Boron Dangling Bonds as Single Photon Emitters in Hexagonal Boron Nitride

Defects in semiconductors are an attractive candidate to realize quantum information applications such as quantum computing and cryptography, as well as nanoscale sensing. Hexagonal boron nitride (h-BN) is a desirable host for these quantum defects due to its two-dimensional crystal structure, excellent stability, and wide band gap. Single-photon emission has been observed in h-BN from point defects in the lattice, but microscopic identification of the underlying defect has proved elusive. In this work, we employ hybrid density functional theory to demonstrate that the properties of boron dangling bonds are consistent with the experimental reports. Specifically, doubly occupied boron dangling bonds give rise to optical emission at 2.06 eV with a Huang-Rhys factor of 2.3. The emission is linearly polarized, with indirect excitation into the conduction band explaining the lack of dipole alignment seen in experiment. The boron dangling bond possesses a metastable triplet state, which can be used to realize spin-sensing applications.