First-Principles Insights in Designing Two-Dimensional BY 1– x Z x (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 BY 1– x Z x (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 BY 1– x Z x 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 BY 1– x Z x 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 BY 1– x Z x 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 BSb 1– x As x, ∼1 eV). However, the edge conduction bands show a relatively small fluctuation, which is the lowest for BAs 1– x P x alloys (∼0.02 eV) on increasing x . The absorption coefficient of BY 1– x Z x alloys as a function of x shifts the peak toward blue. Further, BAs 1– x P x alloys exhibit positive enthalpy of mixing and thus can grow by obeying an endothermic reaction. However, BSb 1– x P x and BSb 1– x As x alloys, with negative mixing enthalpies, can be grown by an exothermic reaction. The binodal and spinodal decomposition curves predict the growth temperature of BAs 1– x P x, BSb 1– x P x, and BSb 1– x As x alloys to be −208, 3082, and 1801 K, respectively.