Kinetics of self-bleaching in some photodarkened Ge–As–S amorphous thin films

Three amorphous Ge–As–S films with the average coordination numbers of 2.4–2.8 were prepared by thermal evaporation. True relaxation that is self-bleaching of photodarkened state has been studied. Considerable differences in kinetics of relaxation of photodarkened state were observed for Ge12As17S71 (Sa 1) and Ge15As20S65 (Sa 3) amorphous thin films. In both cases, the relaxation (self-bleaching) followed stretched exponential, however, flexible matrix of Sa 1 film relaxed significantly faster than the matrix of Sa 3 film. The amorphous film Ge25.5As29.5S45 (Sa 8) was found to be insensitive to illumination. It is suggested that the network rigidity may significantly influence the magnitude of photodarkening and the rate of relaxation of photodarkened state.