High-quality hydrogenated amorphous silicon-germanium alloys for narrow bandgap thin film solar cells

A deposition method, in which similar to 3 nm-thick deposition and hydrogen plasma annealing are alternately repeated, has been employed to fabricate hydrogenated amorphous silicon-germanium (a-Si1-3Gex:H) alloys by changing substrate temperatures from 150 to 230 degrees C. The germanium content, x, remains unchanged at about 0.42 independent of the substrate temperature for a molar fraction of SiH4/GeH4=10. The bonded hydrogen concentration decreases with increasing substrate temperature, resulting in a decrease in the optical bandgap from 1.52 to 1.43eV. It is found that a photoconductivity of 4.5 X 10(-5) S/cm and a photosensitivity, 9.1 X 10(4), under AM 1 (100 mW/cm(2)) illumination are obtained at a substrate temperature of 175 degrees C at an optical bandgap of 1.49 eV.