Shallow N donors, shallow B and Al acceptors and various transition metal impurities were investigated, in 6H-, 4H- and 3C-type single crystals, by using electron paramagnetic resonance, electron nuclear double resonance, and their optically detected analogues. On the basis of a small hyperfine interaction of N donors on the hexagonal sites, it was concluded that the lowest effective mass state was of E-symmetry there, and did not have A1-symmetry; as at the quasi-cubic sites. It was shown that N was on the C sub-lattice. The super-hyperfine interactions could be understood by assuming that the conduction band minimum was near to the L point. The Al and B acceptors behaved quite differently. Thus, while Al acceptors seemed to be effective mass-like, B acceptors could best be described as being B-induced C acceptors with pronounced dynamic features. In the case of 6H-type material, Sc acceptors were identified on 3 sites in the C sub-lattice. A luminescence which had previously been attributed to substitutional Sc acceptors therefore must have had a different origin. The electron paramagnetic resonance of V was measured in the V4+ (S = ½) and V3+ (S = 1) charge states on 3 sites in 6H-type material.

J.M.Spaeth, S.Greulich-Weber, M.März, J.Reinke, M.Feege, E.N.Kalbukhova, S.N.Lukin: Materials Science Forum, 1997, 239-241, 149-54