Transparent and conducting indium tin oxide thin films grown by pulsed laser deposition at low temperatures

Thin films of indium tin oxide (ITO) were grown by conventional and ultraviolet-assisted pulsed laser deposition technique (PLD and UVPLD) on Si and Corning glass substrates at substrate temperatures from 40 to 180 °C. X-ray diffraction investigations showed that films deposited at substrate temperatures up to 70 °C were amorphous, whereas those deposited at temperatures of 120 °C and higher showed good crystallinity, with a (222) texture, A splitting of the (222) diffraction peaks indicated that the films contain a two layer structure possessing different lattice parameters. The ratio of these two peaks intensity strongly depended on the nature of the substrates in spite the fact that their thermal expansion coefficients were very similar, indicating that thermal stress is not very important during growth of ITO thin films. X-ray reflectivity studies showed that the films surface morphology was very smooth with root-mean-square roughness values below 0.5 nm and densities values around 7.20 g/cm³, the tabulated value of ITO. Spectroscopic ellipsometry measurements indicated that the films were very transparent, exhibiting extinction coefficient values below 0.1 in the visible region and refractive index values close to those measured for reference ITO films. X-ray photoelectron spectroscopy investigations showed homogeneous bulk chemical composition with fully oxidized In and Sn atoms and a very small Sn enrichment of the composition in the surface region. The carriers mobility, measured in a van der Pauw configuration by the Hall effect, was rather high for films deposited at 40 and 70 °C and then decreased with the increased of the substrate temperature, because the onset of crystallization at such low temperatures produces a rather defective structure.