Prediction and Control of Optical Properties of hBN Defects From First-Principles for Application as Single Photon Emitters

Point defects in semiconductors have emerged as an attractive candidate for applications in quantum information science. Due to their ability to create well-localized states within the band gap, defects can serve as effectively isolated atoms that can be utilized as single photon emitters. Specially, defects in 2D materials carry the addition advantage of being embedded in an environment with reduced dielectric loss and the possibility of integrating with waveguides and cavities. In our work, we focus on neutral and charged defects in monolayer hexagonal boron nitride (h-BN), using boron and nitrogen vacancies as prototypical examples. We first employ the one-dimensional configuration coordinate diagram approach to calculate optical transition levels, relaxation energies, and approximate Huang-Rhys factors. We then perform full calculations of Huang-Rhys factors involving phonon spectra, where we carefully extrapolate spectral functions towards the dilute defect limit. Such extrapolations are performed using an embedding approach relying on the short-rangedness of interatomic force constants in covalent semiconductors. This embedding method allows us to explore other defects and ways to controllably tune their optical properties by, e.g. an applied electric field or strain. Our results can help us to identify defects that can directly serve as or engineered into ideal candidates for single photon emitters.