Low defect density amorphous silicon germanium alloy (1.5 eV) deposited at high growth rate under helium dilution in RF-PECVD method

Optimized deposition parameters for helium diluted a-SiGe:H material differ from those for hydrogen diluted a-SiGe:H material with the same optical gap(similar to 1.5 eV). Deposition rate of optimized helium diluted film is 3.3 times greater than that of hydrogen diluted film, however the photoconductivities of both type of materials are the same. Defect density (6.72 +/- 1 x 10(15) cm eV(-1)) and Urbach energy (46 +/- 1.5 meV) of helium diluted optimized film is less than corresponding values (8.45 +/- 1 x 10(15) cm(-3) eV(-1), 49 +/- 1.5 meV) of hydrogen diluted alloy materials. Schottky barrier solar cells have been fabricated using both optimized materials. Blue response is greater for the optimized helium diluted a-SiGe:H material than that of optimized hydrogen diluted alloy film. Red response is also greater in the first case in comparison to that in the second case.