Positively charged carbon vacancy defect as a near-infrared emitter in 4H-SiC

Certain intrinsic point defects in silicon carbide are promising quantum systems with efficient spin-photon interface. Despite carbon vacancy in silicon carbide being an elementary and relatively abundant intrinsic defect, no optical signal has been reported associated with it. Here, we revisit the positively charged carbon vacancy defects in the 4H polytype of silicon carbide (4H-SiC) by means of ab initio calculations. We unveil the origin of thermal averaging observed in the EI5 electron spin resonance center associated with the so-called k-site configuration of carbon vacancy as phonon excitations in the strongly coupled electron-phonon system. We further find that the excited state is optically active for the so-called h-site configuration of carbon vacancy, with zero-phonon line at $0.65\phantom{\rule{4pt}{0ex}}\mathrm{eV}$. This defect shows a strong emission with a 9.3 ns optical lifetime. Moreover, the deteriorating effects of phonons on its optical properties are relatively weak, evinced by the calculated quantum efficiency and Debye-Waller factor of 27% and 20%, respectively. Based on these findings, we propose this defect as an exotic paramagnetic near-infrared emitter in the IR-B region.