EPR and theoretical studies of positively charged carbon vacancy in 4H-SiC -: art. no. 235212

The carbon vacancy is a dominant defect in 4H-SiC, and the "EI5" electron-paramagnetic-resonance (EPR) spectrum originates from positively charged carbon vacancies (V-C(+)) at quasicubic sites. The observed state for EI5, however, has been attributed to a motional-averaged state with the C-3v symmetry, and its true atomic structure has not been revealed so far. We here report low temperature (<40 K) EPR measurements on EI5 and show that this center has a C-1h-symmetric structure due to Jahn-Teller distortion. We also performed ab inito calculations of the hyperfine tensors for EI5, and obtained a good agreement between experiment and theory in not only their principal values but also their principal axis directions. A good agreement was also demonstrated for the EI6 center (hexagonal-site V-C(+)) in this paper. The transition from EI5(C-1h) to EI5(C-3v) was found to be thermally activated and its activation energy was measured as 0.014 eV.