Investigation on the Optical Performance of Co and Al Co-Doping ZnO Films

ZnO is a novel kind of semiconductor material, which has hexagonal Wurtzite crystal structure, with a wide band-gap of 3.37eV at room temperature. It owns a large excitation binding energy of 60meV and excellent room temperature stability. ZnO has very useful properties of piezoelectricity, gas & pressure sensitivity etc. Therefore, application researches on low dimensional ZnO materials have become hot topics and significant values.In this paper, ZnO doped thin films were prepared by sol-gel method. Zn (CH3COO)2•2H2O was employed as the precursor, anhydrous alcohol was the solvent, monoethanolamine was the complexant, Co(CH3COO)2•4H2O was used as the source of the Co-dopant, Al(NO3)3•9H2O was used as the source of the Al-dopant in the experiment to yield the doped ZnO films. The sample preparation spin coating number is 6, the average grain size is in nanometer level, and the thermal treatment temperature is 450, 500, 550, 600°C, respectively. The effect of the doping proportion on the crystallization and energy band structure of the ZnO thin films were characterized by X-ray diffraction (XRD), the Infrared spectrum and the ultraviolet-visible transmission spectra (UV-Vis).The results show that the crystalline grain size of the ZnO doped films grown on glass substrates increases, since the thermal treatment temperature rise. In this paper, a best ZnO doped film was obtained at the temperature of 600°C. It preliminarily analyses that Co-doped ZnO films present a absorption peak in infrared area when the thermal treatment is at 550°C. Al or Co doped ZnO films can cause a redshift of ultraviolet absorption peaks. Energy gap is around 3.2eV when doped. The ultraviolet absorption peaks of Al-doped ZnO films will have a shift to high energy, since it has a better crystallinity.