Piezoelectric, dielectric and polarization properties of AlBN

AlN is a material of great importance for acoustic-wave devices and micro-electromechanical systems due to its polar wurtzite structure resulting in strong spontaneous polarization and piezoelectricity. Alloying Sc into AlN leads to even higher piezoelectricity and dielectric permittivity, as well as ferroelectricity. Alloying B into AlN should result in similar desired properties, while avoiding the decrease of the bandgap observed in AlScN. To develop insights into the fundamental properties we employ density functional theory calculations to investigate the spontaneous polarization, piezoelectric constants, and coherent ferroelectric switching barrier of AlBN alloys. We find the somewhat counterintuitive result that both the spontaneous polarization and coherent ferroelectric switching barrier increase with B concentration, while the relevant components of the piezoelectric tensor decrease. Additionally, our systematic study of the dielectric permittivity reveals that ε₃₃ is significantly increased near the B concentration where the wurtzite-to-layered hexagonal phase transition happens. Such enhancement has been observed by both simulating a quasi-random supercell structure and averaging among several randomly picked supercell structures.