Interaction of acetylene on Si(111):: growth and luminescence study of Si1-xCx thin layers

The different carbonization processes of a Si(111) 7 x 7 reconstructed surface exposed to acetylene (C2H2) were studied by ultrahigh-vacuum electronic and luminescence techniques. We found that the molecule breaks at about 450 degrees C and for temperature up to 600 degrees C a Si1-xCx alloy is formed in the near-surface region of the sample. For higher temperatures, up to 850 degrees C, crystalline SiC crystallite precipitation epitaxially grown on the Si surface is observed. The luminescence spectra obtained at each stage of carbonization revealed the formation of well defined Si1-xCx phases (with x equal to a few per cent) and it clearly demonstrates that the exposure to C2H2 is highly efficient procedure to change in a continuous way the near-infrared optical properties of Si surfaces in the spectral range from 0.9 to 1.1 eV. The observation at 650 degrees C exposure of an intense and broadened photoluminescence emission in the range 1.2-1.6 eV is particularly interesting. This indicates the possibility that in the near-surface region a local concentration of the first-nearest-neighbour Si-C bond of between 15-20% is present, indicating the formation of a high C-rich layer.