Optical Properties of Ba_(1-x)Sr_xTiO_3 Thin Films Prepared by Sol-Gel Method

Ba_(1-x)Sr_xTiO_3(0.1≤x≤0.3)(BST) thin films on Si(100) substrates were prepared by Sol-Gel processing.Ellipsometric spectra of BST thin films with various Sr concentration x were measured in the range of photon energy from 2.0 to 5.2 eV.Constructing appropriate fitting models,their optical constants(refractive index n and extinction coefficient k) spectra and band gap energy E_g are determined by means of optimization.It is found that no apparent difference is observed in the refractive indexes of three BST thin films in the lower photon energy region.The absorption edges of the samples with an increased Sr dopant shift to high photon energy,and the band gap E_g increases.