Electronic structure of Ge-As-Te glasses

The electronic structure of Ge(0.2)Te(0.8) and Ge(0.1)As(x)Te(0.9-x) glasses with x = 0.2, 0.46 and 0.54 has been experimentally determined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The values of the Ge 3p(3/2), As 3p(3/2) and Te 3d(5/2) core level binding energy do not vary significantly within this series of glasses in agreement with thr covalent character of the bonds. The atomic contributions to the main observed peaks in the XPS valence bands and XAS spectra are obtained from a molecular calculation. This approach is first used for crystalline As(2)Te(3) and compared to a periodic tight-binding calculation in order to check its accuracy for the analysis of the experimental data in terms of local environments. The electronic structure of Ge(0.2)Te(0.8) is consistent with the existence of GeTe(4) units connected by Te-Te bonds but does not rule out the presence of ce-Ge bonds. The XPS valence bands of the ternary glasses are formed by two broad bands which are due to the s- and p-type valence electrons of the different atoms, respectively. Increase of the As content mainly changes the p-type peak and the main XAS peaks at the As K and Ge K edges. These changes are due to the decrease in the number of As-Te bonds and the increase in the number of As-As bonds. (C) 2000 Elsevier Science Ltd. All rights reserved.