Determination of optical constants of sol-gel derived Zn0.9Mg0.1O films by spectroscopic ellipsometry with various models

The Zn0.9Mg0.1O thin films were prepared on Si (1100) substrates by the sol-gel method. The structural and the optical properties of Zn0.9Mg0.1O thin films, submitted to an annealing treatment in the 400-700 degrees C ranges, are studied by X-ray diffraction (XRD) and ultraviolet (UV)-visible spectroscopic ellipsometry (SE). The thickness, refractive index, and extinction coefficient of these films have been determined by analyzing the SE spectra using parameterized dispersion model. Moreover, we made a detailed comparison among various dispersion models and found that the Sellmeier model was superior to others in fitting the ellipsometric spectra in the transparent region. In the interband transition region, point-by-point fit was used. The spectral dependence of the refractive index and extinction coefficient was obtained in the photon energy range of 1.5-4.71 eV. The influence of annealing temperature on the refractive index, the extinction coefficient, and the optical bandgap energy was also discussed. We found that the refractive index and the extinction coefficient increase with increasing the annealing temperature, meaning the optical quality of Zn0.9Mg0.1O films is improved by annealing. Copyright (C) 2009 John Wiley & Sons, Ltd.