Carbon related defects in irradiated silicon revisited

Electronic structure calculations employing hybrid functionals are used to gain insight into the interaction of carbon (C) atoms, oxygen (O) interstitials, and self-interstitials in silicon (Si). We calculate the formation energies of the C related defects C(i)(Si(I)), C(i)O(i), C(i)C(s), and C(i)O(i)(Si(I)) with respect to the Fermi energy for all possible charge states. The C(i)(Si(I))(2+) state dominates in almost the whole Fermi energy range. The unpaired electron in the C(i)O(i)(+) state is mainly localized on the C interstitial so that spin polarization is able to lower the total energy. The three known atomic configurations of the C(i)C(s) pair are reproduced and it is demonstrated that hybrid functionals yield an improved energetic order for both the A and B-types as compared to previous theoretical studies. Different structures of the C(i)O(i)(Si(I)) cluster result for positive charge states in dramatically distinct electronic states around the Fermi energy and formation energies.