Electronic structure of amorphous and crystalline (GeTe)1-x(Sb2Te3)x investigated using hard x-ray photoemission spectroscopy

We have investigated the valence-band density of states and core levels of the amorphous and crystalline (GeTe)(1-x)(Sb2Te3)(x) (x=0-1/3) pseudobinary compounds using hard x-ray photoemission spectroscopy. In the valence-band spectra, the crystalline phases show three-peak structures which represent the valence band of the average V-valent materials. This structure is maintained during the crystalline to amorphous phase transition, indicating that no drastic changes occur in the s(2)p(3) valence configuration during the phase transition. The crystalline spectrum broadens with increasing x due to the increasing randomness of the atomic arrangement caused by the vacancies. This randomness makes the spectrum of the crystalline phase resemble that of the amorphous phase except for two fine structures, showing that the overall translation symmetry is still held in the high Sb2Te3 composition region in spite of the local randomness near the valence band maximum. In the Sb core-level spectra, we have observed a chemical shift caused by a change in charge distribution during the phase transition. We have also observed the existence of a neutral Sb component in the Sb2Te3-poor crystalline phases with x=1/45 and 1/23. The present results strongly suggest that a reconstruction from sixfold to threefold p-like bonding takes place during the crystalline to amorphous phase transition.