First-principles study of quasiparticle energies and optical excitations of 3C-SiC divacancy*

Using large-scale GW and Bethe-Salpeter equation (BSE) calculations. we investigate the quasiparticle energies and optical absorption spectrum of the divacancy defect in 3C-SiC, a prototypical defect for quantum information applications. Our calculations provide a quantitative prediction of the defect quasiparticle energy levels and zero-phonon absorption line. Interestingly, despite the presence of localized defect states in the gap, we find that the low-energy excitonic states are made primarily of transitions from occupied defect states to continuum conduction states from 3C-SiC, especially from the X point of the Brillouin zone (BZ). The large hybridization between defect states and bulk states in 3C-SiC is different the NV^- center in diamond and the divacancy in 4H-SiC, where the deep defect levels are well separated from bulk states. Our study highlights the important role of frontier conduction bands in the optical properties and formation of low-energy excitons in 3C-SiC divacancy.