Reversible and irreversible photostructural changes in amorphous germanium chalcogenides studied by UPS

Abstract

The photoinduced changes in the valence states of amorphous GeS 2, GeSe 2, GeS and GeSe films were studied by UPS. In the He I spectra of GeS 2 and GeSe 2 films prepared at 298 K, the first peak associated with the chalcogen lone pair state shifts reversibly to the high initial energy during illumination, while the peak shifts irreversibly to the low initial energy for the films prepared at 77 K. In the cases of GeS and GeSe, noticeable changes in the spectra were not observed. The results were interpreted from a microscopic point of view in relation to structural changes in the films.