Preparation And Optical Properties Of ZnO Thin Films Cu-Al Co-doped

ZnO is a new direct wide bandgap Ⅱ-Ⅵ compound semiconductor material, the crystal structure is hexagonal wurtzite structure with lattice constant a=0.32495nm, c=0.52069nm and density of5.606g/cm3, band gap at room temperature of3.37eV and the exciton binding energy up to60meV, which is much larger than the thermal ionization energy of26meV at room temperature. Compared with ZnSe (22meV), GaN (24meV) and ZnS (40meV), ZnO is more suitable for achieving highly efficient laser emission at room temperature or at higher temperatures, and ZnO possesses a high thermal stability and chemical stability, which render it a more preferably short wavelength light-emitting material at room temperature. ZnO also has excellent performance in various fields such as optical, piezoelectric, thermoelectric, ferroelectric etc. Because of these excellent properties, ZnO has a wide range of uses and many potential uses, such as gas sensors, the transparent conductive film, a UV detector, a light emitting device and the thin film transistor and so on and so forth.This paper reviews the aspects of the basic properties of ZnO, the intrinsic defects in the crystal and interaction as well as application development and makes a detailed description of the ZnO film growth method, the characterization of the structure and properties as well as chemical reaction principle of making ZnO-based thin film with sol-gel method. ZnO:Cu-Al thin films have been prepared by Sol-gel spin coating on the glass substrate,the influence of different doping ion concentration, sol concentration and heat treatment temperature on the crystal structure, surface morphology and optical properties of ZnO:Cu-Al thin film have been Characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectrophotometer (UV-Vis), fluorescence spectrometer (FL). And the main conclusions are as follows:(1) Adopt Zn(CH3COO)2-2H2O as raw materials, dried over anhydrous ethanol CH3CH2OH as solvent, diethanolamine C4H11NO2as a stabilizer, copper acetate Cu(CH3COO)2.H2O and aluminum nitrate Al(NO3)3·9H2O as dopant for Cu and Al. Prepare ZnO:Cu-Al polycrystalline film on the glass substrate by the sol-gel spin coating method, with all samples being hexagonal wurtzite structure.(2) Cu-doping concentration affect the intensity and position of the (002) plane diffraction peak. With Cu-doping concentration increases translucent variation; optical band gap decreasing gradually and the red shift of ZnO:Cu-Al thin films. All samples were observed in the UV emission peak and Blu-ray emission peak, the analysis found that the incorporation of Cu ions affect the intensity of short-wave light. The consolidated light-transmissive and light-emitting, when the Cu ion doping concentration of1%, the transmittance of about81%, the Blu-ray emission peak intensity of the strongest.Al doping makes the c-axis orientation weakened and crystal the particle size decreased, the2θangle of (002) crystal plane offset toward the high angle. The residual stress of the film changes from the tensile stress to compressive stress; With Al ion doping concentration increases and the average transmission rate of above80%,weakly doped Al3+is possible to improve the light transmittance of the ZnO:Cu, the optical band gap of the sample is broadened compared with that of ZnO:Cu film; All samples can be observed at368nm,398nm UV emission peak and the weak blue peak around450nm,483nm and468nm or so of the relatively strong blue peak. When weakly doped Al3+ion concentration of0.3%, the transmittance rate reached about80%, and Blu-ray emission peak intensity is enhanced.(3) After500℃annealing of ZnO:Cu-Al (1:0.3at%) film has a relatively complete crystal grain.Appropriate grain size, dense, homogeneous microstructure, in the visible range having a higher transmission rate (83.13%), and the blue region of the visible light, the blue light emitting intensity of the strongest. The type of sol concentration influence the preferred orientation of the film as well as the intensity of the emission peak.Comprehensive doping ion concentration, annealing temperature, the concentration of sol comprehensive analysis of the properties of ZnO films, we have come to the optimal process parameters:the coating timesis6times, annealing time is2h, drying temperature is150℃and cooling mode with the furnace was cooled to the room temperature, the Cu ion doping concentration is1%, Al doping concentration is0.3%, with an annealing temperature of500℃, the solubility of the sol-0.75mol/Loptimum conditions.