Optical properties of tin-doped indium oxide determined by spectroscopic ellipsometry

Abstract

Sputtered tin-doped indium oxide (ITO) coatings were investigated by UV-visible spectroscopic ellipsometry at different angles of incidence. The results were fitted using a classical dispersion formula for the optical constants of ITO in a model structure with a compact homogeneous film and a top layer representing surface roughness. Typical values for the high-frequency dielectric constant ε∞ and the plasma frequency ωp were found to be 3.4–4.0 and 0.68–0.96 eV, respectively. The influence of oxidative and reducing annealing at 400 °C was studied. No difference was observed under reducing conditions, but oxygen annealing reduced the influence of the plasma frequency on the studied UV-visible region significantly. To prove the usefulness of the dispersion formula, TiO2 and Nb2O5 films were grown on ITO by metalorganic chemical vapor deposition using Ti(acac)2(i-pro)2 and Nb(OEt)5 as precursors. These bilayers were studied by spectroscopic ellipsometry and could be successfully described applying the previously determined optical constants of ITO and a transparent Cauchy dispersion formula for the deposited oxide.