A C 1S CORE-LEVEL X-RAY PHOTOELECTRON DIFFRACTION CHARACTERIZATION OFSUBSTITUTIONAL CARBON IN EPITAXIAL SI1-YCY ALLOYS GROWN ON SI(111) AND SI(001)

Epitaxial strained growth of Si1-yCy alloys with rather high C concent rations (y similar to 1.5%) has been performed on Si(111) and Si(001) using molecular beam epitaxy (MBE) Si evaporation and thermal interact ion of the growth surface with a low C2H4 pressure at 500 degrees C. C arbon contents, determined by secondary ion mass spectrometry, infrare d (ir) spectrometry, in situ C 1s and Si 2p x-ray photoelectron spectr oscopy measurements and x-ray diffraction (XRD), are being compared. M onocrystalline quality of the epilayers is checked by low energy elect ron diffraction and x-ray photoelectron diffraction (XPD). As indirect ly ascertained by the ir local vibration mode (LVM) and a shifted part ially strain induced epilayer diffraction line in the theta-2 theta XR D analysis, carbon is accommodated in substitutional sites (C-sub) who se local atomic order,is investigated for the first time by XPD, C 1s polar angle distributions being measured in different azimuthal direct ions. As the data reveal, for a C emitter, next nearest neighbor bond orientations identical to those for Si atoms in a Si matrix, XPD readi ly provides direct evidence in favor of C-sub positions. UP to now our limited angular resolution does not allow observation of possible bon d orientation changes due to local strain-induced lattice distortions around C atoms. Nevertheless, by increasing growth temperature (600-65 0 degrees C) and promoting formation of more C-rich phases (SinC or Si C), the effects of substitution of second or higher nearest Si neighbo rs by C atoms can be clearly evidenced. By the way, a significant C 1s binding energy difference between C-sub and C in C-rich phases is obs erved and may be used as a signature of the C dilution in the grown ep ilayer: a characteristic value of 283.8 eV is obtained for the C-sub S ite giving rise to the LVM. (C) 1997 American Institute of Physics.