Investigation of opto-electronic properties of ZnS polymorphs through modified Becke-Johnson exchange potential

Abstract

The structural, electronic and optical properties of ZnS polymorphs are studied systematically based on Density Functional Theory (DFT). A competition between the Rocksalt (B1), zinc-blende (B3) and wurtzite (B4) as the ground state phase is found depending on whether LDA (Local Density Approximation) or GGA (Generalized Gradient Approximation) is used. In both approximations, we have investigated within Gibbs free energies, the transition pressures of (B3) and (B4) phases to (B1) structure. To calculate the electronic and optical properties of (B3) and (B4) phases of ZnS, the exchange-correlation potential is treated with two approximations, and we have found that the newly modified Becke-Johnson (mBJ) functional, significantly improves the band gap energies. We have predicted a direct band gap for the both phases of the material of interest. Moreover, the densities of states for the two polymorphs are also presented. Additionally, the dielectric function and other parameters are calculated for discussing the optical properties of ZnS. The comparison of the calculated energy band gaps with the available experimental data is indicated that the mBJ provides a better description of the electronic properties of ZnS than the standard approach. Our results are consistent with the literature data.