Electronic-structure and local-order study ofGexSe1−xglasses

X-ray photoelectron spectroscopy (XPS) and tight-binding calculations are used to study the electronic structure and the local order in ${\mathrm{Ge}}_{\mathrm{x}}$ ${\mathrm{Se}}_{1\mathrm{-}\mathrm{x}}$ glasses (0<x<0.42). The shape of the valence electronic density of states in Ge-Se compounds is discussed in terms of (4:2)- or (3:3)-coordinated local structures and Ge-Se, Ge-Ge, and Se-Se bonds. It is shown that Ge 4s and Se 4s band shapes are very sensitive to the presence of Ge-Ge and Se-Se bonds, respectively. Se-rich glasses (x<0.33) can be described with 4:2 coordination and Ge-Se and Se-Se bonds whereas Ge-rich glasses (x>0.33) can be described with 4:2 and 3:3 coordinations and Ge-Se bonds.