Optical properties of silicon nanocrystals embedded in aSiO2matrix

Abstract

Optical properties of isolated silicon nanocrystals $(\mathit{nc}\text{\ensuremath{-}}\mathrm{Si})$ with a mean size of $\ensuremath{\sim}4\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ embedded in a ${\mathrm{SiO}}_{2}$ matrix that was synthesized with an ion beam technique have been determined with spectroscopic ellipsometry in the photon energy range of 1.1--5.0 eV. The optical properties of the $\mathit{nc}\text{\ensuremath{-}}\mathrm{Si}$ are found to be well described by both the Lorentz oscillator model and the Forouhi-Bloomer (FB) model. The $\mathit{nc}\text{\ensuremath{-}}\mathrm{Si}$ exhibits a significant reduction in the dielectric functions and optical constants and a large blueshift $(\ensuremath{\sim}0.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ in the absorption spectrum as compared with bulk crystalline silicon. The band gap of the $\mathit{nc}\text{\ensuremath{-}}\mathrm{Si}$ obtained from the FB model is $\ensuremath{\sim}1.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, showing a large band gap expansion of $\ensuremath{\sim}0.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ relative to the bulk value. The band gap expansion is in very good agreement with the first-principles calculation of the $\mathit{nc}\text{\ensuremath{-}}\mathrm{Si}$ optical gap based on quantum confinement.