Preparation Of ZnO Thin Films And Studied On Their Properties

ZnO is a II-VI semiconductor material with wide band-gap, which has hexagonal wurtzite structure. ZnO thin films were widely applied in solar cell, UV detector, SAW device, gas sensor and transparent electrodes et al for their excellent properties. In recent years, Al-doped ZnO(ZAO)thin films has become a hot issue of transparent conductive thin films field and preferred materials instead of ITO films not only because of their comparable optical and electrical properties( high optical transparency in the visible range, low electrical resistivity) to ITO films, but also because of their lower price and higher thermal and chemical stability under the exposure to hydrogen plasma than ITO.A sol-gel technique is adopted in this work. The starting material used in the present study was zinc acetate dehydrate (Zn(CH3COO)2·2H2O). Isopropanol was used as a solvent, diethanolamine (DEA) as a sol stabilizer and Al(NO3)3·9H2O to provide doping ion. The films obtained were characterized and analyzed by XRD, AFM, SEM, fluorescence spectrum and ultraviolet-visible spectrophotometer. The conduction mechanism was analyzed and the electrical properties were investigated by Van der Pauw method.The experimental results showed that ZnO thin films had good structural, optical and electrical properties. It was found that the obtained films were poly-crystalline and the crystallinity of ZnO thin films became better after annealing. By using AFM and SEM, we found that the surfaces morphology of samples was even and smooth. The films were composed of some excellent columnar crystallites.Study for optical spectra of the films indicates that the average value of the optical transmittance of ZnO and ZAO thin films in the visible region all exceeds 90%. The ZnO thin film annealed at 500℃for 1 h from the sol with Zn concentration of 0.8 mol/L shows an average transmittance of 94% in visible wavelength range. With Al doping concentration and the annealing temperature increasing, the absorption edge of the transmission curve of the films moves toward short wavelength. Investigation for electrical properties of ZAO thin films indicates that Al doping concentration and annealing temperature have a strong influence on the properties of the films. ZnO film with 1% Al has the minimum electrical resistivity. With increasing the annealing temperature, electrical resistivity decreases.In this work, we also prepared Mn doping ZnO films using magnetron sputtering and analyzed the optical and electrical properties.