Photostructural change of lattice-vibrational spectra in Se-Ge chalcogenide glass

Abstract

Far-infrared absorption spectra of amorphous-chalcogenide semiconductors were measured in the frequency region 500–80 cm−1. A reversible change in the lattice-vibrational spectra of amorphous Se-Ge films at room temperature due to photoirradiation and heat treatment is first reported. A peak in the 256.4-cm−1 absorption band is broadened and weakened by light photoirradiation and recovers by heat treatment, an effect which is associated with the ’’photodarkening effect’’ in amorphous-chalcogenide films. By photoirradiation, no changes were observed in Raman scattering spectrum for amorphous Se-Ge. It is indicated that photoirradiation enhances further disorder in the atomic configurations and induces a decrease in band-gap energy. Broadening and weakening are caused by an increased fluctuation in the Se-Ge bond angle by photoirradiation, wherein the increased fluctuation degree corresponds to a frozen-in state of the thermally excited fluctuation. Through the Grüneisen parameter, correlation with several macroscopic properties, such as volume expansion, is discussed.