Study Of The Preparation And Properties On ZnO: Al Transparent Conductive Oxide Films

Zinc oxide (ZnO) is a wide band gap (3.37ev) semiconductor, which crystallizes in the hexagonal wurtzite structure. ZnO thin films is one of the transparent conductive oxide films (TCOs) having a promise application, because of its high transmittance in visible region and amenability to impurity doping. Currently, The most important transparent conductive oxide (TCOs) include In2O3, SnO2, and ZnO, which are typically doped using tin (In2O3:Sn=ITO), fluorine (SnO2:F=FTO), and Al (ZnO:Al=AZO). In recent years, Al-doped ZnO thin flims have attracted much attention due to its comparable optical and electrical properties to ITO films, together with their high chemical and mechanical stabilities, which make them suitable for a variety of applications such as flat panel display electrodes, gas sensors and solar cells etc.The property and application of ZnO are reviewed in this thesis, and then the principles and research progress of ZnO films preparation by sol-gel method are given. AZO films were prepared on glass substrates by sol-gel dip-coating method, using zinc acetate dihydrate, monoethanolamine and 2-methoxyethanol as precursors. And the AZO films have C-axis preferred orientation.The effects of sol concentration, Al-doping concentration, coating number, preheating temperature and annealing temperature on the properties of AZO films were studied by orthogonal experiments. The importance of these factors was fixed by comparing the transmittance and resistivity properties. The transmittance and c-axis preferred orientation of ZnO films were studied by orthogonal experiments, and the results showed that the important factors were preheating temperature and annealing temperature. The optimum technological parametes fixed are that sol concentration is 0.4 mol/L, Al-doping concentration is 2%, coating number is 12, preheating temperature is 300℃and annealing temperature is 500℃.X-ray diffraction (XRD), scanning electron microscope (SEM), four-Point Probe method and ultraviolet-visible spectrum were used to characterize the crystallization behavior, orientation, surface morphology, resistivity and transmittance properties. It is indicated that the crystal dimension is approximately 60nm, and the low resistivity is account to c-axis preferred orientation of AZO films. The average transmittance of thin film in visible region is approximately 90%, the resistivity can reach 9.6×10-3Ω·cm.On the basis of the orthogonal experiments, the effects of the factors on the crystallization behavior, orientation, resistivity and transmittance properties were discussed in detail. The results showed that these factors were influential to the properties of AZO films. First, The AZO films had good c-axis preferred orientation, optical and electrical properties, when preheated at 300℃and then post-heated at 500℃. Second, Al-doping concentration have notable influence on the resistivity and little influence on transmittance. When the Al-doping concentration is 2%, the AZO films have the highes transmittance and lowest resistivity. Third, with the increase of coating number, the resistivity of the AZO films decreased, but the transmittance property decreased first, and then increased. When the coating number is 11, AZO films had the highest transmittance and lowest resistivity. There is a small difference between the conclusion through orthogonal experiments.