Kalluri R. Sarma

Composition variations in directionally solidified InSb-GaSb alloys

Abstract Melts containing 10%, 30% and 50% InSb were directionally solidified horizontally, vertically and in Skylab 3 and 4. The resulting concentration profiles were much more uniform in the ingots solidified horizontally. Fluctuations in composition occurred sooner as the InSb content increased and later in the horizontally processed ingots. In the 10% InSb ingot processed in SL-3 a large orientation-dependent segregation was observed at about 2 cm from the initial position of the interface. A radial variation in composition was also observed, and tentatively attributed to surface-tension driven convection.

Orientation, twinning and orientation-dependent reflectance in InSb-GaSb alloys

Abstract InSb-GaSb solid solution ingots prepared by directional solidification aboard Skylab and on earth consist primarily of twins with (111) twin planes parallel to the direction of solidification and growth directions that lie along 〈211〉, 〈110〉, or 〈321〉 crystallographic directions. The optical bireflectance exhibited by polished samples when observed by reflected plane-polarized white light is symmetrical with respect to twin boundaries, regardless of twin orientation relative to solidification direction, and displays a two-fold rotational symmetry rather than the four-fold symmetry normally associated with uniaxial strain birefringence.

Continuous growth of polycrystalline silicon films by chemical vapor deposition

Abstract Low-cost, polycrystalline silicon films are of great interest in solar cells for terrestrial photovoltaic energy conversion. Conventional silicon chemical vapor deposition (CVD) reactors (e.g. for epitaxial growth or poly film deposition) are not suitable for low cost applications due to their low electrical power and chemical utilization efficiencies and throughput rates. In this paper, a continuous CVD reactor is described for producing polycrystalline silicon films at low-cost. This is a hot-wall reactor, and employs high temperature hydrogen reduction of a chlorosilane such as SiHCl3 for silicon deposition. Effects of various parameters, including deposition temperature and reactant concentration and flow rate, on the silicon film characteristics and reactor performance were investigated. This continuous deposition reactor was found to be characterized by favorable electrical power and chemical utilization efficiencies and film throughput rates compared to conventional cold-wall CVD reactors. Silicon films produced using the present reactor were found to be suitable for fabrication of high efficiency (>12%, air-mass one or AM1) solar cells after grain enhancement, and show promise for meeting the low-cost goals of terrestrial photovoltaics.

Polycrystalline silicon solar cells from recrystallized plasma deposited thin films

Large grain polycrystalline silicon films are produced by a two step process involving plasma deposition of microcrystalline silicon films on a substrate, separation from the substrate, and subsequent grain enhancement of the silicon films. The effects of doping and substrate temperature during deposition on the solar cell conversion efficiency are investigated. Effects of ppm level molybdenum contamination from the substrate, and silicon microstructure after grain enhancement, on solar cell efficiency parameters are also investigated. Solar cells with efficiencies of up to 10.1% under AM1 illumination, were fabricated on these silicon films.