Optical properties of silicon related insulators

We report a study of the optical properties of silicon related insulators. Essentially, the following materials have been considered in this study; noncrystalline Si₃N₄, SiO₂, SiO, and crystalline SiO₂. Utilizing the available data of the refractive index and the extinction coefficient in the literature, the related optical properties such as (i) the real (ε₁) and imaginary (ε₂) parts of the complex-dielectric constant, (ii) absorption coefficient (α), and (iii) electronic polarizability (α_e) are calculated. The optical gaps E_G of these materials have been estimated employing the Tauc rule and the Cody alternative. Extrapolation of the band-structural and spectroscopic models of Penn [Phys. Rev. 128, 2093 (1962)] and Wemple and Didomenico [Phys. Rev. B 3, 1338 (1971)] are then made to evaluate some band-structural parameters of these materials. Interpretations of the energy corresponding to the peak in ε₂ are then sought in terms of the Penn gap E_p. Whenever relevant, comparisons and correlations of the optical properties are also made with some dielectric properties.