Research On ZnO-based Nanomaterials/thin Film Composite Photodetectors

Photodetector has shown a broad application prospect in missile early warning,space detection,environment monitoring,flame detection and many other fields.Zinc oxide(ZnO)is considered as one of the most promising materials for photodetector applications because of its unique advantages such as lower defect density,higher saturated carrier mobility and larger band gap(3.37e V).ZnO nanostructures can prepare excellent photodetectors with large specific surface area,high surface activity and quantum size effect.However,in order to realize the detector with high sensitivity,high detection rate and high responsivity,the following key problems need to be solved:thin film defects,light absorption efficiency,and device design simplicity.Therefore,this paper researches the design and performance regulation of ZnO nanomaterials and thin film composite photodetectors to explore and solve these key problems and technical bottlenecks.The main research contents are as follows:(1)In order to increase the light absorption area,the transversely grown ZnO nanomaterials/thin film photodetectors have been successfully prepared.Through the synthesis of transverse nanomaterials with large specific surface area,a conductive channel is formed,which greatly passivates the defects on the semiconductor surface,improves the morphology of the optical functional layer of the detector,increases a large number of photon absorption sites,improves the absorption efficiency of the detector,and realizes the performance optimization of the detector.At the same time,by changing the width of the depletion layer,the effective electric field intensity was enhanced,the interaction factors between the depletion layer and the surface states of the nanomaterial were balanced,the separation rate of the photogenerated electron hole pairs was accelerated,and the signal intensity of the responsiveness of the detector was increased by nearly ten times.(2)In order to construct the light trapping structure and improve the light absorption efficiency of the detector,the ZnO honeycomb layer and ZnO nanowire were grown vertically on the ZnO thin film,and the photodetector with light trapping structure was fabricated.ZnO nanometer honeycomb layer has a larger interfacial density,which increases the concentration of free carriers.Meanwhile,the surface pit structure can effectively improve the light reflection on the surface of the thin film,which is beneficial to the capture and absorption of light.ZnO nanowires array has the characteristics of anisotropy,which makes the incident light reflect,refract and scatter at different angles in its open interior,thus improving the light capture efficiency of the detector.At the same time,by adjusting the effective path length of light,the light path in the absorption layer of the detector was extended,the reflection of incident light was improved,the absorption rate of ultraviolet light was increased,and the responsivity of the detector was increased by 10²orders of magnitude.By constructing a detector with photohydrazine structure,the light loss is reduced,which provides a feasible way to realize high efficiency and low cost optoelectronic detectors.(3)In order to optimize the structure of the optical functional layer,the nanowires array with light trapping structure could be combined with the heterostructure thin film layer to change the structure of the traditional monolayer nano-detectors.ZnO nanowires/ZnO/Mg_0.2Zn_0.8O and ZnO nanowires/ZnO/NiO ultraviolet photodetectors with heterogeneous double-layer structure have been prepared.The lattice matching degree of Mg_0.2Zn_0.8O thin film and ZnO thin film is high,which reduces the residual stress in the growth of thin film and improves the photoexcitation performance of semiconductor.The remaining holes formed by the ZnO/Mg_0.2Zn_0.8O heterojunction prolong the lifetime of the holes,inhibit the recombination of charge,attract more external electrons and increase the carrier concentration.The introduction of NiO layer causes the formation of pn junction in the detector.Under the action of the internal electric field in the pn junction,the recombination rate in the depletion region is very low,and the free carrier density is improved.The ZnO nanowires/ZnO/NiO UV photoelectric detector was responsive to ultraviolet light without applied voltage,and a minified self-powered detector was realized.Heterogeneous nanowires array composite detector combined with heterostructure and light trapping effect makes the responsivity of the detectors increased by 10²orders of magnitude,and has higher sensitivity and higher detection rate.