Ab initio study of novel III-V nitride alloys B1-xTlxN for optoelectronic applications

In this study, we propose the cubic B1-xTlxN ternary alloy as a promising infrared material. We used the full potential-linearized augmented plane wave (FP-LAPW) method within the Density Functional Theory (DFT) to predict the structural, electronic and optical properties of the B1-xTlxN ternary alloys. The structural properties such as the equilibrium lattice parameter, bulk modulus and its pressure derivative are investigated with the effect of the concentration variation of Tl atom, x (x = 0, 0.25, 0.50, 0.75, and 1). We note that, because of existence of heavy elements in our alloys, spin-orbit coupling (SOC) is incorporated for electronic and optical calculations in order test the effect of spin-orbit interaction on these properties. Our results show the direct nature of the energy band gap of the ternary B1-xTlxN alloy for all composition of Tl-substitution. Furthermore, investigation of the dielectric function and refractive index shows that our materials are active in infrared and visible energy regions. We found that the spin-orbit effects opens up a very small gap at concentrations x = (0.75 and 1), resulting in a nearly metallic behavior of its optical response (imaginary part of dielectric function).