Influence of nanocrystal size on dielectric functions of Si nanocrystals embedded in SiO_2 matrix

摘要

The complex dielectric functions of Si-nanocrystals (nc-Si) with different sizes embedded in SiO_2 matrix synthesized by SiO_x/SiO_2 superlattice approach is obtained by spectroscopic ellipsometry. The Maxwell-Garnett effective medium approximation and the Lorentz oscillator model are employed in the spectra fitting. The dependence of the dielectric functions on the nc-Si size is observed. A significant suppression in amplitude of the dielectric functions with respect to bulk crystalline silicon, and a large influence of the nc-Si size on the E_1 and E_2 critical points are observed and discussed.