The optical properties of thin films of tantalum pentoxide and zirconium dioxide

The indices of refraction and absorption of thin films of tantalum pentoxide and zirconium dioxide have been determined in the wavelength range 250–2000 nm. These were obtained from the spectrophotometrically measured reflectance and transmittance of the films at normal incidence, using the method devised by Denton et al. The Ta 2O 5 films were amorphous and had smooth surfaces, and for these films analysis of the dependence of the absorption on photon energy has shown that there are band gaps of 4.15 and 4.51 eV. It is tentatively suggested that the observed absorption is due to direct transitions from a valence band with a spin-orbital splitting of 0.36 eV. The ZrO 2 films were polycrystalline with rough surfaces and had to be treated as double layer films in order to obtain continuous dispersion curves. They were effectively transparent over the spectral range covered.