Controllable Synthesis Of Re-doped MoS₂ And Its Research On Photoelectric Properties

Today in the post-Moore era,power consumption and heat generation caused by the shrinking of the size of electronic components in integrated circuits have restricted the further development of the semiconductor industry.Therefore,finding a new low-dimensional semiconductor material system is particularly important for the continuation of Moore's Law.In this context,two-dimensional transition metal chalcogenides have attracted wide attention from scientists.Two-dimensional transition metal chalcogenide is a type of layered semiconductor material with ultra-thin thickness,continuously adjustable band gap,and novel optoelectronic characteristics.It is used in new flexible field effect transistors,optoelectronic devices,sensor devices and storage devices.It has huge application potential.There are many types of two-dimensional transition metal sulfides.However,the inherent properties of a single material are limited.Therefore,it is of great significance to adjust and optimize the properties of materials to achieve high-performance optoelectronic device applications.Regulating the inherent properties of two-dimensional transition metal sulfides by doping means is a topic of widespread concern to scientists at home and abroad.Substitution doping,as a means of regulating the properties of semiconductors from within the crystal lattice,has the advantages of high stability,strong controllability and long-range order,and is the preferred way to achieve transition metal doping.Single-layer MoS₂ has excellent optical properties due to its direct band gap,and has great application potential in the field of optoelectronics.In this thesis,a salt-assisted chemical vapor deposition method was used to controllably synthesize MoS₂ monolayer nanosheets doped with Re atoms.The study found that a small amount of Re atom doping can effectively control the optoelectronic properties of single-layer MoS₂,which provides the possibility for its wider application.In the first part of the thesis,a systematic introduction to two-dimensional layered materials was given,and different doping methods of two-dimensional transition metal chalcogenides were reviewed.The second part summarizes and discusses the experimental materials,equipment and characterization methods.The third part is mainly to systematically study the controllable preparation,morphological characteristics and photoelectric properties of MoS₂ and ReS₂.On this basis,the fourth part systematically studied the controllable preparation and photoelectric properties of Re-doped MoS₂ monolayer nanosheets.The specific research is as follows:(1)The controllable preparation of a single layer of MoS₂ was successfully realized by the chemical vapor deposition method.Through the Raman spectroscopy,the Raman vibration mode of the single-layer MoS₂ was obtained,indicating that we successfully prepared the single-layer MoS₂ sample;using a 532 nm laser as the excitation light source,the photoluminescence spectrum of the single-layer MoS₂ was collected.By making MoS₂ into a back-gate field-effect transistor,we studied its electrical properties.(2)The ReS₂ nanosheets were successfully prepared by the salt-assisted chemical vapor deposition method.The optical photos of ReS₂ nanosheets were taken through an optical microscope,and it was found that most of the ReS₂ samples deposited on the Si/Si O₂ substrate were in the shape of a round cake and were easy to accumulate lengthwise and thick.Through the Raman spectroscopy test,the ReS₂ samples were collected.The Raman vibration mode confirms the successful preparation of the sample;finally,Raman spectra were collected on ReS₂ nanosheets of different thicknesses,and it was found that the Raman peak position of ReS₂ did not move with the change of the number of layers.(3)Using the salt-assisted one-step chemical vapor deposition method,by controlling the growth temperature,growth time,gas flow rate,and reaction source ratio and other conditions,the Re-doped MoS₂ monolayer sample can be controlled.The results of high-resolution scanning transmission electron microscopy showed that Re atoms replaced Mo atoms at sites in the MoS₂ single-layer lattice,successfully achieving substitution doping.X-ray photoelectron spectroscopy and photoluminescence characterization further proved that Re atom doping is n-type doping.The peak fitting results of temperature-dependent photoluminescence spectra of pure MoS₂ and Re-doped MoS₂ single-layer nanosheets show that Re-doped MoS₂ has more abundant multi-body interactions and defect emission than pure MoS₂.In addition,the time-resolved photoluminescence results show that the lifetime of the Re-MoS₂ single-layer sample is shorter,which further supports this view.The results of circularly polarized photoluminescence show that the substitution and doping of Re atoms can effectively improve the valley polarization of the MoS₂ monolayer.