A Theoretical Approach to the Optical Gaps of 1D- and 3D-Se_1−xTe_x

Abstract

To study the relation between the interchain and intrachain interactions as well as to compare the chain-like features with the bulk characteristics in chalcogenide alloys, the Te concentration (x) dependence of the optical gap E_g is theoretically analyzed for Se_1−xTe_x of an isolated chain and a trigonal crystal. In the first place, band structures are calculated for an isolated chain and for a trigonal crystal by the tight-binding approximation. The behaviour of the interaction parameters obtained from our calculations indicates that the chain-like nature of a trigonal crystal becomes less distinguished as the increase of x. Secondly, the electronic density of states of Se_1−xTe_x is calculated by the coherent potential approximation. The results show that the optical gap E_g for a bulk mixture decreases as x increases while E_g for a chain does not change very much for x≥0.2. These results are in good agreement with the experimental data.