ELECTRONIC-STRUCTURES AND LOCAL ATOMIC CONFIGURATIONS IN AMORPHOUS GESE AND GETE

The valence-and conduction-band electronic densities of states (DOSs) in amorphous (a-) GeSe and GeTe were investigated by means of ultravio let photoemission and inverse-photoemission spectroscopy (UPS and IPES ), respectively. The UPS spectra for both a-GeSe and a-GeTe are very s imilar to those obtained in previous experiments; a distinct peak appe ars near the top of the valence band. The IPES spectra for both a-GeSe and a-GeTe corrected by subtracting the background exclude the possib ility of a structure with 3(Ge):3(chalcogen) coordination if one compa res them with the theoretical DOS calculated by O'Reilly, Robertson an d Kelly. The corrected IPES spectrum for a-GeSe resembles the broadene d theoretical DOS for chemically ordered 4(Ge):2(Se) structure, wherea s 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 absorpt ion spectroscopy. The Ge and Se 2p(3/2) core absorption spectra of a-G eSe are very similar to those of a-GeSe2, and were discussed using a s imple bonding model with a 4(Ge):2(Se) local configuration. The Ge 2p( 3/2) and Te 3p(3/2) core absorption spectra of a-GeTe were also discus sed using a simple local bonding model. All of the present measurement s indicate that both a-GeSe and a-GeTe have structures with 4(Ge):2(ch alcogen) coordination.