Kinetics of the persistent photocurrent in semiconductors: a case example for amorphous chalcogenides

Although the persistent photocurrent or the residual photocurrent decay (RPD) in photoconductive semiconductors is known to be dominated by dispersive recombination kinetics which produce the stretched exponential functional decay, exp(-Ct^β), where β (<1.0) is the dispersion parameter, the reason for the occurrence of the RPD is still not clear. We discuss the origin of the dispersive nature of long-term photocurrent decay in amorphous chalcogenides (a-Chs) as a case example. The slow recombination path of excess photocarriers in a-Chs can be attributed to their characteristic feature of negative-U defects at which lattice relaxation with multiphonon process may play a role.