We study optical properties of Ta-doped TiO_2 thin film on LaAlO_3 substrate using spectroscopy ellipsometry (SE) analysis at energy range of 0.5 - 6.5 eV. Room temperature SE data for Ψ (amplitude ratio) and Δ (phase difference) between p- and s- polarized light waves are taken with multiple incident angles at several spots on the samples. Here, absorption coefficient has been extracted from SE measurements at photon incident angle of 70° for different Ta concentration (0.01, 0.4, and 5 at. %). Multilayer modelling is performed which takes into account reflections at each interface through Fresnel coefficients to obtain reasonably well the fitting of Ψ and Δ data simultaneously. As the results, we estimate that film thickness increases by increasing Ta concentration accompanied by the formation of a new electronic structure. By increasing Ta impurities, the blueshift of absorption coefficient (α) peaks is observable. This result indicates that TiO_2 thin film becomes optically resistive by introducing Ta doping. Schematic model of interband transition inTiO_2:Ta will be proposed base on obtained optical properties. This study enables us to predict the role of Ta doping on the electronic and optical band structures of TiO_2 thin film.
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