Carbon vacancy-related centers in 3 C -silicon carbide: Negative-U properties and structural transformation

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 degrees 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 VSiC4 -> VCCSiC3. Both defects are deep donors and thus not suitable for achieving semi-insulating properties.