It was recalled that the C vacancy was a dominant defect in 4H-SiC, and that the EI5 electron paramagnetic resonance spectrum originated from positively charged C vacancies (VC+) at quasi-cubic sites. The observed state for EI5 was instead attributed to a motion-averaged state with C3v symmetry. Its true atomic structure had not been revealed so far. Low-temperature (<40K) electron paramagnetic resonance measurements were made of EI5 and it was shown that this center had a C1h-symmetrical structure due to Jahn-Teller distortion. First-principles calculations were also made of the hyperfine tensors for EI5, and good agreement was obtained between experiment and theory; not only in their principal values but also their principal axis directions. Good agreement was also demonstrated for the EI6 center (hexagonal-site VC+). The transition from EI5(C1h) to EI5(C3v) was found to be thermally activated, and its activation energy was 0.014eV.

EPR and Theoretical Studies of Positively Charged Carbon Vacancy in 4H-SiC. T.Umeda, J.Isoya, N.Morishita, T.Ohshima, T.Kamiya, A.Gali, P.Deák, N.T.Son, E.Janzén: Physical Review B, 2004, 70[23], 235212 (6pp)