Study Of Growth,Heterojunction Preparation And Devices Application Of Monolayer MoS₂

Among transition metal metachalcogenides(TMDC)materials,monolayer molybdenum disulfide(MoS2)with a 1.8 eV direct bandgap has strong physicochemical stability and reasonable carrier mobility.MoS2 is thus an important candidate for the semiconducting channel material of transistors,optoelectronics and valleytronics devices.The ultra-thin two dimensional structures without dangling bonds can effectively suppress the short-channel effect and have great potential in the more Moore era.Therefore,this thesis systematically studies the preparation and device properties of monolayer MoS2 and its heterojunctions.At first,the growth of high-quality monolayer MoS2 was studied in this thesis.MoS2 domains with a size of～100 μm were grown at a growth temperature of 850℃ by direct sulfization of molybdenum dioxide(MoO2)via atmospheric pressure chemical vapor deposition(APCVD).Atomic Force Microscopy,Raman spectroscopy,Photoluminescence spectroscopy and X-ray photoelectron spectroscopy were used to characterize the as-grown MoS2 layer material.In order to investigate the mechanism of the CVD growth of MoS2,the influenceof the amount of carrier gas during the growth process,the ratio of the precursors and the growth temperature were studied respectively.To further reducing the growth temperature,we use NaCl as a promotor.The effect of NaCl was studied,and its microscopic mechanism was discussed in detail.The MoS2 flakes grown at 750℃ with 25μg of NaCl show excellent uniformity and large single crystal size.Secondly,due to the important of the transfer process on the preparation of MoS2 heterojunctions,three typical graphene-like material transfer methods consist of Cu-assisted thermal release tape transfer method,Polymethyl Methacrylate(PMMA)substrate etching transfer method and PMMA assisted thermal release tape transfer method(PATRT)were discussed in detail.We studiedthe influence of transfer processon MoS2 and WS2 materials by comparing the Raman and photoluminescence spectra of the materials before and after transfer.The PATRT method combines the advantages of the other two transfer methods,providing sufficient support for the materials during the transfer process and avoiding wrinkle of the materials to.In addtion,PATRT method also makes use of the maturity of the PMMA adhesive removal process to avoid damage to the material caused by the Cu film peeling process during Cu-assisted transfer.In the end,the preparation of MoS2 back-gate field effect transistor was accomplished by series of processes to further study the electrical properties and heterojunction applications of MoS2 materials.The MoS2 FET has the carrier mobility of 2 cm2V-1 S-1,on/of ratio of 107 and a photoresponsivity of 18.9 AW-1 at room temperature and atmosphere.At the same time,the MoS2 is transferred to the monolayer WS2 and WSe2by using the PMMA substrate etching transfer method and the PMMA assisted thermal release tape transfer method.Vertically stacked type Ⅱ MoS2/WS2,MoS2/WSe2 heterostructures were prepared.