A review of the specific role of oxygen in irreversible photo- and thermally induced changes of the optical properties of thin film amorphous chalcogenides

Abstract

Recent results concerning the influence of oxygen on the photo- and thermally induced changes of optical properties of thin amorphous chalcogenides are summarized. It is shown that interaction of the surface of thin films with oxygen considerably affects the shift of the optical gap. The influence of oxygen is perhaps twofold. It behaves probably like a “catalyzer in the process of oxygen-assisted bond reconstruction” as proposed by Spence and Elliott [Phys. Rev. B 39 (1989) 5452], but it also enters directly into the film network forming strong covalent bonds with germanium and chalcogen atoms, respectively. Hence, the presence of oxygen during illumination or annealing of thin amorphous chalcogenide films most probably affects (i) the density of dangling and homopolar bonds, respectively, (ii) and actual chemical composition of the surface layer making this one oxygen rich (in normally deposited thin films) but also, chalcogen poor (in some obliquely deposited thin films). The role of oxygen in the case of illumination or annealing of amorphous chalcogenide films is of considerable importance and should not be neglected.