Carbon-doped beta-FeSi2 films synthesized by ion implantation is investigated with the aim to fabricate high-quality semiconducting beta-FeSi2 layer on silicon substrate. According to our TEM cross-section observations, the carbon-doped films are of better quality than the non-doped ones for their improved uniform film thickness, smooth beta/Si interface and high thermal stability. In particular, annealing at 500-700 degreesC leads to the formation of a flat and continuous beta-type silicide layer. Optical absorption measurements show that the carbon doping does not influence the band structure. We further point out that the presence of multiple and incoherent orientation relationships between beta and Si, discussed within the framework of the near coincident site lattice theory, is a key factor responsible for the difficulty in obtaining high-quality epitaxial beta films. (C) 2004 Published by Elsevier B.V.