Raman Size Effect of Silicon Nanocrystals Embedded in Amorphous Matrix

Different from the traditional size model, this research is based on the phenomenological phonon confinement model to analyze the size effect of Si nanocrystals, considering phonon wave vector q, standard deviation σ and confinement coefficient β and their relative functional relationship comprehensively. The discussions focused on the Raman shift and asymmetry broadening of Si nanocrystals embedded in amorphous SiC. The results show that as the size of the Si nanocrystals decreased to below Bohr radius, the q can change from quasi-continuous form to discrete form participating the scattering, and so this discrete q can more accurately fit the Raman spectral lines of small-sized Si nanocrystals. Standard deviation σ can further precisely adjust the asymmetry of Raman peaks, and the smaller the size, the greater the impact. The confinement coefficient β involves the influence of the limitation barrier height to the Raman shift. Finally, the theoretical model was compared with our experimental results and literature data. It can be found that the comprehensive consideration of the synergistic effect of the q, σ and β should be conducive to evaluating the size effect, crystal morphology and relative proportion of amorphous coated Si nanocrystals.