“Giant” photo-darkening in Ge16As26S58 amorphous thin film

Amorphous Ge16As26S58 thin films prepared by thermal evaporation were illuminated using the monochromatic light with wavelength λ=442nm. “Giant” red shift of the optical gap around 220 meV induced, at the room temperature, was observed. The kinetics of the red shift of the gap follows stretched exponential. Differential infrared spectra indicate that upon illumination a structural arrangement of the well annealed films is slightly changed in direction of as-prepared film. Raman spectra of well annealed film indicate presence of As4S3 molecular units which, however, disappeared upon illumination. Photo-induced changes of the optical gap and the slope of optical absorption edge are interrelated. We suppose that the “giant” photo-darkening observed is associated with structural disorder of studied film driven by nanophase separation.