The interstitial C (CI) impurity vibrational modes in monocrystalline Si-rich SiGe compounds were investigated by Fourier Transform Infra Red spectroscopy and density functional modelling. The two absorption bands of CI were found to be close to those in Si, but lines exhibited shifts in opposite directions with increasing Ge content. The transversal mode band at 932/cm shifted slightly to the high-frequency side, while the longitudinal mode at 922/cm underwent a marked red-shift. Each CI-related band was found to consist of 2 components. Such 2-component structure of bands was suppose most likely to correspond to different combinations of Si and Ge atoms in the neighborhood of the CI atom. The CI in Si1−xGex was found to begin to anneal at lower temperature than in Si and occurred in two stages. During the first stage (210–250K) the main components of bands anneals and revealed components grew in intensity. At above 250K, all components start to disappear. The CI defect was modelled by a super-cell density-functional pseudopotential method. From energetics, it was found that each Ge–C bond costs at least 0.4eV in excess of a Si–C bond. The vibrational mode frequencies taken from several randomly generated SiGe cells produce the observed opposite shifts for the transverse and longitudinal modes. However, structures where Ge atoms were second neighbors to the C atom were marginally bound, and may explain the two-component band structure in the absorption measurements.

Interstitial Carbon-Related Defects in Si1-xGex Alloys. L.I.Khirunenko, Y.V.Pomozova, M.G.Sosnin, A.Duvanskii, V.J.B.Torres, J.Coutinho, R.Jones, P.R.Briddon, N.V.Abrosimov, H.Riemann: Physica B, 2007, 401-402, 200-4