Raman scattering of nanocrystalline silicon embedded in SiO₂

Raman scattering of nanocrystalline silicon embedded in SiO₂ matrix is systematically investigated. It is found that the Raman spectra can be well fitted by 5 Lorentzian lines in the Raman shift range of 100-600 cm^-1. The two-phonon scattering is also observed in the range of 600-1100 cm^-1. The experimental results indicate that the silicon crystallites in the films consist of nanocrystalline phase and amorphous phase; both can contribute to the Raman scattering. Besides the red-shift of the first order optical phonon modes with the decreasing size of silicon nanocrystallites, we have also found an enhancement effect on the second order Raman scattering, and the size effect on their Raman shift.