Optical characteristics of strontium titanate films obtained by the sol–gel method

Using data of multiangle spectrophotometry and spectral ellipsometry in the UV and visible ranges, spectra of the refractive indices and absorption coefficients and width of the forbidden band of one- and five-layer strontium titanate films obtained by the sol–gel method have been calculated. Layer-by-layer deposition of sol on quartz substrates, from one to five layers, leads to an increase in film porosity from 4 to 33%. This causes a decrease in the refractive indices in the middle part of the visible spectrum from 2.33 to 1.87, which leads to a decrease in the reflectance and an increase in the transmittance or transparency of five-layer films. With an increase in the heating temperature of such films from 500 to 750$^{\circ}$C, a shift of the absorption band maximum from 239 to 253 nm takes place and the optical width of the forbidden band decreases from 4.63 to 4.20 eV. The absorption band maximum of the single-layer film falls on the wavelength of 252 nm, and its optical width of the forbidden band is 3.96 eV.