Correlation of lattice distortion with optical and electrical properties of In2O3:Sn films

Polycrystalline In2O3:Sn (ITO) films were prepared by direct current magnetron sputtering at substrate temperatures between 150 and 400 degreesC and at various oxygen admixtures to the sputter gas. X-ray diffraction peaks (position and width) were evaluated with respect to lattice distortion (net increase and fluctuations of the lattice constant). The characteristic optical parameters of the films were obtained by dielectric modeling of experimental transmittance and reflectance spectra. The plasma edge was evaluated with respect to electron density and mobility. The electron density decreases linearly with the lattice distortion. This confirms a model of oxygen incorporation into the lattice during sputtering and allows an estimation of the density of oxygen interstitials from x-ray spectra. The electron mobility inside the grains decreases with decreasing electron density. This is well explained by a model based on scattering at ionized Sn donors that are partially compensated by interstitial oxygen ions. The direct current conductivity is smaller than the conductivity derived from the optically determined parameters because it is hampered by badly conducting grain boundaries. The refractive index decreases linearly with the free electron density which is explained, via the Kramers-Kronig relation, by increasing absorption in the plasma edge and the Burstein-Moss shift of the band edge. (C) 2004 American Institute of Physics.