Some optical properties of Ge–S amorphous thin films

Amorphous GexS1−x films (x=0.27, 0.32, 0.36 and 0.4) were prepared by thermal evaporation. The values of the refractive index, the optical gap and the parameters of the Wemple–DiDomenico single oscillator model were determined. Using Millerʹs generalized rule the values of the third-order non-linear susceptibility were also estimated. Thermally induced bleaching was observed for films studied. Photobleaching was observed for sulfur rich and nearly stoichiometric films (x=0.27, 0.32) while for a germanium rich film (x=0.4) no response to the illumination was observed. The differences in photobleaching are attributed to the role of p-lone pair states and to an overall network rigidity of the films.