Substrate temperature effect on transparent heat reflecting nanocrystalline ITO films prepared by electron beam evaporation

In this study, indium tin oxide (ITO) thin films were preparedon glass substrate by electron beam evaporation technique and then were annealed in air atmosphere at 350 °C for 30 min. Increasing substrate temperature (T_s) from 25 to 380°°C reduced sheet resistance of ITO thin films from 150(Ω/□) to 14(Ω/□). The UV-visible-near IR transmittance and reflectance spectra were also confirmed that the substrate temperature has significant effect on the properties of heat reflecting thin films. High transparency (83%) over the visible wavelength region of spectrum and (over 90%) reflectance in near-IR region were obtained at T_s = 300° C. Plasma wavelength, carrier concentrations (n_e) and refractive index of the layer were also calculated. The allowed direct band gap at the temperature range 100–300° C was estimated to be in the range 3.71–3.89 eV. Band gap widening due to increase in substrate temperature was observed and is explained on the basis of Burstein-Moss shift. XRD patterns showed that the films were polycrystalline. High quality crystalline thin films with grain size of about 40 nm were obtained.