure of 0.79 micron periodicity operates in first order near 12.8 microns and was fabricated prior to the liquid-phase epitaxial growth using holographic exposure techniques. These DFB lasers had moderate thresholds, 3.6 kA/sq cm, and the output power versus current curves exhibited a sharp turn-on free of kinks. Clean, single-mode emission spectra, continuously tunable over a range in excess of 20 per cm, centered about 780 per cm (12.8 microns), and at an average rate of 1.2 per cm-K from 9 to 26 K, were observed. While weaker modes could at times be seen in the spectrum, substantially single-mode operation was obtained over the entire operating range and to over 10 times threshold.

Hsieh, H.-H.↗
NASA NTRS1983

Cleaning chemistry of InSb(100) molecular beam epitaxy substrates

InSb has been used as a substrate for molecular beam epitaxy. For good epitaxial growth, a substrate surface which is smooth and clean on an atomic scale is required. Chemical cleaning procedures provide an oxide film to passivate the surface. This film is then desorbed by in situ heating. The material forming the film should, therefore, have a high vapor pressure at some temperature less than the substrate melting temperature. A chloride film appears to satisfy the latter requirement. The present investigation is, therefore, concerned with the formation of a chloride film rather than an oxide film. Carbon contamination has been found to cause problems in chemical cleaning procedures. The level of carbon contamination found in the case of chloride film formation, is therefore compared with the corresponding level observed in procedures using oxide films. It appears that a chloride film grown in connection with a short exposure time to a Cl2 plasma is preferable to other passivation films studied.

Vasquez, R. P.↗
NASA NTRS1985

Hot-Dipped Metal Films as Epitaxial Substrates

Multistep process forms semiconductor devices on macrocrystalline films of cadmium or zinc. Solar-cell fabrication processes use hot-dipped macrocrystalline films on low-cost sheet-metal base as substrates for epitaxy. Epitaxial layers formed by variety of methods of alternative sequence paths. Solar cells made economically by forming desired surface substance directly on metal film by chemical reactions.

Shlichta, P. J.↗
NASA NTRS1983

In-situ TEM investigations of graphic-epitaxy and small particles

Palladium was deposited inside a controlled-vacuum specimen chamber of a transmission electron microscope (TEM) onto MgO and alpha-alumina substrate surfaces. Annealing and various effects of gas exposure of the particulate Pd deposits were studied in-situ by high resolution TEM and electron diffraction. Whereas substrate temperatures of 500 C or annealing of room temperature (RT) deposits to 500 C were needed to obtain epitaxy on sapphire, RT deposits on MgO were perfectly epitaxial. For Pd/MgO a lattice expansion of 2 to 4% was noted; the highest values of expansion were found for the smallest particles. The lattice expansion of small Pd particles on alumina substrates was less than 1%. Long-time RT exposure of Pd/MgO in a vacuum yielded some moblity and coalescence events, but notably fewer than for Pd on sapphire. Exposure to air or oxygen greatly enhanced the particle mobility and coalescence and also resulted in the flattening of Pd particles on MgO substrates. Electron-beam irradiation further enhanced this effect. Exposure to air for several tens of hours of Pd/MgO led to strong coalescence.

Heinemann, K.↗
NASA NTRS1987

Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

Lin, T. L.↗
NASA NTRS1987

Elucidation of the organometallic vapor phase epitaxial growth mechanism for InP

A new technique for tracing the organometallic vapor epitaxial growth is reported. The pyrolysis of PH3, alone and in the presence of trimethylindium (TMIn), and of TMIn alone was studied by conducting the epitaxial growth of InP in D2 as the carrier gas, tracing growth reactions by mass spectrometric analysis of the product molecules. The TMIn alone pyrolyzes mostly homogeneously in the gas phase, while the PH3 pyrolysis is completely heterogeneous at the InP surface. Adding TMIn to PH3 results in a dramatic decrease in the pyrolysis temperature. PH3 molecules which interact with TMIn in the gas phase pyrolyze at temperatures as low as 250, and those decomposing without TMIn interaction pyrolyze at temperatures approximately 200 C higher. Similarly, the presence of PH3 lowers the TMIn pyrolysis temperature by at least 50 C. TMIn alone in D2 produces mainly CH3D molecules. For high PH3:TMIn ratios, CH4 is the only carbon-containing reaction product.

Buchan, N. I.↗
NASA NTRS1988

Secondary ion mass spectrometry study of ex situ annealing of epitaxial GaAs grown on Si substrates

Samples of epitaxial GaAs grown on (100) Si substrates using molecular beam epitaxy were annealed at four different temperatures, from 800 to 950 C. Following annealing, the samples were analyzed using secondary ion mass spectrometry. Depth profiles of Ga, As, and Si reveal optimum conditions for annealing, and place a lower limit on a damage threshold for GaAs/Si substrates.

