The local vibrational modes of C impurities in relaxed samples were studied, using infra-red absorption spectroscopy, for Ge contents ranging from 5 to 50mol%. This revealed C modes, with frequencies within the range of 512 to 600/cm, in 13C+-implanted samples after annealing at 550C. Measurements of samples which were co-implanted with 12C+ and 13C+ showed that these modes originated from defects which contained a single C atom. On the basis of the variation in mode frequencies with Ge content, the modes were attributed to substitutional C. The observed modes were attributed to specific combinations of the four Si and Ge neighbours of C. The intensities of the modes indicated that the combinations of 4 neighbours deviated from a random distribution.

Substitutional Carbon in SiGe L.Hoffmann, B.Bech Nielsen, A.Nylandsted Larsen, P.Leary, R.Jones, P.R.Briddon, S.Oberg: Physical Review B, 1999, 60[19], 13573-81