On the photo- and thermally-induced darkening phenomena in As_(40)S_(40)Se_(20) amorphous chalcogenide thin films

摘要

Annealing (in vacuum) at a temperature near the glass transition temperature and exposure (in air) with bandgap light of thermally-evaporated As_(40)S_(40)Se_(20) amorphous chalcogenide thin films, were found to be accompanied by structural changes, which lead to changes in the refractive index and shifts in the optical absorption edge. Indications of photo-oxidation were found after light exposure in air. An optical characterization method, based on the transmission spectra at normal incidence of uniform thickness thin films, has been used to obtain the optical constants and the film thicknesses corresponding to the virgin, annealed and exposed As_(40)S_(40)Se_(20) samples. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. The optical absorption edges are described using the `non-direct transition' model proposed by Tauc.