Electronic structures and local atomic configurations in amorphous GeSe and GeTe

Abstract

The valence- and conduction-band electronic densities of states (DOSs) in amorphous (a-) GeSe and GeTe were investigated by means of ultraviolet photoemission and inverse-photoemission spectroscopy (UPS and IPES), respectively. The UPS spectra for both a-GeSe and a-GeTe are very similar to those obtained in previous experiments; a distinct peak appears near the top of the valence band. The IPES spectra for both a-GeSe and a-GeTe corrected by subtracting the background exclude the possibility of a structure with 3(Ge):3(chalcogen) coordination if one compares them with the theoretical DOS calculated by O'Reilly, Robertson and Kelly. The corrected IPES spectrum for a-GeSe resembles the broadened theoretical DOS for chemically ordered 4(Ge):2(Se) structure, whereas that for a-GeTe resembles the theoretical DOS for randomly bonded 4(Ge):2(Te) structure. The characters of the conduction-band DOSs for a-GeSe and a-GeTe were also examined by means of soft-x-ray core absorption spectroscopy. The Ge and Se core absorption spectra of a-GeSe are very similar to those of a-, and were discussed using a simple bonding model with a 4(Ge):2(Se) local configuration. The Ge and Te core absorption spectra of a-GeTe were also discussed using a simple local bonding model. All of the present measurements indicate that both a-GeSe and a-GeTe have structures with 4(Ge):2(chalcogen) coordination.