The effect of annealing on structural, electrical and optical properties of nanostructured ITO films prepared by e-beam evaporation

Tin doped indium oxide (ITO) thin films with composition of 9.42 wt% SnO₂ and 89.75 wt% In₂O_3, and impurities balanced on glass substrates at room temperature have been prepared by electron beam evaporation technique and then were annealed in air at different temperatures from 350 to 550 °C for 1 h. XRD pattern showed that increasing annealing temperature increased the crystallinity of thin films and at 550 °C high quality crystalline thin films with grain size of about 37 nm were obtained. Conductivity of ITO thin films was increased by increasing annealing temperature and conductivity obtained results in 350-550 °C temperature range were also excellently fitted in both Arrhenius-type and Davis-Mott variable-range hopping conductivity models. The UV-vis transmittance spectra were also confirmed that the annealing temperature has significant effect on the transparency of thin films. The highest transparency over the visible wavelength region of spectrum (93%) obtained at 550 °C on annealing temperature. It should be noted that this thin film was deposited on substrate at room temperature. This result obtained is equivalent with those values that have already been reported but with high-level (20 wt%) tin doped indium oxide thin films and also at 350 °C substrate temperature. The allowed direct band gap at the temperature range 350-550 °C was estimated to be in the range 3.85-3.97 eV. Band gap widening with an increase in annealing temperature was observed and is explained on the basis of Burstein-Moss shift. A comparison between the electron beam evaporation and other deposition techniques showed that the better figure of merit value can be obtained by the former technique. At the end we have compared our results with other techniques.