The effect of deposition rate on electrical, optical and structural properties of tin-doped indium oxide (ITO) films on glass at low substrate temperature

Tin-doped indium oxide (ITO) thin films with composition of 9.42 wt% SnO2 and 89.75 wt% In2O3, and impurities balanced have been prepared by electron beam evaporation on glass substrates with different deposition rates at fixed low substrate temperature condition. Subsequently, the films were annealed at 400 degrees C in a thermal furnace for I h in air atmosphere. Hereafter, the films were quenched until room temperature and then have been characterized using X-ray diffraction and UV-visible spectroscopy. The lattice constant and the grain size of all thin films were derived to be 10.118 angstrom and 37 nm in diameter, respectively. A transmittance value of 92% in the visible wavelength region at room substrate temperature was obtained. A similar value was already reported for high-level (20wt%) tin-doped indium oxide thin films at 350 degrees C substrate temperature. The resistivity of the films was found to be 7 x 10(-4) Omega cm for the deposition rate of 0.05 nm s(-1). Results showed that by decreasing the deposition rate, a lower resistivity and a higher transmittance were obtained at the lower substrate temperature. The obtained values were better than those reported by other authors. Further optical studies showed that in these films allowed indirect transitions can take place. The direct optical energy gap deduced from the optical transmittance data using the Tauc relation was estimated to be 3.80 eV. Resistivity measurements showed that by decreasing the deposition rate, highly conductive transparent films can be obtained. Finally, it has been found that the deposition rate is a very important factor in controlling the electrical and optical properties of ITO films. (c) 2005 Elsevier B.V. All rights reserved.