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 scatteringspectrum 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.