Polarization properties and enhanced dielectric permittivity of ferroelectric AlBN

AlBN alloys are attracting growing research interest because it is expected that alloying B into AlN will drive it towards ferroelectricity, making CMOS-compatible ferroelectric memory devices possible. Additional attention has focused on the effects of B incorporation on spontaneous polarization, piezoelectric coefficients, and dielectric permittivity. In this work, we employ density functional theory to thoroughly investigate these properties, using both the virtual crystal approximation and explicit alloy supercell calculations. We find the 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 of AlBN alloys is significantly increased near [B] = 0.5, where a wurtzite-to-layered hexagonal phase transition is expected. We correlate the enhancement in dielectric permittivity with the softening of specific phonon modes during the phase transition. Our theoretical study improves the understanding of AlBN alloys by predicting properties not yet measured experimentally and by providing insights that help interpret existing measurements.