Epitaxial strained growth of Si1-yCy alloys with rather high C concentrations (y∼1.5%) has been performed on Si(111) and Si(001) using molecular beam epitaxy (MBE) Si evaporation and thermal interaction of the growth surface with a low C2H4 pressure at 500 °C. Carbon contents, determined by secondary ion mass spectrometry, infrared (ir) spectrometry, in situ C 1s and Si 2p x-ray photoelectron spectroscopy measurements and x-ray diffraction (XRD), are being compared. Monocrystalline quality of the epilayers is checked by low energy electron diffraction and x-ray photoelectron diffraction (XPD). As indirectly ascertained by the ir local vibration mode (LVM) and a shifted partially strain induced epilayer diffraction line in the θ-2θ XRD analysis, carbon is accommodated in substitutional sites (Csub) whose local atomic order is investigated for the first time by XPD, C 1s polar angle distributions being measured in different azimuthal directions. As the data reveal, for a C emitter, next nearest neighbor bond orientations identical to those for Si atoms in a Si matrix, XPD readily provides direct evidence in favor of Csub positions. Up to now, our limited angular resolution does not allow observation of possible bond orientation changes due to local strain-induced lattice distortions around C atoms. Nevertheless, by increasing growth temperature (600–650 °C) and promoting formation of more C-rich phases (SinC or SiC), the ef- fects of substitution of second or higher nearest Si neighbors by C atoms can be clearly evidenced. By the way, a significant C 1s binding energy difference between Csub and C in C-rich phases is observed and may be used as a signature of the C dilution in the grown epilayer: a characteristic value of 283.8 eV is obtained for the Csub site giving rise to the LVM. © 1997 American Institute of Physics.