First principle investigation of AlAs and AlP compounds and ordered AlAs1-xPx alloys

We have investigated the structural and electronic properties of AlAs and AlP compounds and of ordered AlAs1-xPx alloys using the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) method based on density functional theory. The total energies and structural quantities of those compounds have been calculated for different approximations of exchange-correlation energy. The electronic quantities have been found to be in good agreement with the corresponding measured ones when the compounds were defined by the lattice constants of Perdew-Wang-generalized gradient approximation (PW-GGA) scheme. The PW-GGA approach was also applied on ordered AlAs1-xPx alloys to study the effect of composition on lattice constant, band gap, and refractive index of AlAs1-xPx ternary alloys. The calculated lattice constants scale linearly with composition (Vegard's law). The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. In addition to (FP-LAPW + lo) method, the composition dependence of the refractive index was studied by Reedy and Nazeer model. The thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing Delta H-m as well as the phase diagram. (C) 2010 Elsevier B.V. All rights reserved.