Controllable Preparation, Doping And Optoelectronic Properties Of Two-dimensional WSe₂

Two-dimensional(2D)transition metal chalcogenides(TMDs)have weak van der Waals force between layers,and have excellent optical and electrical properties such as adjustable band gap and high carrier mobility.Therefore,they are widely used in electronics,optoelectronics,sensors,flexible devices and other application prospects.In recent years,in order to meet the requirements of device functionalization,it is necessary to dope TMDs materials,and then adjust their band gap and conductive properties.2D WSe2 is one of the few p-type TMDs materials,with high light absorption coefficient and high photoluminescence efficiency,suitable for application in field effect transistors,photodetectors,photovoltaic devices and other fields.However,there are few studies on the doping modification of 2D WSe2 at present,so the research contents of this paper are as follows:(1)Preparation of two-dimensional WSe2 by chemical vapor depositionBy adjusting the growth temperature and selecting different growth substrates,2D WSe2 can be prepared by chemical vapor deposition(CVD),which lays an experimental foundation for Nb and Re elements doping WSe2.Then the morphology,Raman spectrum,composition and structure of monolayer WSe2 are characterized by optical microscope,atomic force microscope,Raman spectrometer,X-ray photoelectron spectroscopy and field emission ultra-high resolution transmission electron microscope.Finally,a field effect transistor is constructed based on the monolayer WSe2,and its basic electrical and optoelectronic properties are studied.(2)Preparation of Niobium-doped WSe2(Nb-WSe2)by chemical vapor deposition2D Nb-WSe2 is prepared by one-step CVD method by using NbCls.Electrical and optoelectronic tests show that the electrical performance of the monolayer Nb-WSe2 device has been significantly improved,while the photoelectric performance has slightly improved:the mobility has increased by two orders of magnitude to 2.83 cm2·V-1·s-1,and the Ion/Ioff ratio has increased by three orders of magnitude to 4.3 × 107,the responsivity is 2.3 mA·W-1,and the photoresponse time is 89 ms.(The mobility of the monolayer WSe2 device is 0.04 cm2·V-1·s-1,the Ion/Ioff ratio is 4.8 × 104,the responsivity is 1.0 mA·W-1,and the photoresponse time is 83 ms).In addition,Nb element can be observed and uniformly distributed by transmission EDS mapping,and Nb element can also be detected by X-ray photoelectron spectroscopy(XPS).The characteristic binding energy peaks of Se and W elements are shifted towards the direction of low binding energy,which indicates that NbCls is successfully doped into WSe2 as a p-type dopant.(3)Preparation of Rhenium-doped WSe2(Re-WSe2)by chemical vapor deposition2D Re-WSe2 is synthesized by one-step CVD method by using ReO3.XPS can detect Re element,and the characteristic binding energy peaks of W and Se elements move towards the direction of high binding energy,which shows that ReO3 is successfully doped into WSe2 as an n-type dopant.The fluorescence spectrum shows that the fluorescence intensity of monolayer Re-WSe2 is almost quenched and the fluorescence peak is blue-shifted towards low wavelength,which further indicates that ReO3 is an n-type dopant of Re-WSe2.The electrical and photoelectric tests show that the monolayer Re-WSe2 device exhibits bipolar conductivity,in which the p-type conductivity is dominant.However,the mobility decreases(0.02 cm2·V-1·s-1),the Ion/Ioff ratio changes little(9.9 × 104),the responsivity decreases by an order of magnitude to 0.07 mA·W-1,and the photoresponse time changes little(93 ms).