The heteroepitaxial growth of the new ternary, group-IV, semiconductor material,Si1−x−yGexCyon Si(100), has been investigated. The epitaxial quality ofSi1−x−yGexCyis found to be inferior to that ofSi1−xGexwith similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank–van der Merwe to Stranski–Krastanov type growth. We suggest that the very large mismatch between the average bond length in theSi1−x−yGexCymaterial, as determined by Vegard’s law, and the equilibrium Si&sngbnd;C bond length, weakens the Si&sngbnd;C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier for island formation or indirectly through the formation of defects. A decrease in Ge incorporation in theSi1−x−yGexCyfilms with increasing C incorporation suggests a repulsive Ge–C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 °C, whereas at 450 °C no such phase can be observed. The temperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to detect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fraction and its substitutionality is emphasized. ©1997 American Institute of Physics.