Electronic Structures and Optical Properties of GeTe and Ge ₂Sb ₂Te ₅

Abstract

The optical properties of GeTe and Ge 2 Sb 2 Te 5 have been studied by means of the density functional theory (DFT) in the local density approximation (LDA). The electronic band structures were obtained by two methods, the plane wave (PW) and spherical wave (SW) expansions of the wave functions. GeTe was calculated to be semiconductive, and Ge 2 Sb 2 Te 5 to be semimetallic. The frequency dependent optical constants such as refractive index and extinction coefficient were calculated and compared with those obtained experimentally. The origin of the peaks in the extinction coefficient spectra was assigned in terms of the transitions between Ge, Sb and Te p states. Dynamical calculations with respect to Ge 2 Sb 2 Te 5 have also been performed in order to obtain an understanding of its structural features. The displacements of the Te atoms were found to be larger than those of the Ge and Sb atoms.