First-principles calculations of structural, electronic, and thermodynamic properties of ZnO1-xSx alloys

In this study the pseudo-potential method is used to investigate the structural, electronic, and thermodynamic properties of ZnO1-xSx semiconductor materials. The results show that the electronic properties are found to be improved when calculated by using LDA + U functional as compared with local density approximation (LDA). At various concentrations the ground-state properties are determined for bulk materials ZnO, ZnS, and their tertiary alloys in cubic zinc-blende phase. From the results, a minor difference is observed between the lattice parameters from Vegard's law and other calculated results, which may be due to the large mismatch between lattice parameters of binary compounds ZnO and ZnS. A small deviation in the bulk modulus from linear concentration dependence is also observed for each of these alloys. The thermodynamic properties, including the phonon contribution to Helmholtz free energy Delta F, phonon contribution to internal energy Delta E, and specific heat at constant-volume C-V, are calculated within quasi-harmonic approximation based on the calculated phonon dispersion relations.