Optical properties and photoinduced changes in amorphous AsS films

The dependence on composition of optical properties and photoinduced changes in thin films of As_xS_100?x with x between 15 and 45 were investigated. The optical band gap and the single oscillator fitting constants show extreme at the stoichiometric composition x = 40 and they vary almost linearly with sulphur content in specimens containing an excess of chalcogen. In contrast, irreversible and reversible photoinduced changes of the optical properties accompany a characteristic transition at x ≈ 30. This suggests that the origin of these effects is attributable to transformations of AsS and SS bonds in films containing an excess of chalcogen. This speculation is supported by thermal analyses.