Density functional theory studies of optically active defects in two-dimensional hexagonal boron nitride

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Defects in solid-state materials are promising candidates to serve as single-photon emitters in forthcoming quantum technologies. In particular, defects in hexagonal boron nitride (h-BN) have generated significant interest due to their attractive optical and spin properties. Motivated by the desire to develop single-photon sources which can operate at room temperature, we have performed two density functional theory (DFT) studies of quantum defects in two-dimensional h-BN. Recent studies suggest that carbon trimer defects in h-BN might be responsible for single-photon emission in the visible spectral range. In our first study, we combine group theory and DFT calculations to predict properties of the neutral C2CN carbon trimer defect. We calculate the ground and excited state energies, and the radiative and non-radiative rates associated with several transitions. The results of our calculations are then used to simulate an optically detected magnetic resonance experiment. Our findings are important as experimental observations can be compared with our theoretical predictions to aide in the identification of the defects responsible for observed single-photon emission. Our second study is motivated by recent observations of Fourier transform (FT) limited photons emitted from h-BN flakes at room temperature. The mechanism responsible for the narrow lines has been suggested to be a decoupling of the defect from in-plane phonons due to an out-of-plane distortion of the emitter's orbitals. All decoupled emitters produce photons that are directed in-plane, suggesting that the transition dipoles are perpendicular to the h-BN plane. Motivated by the promise of an efficient and scalable source of indistinguishable photons that can operate at room temperature, we have developed an approach using DFT to determine the electron-phonon coupling for defects that have in- and out-of-plane transition dipole moments. We find no indication that an out-of-plane transition dipole is sufficient to obtain FT-limited photons at room temperature. Our work also provides direction to future DFT software developments and adds to the growing list of calculations relevant to researchers in the field of solid-state quantum information processing.
Single-photon sources
Sharman, K. (2022). Density functional theory studies of optically active defects in two-dimensional hexagonal boron nitride (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from