A detailed study was made of the dependence, of vibrational modes in rapid thermal chemical vapour deposited SiGeC samples, upon the substitutional C concentration. It was recalled that it was difficult to incorporate substitutional C at concentrations which were higher than a few tenths of 1at%. It was shown that the simultaneous analysis of X-ray diffraction, infra-red absorption and Raman scattering data could be used to deduce the fraction of substitutional C from the total C content. Uncertainty in defining this fraction was suggested to explain discrepancies between the results of previous studies. Frequency shifts of the C local modes, and the Si-Si mode, were studied in addition to the intensity dependence of the former. Changes in C satellite peaks, and their dependence upon total C concentration, were studied. It was found that there was a large frequency change of these modes; thus indicating that a very large local bond distortion was produced by the presence of C in the lattice. It was shown that the shifts of the Si-Si mode frequencies, due to the Ge and C contents, did not simply involve the addition of each separate contribution. The rate at which they shifted, with changing C concentration, depended upon the Ge content of the alloy. The probability of creating ordered substitutional C-C pairs, rather than randomly distributed C atoms, increased non-linearly as a function of C content.

Short-Range Order and Strain in SiGeC Alloys Probed by Phonons. E.Finkman, F.Meyer, M.Mamor: Journal of Applied Physics, 2001, 89[5], 2580-7