Optical properties of indium tin oxide and fluorine-doped tin oxide surfaces: correlation of reflectivity, skin depth, and plasmon frequency with conductivity

Abstract

Variable angle reflectance FTIR was used to investigate the reflectance of thin films of either indium tin oxide (ITO) or fluorine-doped tin oxide (SFO) on glass substrates in the mid-IR. The reflectance was observed to depend on the incident angle, wavenumber, and the polarization used. The Drude model and the Fresnel equations for reflection at a single dielectric boundary were used to interpret these results in terms of the conductivity, reflectivity, skin depth, and plasmon frequency of the metal oxides. The skin depth of thin film ITO electrodes was found to depend on the sheet resistance linearly, while the reflectance varied according to the square root of the sheet resistance. The method shows that an optical probe can be used to determine the electrical properties of metal oxide films in a noninvasive approach.