Preparation And Low Temperature Treatment In N2 Of Conducting ZnO Films By Sol-gel Method

ZnO film, a semiconductor with wide direct band gap, has been actively studied because of its potential applications. It can be used in solar cell, piezoelectric device, photoelectric device, gas sensor and UV detector and the characteristics can be modulated by appropriate doping. The transparent ZnO conductive thin films doped with suitable dopants have excellent optical and electrical properties, and are applied widely as transparent and conductive oxide electrodes in various electrical and optical devices including liquid crystal display, solar cell and so on.In this paper, the primary objective is researching the stability in N₂ of ZnO flims doped with Al by sol-gel and the influence of dopant concentration and the number of coating on the conductivity and transmittance of ZnO films doped with Li by sol-gel. ZnO thin films doped with Al³⁺,Li⁺ were prepared on microslides by sol-gel method successfully. The sol was prepared with 2-methoxyethanol as solvent, Zincacetate as precursor and MEA as stabilizer. The mixture was heated, stirred to obtain the sol, and then homogenous transparent ZnO thin films were prepared from the sol by dipping, drying, pre-heat treatment in air and annealing in N₂ atmospheres.XRD, SEM, XPS and Four-Point probe method were used to characterize the structure and optical and electrical properties of the ZnO thin films. The results showed that the kind of dopant, dopant concentration, temperature of pre-heat treatment, the number of coating and annealing atmosphere had influence in various extents on the photoelectric performance of the doped ZnO thin films. Increasing the dopant concentration could reduce resistivity of thin films, but over high dopant concentration would increase the resistivity. The difference of dopants has great influence on the stability of films annealed in N2; the stability of ZnO flims doped with Al is good but that doped with Li is bad. Increasing the number of coating could increase the thickness of thin films, which would reduce the resistivity and the transmittance within the range of visible light. The transmittance of thin films in the range of visible light was not impacted greatly by different dopant concentrations and annealing atmosphere. The different atmospheres can directly influence the electric conductivity. The film with low resistivity can be obtained by heat treatment in N2 at 300℃. In this experiment, the surface configuration of the films is compact, the sizes of crystal grain is uniform, the lowest sheet resistance is 270?/â–¡and the maximum transmittance within the range of visible light is about 83%. The optimum technological parameters for AZO and LZO thin film by sol-gel are as follows: the sol concentration is 0.6 mol/L; the dopant concentrations of Al and Li are 1at% and 2.3at%, respectively; the number of coating is 15 and 10, respectively; the pre-heat treatment temperature is 450℃and the annealing temperature is 550℃in air, 300℃in N₂.