Tight-binding calculations of the optical properties of Si nanocrystals in a SiO2 matrix

Abstract

We develop an empirical tight binding approach for the modeling of the electronic states and optical properties of Si nanocrystals embedded in a SiO₂ matrix. To simulate the wide band gap SiO₂ matrix we use the virtual crystal approximation. The tight-binding parameters of the material with the diamond crystal lattice are fitted to the band structure of β-cristobalite. This model of the SiO₂ matrix allows us to reproduce the band structure of real Si nanocrystals embedded in a SiO₂ matrix. In this model, we compute the absorption spectra of the system. The calculations are in an excellent agreement with experimental data. We find that an important part of the high-energy absorption is defined by the spatially indirect, but direct in k-space transitions between holes inside the nanocrystal and electrons in the matrix.