Optically excited states of point defects in hexagonal boron nitride

Point defects in hexagonal boron nitride (hBN) are often discussed as single-photon emitters for quantum technologies, but in many cases the atomic nature of the defects is still not known. Understanding the dependence of electronic and optical properties on the geometry might help to identify the defects and is also crucial in order to make these emitters applicable. Here, we study a number of defects in a monolayer of hBN using ab-initio techniques. Starting from ground-state density-functional theory (DFT), electronic and optical states are evaluated within many-body perturbation theory (i.e., GW approximation plus Beth-Salpeter equation, BSE). For several defects, significant geometrical changes occur in the excited state, leading to Stokes shifts and spectral broadening. Here we employ constrained DFT to identify excited-state relaxed structures, confirmed by BSE for selected configurations.

[1] A. Kirchhoff, T. Deilmann, P. Krueger, and M. Rohlfing, Phys. Rev. B 106, 045118 (2022).

[2] A. Kirchhoff, T. Deilmann, and M. Rohlfing, Phys. Rev. B 109, 085127 (2024).