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 d iffer from those for hydrogen diluted a-SiGe:H material with the same optical gap(similar to 1.5 eV). Deposition rate of optimized helium di luted film is 3.3 times greater than that of hydrogen diluted film, ho wever 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 correspondin g values (8.45 +/- 1 x 10(15) cm(-3) eV(-1), 49 +/- 1.5 meV) of hydrog en diluted alloy materials. Schottky barrier solar cells have been fab ricated using both optimized materials. Blue response is greater for t he optimized helium diluted a-SiGe:H material than that of optimized h ydrogen diluted alloy film. Red response is also greater in the first case in comparison to that in the second case.