Silicon and carbon vacancies in neutron-irradiated SiC: A high-field electron paramagnetic resonance study

Electron-paramagnetic-resonance (EPR) and electron-spin-echo (ESE) studies have been performed that show that isolated VSi^-, VSi⁰, and VC vacancies are the dominant intrinsic paramagnetic defects in SiC treated by room-temperature neutron irradiation with doses up to 10¹⁹cm^-2. This conclusion is supported by the observation of high concentrations of all these defects in 4H- and 6H-SiC that are almost proportional to the irradiation dose. The 95-GHz EPR spectra at 1.2 K prove that the ground state of VSi⁰ corresponds to $S=1$ and that the zero-field splitting parameter D is positive. A possible energy-level scheme and optical pumping process which induces the spin polarization of the ground triplet state of the VSi⁰ vacancy in SiC is presented. In the EPR spectra of VSi^- in 4H-SiC an anisotropic splitting of the EPR lines is observed. This splitting is assumed to arise from small differences in the g tensor of the quasicubic (k) and hexagonal (h) sites. Anisotropic EPR spectra with S=1/2 that are related to the carbon vacancy have also been observed in the n-irradiated SiC crystals. The hyperfine (hf) interaction with the first shell of Si atoms is almost identical to that observed in electron-irradiated SiC crystals. The observed additional 6.8-G hf splitting with 12 carbon atoms in the second shell is considered as a confirmation for the isolated carbon vacancy model.