First principles calculations of structural, electronic, thermodynamic and optical properties of BAs1-xPx alloy

First principles calculations have been used to investigate the structural, electronic, thermodynamic and optical properties of boron ternary alloy BAs1-xPx, using a hybrid full-potential (linear) augmented plane wave plus the local orbitals (APW + lo) method within the density-functional theory (DFT). The Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) as well as the Engel-Vosko (EV)-GGA are used to calculate the band gap. We investigated the effect of composition on lattice constant, bulk modulus and band gap. Deviations of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the alloy. Using the approach of Zunger and co-workers, the microscopic origins of the gap bowing are explained. The thermodynamic stability of the alloy is investigated by calculating the excess enthalpy of mixing Delta H-m as well as the phase diagram. The calculated phase diagram showed a broad miscibility gap for the alloy of interest with a high critical temperature. For optical properties, the compositional dependence of the refractive index and the dielectric constant is studied.