12C(α,α)12C resonant elastic scattering at 5.7 MeV as a tool for carbon quantification in silicon-based heterostructures

The incorporation of carbon into substitutional sites in Si or Si1 - xGex attracts increasing interest due to the enhanced possibilities in strain and band gap engineering of group IV heterostructures. Precise and accurate measurement of carbon concentration is, however, quite difficult to achieve. We focused our attention on the study of the alpha resonant elastic scattering in the 5.7 MeV energy region. We measured the scattering cross-section in the range 5.4-6.0 MeV at a laboratory scattering angle of 170 degrees. The results indicate that the cross-section value is enhanced with respect to the Rutherford one of an almost constant factor (x130) in an energy interval about 100 keV wide. This allows a more accurate measurement of carbon concentration than with the normally used 4.265 MeV resonance. The experimental procedure to deal with non-Rutherford scattering of Si has been also determined. The resonant scattering at 5.72 MeV has been used, in combination with Rutherford Backscattering Spectrometry (RBS) at 3.0 MeV, to determine the carbon content of three Si1 - x - yGexCy samples. This has also been used, in channelling geometry, to determine the substitutional carbon fraction of the samples.