Synthesis And Properties Of ZnO/Cu₂O Nano-heterojunction Arrays

Under normal circumstances, semiconductor ZnO materials only show n-type conductiveproperties. Such phenomenon greatly restricts its application in ZnO-based solar cell andoptoelectronic devices. For further expand the application fields of ZnO semiconductormaterials, the synthesis of Cu₂O/ZnO nano-heterojunction arrays and its characteristicresearch works were carried out with the n-type conductive property of Cu₂O semiconductorsin this thesis. The main research contents are as follows:1) By using of hydrothermal synthesis method, aligned one-dimensional ZnO nanowirearrays were prepared. And the morphology, micro-structure and photoluminescenceproperties of as-prepared samples were characterized by XRD, SEM and PL spectrum,respectively. The results showed that the micro-structure of the as-prepared single ZnOnanowire represented the hexagonal wurtzite structure, the XRD diffraction peak of （002）lattice plane is strongest ones. The synthesized ZnO nanowires have a smooth surface andwell-distributed diameters. And the mean diameter and length of the NWs are related with thesolution concentration and reaction time. The room-temperature PL spectrum of thesynthesized ZnO NW arrays gave a sharp UV emission peak near379nm. And compare itwith the theoretical value of the free exciton recombination near the bandgap, it cause a blueshift around1nm. There is a wide red emission band near597nm, which caused by theoxygen vacancy and zinc deficiency. The analytic results showed that the best experimentalcondition is volume ratio of the NH3·H2O and H2O solution is1:5, and the reaction time is10h, reaction temperature is95℃at normal pressure.2) By electrochemical deposition and hot dip plating method, one-dimensional ZnO/Cu₂Onano-heterojunction were prepared with the as-synthesized ZnO nanowire arrays as thesubstrate. The prepared nano-heterojunction samples were characterized by XRD, XPS, SEM,TEM and PL methods, respectively. The result show that the oxide of copper deposited on thesurface of ZnO NWs is Cu₂O coating layer. And the Cu₂O coating layer is composed of lotsof single-crystalline nano-particles capped on the surface of ZnO NWs, and the nano-particlesprefer growth along （111） lattice plane. After electrochemical deposition and hot dip platingprocess, the surface of ZnO NWs become coarser and its diameter increased obviously. Ourresearch results found that the deposited time and solution concentration will seriously affectthe morphology and surface microstructure of the ZnO/Cu₂O nano-heterojunction. Meanwhile,a relative longer deposition time and a larger solution concentration are unfavorable forcrystallization of Cu₂O particles. The PL spectral analysis showed that there is a sharp UV emission peak near381nm, and there is also a green emission band near523.4nm. Comparedwith the pure ZnO NW arrays, the UV emission peak of ZnO/Cu₂O nano-heterojunctionarrays had a red-shifted around2.4nm. This result suggested that the UV emission peak iscauseed by the free exciton recombination near bandgap edge, and a widely green emissionpeak near523.4nm is caused by lots of lattice defect in ZnO/Cu₂O ano-heterojunctions whenCu₂O nano-particles capped on the surface of ZnO NWs. The comparison found,a relativeshorter deposition time and the lower solution concentration can acquire better ZnO/Cu₂Oheterojunction when synthesize heterojunction by dip coating method,and deposition time as20s can acquire better ZnO/Cu₂O heterojunction when synthesize heterojunction bydeposition method.3)The analysis of the I-V characteristics of as-prepared found that the heterojunctionshowed a schottky contact characteristics.The thesis analysis and contrast different samples’photoresponse features at different light or dark condition.The result shows ZnO/Cu₂Onanowire p-n heterojunction composite arrays will emerge high-sensitivity under thecondition of0.6V,20s.