First-principales calculations on the origins of the gap bowing in Pb1−xCaxS, Pb1−xCaxSe and Pb1−xCaxTe alloys

Abstract

The ab initio full potential linearized augmented plane wave (FP-LAPW) method within density functional theory was applied to study the effect of composition on the structural and electronic properties of Pb1−xCaxS, Pb1−xCaxSe and Pb1−xCaxTe ternary alloys. The effect of composition on lattice parameter, bulk modulus, band gap was investigate. Deviations of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence were observed for all three alloys. In addition, the microscopic origins of compositional disorder were explained by using the approach of Zunger and co-workers. The disorder parameter (gap bowing) was found to be strong for the three alloys and was mainly caused by the chemical charge transfer effect. The volume deformation contributions for all alloys were also found to be significant, while the structural relaxation contributions to the gap bowing parameter were relatively smaller for all alloys.