Crossover from photodarkening to photobleaching in a-GexSe100-x thin films

In this Letter, we present the interesting results of photodarkening (PD), transition toward photostability, and a slow crossover from PD to photobleaching when composition of the chalcogenide glassy thin film changes from Ge-deficient to rich. A subsequent Raman analysis on these as-prepared and irradiated samples provide the direct evidence of photoinduced structural rearrangement, i.e., photocrystallization of Se and the removal of edge-sharing GeSe4 tetrahedra. Further, our experimental results clearly demonstrate that light-induced effects can be effectively controlled by choosing the right composition and provide valuable information on synthesizing photostable/sensitive glasses.