Dielectric modeling of transmittance and ellipsometric spectra of thin In2O3:Sn films

Thin ITO films with thickness between 0.05 and 0.4 mu m were deposited on quartz substrates by direct-current magnetron-sputtering. The films' ellipsometric and transmittance spectra between 280 and 2500 nm were simulated simultaneously with a computer program based on dielectric modeling. The dielectric function used is the sum of three types of electronic excitations: intraband transitions of free electrons (extended Drude model), band gap transitions, and interband transitions into the upper half of the conduction band. A successful fit of the simulated to the experimental curves was obtained with a two-layer model (bulk and surface layers) and applying the Bruggeman effective-medium approach. From the simulation, film thickness, refractive index, band gap, and free carrier density can be obtained. The thickness of the surface layer is comparable with the surface roughness determined by AFM measurements. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim