Molecular beam epitaxy (MBE) growth of GeC epilayers on Si(001) substrates was attempted using an arc plasma gun as a novel C source for the first time. In preliminary experiments, the C beam generated by the gun was confirmed to consist mainly of 12 C and to include very few microparticles. In order to improve crystalline quality and obtain a higher substitutional C content x in Ge1-xCx epilayers, the variation in the growth mode and C incorporation with the supplied C fraction x(C) and growth temperature T-S was investigated systematically by reflection high-energy electron diffraction, X-ray diffraction (XRD) and Raman spectroscopy analyses. At x(C) = 7.3 % and T-S = 400degreesC, the maximum x value of 2.6% in a single-crystalline structure was obtained from XRD studies. It was clarified that use of the arc plasma gun and enhancement of non-equilibrium growth play important roles in the incorporation of substitutional C and in restraining C-cluster formation in the MBE growth of GeC/Si. (C) 2002 Elsevier Science B.V. All rights reserved.