First-principles calculation of sulfur-selenium segregation in ZnSe1-xSx: The role of lattice vibration

First-principles phase diagram calculations based on density functional theory within the generalized gradient approximation in combination with Monte Carlo (MC) techniques and cluster expansion were performed for the ZnSe1-xSx alloys. Formation energies were used as a basis for fitting cluster expansion Hamiltonians. All formation energies of ZnSe1-xSx alloys are positive, showing that ZnSe1-xSx alloys is a miscibility gap system and has a tendency to phase separation. For ZnSe1-xSx alloys the phase diagram computed with conventional cluster expansion shows a miscibility gap with consolute temperature T-c = 327 K. The contributions of lattice vibration reduce T-c to 281 K (about 15%). We presented a MC study of the spatial distribution of S and Se in ZnSe0.5S0.5 alloys. We found that, the system becomes more homogeneous including lattice vibration at lower temperature. It is consistence with the calculation of phase diagram of ZnSe1-xSx alloys. (C) 2015 Elsevier Ltd. All rights reserved.