The Ky1, Ky2 and Ky3 centers were the dominant defects produced in the electron-irradiated p-type 6H-SiC crystals. An electron paramagnetic resonance study of these defects was performed at 4.2 to 300K for X, K, and Q bands. The centers were characterized by the fourfold Si coordination established on a basis of the observed hyperfine structure. At low temperatures both Ky1 and Ky2 defects revealed the CS symmetry that only slightly deviates from the D2d one. At high temperatures, the thermally activated reorientation from one Jahn-Teller distortion to the others caused the averaging of the Ky1 and Ky2 spectra in such a manner that their spin-Hamiltonians correspond to the axial symmetry. The Ky3 center had axial symmetry in all the temperature range under investigation. Its hyperfine parameters for the first-shell Si atoms were substantially different from those determined for the Ky1 and Ky2 centers. Based on the density functional theory, the calculations of the electronic structure of a number of fourfold Si coordinated defects were carried out for the unambiguous identification of the observed defects through the comparison of experimentally determined and calculated hyperfine parameters. The present study proves an assignment of the Ky1, Ky2 and Ky3 centers to the positively charged C vacancy located in two quasicubic and hexagonal sites of the 6H-SiC lattice, respectively. The features of the VC+ defect related to the multi-valley character of its potential energy surface were also considered. It was shown that this defect could be localized in the minima of different symmetry depending on the occupied lattice site, and these minima were experimentally distinguishable by the values of the hyperfine parameters.

Positively Charged Carbon Vacancy in Three Inequivalent Lattice Sites of 6H-SiC - Combined EPR and Density Functional Theory Study. V.Y.Bratus, T.T.Petrenko, S.M.Okulov, T.L.Petrenko: Physical Review B, 2005, 71[12], 125202 (22pp)