First-Principles Insights in Designing Two-Dimensional BY _{1– <i>x</i>} Z _<i>x</i> (Y, Z = P, As, and Sb, but Y ≠ Z) Alloys: A Potential Candidate for Thin-Film Optoelectronic Devices

Forming two-dimensional (2D) alloys provides a unique way to tune the structural parameter and the electronic structure of a material in comparison to their pure counterparts. By taking motivation from this fact, we are presenting a detailed analysis based on first-principles density functional theory calculation for 2D BY1–xZx (Y, Z = P, As, and Sb, but Y ≠ Z) alloys. From a synthesis point of view, it would be interesting to predict (a) How the structural parameters and electronic structure of BY1–xZx alloys are going to change with doping concentration (x)? (b) How will x affect the thermodynamical stability of alloys? and (c) What are the growth temperatures of these alloys? Our calculations reveal that an increase in x decreases the lattice constant of BY1–xZx alloys, which is in accordance with Vegard’s law. Electronic structure calculations predict a direct band gap for pristine BP, BAs, and BSb at high symmetry point K, equal to 1.35, 1.18, and 0.60 eV, respectively. We notice that for BY1–xZx alloys, the band gap remains direct and shows bowing at x = 0.33. There is a sharp fluctuation in edge valence bands during the band alignment of alloys (maximum for BSb1–xAsx, ∼1 eV). However, the edge conduction bands show a relatively small fluctuation, which is the lowest for BAs1–xPx alloys (∼0.02 eV) on increasing x. The absorption coefficient of BY1–xZx alloys as a function of x shifts the peak toward blue. Further, BAs1–xPx alloys exhibit positive enthalpy of mixing and thus can grow by obeying an endothermic reaction. However, BSb1–xPx and BSb1–xAsx alloys, with negative mixing enthalpies, can be grown by an exothermic reaction. The binodal and spinodal decomposition curves predict the growth temperature of BAs1–xPx, BSb1–xPx, and BSb1–xAsx alloys to be −208, 3082, and 1801 K, respectively.