An ab initio study of the "direct-indirect band gap" transition in Al_xIn_1-xP alloys

The composition-induced "direct-indirect" band gap transition in the Al_xIn_1-xP alloys was studied theoretically. Two different approaches - virtual crystal approximation and supercell-based calculations, both in the general gradient and local density approximations - were used to model the influence of the chemical composition on the structural and electronic properties of the Al_xIn_1-xP system in the whole range of Al concentration x from 0 to 1. The band gap crossover from the direct to indirect band gap was shown to take place at x=0.406, in excellent agreement with the experimental result x=0.408 of Beaton et al. It was also demonstrated that the supercell-based calculations are better suited to describe variation of the composition-driven structural properties, whereas the virtual crystal approximation is better to be employed for the analysis of the electronic properties of the title system.