Study on the composite dispersion model of optical constants of metal-oxide films in the range from ultraviolet to near infrared

Metal-oxide films as important high refractive index material are widely used in coating technology from ultraviolet to near infrared region. The optical constants (refractive index and extinction coefficient) and band gap properties of the films are essential for the optical multilayer design and applications. Based on the Tauc-Lorentz and Cody-Lorentz dispersion models, the composite model for the inverse calculation of optical constants from ultraviolet to near infrared region was studied. The method is proposed to link up the interband transition absorption and transparent region absorption more reasonably. Problems such as the characterization of weak absorption in transparent region and the step cutoff of the absorption near band gap, which were caused by using single physical dispersion model, were solved. Two kinds of films (HfO₂ films and Ta₂O₅ films) were prepared by ion beam sputtering. Reflectance and transmittance spectra of the prepared films were used as the complex object for inversion calculation of the optical constants by the developed model. The performance of the fitness was compared with that of single physical dispersion model. Results show that the developed physical dispersion model of optical constants has a explicit physical meaning and versatility in the range from ultraviolet to near infrared region.