Observation of photoluminescence from spin triplet states of excitons bound to interstitial carbon-oxygen complexes (Ci-Oi) in silicon was reported. New luminescence peak labelled as CT line emerges at the energy 2.64meV below the well-known luminescence from the no-phonon transition of a Ci-Oi singlet state situating at 790meV (C line). Observations of local vibrational modes associated with CT line and the temperature dependence of the relative intensity between CT and C lines led to unambiguous identification of CT line as the no-phonon line from Ci-Oi defects. In addition, the host silicon isotope shift of CT line was equal to that of C line, indicating that CT line was no-phonon luminescence as well. Furthermore, the photoluminescence measurements carried out in magnetic field showed that CT line was associated with an isotropic spin triplet state due to quenching of orbital angular momentum of the hole composing the bound exciton.

Optical Properties of Triplet States of Excitons Bound to Interstitial-Carbon Interstitial-Oxygen Defects in Silicon. T.Ishikawa, K.Koga, T.Itahashi, K.M.Itoh, L.S.Vlasenko: Physical Review B, 2011, 84[11], 115204