| In recent years,UV detection technology has been widely used in biochemical analysis,environmental monitoring,flame and radiation monitoring,optical communication,missile early warning,civil and military fields.With the rapid development of technology in different fields,the demand for UV detection is also increasing.Therefore,high-performance UV photodetectors have attracted extensive attention.Among many UV detection materials,ZnO,as a typical wide band gap semiconductor material,has relatively high conductivity and transparency.At the same time,the preparation process of ZnO is relatively simple and mature,and the requirements for preparation conditions and environment are low.The preparation of raw materials has low cost and various methods.So it is an ideal material that can be applied in a wide range.At the same time,ZnO has large radiation resistance,so it has stable photoelectric performance and can work in various environments.ZnO,as a low dimensional semiconductor,has many defect states on the surface,such as dangling bond and surface state.Under illumination,these defect states will capture photogenerated carriers,produce continuous photoconductivity effect,increase the rise and fall time of the detector,and greatly hinder the response performance of ZnO photodetector.In this paper,multiwavelength Cd Se quantum dots are used to modify ZnO microwires(MWs)to form type II heterojunction structure.Through the surface passivation of ZnO microwires by Cd Se quantum dots(QDs),the influence of ZnO surface state is significantly reduced,and its response speed and responsivity are improved.Finally,the improvement mechanism of detector performance is systematically analyzed The main research results are as follows:(1)ZnO MWs was grown by chemical vapor deposition technology,based on which a single ZnO MWs detector was prepared.CdSeQDs/ZnO MWs UV photodetector was prepared by modifying CdSeQDs on the surface of ZnO MWs.The type II band structure formed between Cd Se and ZnO and the surface passivation effect of CdSeQDs on ZnO effectively inhibit the influence of ZnO surface state.Under UV irradiation,a built-in electric field is formed between ZnO and Cd Se,which promotes the separation of photogenerated electron hole pairs and accelerates the transport of carriers.The maximum response of the detector is increased to 10.5 m A/W,which is 6times higher than that of ZnO MWs detector;At the same time,the response time of the detector is greatly shortened,and the rise and fall time are shortened by 87.7% and76.2% respectively.(2)We further study the performance of multi-wavelength CdSeQDs modified ZnO MWs.Quantum dots with different sizes are prepared by changing the synthesis temperature of CdSeQDs synthesized by heat injection method.Due to the size effect of quantum dots,the band gap width,absorption wavelength and absorption coefficient of quantum dots are adjusted by controlling the size of CdSeQDs.Finally,ZnO microwires are modified by multi-wavelength Cd Se quantum dots to obtain significant UV photoelectric gain,and expand the ZnO response wavelength to the visible band.(3)The effect of Annealing on the photoelectric properties of multi wavelength CdSeQDs modified ZnO MWs at different temperatures was studied.Annealing improves the crystallization quality of ZnO MWs,further reduces the influence of ZnO surface state,at the same time,the effects of surface adsorbed oxygen and internal defect states on photogenerated carriers are reduced.In the high temperature environment of annealing,the interface quality between CdSeQDs and ZnO MWS will be further improved,and the transmission of electron hole pairs between Cd Se and ZnO will be improved.In short,through annealing,the detector can obtain higher photoelectric response and faster response speed. |
