First-principles investigation of donor-acceptor pairs in proximity of silicon carbide surfaces

We recently proposed¹ that donor-acceptor pairs (DAPs) in diamond and silicon carbide (SiC) may be utilized to achieve optically controllable, long-range interactions between point defects. A key challenge in using DAPs for this purpose is that their dipoles are randomly oriented in bulk crystals. Using first-principles calculations in Quantum Espresso and WEST codes, we address this problem by considering DAPs in proximity of surfaces. Specifically, we investigate a vanadium defect near a (2x1) OH-terminated SiC surface. This configuration leads to the alignment of the dipole moment formed between the vanadium and surface atoms in the direction perpendicular to the surface, which significantly enhances dipole-dipole coupling, thus paving the way to engineering 2D arrays of vanadium defects. We characterize near surface vanadium DAPs by computing several properties, including zero-phonon line energies, radiative lifetimes and electron-phonon coupling. In addition, we investigate the photostability of the vanadium defect, and compute its stimulated emission and photoionization cross sections, as well as their dependence on the polarization angle of an incident laser. We find that such polarization can be efficiently used to either enhance or completely suppress stimulated emission or photoionization. The polarization-based modulation of optical behavior identified here can be extended to other defect systems, including NV⁰ and NV^- centers in diamond, where photoionization plays a crucial role.