Reversible photoinduced change of ac conduction in amorphousAs2S3films

Prolonged exposure to strongly absorbed light increases the ac conductivity (${\sigma }_{\mathrm{ac}}$) of well-annealed amorphous ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ films, suggesting that new localized states are induced in the band gap. This change is enhanced by low-temperature illumination. Although the change caused by room-temperature illumination is removed by annealing near the glass temperature $T_g$, the change caused by low-temperature (90 K) illumination is annealed out at around 200 K. This suggests that different centers, which depend on temperature, are induced by illumination. As the change in the optical gap ($E_0$) induced by low-temperature illumination is removed by annealing at $T_g$ (and is not removed at 200 K), the change in $E_0$ appears not to be directly related to this defect formation.