Fabrication Of P-NiO/n-ZnO Heterojunction Ultraviolet Photodetectors And Their Photoresponse Performance

UV photodetector has very important application value in the civilian and military area,which needs small volume,fast response,high sensitivity,low cost and so on.Zinc oxide(ZnO),as a direct band-gap semiconductor,is considered a promising material for fabricating ultraviolet(UV)semiconductor detectors owing to its wide band gap(3.37eV),no absorbing at visible wavelengths,chemical stability,as well as rich raw materials.In this dissertation,we carried out a series of research work on the growth of ZnO nanorods array and ZnO continuous dense film,the construction of p-NiO/n-ZnO heterostructures,as well as the UV response performance of the corresponding photodetectors.The focus is the recovery performance of the devices.The main research contents and results are as follows:(1)ZnO nanorods array were grown on sapphire substrate by room temperature radio frequency magnetron sputtering and hydrothermal method.Scanning electron microscopy(SEM),energy-dispersive X-ray(EDX)spectroscopy,X-ray diffraction(XRD),and PL spectral analysis were used to characterize the ZnO nanorods array.The influence of annealing for the performance of ZnO UV photodetector is studied.The results showed that annealing can reduce the defect density of ZnO nanorods,thereby increasing the sensitivity of ZnO photodetector.(2)NiO thin film was fabricated by thermal oxidation at different temperatures and was characterized.The results showed that with the increase of oxidation temperature,the defect density of NiO thin film decreased,thereby the crystal quality improved.On this basis,the high-quality ZnO nanorods array were grown on the NiO film by hydrothermal growth processes.The performance of UV photodetectors based on the p-NiO/n-ZnO heterojunctions was characterized,illustrating that in the studied temperature range,the recovery speed of the devices was accelerating with decreasing defect density of the NiO thin film.(3)NiO thin films were prepared on flexible Ni foils by thermal oxidation process.And the continuous and dense ZnO films were fabricated on these NiO thin films using hydrothermal growth processes with Na3C6H5O7 as a crystal morphology-controlling agent.The ZnO film will reduce the adsorption quantity of oxygen and other gases,and then improve the photoresponse performance of NiO/ZnO heterojunction UV photodetectors.The recovery time of the heterojunction UV photodetector with ZnO film changes from 25s to 8s compared to the device with ZnO nanorods array.The piezotronic and piezo-phototronic effect of ZnO was used to further enhance the performance of UV photodetector.The compression strain had an enhancement effect on the time response of the photocurrent.The recovery time of the device reduced from 8s(0 strain)to 7s,3.6s and 2.4s under the compression strain of-1%,-2%and-4%.