Persistent photocurrent in amorphous chalcogenides

The long-term photocurrent decays following the steady-state photoexcitation have been reported in amorphous ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$, ${\mathrm{As}}_2$ ${\mathrm{S}}_3$, GeSe, ${\mathrm{GeSe}}_2$, and ${\mathrm{GeS}}_2$ films. The photocurrent decays empirically as exp(-${\mathrm{Ct}}^{\alpha }$) which is called the extended exponential. This behavior can be well interpreted in terms of the dispersive diffusion-controlled recombination of localized electrons and holes. The photocurrent reduces after prolonged strong photoillumination, suggesting that new localized states are induced in the band gap.