Synthesis of epitaxial Si1-yCy alloys on Si(001) with high level of non-usual substitutional carbon incorporation

Si1-yCy epilayers have been grown at 600 degrees C on Si(001) associating solid source molecular beam epitaxy for Si supply and C2H4 thermal cracking or CH4 ECR (electron cyclotron resonance) H-2 plasma decomposition as C sources. The samples have been analyzed in situ by X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), and X-ray photoelectron diffraction (XPD) and ex situ by Rutherford backscattering (RES), Raman and IR spectroscopies. Increasing C content degrades the crystalline quality; however, up to y values ranging roughly from 3% to 5%, depending on sample thickness and used C precursor, the layers grow epitaxially as revealed by LEED spots, structured Si2p XPD angular scans and RES measurements. The relevant C 1s binding energy, indicative of Si-C bonds, excludes the presence of C-C bonds and no silicon carbide precipitation could be detected. Nevertheless, even in the C-concentration range of good epitaxial growth, neither C 1s XPD polar profiles with Si cubic symmetry, nor marked local vibrational mode at 604 cm(-1) in Raman or IR could be detected. These observations prove that, at low growth temperature, unexpectedly high amounts of C can be accommodated in a monocrystalline Si lattice via an incorporation scheme different from the usually invoked substitutional mode.