Research On Performance Regulation Of ZnO Based Flexible Ultraviolet Photodetector

Ultraviolet（UV）detection technology is known as one of the most influential dual-use technologies in the 21st century by virtue of its advantages such as low background radiation,low false alarm rate,high concealment and simplified system structure.Its core is the UV detector with low noise,small volume and high sensitivity.Zinc oxide（ZnO）,as the third-generation II-VI group direct wide-bandgap semiconductor material,has excellent photoelectric,piezoelectric and semiconductor properties.It has shown great application prospects in the production of high-performance UV detectors.In particular,ZnO can form a ternary compound Mg_xZn_1-xO（0≤x≤1）with adjustable band gap by doping with Mg element to realize detection of different UV bands.The existing ZnO-based UV photodetectors have two main problems in practical applications:First,it is limited by the brittleness and inflexibility of the hard substrate,which makes it difficult to meet the requirements of the complex and harsh actual environment;Second,the performance of the detector cannot be regulated.Therefore,how to solve the above problems has become a bottleneck in the practical application of ZnO-based UV photodetectors.This dissertation uses polyethylene terephthalate（PET）as the substrate,which is a flexible material that can withstand large deformations such as tension,compression,and bending.Based on ZnO-based nanomaterials,ZnO-based thin film flexible flexible UV photodetectors were fabricated.The photoelectric performance of the detector is regulation by the piezophototronic effect which coupled with the photoelectric,piezoelectric and semiconductor characteristics of ZnO.The main research contents and relevant conclusions are as follows:In the research of regulating the performance of ZnO flexible UV photodetector,the ZnO flexible UV photodetector with metal-semiconductor-metal structure was prepared on PET substrate by using radio frequency magnetron sputtering and photolithography.The performance of the detector was regulated by piezophototronic effect.Firstly,the crystallinity of ZnO film was improved by optimizing the flow ratio of oxygen to argon during the growth of ZnO film on PET substrate.When the flow ratio of oxygen to argon was 10:40,the crystallinity quality of ZnO film was higher.Secondly,the synergistic regulation effect between the performance of ZnO flexible UV photodetector and piezophototronic effect was studied,and the interface regulation mechanism of piezophototronic effect on Schottky device was obtained.Piezoelectric polarization charges generated by strain act on the Schottky junction interface of the metal-semiconductor contact,and the transport of carriers at the junction interface is changed to realize the regulation of the performance of the detector.The effects of different strains on the performance of the detector were investigated.The responsivity of the detector under tensile strain（ε=0.2）was increased by 0.51 times compared with that under unstretched strain（ε=0）.At the same time,under strain,it is found that the piezophototronic effect of the ZnO film increases with the decrease of the incident light intensity,which can significantly improve the detection ability of the detector to weak light.Finally,a quantitative model of the regulation mechanism of the relationship between the responsivity of the ZnO flexible UV photodetector and the strain was established,and it was verified that the use of piezophototronic effect to regulated the photo response behavior of the ZnO flexible UV photodetector has great repeatability and credibility.It provides some guidance for the practical application of piezophototronic devices.In the research of regulating the performance of different Mg content of Mg_xZn_1-xO flexible UV photodetector,the Mg_xZn_1-xO thin film was prepared on PET substrate by using radio frequency magnetron sputtering technology,and on this basis,the flexible UV photodetector was constructed,realizing the regulation of the performance of the detector by piezophototronic effect.Firstly,the effect of the width of the interdigital electrode width on the performance of the detector was investigated by Mg_0.2Zn_0.8O flexible UV photodetector,and the optimal interdigital electrode width was determined to be 5μm.The Mg_0.2Zn_0.8O,Mg_0.39Zn_0.61O and Mg_0.52Zn_0.48O thin films with single hexagonal phase structure were prepared at room temperature were prepared into flexible UV photodetectors based on the width of 5μm interdigital electrode width to realize the detection of solar-blind.On this basis,the influence of different strain on the performance of three detectors were investigated.The responsivity of the Mg_0.2Zn_0.8O,Mg_0.39Zn_0.61O and Mg_0.52Zn_0.48O flexible UV photodetectors under tensile strain（ε=0.2）are increased by 2.60 times,3.07 times and 5.23 times,respectively,which compared with that under unstretched strain（ε=0）.The regulation mechanism of Mg content on piezophototronic effect was obtained.Finally,a quantitative model of the regulation mechanism of the relationship between the responsivity of the Mg_xZn_1-xO flexible UV photodetectors and the Mg content and strain was established to verify the great repeatability and credibility of the experimental results.In the aspect of regulating the performance of Mg_0.2Zn_0.8O/ZnO flexible UV photodetector,the Mg_0.2Zn_0.8O/ZnO flexible UV photodetector was prepared,and the performance of the detector was regulated by piezophototronic effect.The stability of the detector was also studied.Firstly,the research found that the Mg_0.2Zn_0.8O film grown on ZnO for 120 min has low dislocation density and good crystal quality,which can improve the photodetection ability ability of the detector.Secondly,the mechanism of the piezophototronic effect on the responsivity of the Mg_0.2Zn_0.8O film and ZnO film in the flexible Mg_0.2Zn_0.8O/ZnO UV photodetector was studied,and the piezoelectric polarization charge on the Schottky was obtained.The regulation mechanism of the piezoelectric polarization charge on the transport behavior was obtained when Schottky junction and heterojunction coexist.The effects of different strains on the performance of the detector were investigated.The responsivity of Mg_0.2Zn_0.8O and ZnO thin film layers of the detector increased by 2.69 times and 3.16times under tensile strain（ε=0.18）compared with under unstretched strain（ε=0）.This is due to the application of strain to the detector,the resulting piezopotential acts on the interface between the Schottky junction and the heterojunction to control the transport behavior of carriers,which realizes the effective regulation of the performance of the UV dual-band detector.Thirdly,a quantitative model of the regulation mechanism of the relationship between the responsivity of Mg_0.2Zn_0.8O film and the ZnO film in the Mg_0.2Zn_0.8O/ZnO flexible UV detector was established through experiments.The experimental results show that the responsivity of the Mg_0.2Zn_0.8O film has a linear relationship with the strain,and the responsivity of the ZnO film has a nonlinear relationship with the strain,verifying that piezophototronic effect has a significant effect on the heterojunction.Finally,it can be inferred that the detector has great environmental stability,mechanical stability and repeatability from the bending cycle experiment and the long-term storage experiment.