Preparation And Electrical Transport Character-Istics Of ZnO/GR Heterojunction Based On Flexible Substrate

The ZnO has been widely used in optoelectronic devices,such as green lighting,optical communication and UV detector,which was due to its large exciton binding energy,low preparation cost,and low environmental pollution.As for ZnO ultraviolet devices,the metal materials are usually selected as electrodes.However,metal electrodes(such as Pt)generally have poor transparency and large contact resistance,which has become one of the bottlenecks in the preparation and research on the development of ZnO ultraviolet electrical devices.In recent years,with the rapid development of graphene(GR)and indium tin oxide(ITO)conductive thin film materials,the problems of poor transmittance and high contact resistance of metal electrodes can be avoided by using these two kinds of materials as electrode materials for ZnO optoelectronic devices.Therefore,it is a great significance for the preparation and industrialization of ZnO optoelectronic devices as for systematically study the electrical transport properties at the interface of ion doped ZnO/GR and ZnO/ITO heterojunction.In this paper,GR and ITO were selected as electrode materials.The ZnO nanorods were deposited on flexible PETGR and PET-ITO substrates by hydrothermal method for the fabrication of ZnO/PET-GR and ZnO/PET-ITO heterojunction.The structure,morphology and performance of ZnO nanorods were analyzed.The electrical properties of ZnO heterojunctions under different ion doping(B3+.Al3+,La3+,Zr4+)were studied with the temperature-dependent current-voltage characteristic curve.The electrical transport properties at the interface were discussed.The main research contents are as follows:(1)By adopting hydrothermal method,the hexagonal wurtzite ZnO nanorods(undoped)perpendicular to the substrate plane were grown on the surface of ITO and GR of PET flexible substrate as the bottom electrodes.The effects of ITO and GR on the growth structure,morphology and properties of ZnO nanorods were studied.It is found that the ZnO rods have good crystallization properties in this experiment.Compared with ITO substrate,the top section size of ZnO nanorods on the surface of GR substrate has no obvious reduction.The oxygen vacancy defects of ZnO rods in ZnO/GR heterojunction were less than ZnO/ITO structure.The J-V curves show that the ZnO/GR and ZnO/ITO heterostructures exhibit obvious rectification characteristics,indicating that the interface between ZnO and electrode has obvious barrier.However,the leakage current of ZnO/GR heterojunction is smaller than ZnO/ITO heterojunction,indicating that the performance of heterojunction with GR as the bottom electrode is better than that of ITO electrode.(2)The ion doped(B3+,Al3+,La3+,Zr4+)nano ZnO rods were deposited on the surface of flexible PET-GR substrates.The effects of the particle doping ratio on the growth and structural characteristics of nano ZnO rods were studied.In the range studying,the hexagonal wurtzite ZnO perpendicular to the bottom plane can be grown under the conditions of the above elements and different doping ratios.With the increasing of B3+doping,the lattice constant of ZnO rod decreases gradually,while the lattice constant of ZnO rod increases gradually with the increase of Al3+,La3+,Zr4+doping.Meanwhile,the size of ZnO nanorods decreases with the increase of the doping concentration of the above four elements.In addition,with the increase of ion doping concentration,the defect state oxygen and optical band gap in ZnO rod decreases.(3)The relationship between the electrical transport characteristics and temperature at the interface of ZnO/GR heterostructures prepared with the different types and concentrations of ion doping was studied.The results of J-V curve show that the ZnO/GR heterostructures have obvious rectification characteristics after doped with B3+,Al3+,La3+and Zr4+.With the increase of doping concentration,the current density of ZnO/GR heterostructures first decreases and then increases under the same voltage.Especially for B3+,Al3+,La3+ions doping,the current density is the lowest with the ion doping concentration about 3%,while the current density is the lowest for Zr4+doped with 6%.Meanwhile,the corresponding barrier height is the highest.In addition,it is found that the forward electrical transport characteristics of ZnO/GR heterojunction with the increasing of forward voltage are mainly electron tunneling mechanism and Schottky emission mechanism.(4)Based on I-V-T test,it is observed that the forward saturation current of ZnO/GR Schottky contacts increase and the reverse leakage rises with the rise of temperature;combined with TE model,the variation trend of barrier height at the interface is studied.It is indicated that the barrier height increases and the ideal factor decreases with the increase of temperature,which shows that the distribution of barrier height at the interface is uneven.Meanwhile,the modified Richardson constant is obtained by using the Gaussian distribution model to quantitatively describe the heterogeneity of Schottky barrier height.