First-principles investigation of BNxP1-x, BNxAs1-x and BPxAs1-x ternary alloys

First-principles calculations have been used to investigate the structural and electronic properties of boron ternary alloys (BNxP1-x,BNxAs1-x and BPxAs1-x)using full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). We investigated the effect of composition on lattice constants, bulk modulus and band gap. A strong deviation of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for BNxP1-x and BNxAs1-x alloys, while in the case of BPAs1-x alloy only a marginal deviation were found for both properties. This is mainly due to the large mismatch of the lattice parameter and bulk modulus of BN with the corresponding values at the other two binary semiconductors. 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 BNxP1-x and.BNxAs1-x alloys and was mainly caused by the chemical charge transfer effect. The volume deformation contributions for both alloys were also found to be significant, while the structural relaxation contributions to the gap bowing parameter were relatively ignorable. The gap bowing of BPxAs1-x alloy was found to be much smaller than those of the other two alloys. In order to investigate the thermodynamic stability of BNxP1-x, BeNxAs1-x and BPxAs1-x alloys we first calculated the excess enthalpy of mixing Delta H-m as a function of concentration (x). Then by using a regular model solution the x-dependent interaction parameter, Omega, was obtained from the result of Delta H-m versus x. Finally, by using this Omega value, the phase diagram of the alloys was calculated. It was shown that all of these alloys are stable at lowtemperature. (c) 2005 Elsevier B.V. All rights reserved.