First principles study of the electronic and optical properties of crystalline and liquid Sb2Te3: Phase-transition-induced changes in optical properties

To clarify the mechanism by which the optical properties of Sb2Te3 change because of its solid-liquid phase transition, we carried out ab initio calculations of the electronic and optical properties of Sb2Te3 in both the crystalline and liquid states. The calculated results indicate that the density of states around the Fermi level increases because of melting and that the energy bandgap observed in the crystalline state consequently disappears. The imaginary part of optical dielectric functions of crystalline Sb2Te3 has a large peak at a photon energy of (h) over bar omega = 1.5 eV. When Sb2Te3 melts, it exhibits somewhat metallic optical properties and its optical absorption at (h) over bar omega = 3.06 eV, which is used in Blu-ray Disc systems, decreases. This decrease in optical absorption is proposed to result from a large reduction of the optical transition strength at (h) over bar omega approximate to 1.5 eV. (C) 2018 The Japan Society of Applied Physics