Preparation And Device Application Research On 2D Layered MoS₂ Material

With the continuous development of chip manufacturing,semiconductor devices have the characteristics of continuously shrinking feature size and higher integration,and the physical limit would greatly restrict and affect the development of integrated circuits.The two-dimensional Transition Metal Dichalcogenides materials(2D TMDCs)with tunable band gap width have attracted the attention of researchers.Among them,monolayer molybdenum disulfide(MoS2)material has the surface without dangling bonds,good carrier mobility,and the direct bandgap of 1.8 e V,which can meet the demand for the continuous reduction of feature sizes.Therefore,it has great development prospects in the fields of microelectronics and optoelectronics.The growth,preparation and device properties of MoS2 and its heterojunction materials were systematically studied in this paper.The main research contents include the preparation,spectral properties,physical properties,test characterization,devices and applications of MoS2/WS2,MoS2/graphene,WS2/graphene,MoS2/h-BN,WS2/h-BN van der Waals heterostructure materials.The following are the main research contents.1.The large-scale high-quality monolayer MoS2 material was grown on SiO2/Si substrate by atmospheric pressure chemical vapor deposition(APCVD)method in the tube furnace.The effects of growth factors on the quality and size of MoS2 material were systematically studied,such as sulfur source amount,molybdenum source amount,temperature and argon flow rate.The SiO2/Si substrates were treated by using auxiliary means such as oxygen plasma and graphene quantum dot solution,and the growth process parameters of MoS2 material were regulated.And the effects of oxygen plasma treatment time,power,and the amount of graphene quantum dot solution on the quality and size of MoS2 material were systematically analyzed,which can explore the growth improvement method of large-scale high-quality monolayer MoS2 material.Besides,MoS2 material can be systematically tested and characterized by optical microscope(OM),atomic force microscope(AFM),X-ray photoelectron spectroscopy(XPS)and Raman spectroscopy,which can obtain the triangular monolayer MoS2 material with a single crystal size of 200 μm,the size has doubled.Therefore,the assisted treatments of SiO2/Si substrate were very effective for the growth of MoS2 material.To further measure the crystal quality,the field effect transistors based on monolayer MoS2 material were prepared by the photolithography and electron beam evaporation processes.The electrical properties of FET device were measured and investigated.And the device has the good ohmic contact,lower gate leakage current and static power consumption.2.The high-quality MoS2 material were grown on SiO2/Si and sapphire substrates by APCVD method,and the effects of layer number and external substrate environment on the spectral characteristics of MoS2 material are studied.The atomic force microscopy,optical microscopy and Raman spectroscopy were used to systematically probe the optical properties of MoS2 material under different substrates and different laser power.Compared with SiO2/Si substrate,the monolayer and double-layer MoS2 materials on sapphire substrate have the higher characteristic peak intensity of PL spectrum.Besides,MoS2/WS2 heterojunction material were prepared by CVD and wet transfer methods,the interlayer coupling and charge transfer phenomena of MoS2/WS2 heterojunction material were studied by optical microscope,Raman spectrometer,AFM and SEM.Compared with WS2 material,the photoluminescence intensity of MoS2/WS2 heterojunction material is significantly reduced,which is due to the effective photoelectron hole separation phenomenon in recombination process.3.The defects would affect the spectral characteristic of Graphene material,and the effects of different irradiation condition on the number and spatial distribution of vacancy defects were simulated and analyzed.The MoS2/WS2,MoS2/h-BN,MoS2/graphene,WS2/h-BN and WS2/graphene vd Ws heterojunction materials can be successfully prepared by chemical vapor deposition and wet transfer methods.And the morphology,composition and optical properties of vd Ws heterojunction materials were systematically characterized by optical microscopy,Raman spectrometer,EDX,AFM and SEM.The understanding of interlayer coupling can be improved by analyzing and studying the growth mechanism and spectral characteristics of heterojunction materials,which can obtain and master the morphology and luminescence laws.With the increase of laser power,the G peak and 2D peak positions of MoS2/Graphene heterostructure material are blue shifted and red shifted,respectively.And the A exciton peak position of PL spectrum is red shifted.Compared with MoS2 material,the Raman spectrum and PL spectrum of MoS2/h-BN heterojunction material show the blue shift.This is because the existence of the local strain ande charged impurities.The G and 2D peak positions of WS2/Graphene heterostructure material increase compared with graphene material.4.The physical properties of heterojunction materials can be adjusted by stacking the 2D materials with different bandgap width and energy band.The WS2/h-BN and MoS2/graphene heterostructure materials were prepared by chemical vapor deposition and wet transfer methods,and characterized by XPS,SEM,EDS,AFM and Raman spectroscopy,which can reasearch and analyze the influence of interlayer coupling.The FET devices were fabricated based on WS2/h-BN and MoS2/graphene heterostructure materials by the photolithography and electron beam evaporation processes,and the electrical properties were tested and analyzed.The FET device based on WS2/h-BN heterojunction material can reduce the scattering of charged impurities,which can meet the requirements of logic operations.Compared to MoS2/metal FET device,the on-state current,on-off ratio and off-state current of MoS2/graphene FET device increased by an order of magnitude,the mobility and transconductance can also be increased,which can provide the guidance for the application of vdws heterostructure materials in the field of optoelectronic devices.