Preparation Of 2D-MoS₂ Heterojunction And Its Photoelectric Response To Polarized Light

The transition metal disulfide,represented by two-dimensional(2D)molybdenum disulfide(MoS2),shines in the field of materials science due to its excellent electrical and optical properties.In this paper,the effects of valley polarization on the photoelectric properties of 2D-MoS2 heterojunctions prepared by chemical vapor deposition under different angles of polarized light excitation are studied in detail.In addition,the variation of the energy band structure of the 2D-MoS2 heterojunction under the excitation of polarized light was investigated by scanning tunneling spectroscopy(STS),and the influence of valley polarization effect on the 2D-MoS2 electrical structure was studied.This paper is divided into 5 parts:In the first chapter,the research background,crystal structures and electrical structures,valley polarization characteristics of 2D-MoS2 are introduced.Then,the preparation methods,characterization techniques and application fields of several commonly used 2D-MoS2 are introduced.Finally,the research content and significance of this paper are discussed.In the second chapter,the preparation and characterization of 2D-MoS2 thin films and their heterojunctions are introduced in detail.In the third chapter,the characterization results of 2D-MoS2 thin films and the photoelectric test results of 2D-MoS2 planar devices and vertical heterostructure devices are analyzed.Firstly,the transmission electron microscope(TEM)results show that the crystal of MoS2 samples are 2H polytype and the selected area electron diffraction results show that the samples are six-fold symmetrical.Subsequent tunneling scanning microscope(STM)characterization of its surface morphology and thickness revealed that the thinnest layer was only 1.4 nm thick,about 2 layers MoS2 atomic thickness.When polarized light is applied to the sample,the open circuit voltage of 2D-MoS2 plane prototype changes with the polarization angle of polarized light in a period of 2?,and the current and open circuit voltage of MoS2/graphene vertical heterostructure change with the polarization angle of polarized light in a period of ?and ?/2,respectively.In the fourth chapter,the STM/STS test results of MoS2 vertical heterojunction devices are processed and analyzed.The 2D-MoS2 samples deposited on highly doped p-Si substrate and highly doped n-Si substrate and graphene substrate are denoted as P-sample and N-sample and G-sample respectively.The results present that under the excitation of polarized light,the bandgap Eg and work function ? of 3-type different MoS2 heterojunctions change regularly with the polarized light angle ?,including Eg-P>Eg-G>Eg-N.In addition,for G-sample and N-sample,the Eg increases first and then decreases with ?,and has the maximum value at ?=45°;for P-sample,the Eg decreases first and then increases with ?,and has the minimum value at ?=45°,while the trend of? with a is opposite to that of Eg with ?.The main mechanism of the above experimental phenomena is the valley polarization effect in 2D-MoS2.In addition,the charge transfer effect and the tip induced band bending also affect the experimental phenomena.In the fifth chapter,we summarize and prospect of this study.