Role of annealing temperature on microstructural and electro-optical properties of ITO films produced by sputtering

This study probes the effect of annealing temperature on electrical, optical and microstructural properties of indium tin oxide (ITO) films deposited onto soda lime glass substrates by conventional direct current (DC) magnetron reactive sputtering technique at 100 watt using an ITO ceramic target (In2O3:SnO2, 90:10 wt%) in argon atmosphere at room temperature. The films obtained are exposed to the calcination process at different temperature up to 700 A degrees C. X-ray diffractometer (XRD), ultra violet-visible spectrometer (UV-vis) and atomic force microscopy (AFM) measurements are performed to characterize the samples. Moreover, phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. The results obtained show that all the properties depend strongly on the annealing temperature. XRD results indicate that all the samples produced contain the In2O3 phase only and exhibit the polycrystalline and cubic bixbite structure with more intensity of diffraction lines with increasing the annealing temperature until 400 A degrees C; in fact the strongest intensity of (222) peak is obtained for the sample annealed at 400 A degrees C, meaning that the sample has the greatest ratio I (222)/I (400) and the maximum grain size (54 nm). As for the AFM results, the sample prepared at 400 A degrees C has the best microstructure with the lower surface roughness. Additionally, the transmittance measurements illustrate that the amplitude of interference oscillation is in the range from 78 (for the film annealed at 400 A degrees C) to 93 % (for the film annealed at 100 A degrees C). The refractive index, packing density, porosity and optical band gap of the ITO thin films are also evaluated from the transmittance spectra. According to the results, the film annealed at 400 A degrees C obtains the better optical properties due to the high refractive index while the film produced at 100 A degrees C exhibits much better photoactivity than the other films as a result of the large optical energy band gap.