On the nature of bleaching of amorphous Ge30S70 films

The irreversible photobleaching of amorphous Ge30S70 films is found to depend on the air pressure during exposure. This is most probably a result of photo-oxidation and/or hydrolysis of the layers. The appearance of a Ge-O-Ge vibrational band in the infrared transmission spectra of exposed layers clearly indicates the extrinsic origin of photobleaching. Annealing of the layers is also accompanied by considerable bleaching. In this case the role of oxygen seems to be of less importance and an increase in the density of Ge-S bonds is most probably responsible for the increase of the optical gap.