Optical study of Ba(Mn_xTi_(1-x)O₃) thin films by spectroscopic ellipsometry

Stoichiometric Ba(Mn_xTi_(1-x)O₃) (BMT) thin films with various values of x were deposited on Si(111) substrates by the sol-gel technique. The influence of Mn content on the optical properties was studied by spectroscopic ellipsometry (SE) in the UV–Vis–NIR region. By fitting the measured ellipsometric parameter (Ψ and Δ) with a four-phase model (air/BMT+voids/BMT/Si(111)), the key optical constants of the thin films have been obtained. It was found that the refractive index n and the extinction coefficient k increase with increasing Mn content due to the increase in the packing density. Furthermore, a strong dependence of the optical band gap E_g on Mn/Ti ratios in the deposited films was observed, and it was inferred that the energy level of conduction bands decreases with increasing Mn content.