Transparent Conductive Tin Doped Indium Oxide : Characterisation of Thin Films Made by Sputter Deposition with Silver Additive and by Spin Coating from Nanoparticle Dispersions

Abstract: Thin films of tin doped indium oxide (ITO) were prepared by two different methods: by sputter deposition with silver additive and by spin coating of a nanoparticle dispersion.ITO films doped with ≤ 20 at% of silver were prepared either as homogenous blends of ITO and silver or as intermixed layers. A silver content of up to 2 at% yielded a small enhancement in the electrical conductivity with an ensuing decrease in the luminous transmittance. The lowest resistivity was 3.2·10-4 Ωcm. The refractive index was determined in two ways: from ellipsometry data and from Kramers-Kronig calculations where the extinction coefficient was calculated from transmittance and reflectance data. The optical properties were modelled by Maxwell-Garnett effective medium theory, which allowed an estimation of the amount of silver particles present in the films. The average particle diameter was determined to be a few nanometers, which was confirmed by transmission electron microscopy.Optical and electrical properties as well as sintering behaviour of the nanocomposite films were studied. The luminous transmittance was found to be above 90 % and the resistivity as low as 9.7·10-3 Ωcm, for highly porous layers. Grain growth was found to start at about 800°C. Impedance spectroscopy data were interpreted in terms of an equivalent circuit model with separate elements representing the bulk of the grains and the grain boundaries, respectively. The data were consistent with dopant segregation in the particles.