Epitaxial strained growth ofSi1−yCyalloys with rather high C concentrations(y∼1.5&percent;)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 lowC2H4pressure at 500 °C. Carbon contents, determined by secondary ion mass spectrometry, infrared (ir) spectrometry,in situC 1sandSi 2px-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 &thgr;-2&thgr; XRD analysis, carbon is accommodated in substitutional sites(Csub)whose local atomic order is investigated for the first time by XPD,C 1spolar 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 ofCsubpositions. 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(SinCor SiC), the effects of substitution of second or higher nearest Si neighbors by C atoms can be clearly evidenced. By the way, a significantC 1sbinding energy difference betweenCsuband 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 theCsubsite giving rise to the LVM. ©1997 American Institute of Physics.