Spectroscopic ellipsometry study of compound-induced changes in chemical and optical properties of In2O3:Sn-ZnO:Al films

In this study, indium-zinc oxide (IZO) films of different compositions were deposited on quartz glass by alternate sputtering of ZnO:Al and In2O3:Sn targets at room temperature. Spectroscopic ellipsometry (SE) measurements were carried out over the wavelength range 193-1690 nm in order to estimate the chemical, optical, and electrical properties of the IZO films using various dispersion models, i.e., the Tauc-Lorentz (TL), and Lorentz, Gaussian, and Drude models. The experimental results showed that the tail absorption was essentially affected by the Zn content and crystallinity of the film. The optical constants of the amorphous IZO films were accurately estimated using the TL and Drude models, and inclusion of the Lorentz model in the SE analysis overcame the inhomogeneity effect caused by preferential orientation growth. On the basis of these results, a k factor was defined and used to estimate the Zn contents of the IZO films. The variations in the k factors as a function of Zn content agreed well with those of the band gaps of the IZO films. Furthermore, for films with better conductivities, the resistivity values obtained using the SE and Hall methods were similar, but low carrier concentrations caused failure of the Drude model.