Optical properties of nonstoichiometric silicon oxide SiO$_{x}$ ($x<$ 2)

The optical properties of amorphous nonstoichiometric silicon oxide SiO$_{x}$ films of variable composition ($x$ = 0.62–1.92) formed by plasma-enhanced chemical vapor deposition are studied in the spectral range of 1.12–4.96 eV. Spectral ellipsometry showed that the refractive index dispersion character allows one to assign the formed SiO$_ x$ films to silicon-like films, dielectrics, or intermediate-conductivity-type films depending on the content of oxygen in the gas phase during synthesis. A model of the SiO$_ x$ structure for ab initio calculations is proposed and describes well the experimental optical spectra. Ab initio calculations of the dependences of the SiO$_{x}$ refractive index and band gap on stoichiometry parameter $x$ are performed.