The incorporation of substitutional carbon (Csub) in low-temperature epitaxial Si1-x-yGexCy thin films using SiH4, GeH4 and C2H4 by ultra-high-vacuum chemical vapor deposition was investigated in this work. The Si1-x-yGexCy alloys have been grown at a temperature range from 550 to 600 °C. The Csub content in Si 1-x-yGexCy increases with increasing C 2H4 partial pressure under the same SiH4 and GeH4 condition. The addition of excessive C2H4 causes the degradation of Si1-x-yGexCy crystallinity, surface roughening and the suppression of Ge incorporation. The C-C double bonds in C2H4 were responsible for the highest percentage of Csub, only 0.2%, incorporated in Si 0.8-yGe0.2Cy. The Ge, B and C concentration were determined by secondary ion mass spectroscopy (SIMS). The total C atoms incorporation efficiency is ∼0.05. The maximum concentration of C sub in Si1-x-yGexCy increases with the decrease of Ge content. In the ambient of hydride-based CVD at low-growth pressure and temperature, the presence of GeH4 would impede the incorporation of Csub in Si1-x-yGexC y/Si heterostructure using C2H4 as C source.