Identification and thermal stability of point defects in neutron-irradiated hexagonal boron nitride (h-BN)

Abstract

Point defects in wide-bandgap semiconductors, such as hexagonal boron nitride (h-BN), have driven enormous amounts of research due to their interesting optical properties such as quantum emission at room temperature. Defect engineering by particle irradiation is a very interesting strategy for producing quantum emitters in a controlled way. The identification of most point defects is done by electron paramagnetic resonance and related advanced techniques. Following our recent works, we present new data about point defects produced by neutron irradiation at room temperature and investigate their thermal stability in crystalline, flake and ultrafine h-BN powder. Our experimental data indicate the formation of the nitrogen antisite defect next to a nitrogen vacancy in its neutral charge state, (NBVN)0, with spin S= 1/2 in all types of h-BN showing strong axial hyperfine interaction (A || ≈ 95 MHz and A ⊥ ≈ 5 MHz). It is thermally stable up to ~600 ºC, which is similar to the disappearance of the negative charged boron vacancy, . In addition, after neutron irradiation of h-BN powder samples, a spin S= 1/2 point defect is observed presenting an axial superhyperfine interaction with two equivalent nitrogen nuclei (14N, I = 1, 99.68%), which we tentatively assign to the CNVB defect. It is thermally stable up to ~850 ºC. Another, yet-unidentified S = 1/2 center acts as a charge compensating defect at specific annealing temperatures. Our experimental results are compared and discussed with theoretical models available in the literature.