3RD-NEAREST-NEIGHBOR CARBON PAIRS IN EPITAXIAL SI1-YCY ALLOYS - LOCALORDER FOR CARBON IN SILICON CHARACTERIZED BY X-RAY PHOTOELECTRON DIFFRACTION AND RAMAN-SPECTROSCOPY

The local order around carbon atoms in epitaxial Si1-yCy alloys (with y around 1%) grown by Si molecular-beam epitaxy and thermal decomposit ion of C2H4 on Si(001) or Si(111) has been studied as a function of gr owth temperature. To this end, information from local probes such as x -ray photoelectron spectroscopy C Is binding energies, experimental an d simulated C 1s core-level x-ray photoelectron diffraction (XPD) dist ributions, and Raman spectroscopy are compared. Between the growth con ditions leading to a solid solution of substitutional C at lower tempe rature and those leading to SiC precipitation at higher temperature, o riginal metastable and ordered C-rich alloy phases appear, which may b e coherently embedded in Si without degrading crystal quality. The res ults for such phases probed by the two latter techniques are indicativ e of a crystal line order implying concentrated third-nearest-neighbor (NN) carbon pairs. The comparison of experimental XPD distributions r ecorded in different azimuthal planes with simulated ones with C eithe r in substitutional or in interstitial sites is in favor of substituti on with a local contraction of the first-neighbor Si-C bond length bet ween 10% and 20%. If we admit that the surface ordering of the C atoms in the Si(001) surface layers is the extension of such particular bul k arrangements in third NN C pairs we are able to explain an experimen tally observed c-(4x4) low-energy electron diffraction pattern.