Excitons and Radiative Lifetimes at Point Defects in Hexagonal Boron Nitride from First Principles*

Point defects in hexagonal boron nitride (hBN) have been recently investigated as promising single-photon emitters. Previous theoretical work has proposed candidate atomic structures for these localized emitters using density-functional theory (DFT) calculations, which focused on the defect formation energy, symmetry, and single-particle electronic transitions. Here, we use DFT plus the GW-Bethe-Salpeter equation method to compute the ground and excited states of a set of candidate hBN defect structures. Our calculations can predict the band gap, excitons and radiative lifetimes of the various defects, while including anisotropic dielectric screening and spin-orbit interaction effects. We show that the radiative lifetime can differ by orders of magnitude among different candidate structures, and it can be used as an effective physical quantity to rule out candidate defects. We analyze our results for the most promising structure, which exhibits energy and radiative lifetime in very good agreement with experiment. Through a statistical analysis, we comment on the likelihood that our calculations can successfully identify the structure behind the single-photon emitters observed experimentally.