An electron paramagnetic resonance signal which was observed in C-doped float-zone material after irradiation with 2MeV electrons at room temperature was investigated. It was attributed to a defect with S = 1/2, an apparently isotropic g-factor of 2.0030, and a complicated hyperfine structure from 29Si nuclei in 5 shells that were consistent with an overall trigonal symmetry. Subtle asymmetries of the hyperfine pattern indicated the presence of a small trigonal component of the g tensor. An additional pair of satellite lines was attributed to 13C which occupied 2 equivalent sites on the trigonal axis. Several defect structures which contained 2 equivalent C atoms on a trigonal axis were investigated by using ab initio Hartree-Fock calculations. Only the negative charge state of a center in which the C atoms occupied adjacent substitutional sites, Cs-Cs, was found to be consistent with the electron paramagnetic resonance data.

Dimer of Substitutional Carbon in Silicon Studied by EPR and ab initio Methods J.R.Byberg, B.Bech Nielsen, M.Fanciulli, S.K.Estreicher, P.A.Fedders: Physical Review B, 2000, 61[19], 12939-45