Investigations of the Optical Properties of Ba0.9Sr0.1TiO3 Ferroelectric Thin Films by Spectroscopic Ellipsometry

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Ba0.9Sr0.1TiO3 (BST) ferroelectric thin films with different film thickness were grown on Pt/Ti/SiO2/Si (100) substrates by a modified sol–gel method. X-ray diffraction (XRD) patterns show that the crystallization of the BST films strongly depends on the film thickness. Spectroscopic ellipsometry (SE) was used to characterize the BST thin films in the photon energy range of 1.5–5.0 eV. By fitting the measured ellipsometric parameter ($\tan\Psi$ and $\cos\Delta$) data with a four-phase model (air/surface rough layer/BST/Pt), the optical properties of the BST thin films with different film thickness have been systematically investigated. Based on the analysis of dispersion in the refractive index, the refractive index dispersion parameters in the single-term Sellmeier relation were determined to be $5.15--7.13\times 10^{-14}$ eVm2. The fitted values of the optical band gap energy $E_{0}$ for the samples indicate the band-gap energy of the BST thin films shifts to lower energies with increasing film thickness.
2003-03-15