Origin of photoinduced metastable defects in amorphous chalcogenides

Prolonged exposure to band-gap light decreases the photoconductivity of annealed films of amorphous chalcogenides (${\mathrm{As}}_2$ ${\mathrm{S}}_3$, ${\mathrm{As}}_3$ ${\mathrm{S}}_7$, AsS, ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$, ${\mathrm{GeS}}_2$, ${\mathrm{GeSe}}_2$, and GeSe). This can be attributed to photoinduced metastable defects, which could act as additional trapping and/or recombination centers. These metastable centers are removed by annealing near the glass transition temperature. The kinetics of the temporal change of photocurrent during illumination are discussed in a model of defect-conserved bond switching.