Fabrication And Properties Of ZnO Based UV Photodetectors

UV photodetectors have many applications in communication,astronomy,environment monitoring,chemical analysis and medical instrument,etc.ZnO has become one of the most promising UV photodetector materials owing to its direct and wide gap of 3.37 eV,a large excitation binding energy of 60 meV and its high electron mobility.But many reported ZnO based UV photodetectors suffer the problems of low responsivity,long response time and complex fabrication method.In this paper,we synthesized nano-materials with controllable morphologies,prepared ZnO nanorod arrays based UV photodetectors with different structures and studied the principle of the devices to improve the photo response performance of the devices.The main acheivements are as follows:1.Photochemical synthesis:UV photodetector based on CuO/ZnO heterostructureWe used the photochemical method to synthesize Cu2(NO3)(OH)3/ZnO heterostructure precursor.The ZnO nanorod arrays(NRs)were put into Cu(NO3)2 solution and illuminated by UV light for several minutes.Then plate-like Cu2(NO3)(OH)3 nanostructure was successfully deposited on the surface of ZnO nanorod arrays.CuO/ZnO was prepared by annealing the Cu2(NO3)(OH)3/ZnO heterostructure precursor in air atmosphere.The morphology of CuO nanostructures can be rationally tailored by controlling the growth conditions.The fabricated CuO/ZnO NRs UV detectors exhibit improved photosensitivity compared with the bare ZnO NRs device.The presence of the barrier at the heterojunction interface reduce the dark current and increase the separation efficiency of electrons and holes,which results in the increase of photosensitivity and response speed.The CuO/ZnO heterostructure,preapared in the optional condition,shows the maximum photosensitivity of 71,which is increased for 50 times than that of the bare ZnO NRs device.The rise time is reduced by 30%and the decay time is reduced by one order magnitude.2.Tuning the performance of ZnO/PSS:PEDOT heterojunction UV photodetector by hydrogen annealingWe prepared a ZnO/PSS:PEDOT heterojunction UV photodetector by spin coating PSS:PEDOT on the surface of ZnO NRs synthesized using a hydrothermal method.ZnO NRs were annealed under hydrogen atmosphere at different temperature.We discovered that hydrogen annealing had great effect on the defects and the Fermi level of ZnO NRs.We fabricated ZnO/PSS:PEDOT heterojunctions and studied the optoelectronic properties of the devices.Hydrogen annealing increased ?b of the ZnO/PSS:PEDOT heterojunctions and improved the photocurrent and photosensitivity of the devices.The ZnO/PSS:PEDOT heterojunction with 300? annealed ZnO NRs shows the highest rectification ratio of 255 at 2 V bias and the highest barrier height of 0.84 eV.The device also has excellent response performance.The response time is less than 1 s and the photosensitivity is 1000 at zero bias and 365 nm UV illumination,which is 10 times of the device with unannealed ZnO NRs.3.Photoelectrochemical cell type UV photodetectors based on ZnO nanorod arrays,[Co(bpy)3]2+/3+ electrolyte and PEDOT/ITO counter electrodeWe fabricated a high performance ZnO based selfpowered PECC-type UV photodetector with a facile method.It is demonstrated that the combination of[Co(bpy)3]2+/3+ complex with PEDOT/ITO CE ensures a high VOC and fast regeneration of[Co(bpy)3]2+ at the CE.The UV photodetector with PEDOT/ITO CE exhibits a high photosensitivity of 263 and a rapid response speed(response time<0.2 s)at zero bias.The high performance of the detector,together with the Pt-free PEDOT/ITO CE and the facile fabrication method,makes the device promising in optoelectronic applications.