Band bowing and the direct-to-indirect crossover in random BAlN alloys

Boron-containing nitride alloys such as BAlN are being explored as novel members of the nitride family of materials for electronic and optoelectronic applications. Using hybrid density functional calculations we determine structural properties, band gaps, and band-gap bowing of random wurtzite BAlN alloys. The fundamental band gap of BN is indirect while AlN is a direct-band-gap semiconductor. This leads to a crossover in the band gap from direct to indirect at $28%$ boron. We find that the direct band gap experiences extreme bowing, leading to a fundamental gap that changes very little up to 17% boron incorporation.