Carbon incorporation in Si and SiGe heteroepitaxial structures offers exciting opportunities in the design of novel, Si-based electronics. Recent results suggest that in order to realize the potential of this material system, methods for achieving high carbon concentrations (in excess of 5 at.%) without sacrificing crystalline quality must be developed. We have investigated the use of Sb as a surfactant to assist in the incorporation of carbon during growth of Si and SiGe epitaxial layers by molecular beam epitaxy. For samples in which Sb is not used, reflection high-energy electron diffraction (RHEED) shows that the wafer surfaces roughen soon after the carbon is introduced. As growth proceeds, the layers eventually twin and become defective, especially for thicker layers and higher carbon concentrations (> 2%). Roughening occurs at even lower carbon concentrations for the case of SiGeC growth as we have grown Si1-x-yGexCy/Si1-yCy’ heterostructures with y’ > y, and observe RHEED patterns are streaked during the Si1-y’Cy’ deposition but spotted during the Si1-x-yGexCy deposition. The presence of less than or equal to 1 monolayer of Sb on the surface of the substrate prior to epitaxy is shown in this work to substantially reduce roughening of the growth front, resulting in a dramatic reduction in defect density with minimal Sb incorporation (<10(17) cm(-3)). Transmission electron microscopy and secondary ion mass spectrometry data relating to the quality of the layers and the amount of Sb incorporation will be discussed.