Third-nearest-neighbor carbon pairs in epitaxial Si 1 − y C y alloys: Local order for carbon in silicon characterized by x-ray photoelectron diffraction and Raman spectroscopy

The local order around carbon atoms in epitaxial ${\mathrm{Si}}_{1\ensuremath{-}y}{\mathrm{C}}_{y}$ alloys (with $y$ around 1%) grown by Si molecular-beam epitaxy and thermal decomposition of ${\mathrm{C}}_{2}{\mathrm{H}}_{4}$ on Si(001) or Si(111) has been studied as a function of growth temperature. To this end, information from local probes such as x-ray photoelectron spectroscopy C $1s$ binding energies, experimental and simulated C $1s$ core-level x-ray photoelectron diffraction (XPD) distributions, and Raman spectroscopy are compared. Between the growth conditions leading to a solid solution of substitutional C at lower temperature and those leading to SiC precipitation at higher temperature, original metastable and ordered C-rich alloy phases appear, which may be coherently embedded in Si without degrading crystal quality. The results for such phases probed by the two latter techniques are indicative of a crystalline order implying concentrated third-nearest-neighbor (NN) carbon pairs. The comparison of experimental XPD distributions recorded in different azimuthal planes with simulated ones with C either in substitutional or in interstitial sites is in favor of substitution with a local contraction of the first-neighbor Si-C bond length between 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 bulk arrangements in third NN C pairs we are able to explain an experimentally observed $c\ensuremath{-}(4\ifmmode\times\else\texttimes\fi{}4)$ low-energy electron diffraction pattern.