Optical properties and band gap characterization of high dielectric constant oxides

The optical characterization of amorphous and crystalline HfO2, SrHfO3, BaZrO3, BaHfO3, BaHf0.5Ti0.5O3, SrTiO3, Sr2Ta2O7 and Ta3Ti2Ox high dielectric constant thin (15–50 nm) films was performed using a combination of spectroscopic ellipsometry and reflectometry in the photon-energy range 1.5–6.8 eV. The optical dielectric function, absorption coefficient, optical band gap energies Eg, Urbach energy Eu and 3D interband critical point energies were obtained from these studies. The Eg as well as the Eu of the dielectric materials are important for device performance. Indirect Eg was obtained for all materials investigated. Lower Eg tends to result in higher value of permittivity κ. The results obtained deliver the necessary information for the selection of alternative high-κ dielectrics with adequate Eu, Eg and κ values and additionally provide optical metrology for such films.