Identification of an Oxygen Defect in Hexagonal Boron Nitride

Single-photon emitters in hexagonal boron nitride have been extensively studied recently as they are promising building blocks for quantum information processing. Although numerous defect-related single-photon sources have been found, except for the boron vacancy (V_B), their identification is still elusive. Electron paramagnetic resonance (EPR) could be a powerful tool to identify the structure of point defects. A spin S = 1/2 point defect D3 was observed recently in experiment [1]. Based on the unique EPR line shape, we proposed V_B + X_N defect that containing V_B with one nearest nitrogen atom replaced by an impurity atom “X”. In the V_B + X_N model, the impurity atom should have very low natural abundance of nuclear spin isotopes, for example, carbon (¹³C = 1.1%) and oxygen (¹⁷O = 0.037%). However, we found C_NV_B cannot keep C_2v symmetry and could easily transform to V_NC_B. Formation energy calculations show that the V_NC_B is the dominant defect over C_NV_B [2]. Instead, the negatively charged O_NV_B well reproduces the hyperfine constant and EPR spectra by means of the many-body perturbation theory method on top of hybrid density functional calculations. To our surprise, it also produces a coherent emission around 2 eV with well agreement with previously recorded PL spectrum of some quantum emitters, according to our calculations [3].