Gas source molecular beam epitaxy is used for the growth of SiGeC layers from disilane, germane and methylsilane precursors at low substrate temperatures. A systematic method of carbon concentration determination based on a combination of X-ray diffraction and X-ray reflectivity is examined. The grown layers were annealed using rapid thermal annealing and analysed with X-ray diffraction, X-ray reflectivity and secondary ion mass spectrometry. The recovery of compressive strain in the SiGeC layer is correlated to the loss of carbon through diffusion and indicates that the carbon atoms are incorporated substitutionally in the as-grown layers. © 2005 Elsevier B.V. All rights reserved.