Study of dopant concentration effect on the physical properties of spin coated anatase TiO 2 :Al 3+ thin films

Abstract In this work, transparent undoped and Al-doped TiO₂thin films have been deposited on heated glass substratesthrough spin coating sol-gel processingtechnique.PristineTiO₂and Al-doped TiO₂thin filmswere synthesized with different Al doping ratio ranged from 0 to 6%.The influence of Al doping on the structural, morphological, optical, and electrical properties of TiO₂thin films have been investigated.The synthesized samples were characterization via various techniques including X-ray diffraction (XRD), scanning electron microscope, Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometer, photoluminescence (PL) spectra and four-point probe measurement, respectively. The XRD analysis pattern confirms the existence of the anatase TiO₂ phases with preferred orientation along the (101) direction. Furthermore, as the Al doping concentration increases, the crystallite size firstly decreased from 20.3 to 15.7 nm and then increased from 15.7 to 19.8 nm. The surface morphology analysis of the deposited Al:TiO₂ thin films reveals the homogenous distribution of condensed spherical shape particles and agglomerates small grains on glass substrate surface. Moreover, the optical analyses exhibit that the films have a high transmittance in the visible range reach to 87%. Moreover, the addition of Aluminum (Al) is found that film’s optical band gap varies in the range from 3.64 to 3.73 eV. In addition, according to FTIR spectra confirmed the successfully formation of the TiO₂ phase in all samples. The photoluminescence (PL) spectra analysis shows the distinguishable emission peaks located in the ultraviolet and visible regions for all samples. The films electrical resistivity showed an apparent dependence on Al content, which substantially decreases with the increasing Al concentration from 9.5×10⁻ ² to 9×10⁻ ³ Ω.cm.