Effect of Environmental Screening and Strain on Optoelectronic Properties of 2D Hexagonal Boron Nitride Quantum Defects*

Point defects in hexagonal boron nitride (hBN) are promising candidates as single-photon emitters (SPEs) in nanophotonics and quantum information applications. The precise control of SPEs requires in-depth understanding of their optoelectronic properties. However, how the surrounding environment of host materials, including number of layers, substrates, and strain, influences SPEs is not fully understood. In this work, we study the dielectric screening effect due to the number of layers and substrates, and the strain effect on the optical properties of carbon dimer and nitrogen vacancy defects in hBN from first-principles many-body perturbation theory. We report that the screening effect causes a red shift of the GW gap and lowering of the exciton binding energy, leading to nearly constant excitation energy and radiative lifetime. We explain the results with analytical models starting from BSE Hamiltonian in Wannier basis. We show that optical properties of the defects are largely tunable by strain with highly anisotropic response, comparing well with experimental measurements. Our work clarifies the effect of environmental screening and strain on optoelectronic properties of 2D quantum defects, facilitating future applications of SPEs in low-dimensional systems.