Investigation On Controllable Preparation And Optoelectronic Device Of Indium Doped Zinc Oxide Nanorods

Zinc oxide(ZnO),which has wide bandgap of 3.37 eV and large exciton binding energy of 60 meV,has attracted widespread attention in recent years.Moreover,one-dimensional ZnO nano-material is especially attractive because of its high surface-to-volume and carrier transport confinement in one-dimensional direction,which could improve device performance.With simple hydrothermal growth and passivation layer,researchers can get ZnO horizontal nanorod array,which can be used in field effect transistors(FET),field emitter(FE),ultraviolet(UV)photodetector.However,one-dimensional ZnO nanorods by hydrothermal growth still have difficulty in satisfying the requirements of photoelectronic device practical application,such as low on-current and low mobility for FET,low field emission current for field emission devices,high dark current and long response and recovery time for UV photodetector.In order to solve the application problems of these devices,we adopted the way of indium doping,got some indium doped ZnO(IZO)nanorod optoelectronic devices,and improved their performance to a certain extent.Because of large dark current of IZO nanorod UV photodetector,we chose ZnO nanorods for UV detector,reduced the dark current and improved photosensitive properties with bilayer electrodes of Au/ITO and Ni/ITO.Based on the hydrothermal preparation of ZnO nanorod array,we prepared IZO nanorod array,explored the mechanism of controllable preparation of IZO nanorod array,optimized the experiment preparation conditions,and studied its optoelectronic performance in FET,FE,and ZnO nanorod array for UV photodetector.The work provides scientific reference for optoelectronic property of ZnO nano-material and further widens the scope of its optoelectronic application.The specific contents are as follows:First of all,we studied some key factors’ impact on the IZO nanorod arrangement for high performance optoelectronic device.The factors included the reaction temperature,ZnO seed layer thickness,thickness of ITO passivation layer and In doping concentration.According to the arrangement of IZO nanorods,the optimum conditions of the IZO nanorods lateral growth were as follows:reaction temperature of 85℃,ZnO seed layer thickness of 300 nm,ITO passivation layer thickness of 70 nm,In doping concentration of 2 at%.We found that we got IZO nanorod array with XRD and EDS analysis.In doping was combined with Zn2+ and OH-into the ZnO lattice,oxygen vacancies were formed and generated one or two free electron.In doping could not only increase electron concentration,but also affect the morphology and arrangement of IZO nanorods.After In doping,IZO nanomaterials showed sharp band structure instead of typical prismatic structure.In addition,indium doping affected the arrangement of IZO nanorods.The arrangement of IZO nanorods included two parts.The bottom layer was fully grown,and the upper layer was gradually grown close to each other when the indium doping concentration increased.Secondly,IZO nanorod array was prepared for high on-current field effect transistor.Compared with ZnO nanorod FETs,the performance of IZO nanorod FETs was improved.The ZnO nanorod FETs showed on-current of 1.86×10-5 A at Vas=5 V and Vgs=60 V,while the IZO nanorod FETs showed on-current of 6.39×10-4 A at Vds=5 V and Vgs=60 V and field effect mobility of 26.3 cm2 V-1 s-1.Device performance improvement after In doping was because of the increase of carrier concentration,also attributed to better band morphology,better growth arrangement,better contact and transport performance.The IZO nanorod preparation method of field effect transistor has certain reference value,and is expected to be used for large driving current power devices.In addition,we explored the IZO nanorods internal mechanism.After doping,indium was effective with In-O-Zn without In2O3 or In(OH)3,which increased the oxygen vacancy concentration,thus increased the electron concentration,and ultimately increased on-current of FETs.Thirdly,the IZO nanorod array was prepared for high field emission current of field emission devices.By the adjustment of array density,arrangement,morphology,length to diameter ratio and distance between electrodes,we realized effective control of IZO nanorod field emission performance.We studied the the inner mechanism of the field emission after In doping.Under the applied electric field,the ZnO nanorod or IZO nanorod accumulated electrons at the top,barrier height was reduced,probability of electron tunneling increased,and after In doping,IZO nanorods had more tunneling electrons,so that the field emission current increased at the same voltage,field emission performance was improved.The IZO nanorod field emission performance was the best when the electrode spacing was 70 μm,the turn-on field is 1.4 V/μm,field enhancement factor was 2252,the biggest field emission current of 26.15 pA at 7 V/μm,its field emission performance was significantly better than that of ZnO nanorod field emission devices.Finally,with Ni/ITO and Au/ITO bilayer electrodes we prepared ZnO nanorod UV photodetector,and the dark current was reduced.The effects of Au/ITO,Ni/ITO on growth morphology and arrangement were studied.And The effects of Au/ITO,Ni/ITO on photocurrent,dark current,sensitivity,response time and recovery time were also studied.We discussed the mechanism of ZnO nanorod UV photosensitive detection.There are two parts of the schottky barrier,one is between ZnO nanorods and nanorods,the other part of the schottky barrier is between the metal electrode and semiconductor associated with the work function of the metal.The schottky barrier between Au/ITO,Ni/ITO and semiconductor was close,but Au/ZnO photodetector formed shottky barrier between ZnO nanorods and nanorods,had higher schottky barrier than that of Ni/ITO photodetector,impeded the carrier injection and transport,so Au/ITO photodetector had lower dark current.Photogenerated electron-hole were separated by schottky barrier built-in electric field,which reduced electron-hole recombination,increased the life of the carrier,reached the maximum photocurrent faster to improve response time.The recovery time of the Au/ITO photodetector was faster after the light was switched off,that was because the oxygen molecules were reabsorbed near schottky barrier interface between ZnO nanorods and nanorods,and returned to the dark current more quickly.The preparation of optoelectronic device is usually complex and time consuming,but the preparation of lateral IZO nanorods in this work is just based on a simple hydrothermal method with the appropriate device structure design,it is succeeded in preparation of the field effect transistor,field emission device and UV photodetector.The working mechanism and performance of these devices were studied and discussed.The work provides scientific reference for optoelectronic property of ZnO nano-material and furtherly broadens the scope of its optoelectronic application.