Study On The Al³⁺-Doped ZnO Thin Films Prepared By Sol-Gel Process

Al3+-doped ZnO(ZAO)thin films are emerging as an alternative potential candidate for ITO (Sn-doped In2O3) films recently not only because of their comparable optical and electrical properties to ITO films, but also because of their excellence of the abundance of the materials in nature, simple production procedure, low cost absence of toxicity, high thermal and chemical stability.In this paper, the properties, preparation methods, applications and developments of Al3+-doped ZnO thin films were reviewed. Al3+-doped ZnO thin films were deposited on quartz substrates by sol-gel technique. The X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the crystallization behavior, orientation and surface morphology of the ZAO thin films. The influence of the dopant concentration, annealing temperature and sol concentration on the microstructure and surface morphology of ZAO transparent conductive film has been found. The XRD results show that the crystal structure of the ZAO thin films are the same as ZnO and the Al was doped into ZnO lattice successfully. The SEM results indicate that with the sol concentration increasing, the surface of the thin film became more compact and uniform.Conducting mechanism of the ZAO thin films was investigated. The result indicates that dopant concentration, annealing temperature have strong influence on the sheet resistance of the films. With increasing the annealing temperature, the sheet resistance performs decreasing previously and increasing later. The lowest sheet resistance of ZAO thin films was about 574Ω/□.The measurement of infrared transmittance and infrared emissivity of the ZAO thin films were completed in the paper and the effects of the dopant concentration and annealing temperature on the infrared transmittance and infrared emissivity of the ZAO thin films were investigated and compared. The results show that The results show that with the heat-treatment temperature increases, the infrared transmission which in the range of 8μm～14μm waveband of ZAO thin films was increased firstly and then reduced. The maximal average infrared transmission of ZAO thin films is up to 76% when the heat-treatment temperature at 700℃. With the dopant concentration of Al3+ increasing, the infrared emissivity of ZAO thin films were reduced firstly and then increased. The infrared emissivity of ZAO thin films whose dopant concentration was 5at%is lowest. The infrared emissivity of ZAO thin films were reduced firstly and then increased when the heat-treatment temperature increases. The infrared emissivity of ZAO thin films is lowest when the heat-treatment temperature up to 700℃.The effects of the technological parameters for preparing ZAO film were investigated and compared. The optimum technological parameters for the best optical and electrical properties of ZAO thin films were that the sol concentration was 0.5 M/L, the dopant concentration was 5at%, and pre-heat-treatment was temperature was 120℃, the annealing temperature was 700℃.There are 17 figures,3tables and 45 references in this paper.