Electronic structure theory of unusually matched BAs1-xPx alloys using high-throughput ab-initio computation

Abstract

BAsP alloys symbolize an appealing class of highly matched ternary III-V semiconductors alloys; do to their unique weak unlikeness in electronegativity and atomic size mismatch between Arsenic (As) and Phosphorus (P). Here using evolutionary algorithm and density functional theory, we explore local atomic structure, thermodynamic, mechanical, dynamical, electronic and band gap variation of BAs-BP system. From out of structure search, tetragonal B2AsP phase (space groupP4‾m2) has been unveiled. The calculated very weak mixing enthalpy for the ordered B2AsP phase, suggest its thermodynamic borderline instability. Analysis of computed elastic constants and phonon spectrum reveal that B2AsP compound is mechanically and dynamically stable. Moreover it is found that the first neighbor cation-anion distances B–As and B–P remain very close to that in the pure binary compounds and corresponds to only ~25% of the change predicted in the virtual crystal approximation. The phonon band structure of B2AsP evinces multiple atypical features such as over bending of the upmost optical phonon branch and a missing LO-TO splitting at zone-centre. Furthermore the Born effective charge of B, As, and P reveals a rather weak dependence with composition. For the electronic properties, we find that the valence band maximum of the ordered B2AsP phase evidence unusual strong coupling between B–As and B–P p-states which reflects strong anomalous B–As and B–P covalent bonds. Finally a nearly vanishing band-gap bowing (b~0.1eV) has been found which results from the small size and chemical differences between As and P atoms.