Thermally induced effects in evaporated chalcogenide films. II. Optical absorption

The shift of the optical-absorption edge when evaporated films are annealed at the glass-transition temperature is investigated in amorphous Ge${\mathrm{Se}}_2$, ${\mathrm{As}}_2$ ${\mathrm{S}}_3$, and ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$, and is related to structural studies described in the previous paper. A higher density of homopolar bonds in as-evaporated films, compared to annealed films, is responsible for the difference in absorption. A model is described that evaluates the effect of homopolar bonds in terms of the absorption in off-stoichiometric bulk glasses, and a good agreement with experiment is obtained.