Structural And Optical Properties Of Na-Mg Co-doped ZnO Film

ZnO is self activated wide band gap semiconductor material composed ofⅡ-Ⅵelements with P6 mm point group symmetry hexagonal wurtzite crystal structure. The band gap is 3.37eV at room temperature, and the excitation binding energy is as high as 60m eV. In the plane perpendicular to c-axis, ZnO has symmetric flexibility and electrical properties, while in the c-axis plane, the polycrystalline thin films ZnO has properties that are similar to single crystals in piezoelectric properties and optical properties. For the excellent Piezoelectric performance, transparent conductivity, etc., the Zno films are widely used in many fields such as the solar cells, piezoelectric devices, surface acoustic wave devices, gas sensors, and there are great potential in the development of UV detectors, LED, LD and other fields for its excellent ultraviolet-electric property. What's more, study of the P-doped ZnO is another hot but difficult problems recently. The ZnO films are often doped to expand the use of zinc oxide, for example in the LED, UV detectors, surface acoustic wave devices, varistor devices and so on. In recent years, Ohtomo A et al found that Mg doping can control the energy band of ZnO structure. With the variation of Mg concentration, the band gap varies from 3.37 eV to 3.87 eV and transition of ZnO can be realized with the dope of I group elements.In this paper,, we select the sol-gel method based on fully understanding of crystal structure of zinc oxide, piezoelectric and optical properties of zinc oxide thin films, buffer layer and integrated optical applications of multi-layer thin film epitaxial growth, as well as all kinds of zinc oxide thin film fabricating techniques. Using methanol as solvent, zinc acetate, magnesium chloride, sodium chloride as starting materials, and diethanolamine as stabilizer, with the spin coating method in the conventional quartz glass,after drying, preheating, annealing, we finally successfully prepared the c-axis orientation preferred,Na-Mg co-doped, uniform and transparent polycrystalline ZnO thin films. The results of XRD, SEM and PL spectrum analysis show that:Na-Mg co-doped ZnO thin films is in favor of C-axis preferred orientation growth, and with the increase of Na+doping concentration, grain size firstly increases and then decreases. Comparisons of the different doping PL spectra of ZnO thin films suggest that the UV light emission locating at 380nm is related to ZnO free excitation recombination and band gap of Mg doped ZnO is indeed increased. In the series of Na-Mg co-doped ZnO thin films, the film Na0.02Mg0.2Zn0.78O has better crystalline property and optical properties, and the PL spectra of Na0.04Mg0.2Zn0.76O show that this kind of films have high strength violet emission, the near band edge UV emission luminous intensity is nearly 10 times of the undoped ZnO, thus the UV emission properties of thin films are greatly enhanced. The films in this experiment are spin-coated of 5 layers and annealed at the temperature of 560℃.