Irreversible photobleaching, photorefraction and photoexpansion in GeS2 amorphous film

The photoinduced irreversible effects in thermally evaporated amorphous GeS2 films were investigated. The magnitude of the photobleaching induced by gap photons was found at around ≈13%. The photoinduced increase in the optical band gap and the increase in the slope of the short wavelength absorption edge are discussed within the Davis–Mott model and within Tauc's model for optical transitions in amorphous solids. Based on the optical measurements and the Atomic Force Microscopy we also observed photoexpansion at around ≈4.8% accompanied by a decrease in the refractive index from n = 2.02 for the virgin film to n = 1.94 for a film illuminated until a nearly steady state.