Theoretical Investigation of Structural, Optoelectronic and Thermodynamic Prpperties of Chalcogenides Based Magnesium

Abstract

The structural, electronic, optical and thermodynamic properties of MgSe_xTe_1-xternary mixed crystals have been studied using the ab initio full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the Perdew–Burke–Ernzerhof-generalized gradient approximation (PBE-GGA)was used for the exchange-correlation potential. Moreover, the recently proposed modified Becke Johnson (mBJ) potential approximation, which successfully corrects the band-gap problem was also used for band structure calculations. The ground-state properties are determined for the wurtzite bulk materials MgTe, MgSe and their mixed crystals at various concentrations (x = 0.25, 0.5 and 0.75)in the wurtzite phase. The effect of composition on lattice constant, bulk modulus and band gap was analyzed. Deviation of the lattice constant from Vegard’s law and the bulk modulus from linear concentration dependence (LCD) were observed for the ternary MgSe_xTe_1-x alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing, ∆Hm as well as the phase diagram. It was shown that these alloys are stable at high temperature. For the optical properties, the compositional dependence of the refractive index and the dielectric constant was studied.