Effect of the fluorine content on the structural and electrical properties of SnO2 and ZnO-SnO2 thin films prepared by spray pyrolysis

Transparent conducting oxide thin films of SnO2 (TO) and of ZnO-SnO2 binary-binary system (ZO-TO system) have been prepared by the spray pyrolysis method. In this work, we study the influence of fluorine doping concentration on the structural, optical and electrical properties of films above mentioned. Fluorine doped tin oxide (FTO) thin films on glass present resistivity around to 4×10−4 Ω cm, high optical transmission close to 80% and optical band gap close to 4.5 eV. X-ray diffraction measurements show that the FTO films are highly oriented along the (200) plane parallel to the substrate. ZO-TO films deposited at substrate temperature of 450 °C using alcoholic solutions of ZnCl2/SnCl4 with a Zn/Sn=0.40 atomic ratio, presented polycrystalline structures with a mixture of zinc oxide and tin oxide phases (ZO-TO system). These films present a resistivity close to 6 Ω cm and an optical transmission in the visible range of 82%. Further addition of NH4F to the starting solution lowered the resistivity of ZO-TO thin films to 2.43×10−1 Ω cm as a consequence of fluorine incorporation. From electrical and optical measurements, the Moss-Burstein effect was found in both TO and ZO-TO thin films.