Si and epitaxial SiGe strained and relaxed layers have been implanted with C+ ions to investigate the formation of SiCy and SiGexCy alloys (medium doses) as well as the ion beam synthesis of SiC in SiGe matrices (high doses). These layers have been analyzed by Raman scattering, in correlation with XRD, XPS and TEM. These data show that for implant temperature of 500 degree(s)C (crystalline target), carbon is not incorporated in substitutional sites, and (beta) -SiC precipitates aligned with the implanted matrix are formed. The residual strain and the degree of missorientation of these precipitates depend on the strain, defects and bond length of the implanted matrix. Moreover, precipitation of (beta) -SiC in the implanted region causes an enhanced Ge migration, mainly towards the surface. This determines a Ge enrichment and consequent relaxation of the Si1-xGex matrix. This contrasts with the room temperature implants performed in preamorphized Si layers, where carbon incorporation in substitutional sites (Cs) takes place after thermal annealing. The maximum amount of Cs is found for the implanted dose corresponding to a peak carbon concentration of 1.3%. For higher doses, there is a degradation of the crystal quality of the recrystallized layer.