Optical constants and band gap expansion of size controlled silicon nanocrystals embedded in SiO2 matrix

Silicon nanocrystals (Si-NCs) with different sizes embedded in SiO2 matrix were synthesized by phase separation and thermal crystallization of SiOx/SiO2 supperlattice approach. The optical constants and band gap expansion of Si-NCs have been investigated by spectroscopic ellipsometry, based on the Maxwell–Garnett effective medium approximation and the Forouhi–Bloomer optical dispersion model. Similar spectra shapes but smaller values of Si-NCs optical constants with respect to bulk crystalline Si is observed. With the size of Si-NCs decreasing from 6 nm to 2 nm, the band gap increases from 1.64 eV to 2.56 eV. The band gap expansion, as compared to bulk crystalline Si, which agrees with the prediction of first-principles calculations based on quantum confinement effect, is presented in this paper.

► Size-controlled silicon nanocrystals embedded in SiO2 matrix are investigated by spectroscopic ellipsometry.
► The complex optical constants and optical band gap for silicon nanocrystals, as a function of their size, are obtained.
► The band gap expansion compared to bulk crystalline silicon agrees with the theoretical calculations.