Optical and electrical properties of tin-doped indium oxide transparent conducting films deposited by magnetron sputtering

Tin-doped indium oxide (ITO) thin films were prepared on the glass substrates by DC magnetron sputtering technique using a sintered ceramic target, followed by in-situ annealing. The thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), four-point probe and spectrophotometer, respectively. The effect of the deposition rate on the microstructural, optical and electrical properties of the films was investigated. Experimental results show that the ITO films are polycrystalline in nature having a cubic bixbyite type crystal structure with a preferred grain orientation in the (222) direction. The deposition rate significantly affects the crystal structure and optoelectrical properties of the films. The ITO samples fabricated at the deposition rate of 4 nm/min exhibit the highest figure of merit (7.9×10² S·cm^-1), which have the maximum grain size (32.5 nm), the lowest resistivity (1.1×10^-3 Ω·cm), the highest average visible transmittance (86.4%). Furthermore, the energy gap of the thin films was calculated by the Tauc's law. A red shift of the optical energy gap is observed with an increase in the deposition rate. It suggests that the deposition rate is a very important factor in controlling the electrical and optical properties of ITO thin films.