The Fabrication And Characterization Of ZnO-Based Flexible UV Photodetectors

Along with the popularity of portability,foldability and transferability,flexible UV photodetectors have attracted much attention in recent years.ZnO material has three characteristics of semiconductor behavior,photoexcitation and piezoelectricity,the coupling between them is the piezo-phototronic effect.By adding Mg into ZnO material can form Mg_0.2Zn_0.8O alloy which also has the piezo-phototronic effect.As a result,the band gap increases and the detection region extends to the shorter wavelength.In this paper,we select PET as the substrate,it is a flexible material which can withstand large deformation such as tension,compression and bending.The fabrication of ZnO thin film,Mg_0.2Zn_0.8O thin film and ZnO/Mg_0.2Zn_0.8O double-layer films structure flexible UV photodetectors were realized and the performance gains of the devices under different external stresses were tested.The regulation mechanism of piezoelectric polarization charge affecting carrier transport in schottky junction and heterogeneous junction was studied systematically.It provides ideas and guidance for the design and development of new flexible UV photodetectors.The main research results are as follows:?1?ZnO thin film schottky junction flexible UV photodetectors were constructed and the influence of oxygen and argon flow ratio in RF magnetron sputtering on the growth quality of ZnO thin films was studied.When the ratio of oxygen to argon flow was 10:40sccm,the ZnO thin film owned high crystalinity because oxygen could not only fill the vacancy defect but also not hinder the deposition of target particles.On the basis,the regulation mechanism of ZnO/Au schottky junction interface carrier generation,separation,transport and composite behavior by the change of external stress was studied.It is found that the piezoelectric polarization charge directly changes the barrier height and depletion layer width in the contact junction.At 50v bias,the 0.134 tensile strain increased the responsivity of the photodetector by 257%,the photocurrent and sensitivity were also enlarged.?2?Mg_0.2Zn_0.8O thin film schottky junction flexible UV photodetectors were prepared and the numbers of interdigitated electrode pairs were changed.A theoretical model based on parallel effect is proposed to control the performance of the photodetector.Under the condition of constant external bias,increasing the numbers of interdigitated electrode pairs can effectively improve the responsivity of the photodetector.In addition,based on the piezo-phototronic theory of ZnO/Au schottky junction,the influence rule of the piezoelectric polarization charge in the Mg_0.2Zn_0.8O/Au schottky junction on the carrier collection process was analyzed.At 30 V bias,the 0.153 tensile strain resulted in the accumulation of negative polarization charge at the interface,which increased the responsivity of the photodetector by 308%.?3?Dual-wavelength ZnO/Mg_0.2Zn_0.8O heterojunction flexible UV photodetectors were prepared by combining ZnO and Mg_0.2Zn_0.8O in the form of a double-layer film.It is found that increasing ZnO film thickness can significantly increase the peak responsivity of Mg_0.2Zn_0.8O film layer.Meanwhile,varying external stresses were applied to study carrier transport mechanism of the controlled dual-UV wavelength based on piezo-phototronic effect.Under increasing tensile strain,the peak responsivity of Mg_0.2Zn_0.8O thin film layer grows faster than that of ZnO thin film layer.At 30 V bias,the 0.141 tensile strainincreased the peak responsivity of Mg_0.2Zn_0.8O and ZnO by 278%and 218%,respectively.