Photoelectric Properties Of Two-dimensional Bi₂O₂Se Semiconductor And Its Heterostructure

Two-dimensional(2D)materials bring rich physical properties with their unique structures,and demonstrate promising potential in flexible transistors,optoelectronics,sensing and memory devices.With the deepening of exploration,tremendous progress of 2D materials has been achieved in performance optimization,function expansion,structural design,and new materials development.Recently,2D ternary Bi₂O₂Se semiconductor has attracted increasing attention of researchers at home and abroad for the high electron mobility,suitable band gap,excellent air stability and convenient synthesis method,and shows great application prospects in the fields of electronics and photoelectronics.Nevertheless,the synthesis of high-quality ultra-thin Bi₂O₂Se nanosheet is still at an early stage,and the research on its photoelectric properties and the application of photodetection are also in urgent need of development.On the other hand,although 2D Bi₂O₂Se has great potential in excellent visible photoresponse and broadband photodetection,its shortcomings such as weak absorption efficiency to infrared light,large dark current and high carrier concentration limit the further development of high performance Bi₂O₂Se infrared photodetectors and high light on/off ratio and ultra-fast photodetection.Based on these,this research focuses on the optoelectronic properties of the emerging 2D semiconductor Bi₂O₂Se and its heterostructures.The first chapter mainly introduced the research status of 2D Bi₂O₂Se in recent years,and the following three chapters discussed in detail its photoelectric performance and the heterostructure engineering.The main research contents and results are as follows:(1)High quality ultrathin Bi₂O₂Se square nanosheets were synthesized on mica substrate by atmospheric pressure chemical vapor deposition.The thickness of Bi₂O₂Se nanosheet could reach 2.4 nm and the lateral size was about 85?m,which could be connected into sub-millimeter films.Systematic sample characterization proved the high crystalline quality of Bi₂O₂Se nanosheets after vapor deposition or wet transfer.Furthermore,a Bi₂O₂Se based field effect transistor was constructed and it demonstrated n-type semiconductor properties,high mobility(?10² cm²V^-1S^-1)at room temperature,carrier concentration(?10¹⁸-10¹⁹ cm^-3)and on/off ratio(10⁵).More importantly,the performance of Bi₂O₂Se photodetector was investigated and the photoresponsivity could reach 667 A/W under 532 nm,the detectivity was about 4.71×10¹⁰ Jone.What's more,the photodetector covered broadband wavelength ranged from 400 to 1500 nm and had fast infrared response speed about 100 ms and 240 ms.(2)A high performance 0D/2D mixed-dimensional heterostructure infrared detector was fabricated by combining high mobility 2D Bi₂O₂Se with zero-dimensional Pb Se colloidal quantum dots,which could improve the infrared detection ability of 2D Bi₂O₂Se and further broaden the photoresponse range.Through a simple spin-coating process,the light absorption of the device was enhanced,which resulted in the increasing of infrared responsivity of Bi₂O₂Se and broadband detection range up to 2?m.The type II band alignment in the interface of heterostructure promoted the rapid separation of photogenerated carriers and achieved a fast response speed less than 4 ms at 2?m.Furthermore,the photocurrent generation mechanism could be tailored from a photoconductive to photogate dominated response under back gate voltage,and rendering a high infrared response>10³ A/W at 2?m.(3)A Bi₂O₂Se/WSe₂ P-N heterostructure with type II band alignment was designed to suppress the large dark current of Bi₂O₂Se detector and improve the light on/off ratio by built-in electric field.The strong interlayer coupling and large conduction band offset provided Bi₂O₂Se/WSe₂ diode with high rectification ratio(10⁵)and low reverse current(10^-11A),which resulted in enhanced light on/off ratio(618),ultrafast response speed(2.6?s),broadband photodetection(365?2000 nm)and high responsivity(638 m A/W)of Bi₂O₂Se/WSe₂heterostructure photodetector.More importantly,for the firstly time,self-driven photodetection was realized in Bi₂O₂Se/WSe₂ heterostructure with light on/off ratio up to 10⁵and responsivity about 284 m A/W.Finally,a summary of the whole work was given and the future research was prospected.