First principle investigation of mercury chalcogenides and their HgSxSe1−x and HgSxTe1−x ternary alloys

Total-energy calculations of HgS, HgSe, HgTe and their HgSxSe1−x and HgSxTe1−x ternary alloys using first principle full potential-linearized augmented plane wave (FP-LAPW) plus local orbital method within the density functional theory (DFT). The structural properties at equilibrium are investigated by using the new form of generalized gradient approximations (GGA_PBEsol) that are based on the optimization of total energy. For band structure calculations, both GGA and modified Becke–Johnson (mBJ) of the exchange–correlation energy and potential, respectively, are used. HgS is found to be a semiconductor while HgSe and HgTe semi-metallic. The lattice parameters and mechanical properties of binary compounds have been determined. Our investigation on the effect of composition on lattice constant, bulk modulus and gap energy shows almost nonlinear dependence on the composition. The HgSxSe1−x alloys remain semiconductor with a positive energy gap for the whole concentration range which is not the case for HgSxTe1−x ternary alloys. The bowing of the fundamental gap versus composition for HgSxSe1−x is marginal. Besides, a regular-solution model is used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. Temperature dependent thermal properties including the thermal expansion, Debye temperature and heat capacity are calculated using model based on the quasi-harmonic approximation (QHA).