Characterization of porous indium tin oxide thin films using effective medium theory

Effective medium theory was used to model optical properties in the 0.3 – 30 μm wavelength range for films comprised of nanoparticles of a transparent conducting oxide that are connected in a percolating network characterized by a filling factor f. The model is based on charge carrier density ne and resistivity ρ of the particles, and it enables analyses of these microscopic parameters upon posttreatment of the film. The theory was used to interpret data on spin coated layers consisting of nanoparticles of indium tin oxide (i.e., In2O3:Sn) with f close to the percolation limit. It showed that the as-deposited film contained nanoparticles with ne as large as ∼5×1020 cm−3 and ρ≈5×10−4 Ω cm. The model also provided important data on f, ne, and ρ after heat treatment of the film.