A study on low cost-high conducting fluorine and antimony-doped tin oxide thin films

Abstract

Thin films of undoped, fluorine- and antimony-doped tin oxide on glass at 400 °C was prepared by spray pyrolysis technique. Tin chloride (SnCl 2), ammonium fluoride (NH 4F), and antimony trichloride (SbCl 3) were used as source for tin (Sn), fluorine (F), and antimony (Sb), respectively. To ensure the control of solution concentration on growth rate, fluorine-doped tin oxide (SnO 2:F) thin films were first prepared with different amount of tin precursor, in the range of 5–12 g, which has resulted in deposition of films with different thickness values. The optimum amount of tin precursor found from this study (11 g) was fixed constant for preparing SnO 2 films with different doping levels of F and Sb. From the X-ray diffraction analyses, it is understood that the preferred orientation of SnO 2:F films is dependent on their thickness and the solution concentration. The variation in the solution concentration and orientation of the films was reflected in their morphology as examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM studies showed that the variation in the solution concentration lead to different grain shapes for different orientations. The AFM study showed that the RMS roughness of undoped films reduced considerably from 86 to 24 nm due to fluorine doping (15 wt.%), whereas the antimony doping (2 wt.%) has no significance effect on RMS roughness (93 nm). The electrical properties of the films were examined by a Hall measurements setup in van der Pauw configuration. A minimum sheet resistance of 1.75 and 2.17 Ω/ ▪ were obtained for F and Sb doped films, respectively. From the optical studies, it is found that the transmittance of undoped films increased from 42% to a maximum 85% on 30 wt.% fluorine doping, whereas that has been decreased to a minimum of 12% on 4 wt.% antimony doping (800 nm). A discussion on the effect of type of dopants and their concentration on the structural, electrical and optical properties of the SnO 2 film have been presented.