Fabrication And Properties Of ZnO Based Thin Films By Electrodeposition

ZnO materials are widely used in optoelectronics,sensors and other fields due to their excellent electrical and optical properties.The morphology and structure of ZnO have a significant effect on their properties.Fabrication and adjusting nanostructures of ZnO by various methods have become a research hotspot.As a traditional method,the electrodeposition process is classified into electrophoretic deposition and electrochemical deposition,based on different deposition mechanisms.The properties can be optimized by doping because of a number of defects existing in ZnO crystal.In this paper,ZnO thin films were fabricated by electrophoretic deposition,and the effect of deposition processes on morphology of thin films was investigated.Then Cu-doped ZnO films were fabricated by the same method,and the resistance switching?RS?behavior and mechanism were discussed.Finally,both one-dimensional?1D?ZnO nanowires and two dimensional?2D?ZnO thin films were fabricated on different substrates by electrochemical deposition.The effect of the deposition processes and the reactant concentration on the morphology of ZnO was analyzed,and the growth mechanisms of two different ZnO nanostructures were discussed.The main contents are as follows:?1?Investigation on the fabrication of ZnO thin films by electrophoretic deposition.The effect of NaOH concentration,curing time of colloid,applied voltage and time duration on the microstructure of films was investigated.The results indicate that dense nanocrystalline thin films with uniform and fine grains can be obtained at a deposition voltage of 300 V and time duration of 10 min when NaOH concentration is 1.25×10^-2mol/L and colloid is aged for 2 to 5 days.The effect of zinc nitrate solution of 0.1mol/L in colloidal solution on the morphology of precursor particles and thin films was studied,and the possible formation mechanism was analyzed.Due to the addition of zinc nitrate as binder and supporting electrolyte,precursor particles grow into nanosheets with average particle size of about 1.5?m and the thickness of about 30 nm.The morphology of the films can be changed by increasing the current density,leading to the arragement of nanoplates from parallel to normal to the surface of substrate and forming reticular structure.Heat-treatment at elevated temperature enhances the porous structure of the films.?2?Investigation on the Resistance Switching?RS?behavior of Cu-doped ZnO thin films.Cu-doped ZnO films were fabricated by electrophoretic deposition.The effect of Cu²⁺ doping on morphology and photoluminescence?PL?spectra of thin films was investigated.I-V curves of thin films were measured,and both the RS behavior and mechanism were discussed.PL spectra indicate that Cu doping introduces deep acceptor level in the bandgap and decreases the concentration of oxygen vacancy,which result in the decreasing intensity of ultraviolet,blue and green luminescence.The R_off/R_on ratio of the deposited films is up to105.The resistive switching behaviors are governed by Ohm's law in the LRS and Space Charge Limited Conduction?SCLC?in the HRS,respectively.Good endurance characteristics can be retained after 100 switching cycles without any obvious fluctuation in R_off/R_on ratio.Cu²⁺ doping has little influence on Low Resistance State?LRS?,but decreases the dispersion in High Resistance State?HRS?and switching voltage V_SET.When Cu doping content x=0.04,the devices show good properties: R_off?10⁶?,R_off/R_on?10⁴,and the value of V_SET is between +0.4 and +3.03 V.?3?Fabrication and characterization of ZnO nanostructures by electrochemical deposition.1D ZnO nanowires and 2D ZnO nano films were fabricated by electrochemical deposition.The effect of deposition parameters on the morphology was investigated,and the growth mechanisms of different morphologies were discussed.1D ZnO nanowires were fabricated using porous anodic aluminum oxide?AAO?film as template,and continuous growth of nanowires in the template holes was achieved at suitable current density.2D ZnO nanosheets structures were deposited from zinc nitrate /KCl electrolyte and the growth along the?0001?plane is hindered by the adsorption of Cl-ions,which resulting in the formation of ZnO nanosheets.The morphology of ZnO 2D nanostructures could be changed by adjusting the concentrations of zinc nitrate and KCl.