Carbon effect on strain compensation in Si1-x-yGexCy films epitaxially grown on Si(100) at 500 degrees C has been investigated using an ultraclean hot-wall low-pressure chemical vapor deposition. The introduction of C into thin strained Si1-xGex films reduces the average lattice constant. On the other hand, results of the Raman scattering measurement show that C incorporation scarcely affects on local strain of Si-Si, Si-Ge and Ge-Ge bonds. The critical thickness at which the Raman shift peak begins to be decreased tends to become larger for the higher C fraction. It is considered that the C introduction effectively increases the critical thickness by relieving the overall strain. (c) 2005 Elsevier B.V. All rights reserved.