Study On Co-doped Transparent Conductive ZnO Thin Film

With the development of science and technology, especially the utilization of solar energy, display technology and the hot spots in other field, transparent conducting oxide film occupies more and more important position in new thin film materials. The materials with excellent chemical stability, high transmittance and low resistivity can be used in many fields, such as the thin film solar cell, liquid crystal display and gas sensor, etc. Because of low cost, non-toxic, simple preparation process, low deposition temperature, and excellent stability in hydrogen plasma environment, ZnO transparent conductive thin films are regarded as one of the most suitable replacement of ITO (In2O3:Sn). There are many problems with metal ion doped ZnO transparent conductive thin films, such as the low carrier mobility, unsatisfactory conductivity, clusters of metal ions and formation of metal oxide impurities as the doping concentration too high. In order to further improve the photoelectric properties of thin films, the multiple elements co-doping method has been used to prepare the new ZnO based transparent conductive thin film in this paper. The structure, composition and surface morphology of the co-doped ZnO films have been studied. The photoelectric properties of the films were tested, and the influence of doping elements on the photoelectric properties of the films was also studied. The preparation process was optimized, and optimum process parameters were obtained.The multiple elements co-doping method is to make the metal and non-metallic elements with similar atomic radius doped into ZnO, occupying the Zn+or O2-lattice and being substitutional atoms. Due to the excess of the valence electrons, the conduction electrons in the crystal increase and conductivity improve. Through the interaction of the elements, the reduction of mobility and formation of impurities has been avoided.Ga, Al co-doped ZnO films were successfully synthesized by the sol-gel method using spin coating technique on the glass. By using the orthogonal test, the preparation process of GAZO thin film has been optimized. Sol concentration, heat treatment temperature, thickness and other factors on photoelectric property of these thin films also been studied. The light transmittance and sheet resistance were used as evaluation index to determine optimum parameters of GAZO films. The optimum parameters are sol concentration l.Omol/L, Al doping concentration2.0at.%, Al/Ga doping ratio2:1, preheating temperature350℃, annealing temperature600℃and the film layer number10. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), spectrophotometer, four probe resistivity tester and other technologies have been used to analyze and test the films. The XRD tests show that the incorporation of Al and Ga do not affect the crystal structure of ZnO, and do not generate other impurities oxide. Under optimum conditions, the transmittance of the film in the visible range is88.458%, and the resistivity is2.66x10-3Ω·cm.The single-doped [ZnO:Al (AZO) and ZnO:Ga (GZO)] and pure ZnO thin films were synthesized respectively. The structure, surface morphology and photoelectric performance of these films were studied, compared with GAZO film. The results show that, co-doping and single-doping can effectively improve the resistivity of the ZnO film. The effect of single-doped Al is the most obviously. All the films are polycrystalline with a hexagonal structure and a preferred orientation along the (002) C-axis. Ga, Al co-doping has many advantages, such as promoting the growth of the crystal lattice, refining the grain and improving transmittance in a certain range.The co-doped ZnO thin films [ZnO:Al/N/F] were successfully synthesized by the sol-gel method using spin coating technique. The factors, including the sol concentration and doping concentration, which have great influence on the structure, surface morphology and photoelectric properties of the films have been studied. The results show that the surface morphology of the ZnO:Al/N/F films is smooth and dense, the grain size is uniform, and the films are high crystalline quality of (002) preferred along the C-axis orientation. In the range of visible light (390-780nm), the average transmittance is87.9%when the sol concentration is0.75mol/L and the doping concentration is0.9at.%. The minimum resistivity is0.23Ω·cm when the doping concentration is1.05at.%.