First Principles Investigation of the Optical Properties of BNxP1−x (0 ≤ x ≤ 1) Boron Ternary Alloys

The effect of different concentrations of N on the electronic and optical properties of BNxP1−x (0 ≤ x ≤ 1) boron ternary alloys was studied using the full potential linearized augmented plane wave method within the density functional theory (DFT) and time-dependent DFT (TDDFT). The exchange–correlation potential is described in generalized gradient approximation (GGA) within the Perdew et al. scheme. Also, we have used the GW formalism to improve the band gap results, and the calculated band gap within GW shows substantial improvement over GGA. The real and imaginary parts of the dielectric function ε(ω), optical reflectivity R(ω), absorption coefficient α(ω), refractive index and electron energy loss function are computed by random phase approximation for DFT and adiabatic local density approximation for TDDFT. The interband transitions responsible for the structures in the spectra are specified. It is shown that, for ternary alloys, N 2p states and N 2s, P 3d states play a major role in optical transitions as initial and final states, respectively. The results for these alloys indicate that the band gap increases, the static dielectric constant decreases, and all existing structures move toward higher energies by increasing the concentration of nitrogen atoms. The results are compared with other available theoretical and experimental data.