Electronic structure of Ge-As-Te glasses

The electronic structure of Ge0.2Te0.8 and Ge0.1AsxTe0.9-x glasses with x = 0.2, 0.46 and 0.54 has been experimentally determined by X-ray photoelectr on spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The values o f the Ge 3p(3/2), As 3p(3/2) and Te 3d(5/2) core level binding energy do no t vary significantly within this series of glasses in agreement with thr co valent character of the bonds. The atomic contributions to the main observe d peaks in the XPS valence bands and XAS spectra are obtained from a molecu lar calculation. This approach is first used for crystalline As2Te3 and com pared to a periodic tight-binding calculation in order to check its accurac y for the analysis of the experimental data in terms of local environments. The electronic structure of Ge0.2Te0.8 is consistent with the existence of GeTe4 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 tw o broad bands which are due to the s- and p-type valence electrons of the d ifferent 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 chang es 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 reser ved.