Optical properties of a-HfO2 thin films

Amorphous hafnium oxide (a-HfO2) thin films were grown on silicon and quartz substrates by RF reactive magnetron sputtering at temperature < 52 degrees C. X-ray diffraction revealed that the thin films grown on the substrates are amorphous. The optical constants of a-HfO2 films were obtained by analysis of the measured ellipsometric spectra in the wavelength range 200-1400 nm, using the Cauchy-Urbach and Sellmeier models. Refractive indices and extinction coefficients of the films were determined to be in the range 1.86-2.15 and 0.07-2.6 x 10(-5), respectively. The absorption coefficients, alpha, of a-HfO2 has been determined by spectroscopic ellipsometry and spectrophotometric methods over the energy range 0.88-6.2 eV Analysis of alpha shows the bandgap energy of the films to be 5.68 +/- 0.09 eV. Measurement of the polarized optical properties reveals a high transmissivity (80%-97%) and low reflectivity (< 15%) in the visible and near infrared regions at angles of incidence between 10 degrees to 80 degrees. (c) 2006 Elsevier B.V. All rights reserved.