Fabrication And Photoelectric Properties Of Two-dimensional MoS₂ Prototype Devices

Two-dimensional molybdenum sulfide has received great attention due to its special band structure with excellent photoelectric properties and has been widely used in various fields.The main content of this paper is the fabrication and photoelectric properties of two-dimensional MoS2 prototype devices.Two-dimensional MoS2 ultrathin films were prepared by chemical vapor deposition method.Some characterization methods such as X-ray diffractometer(XRD)and atomic force microscopy(AFM)were carried out for crystal structure analysis and surface morphologies in order to ensure the film quality and thickness of two-dimensional MoS2.On this basis,the films were prepared by the corresponding template method to obtain the two-dimensional MoS2 planar prototype device with four endpoints and two endpoints.In addition,N-type high-doped silicon and P-type high-doped silicon were used as the substrates of two-dimensional MoS2.So that MoS2 forms van der Waals heterojunctions with different kinds of high-doped silicon in the vertical direction,and the corresponding two-dimensional MoS2 vertical prototype device can be obtained.At the same time,in order to study the physical mechanism of the two-dimensional MoS2 prototype devices,the influence of substrate type and film thickness on the electronic structure of MoS2 in the heterojunction was further studied by the scanning tunneling spectrum.This paper is divided into five chapters:The chapter 1 is the introduction,which mainly introduces the research background,physical and chemical properties,crystal structure,band structure and valley selection characteristics of two-dimensional MoS2.The current preparation processes of two-dimensional MoS2 films and the corresponding characterization techniques are summarized.And the research content and significance of this paper is briefly introduced.The chapter 2 mainly describes the experimental part of the research,including the chemical vapor deposition process of the MoS2 film and the tests of the MoS2 device.The chapter 3 summarizes the experimental results and analyses the data of two-dimensional MoS2 planar prototype devices.First,the XRD result indicates that the film sample obtained by the preparation is 2H-MoS2.Secondly,the AFM result shows that the thickness of o samples in the thin region is about 1.45 nm,which is corresponding to the thickness of two layers and belongs to the two-dimensional scale.Therefore,it was confirmed that the sample were two-dimensional MoS2 films.On this basis,the electrical test results of the four-terminal MoS2 planar prototype device show that the oscillation period of the test voltage can be modulated by the back electrode bias and illumination conditions.The two-terminal MoS2 planar prototype device has obvious open-circuit potential change for the presence or absence of light conditions.In addition,using the valley selection characteristics of two-dimensional MoS2,the response of the two-terminal MoS2 planar prototype device to circularly polarized light is studied.The results show that the resistance value and the quiescent current change with the angle of incident polarized light and the period is about ?.The chapter 4 summarizes the experimental results and analyses the data of the two-dimensional MoS2 vertical prototype device.First,the electrical test I-V curves were presented as the exponential growth,which indicates that the heterojunction structures formed by MoS2 and high-doped silicon have volt-ampere characteristics of peak barrier.In addition,the effects of different substrate types and film thicknesses on the energy level location,energy gap and work function of MoS2 in heterojunctions were studied by STS.The experimental results indicate that the substrate type and sample thickness have a modulation effect on the electronic structure of MoS2 in the heterojunction.For the two-dimensional MoS2 vertical heterojunction,the energy gap(Eg)of MoS2 decreases with the increase of thickness at the range of atomic-layer thickness.The energy gap of the double-layer MoS2 on different substrates is about 1.6?2.5 eV,and the work function(?)will become larger as the thickness increases.Here,the Symbol of N,P,and C represent N-type high-doped Si,P-type high-doped Si and SiO2 substrates,respectively.Under the same thickness conditions,the energy gap of different substrate samples is EgN>Egc>EgP,and the work function is?P>?N>?C.The corresponding intrinsic influence mechanisms mainly include the charge transfer effect,electrostatic shielding effect and tip-induced band bending(TIBB).The chapter 5 summarizes the research content of the paper.