High-throughput first-principles investigation of GaN-AlN ternary system

Abstract

The ternary III-Nitride AlxGa1-xN ternary is one of the paradigm materials that have recently revolutionized lighting technology in the ultraviolet spectrum. A systematic investigation of the GaN-AlN system using ab initio evolutionary algorithm evidence that AlxGa1-xN alloys exist in ordered ground-state structure at ambient conditions. Cubic (AlGa3N4 (x = 0.25), Al3GaN4(x = 0.75)) and tetragonal (AlGaN2 (x = 0.5)) are found thermodynamically quite or nearly stable. Computed elastic constants and phonons show that these phases are mechanically and dynamically stable. Using state-of-the-art LDA-1/2 approach we determine the direct band gap bowing of AlGaN alloys. We found a downward bowing parameter of b∼1.39eV over the entire composition range. Furthermore the optical band gap bowing is found composition-dependent. For x = 0.5, our theoretical analysis divulges that chemical effects are the main factor leading to b parameter.