Picosecond photomodulation spectroscopy in amorphous semiconductors

Picosecond trapping of photogenerated carriers in gap states of doped, compensated and undoped amorphous hydrogenated silicon (a-Si:H) and of a-Si:H based superlattices was studied by the pump and probe photomodulation technique. In undoped a-Si:H the photogenerated carries are trapped in band-tail states and in compensated a-Si:H in impurity states introduced by doping. In singly charged dangling bond defects. In a-Si:H/a-SiNx:H superlattices photocarriers are trapped in interface related defects. In all cases we tron hopping rate among localized states in the conduction band-tail.