LAUSR

Combining electron paramagnetic resonance (EPR) spectroscopy and first-principles density functional theory calculations we have identified the carbon monovacancy center and a second carbon vacancy-related defect, the carbon vacancy--carbon antisite defect in $3C$-SiC. In close analogy to the vacancy in silicon, the carbon vacancy in $3C$-SiC with its four potentially equivalent silicon dangling bonds shows a strong Jahn-Teller effect, confirming previously predicted negative-$U$ properties. High-temperature annealing (above 700 \ifmmode^\circ\else\textdegree\fi{}C) of electron or proton irradiated samples anneals out the primary silicon monovacancies and generates a new defect, which we assign to the carbon vacancy--carbon antisite complex. As predicted by theory, this defect is the result of a structural instability of the silicon vacancy in the positive charge state, which transforms at high temperatures according to ${V}_{\mathrm{Si}}{\mathrm{C}}_{4}\ensuremath{\rightarrow}{V}_{\mathrm{C}}{\mathrm{C}}_{\mathrm{Si}}{\mathrm{C}}_{3}$. Both defects are deep donors and thus not suitable for achieving semi-insulating properties.