Radhakrishnan, G.↗
NASA NTRS1988

Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

Mii, Y. J.↗
NASA NTRS1988

Growth of (111) GaAs on (111) Si using molecular-beam epitaxy

(111) GaAs layers have been grown epitaxially on (111) Si wafers, both on-axis as well as 3-deg off-axis towards the 1 -1 0 direction, using molecular-beam epitaxy. The grown layers have been characterized by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy.

Radhakrishnan, G.↗
NASA NTRS1988

The use of heterogeneous and epitaxial nucleants to promote the growth of protein crystals

Fifty different mineral samples were tested as potential heterogeneous or epitaxial nucleants for four commonly crystallized proteins. It was found, using conventional protein crystallization techniques, that for each protein there was a set of mineral substrates that promoted nucleation of crystals at lower critical levels of supersaturation than required for spontaneous growth. In at least one case, the growth of lysozyme on the mineral apophyllite, it was shown by lattice analysis and X-ray diffraction that the nucleation and growth of the protein crystal on the mineral was likely to be truly epitaxial.

Mcpherson, Alexander↗
NASA NTRS1989

Molecular-Beam Epitaxy Of CrSi2 on Si(111)

Crystalline layers grown in commercial apparatus. Experiments show CrSi2 grown on (111) face of single-crystal Si substrate by molecular-beam epitaxy. Epitaxial CrSi2 produced thus far not in desired single-crystal form. Because CrSi2 semiconductor with band gap of 0.3 eV, experimental process potential for monolitic integration of microelectronic devices based on CrSi2 (e.g., infrared detectors) with signal-processing circuitry based on Si.

Fathauer, Robert W.↗
NASA NTRS1989

Molecular beam epitaxial growth of high-quality InSb on InP and GaAs substrates

Epitaxial layers of InSb were grown on InP and GaAs substrates by molecular beam epitaxy. The dependence of the epilayer quality on flux ratio, J sub Sb4/J sub In, was studied. Deviation from an optimum value of J sub Sb4/J sub In (approx. 2) during growth led to deterioration in the surface morphology and the electrical and crystalline qualities of the films. Room temperature electron mobilities as high as 70,000 and 53,000 sq cm /V-s were measured in InSb layers grown on InP and GaAs substrates, respectively. Unlike the previous results, the conductivity in these films is n-type even at T = 13 K, and no degradation of the electron mobility due to the high density of dislocations was observed. The measured electron mobilities (and carrier concentrations) at 77 K in InSb layers grown on InP and GaAs substrates are 110,000 sq cm/V-s (3 x 10(15) cm(-3)) and 55,000 sq cm/V-s (4.95 x 10(15) cm(-3)), respectively, suggesting their application to electronic devices at cryogenic temperatures.

Oh, J. E.↗
NASA NTRS1989

Surface morphologies and electrical properties of molecular beam epitaxial InSb and InAs(x)Sb(1-x) grown on GaAs and InP substrates

Surface morphologies and electrical properties of molecular beam epitaxial InSb and InAs(x)Sb(1-x) grown on GaAs and InP substrates are discussed. The crystals are all n-type at 300 K and lower temperatures. The surface morphology and electrical characteristics are strongly dependent on Sb(4)/In flux ratio and substrate temperature. The highest mobilities in InSb on InP are 70,000 at 300 K and 110,000 cm(2)/V.s (n=3x10(15) cm(-3)) at 77 K. The mobilities in the alloys also increase monotonically with lowering of temperature. Good quality InAs(x)Sb(1-x) was grown directly on InP substrates by molecular beam epitaxy.

Oh, J. E.↗
NASA NTRS1988

Growth and characterization of GaAs layers on Si substrates by migration-enhanced molecular beam epitaxy

Migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layer on Si substrates (GaAs/Si) are reported. The MEMBE growth method is described, and material properties are compared with those of normal two-step MBE-grown or in situ annealed layers. Micrographs of cross-section view transmission electron microscopy and scanning surface electron microscopy of MEMBE-grown GaAs/Si showed dislocation densities of 10 to the 7th/sq cm. AlGaAs/GaAs double heterostructures have been successfully grown on MEMBE GaAs/Si by both metalorganic chemical vapor deposition and liquid phase epitaxy.

Kim, Jae-Hoon↗
NASA NTRS1989

Epitaxial growth of InSb (111) on sapphire (0001)

Indium antimonide has been epitaxially grown directly on sapphire. Reflection high-energy electron diffraction, TEM, and SEM data are presented to show that the indium antimonide layer is epitaxial, has an abrupt interface with the sapphire, and grows in the 111-line direction. Mobility data show room-temperature mobilities as high as 10,000 sq cm/V s from some regions on the wafer.

Jamison, K. D.↗