Determination of the optical properties of sol-gel-derived BaxSr1-xTiO3 thin film by spectroscopic ellipsometry

The optical properties of amorphous and polycrystalline BaxSr1-xTiO3 (BST) thin films fabricated on Si(100) substrates by a sol-gel spin-coating techn ique were investigated by spectroscopic ellipsometry (SE). The spectrum of the extinction coefficient k was obtained by using the refractive index and structure parameters determined by SE in the photon energy range of 2.1-5. 2 eV. A four-phase fitting model was employed to describe the optical prope rties of the BST thin films; the spectra of their optical constants and the band gap energy E-g were determined by means of optimization. In addition, the refractive index dispersion data related to the short-range-order stru cture of the films agreed well with the single-oscillation energy model. Th e dependence of the refractive index, k and E-g on annealing temperature we re analysed. The variation of optical band gap energy with composition was investigated by changing the content of barium in the films.