Construction And Photoelectric Properties Of ZnO Based Core-shell Nanostructures

With the rapid development of modern society,people’s demand for low-cost,high-performance and multi-functional optoelectronic devices is more and more urgent.In the past,single-character semiconductor devices are difficult to meet the needs of energy and technological development.Among them,the core-shell nanostructure can not only overcome the defects of a single material,but also integrate the advantages of different materials and generate new synergistic effects,it can expand its application in the fields of optoelectronic devices and catalysis.Compared with conventional planar devices,the highly ordered one-dimensional core/shell nanostructures possesses larger interfacial area and better light absorption ability,which can make those materials show their advantages to construct high-performance integrated electronic and photonic systems devices.Therefore,the rational design of core-shell nanostructures,especially the choice and combination of core-shell materials,is of great significance in regulating their properties and functions.Zinc oxide（ZnO）is widely used in catalysis,laser and other fields due to its excellent electrical and optical properties,such as wide direct band gap（3.37 e V）and strong exciton binding energy（60 me V）.Combining the good semiconductor properties of ZnO with other semiconductors is expected to produce micro-nano devices with better performance and more integrated functions.However,it is still a challenge to achieve nano-level operation and control the shell crystal phase,thickness and core-shell interface.Currently reported methods for preparing core-shell structures include multiple complex processes,and the structures are mostly composed of rough nanoparticles or polycrystalline shells,which will inevitably introduce new defects to affect optoelectronic performance.In this paper,we are devoted to the preparation of perfect core-shell structure by simple technology to obtain superior performance in the fields of photodetectors,photocatalysis,lasers.Vertically grown ZnO nanorod/wire array were prepared by using the vapor deposition method as a core,and a series of perfect core-shell nanorods/wires were grown in combination with magnetron sputtering,and the corresponding optoelectronics were constructed.The specific content mainly includes:1.In order to enhance the ultraviolet luminous efficiency and photodetection performance of ZnO,AlN with a wide direct band gap（6.2 e V）and lattice matching with the ZnO was used as the shell layer,and a single crystal ZnO nanowire with uniformly coated AlN was successfully constructed.Compared with pure ZnO,the crystal AlN shell dramatically enhanced ultraviolet（UV）emission by up to 24 times.Individual core/shell nanowire photodetector shows dominant photoresponses at UVA region（325 nm）,including a higher light response（from 3.8×10³A/W enhanced to2.05×10⁴A/W）,higher light-dark current ratio（from 453 to 1.1×10⁴）,faster light response（397 ms to 28 ms）,and the core-shell detector also show outstanding performance in vacuum ultraviolet（193 nm）light detection.2.In order to develop a high-performance and fast-response solar blind（200-280nm band）photodetector,a vertically grown ZnO/Ga₂O₃core-shell nanowire array was successfully constructed for the self-driven solar blind photodetector.This device exhibited excellent photosensitive characteristics with a large I_light/I_darkratio of 2.64×10⁴,ideal detectivity of 6.11×10¹²cm Hz^1/2W^-1,and superior responsivity of 137.9m A/W under 254 nm light without an exterior power supply,which is much higher than other previously reported self-powered Ga₂O₃-based photodetectors.What is more,an ultrafast response speed of（rise time～28.9μs,fall time～85.7μs）is observed in the photodetector by time-resolved photoresponse test.Such excellent performances are assigned to the unique core–shell nanoarchitecture and built-in electric field at ZnO and Ga₂O₃junction interface can rapid separate photogenerated carriers.3.In order to realize a photodetector that integrates high-performance and wide-band detection functions,a self-powered core/shell photodetector was fabricated by sputtering a uniform p-type ZnTe layer on n-type ZnO nanorod array.Based on the pyroelectric effect of ZnO and the photovoltaic effect of the ZnO/ZnTe pn heterojunction,the photodetector realizes broadband detection from 325 nm ultraviolet to 1064 nm near infrared under zero bias.The maximum responsivity and detectivity reach 196.24 m A/W and 3.47×10¹²cm Hz^1/2/W for 325 nm laser illumination with power density 2.13 m W/cm²,respectively,which are improved10-fold relating to the device responded to photovoltaic effect only.While the rise and fall time are drastically reduced from 1.222 ms to 62μs and 1.563 ms to 109μs,respectively.4.In order to solve the problems of rapid recombination of photogenerated charges and low light utilization efficiency of ZnO as a photocatalyst,a three-dimensional ZnO-WS₂@CdS core-shell nanorod array was constructed as an efficient visible light catalyst.This excellent core-shell structure not only can broaden visible light absorption,increase the active sites for photocatalytic hydrogen production,and build effective energy levels and spatial structures,which are conducive to the generation,separation,and transfer of electron holes.Based on the synergy effect,the optimal ZnO-WS₂@CdS visible light（>420 nm）hydrogen production rate reaches 15.12mmol h^-1g^-1,which are 39,9 and 8 times than pure CdS,ZnO-CdS and CdS-WS₂hydrogen production rates,respectively.The quantum efficiency reach 14.92%and exhibit excellent stability and repeatability.5.On the basis of successfully constructing a series of core-shell nanostructures,a ZnO-CdS-NiOx core-double-shell nanostructure with band gap cross-linking was constructed to further solve the problems of rapid recombination of photogenerated charges,low light utilization efficiency,and photocorrosion of photocatalysts.By adjusting the shell thickness of CdS and NiOx,the rate of hydrogen evolution(84834μmol h^-1g^-1)of ZnO-CdS-NiOx under simulated sunlight is 420.8,42.7,and 4.2 times that of ZnO,CdS,and ZnO-CdS,respectively.The apparent quantum yield is 33.89%at 380 nm,and the long-term lighting（12 cycles）still shows excellent stability.