Gallium Arsenide Thin Films on Tungsten/Graphite Substrates: Phase II. Topical Report: Thin Film Gallium Arsenide Solar Cells on Tungsten/Graphite Substrates

摘要

The use of a thin film of gallium arsenide on a low cost substrate appears to be a promising approach for the fabrication of low-cost high-efficiency solar cells. Gallium arsenide films have been deposited on tungsten/graphite substrates at 775 exp 0 C by the reaction of gallium, hydrogen chloride, and arsine in a gas flow system. The deposited films are essentially polycrystalline with an average crystallite size of about 10 mu m. Without intentional doping, the deposited films are n-type with carrier concentrations in the range of 2 x 10 exp 16 to 8 x 10 exp 16 cm exp -3 at room temperature. N-type gallium arsenide films of higher dopant concentrations can be readily deposited by using hydrogen sulfide as a dopant. The MOS approach has been used for the preparation of solar cells. After the successive deposition of n exp + - and n-gallium arsenide films on a tungsten/graphite substrate, the surface of the film was oxidized in situ with an argon-oxygen mixture and in some cases, followed by a water vapor treatment at room temperature. The gold barrier and silver grid contacts were applied by evaporation. An antireflection coating of titanium dioxide was deposited at 80 to 100 exp 0 C by the hydrolysis of tetraisopropyl titanate in an argon atmosphere. A number of large area (6 to 9 cm exp 2 ) solar cells have been prepared, and the best cells have an AM1 efficiency of about 5.5%. (ERA citation 06:030144)