Native point defects and impurities in hexagonal boron nitride

Hexagonal BN (h-BN) is attracting a lot of attention for two-dimensional electronics and as a host for single-photon emitters. We study the properties of native defects and impurities in h-BN using density functional theory with a hybrid functional. Native vacancy and antisite defects have high formation energies, and are unlikely to form under thermodynamic equilibrium for typical growth conditions. Self-interstitials can have low formation energies when the Fermi level is near the band edges, and may form as charge compensating centers; however, their low migration barriers render them highly mobile, and they are unlikely to be present as isolated defects. The defect chemistry of h-BN is most likely dominated by defects involving carbon, oxygen, and hydrogen impurities. Substitutional carbon and oxygen, as well as interstitial hydrogen and boron vacancy-hydrogen complexes, are low-energy defects in h-BN. Based on our results, we can rule out several proposed sources for defect-related luminescence in h-BN. In particular, we find that the frequently observed 4.1 eV emission cannot be associated with recombination at C-N, as has been commonly assumed. We suggest alternative assignments for the origins of this emission, with C-B as a candidate. We also discuss possible defect origins for the recently observed single-photon emission in h-BN, identifying interstitials or their complexes as plausible centers.