Raman spectra and photostructural changes in the short-range order of amorphous As–S chalcogenides

Abstract

Photoinduced changes of optical transmission, diffuse reflectance, refractive index and Raman spectra of As x S 100− x stoichiometric ( x=40) and non-stoichiometric ( x=38, 42) films, bulk glasses and glassy powders were measured. The photoinduced changes of the absorption edge, diffuse reflectance and refractive index were accompanied by changes in Raman band intensities and positions and, therefore, by changes of structure. The Raman spectra of freshly evaporated films, and spectra of As-rich, contain some bands of As 4S 4 molecules whose content (e.g. ⩾20 mol% in As 42S 58 freshly evaporated films, ∼10 mol% for As 42S 58 glasses) depends on the stoichiometry and state of the films (freshly evaporated, exposed or annealed films) or upon the state of samples (bulk, powdered glass, exposed or annealed powder). The As 4S 4 content decreased by light exposure and also by annealing, while irradiation increases the content of As–As bonds. A model is proposed in which the photoinduced changes of the optical properties in As–S glasses are connected with photostructural changes, which change the short-range order, namely the densities of individual chemical bonds.