First-principle study of optical properties of Cu-doped CdS

Based on the full-potential linearized augmented plane wave (FLAPW) method, we study the electronic structure and optical properties in the Cu-doped CdS semiconductor. We find that the d orbitals of Cu are strongly hybridized with the p orbitals of S near the Fermi level, resulting in p and d charge transfer between Cu and S atoms. These lead to transit from a semi-metal to metal with increase of Cu dopant concentrations, enhancing the conductivity of CdS significantly. As a consequence, the optical transition between valence band and unoccupied d states of Cu enhances greatly, and is stronger than the intrinsic optical transition of CdS semiconductor. Along with the increase of Cu concentrations, the absorption spectra gradually shift to higher energy (blue shifts), and optical absorption of Cd1−xCuxS increases in the visible range.