Light-induced defects in hydrogenated amorphous silicon alloys

The effect of light illumination on gap state absorption of hydrogenated amorphous silicon (a-Si) alloys has been investigated using photothermal deflection spectroscopy. The alloys studied were the large gap materials a-SiC and a-SiO and the narrow gap a-SiGe and a-Ge. The results indicate a direct relationship between the gap energy and defect formation. As the gap opens, the number of metastable defects increases; whereas for the narrow gap materials, significantly fewer defects are observed. This behavior is consistent with the interpretation of defect formation by electron-hole recombination.