Study On Optical And Electrical Properties Of Two-dimensional Van Der Waals Heterojunction

Two-dimensional nanomaterial semiconductor materials have a wide range of potential applications because of their large surface area and unique electronic properties.In the past few decades,it has been favored by more and more researchers.Transitional metal dichalcogenides(TMDCs)have great application value in many scientific fields such as spintronics,optoelectronics,field effect tubes,detectors,sensors,quantum devices,and solar cells.Recently,research on ultra-thin two-dimensional Van der Waals heterojunctions and their devices has been favored.These Van der Waals heterojunctions formed by the interaction of weak Van der Waals forces between layers show new characteristics far beyond their single components.The main research results are as follows:1.The MoS₂ flakes are prepared by changing the size(length and width)of the precursor crucible in a double-tube furnace heating Chemical Vapor Deposition(CVD)system.Experimental analysis shows that the geometry of these crucibles significantly affects the success of the experiment and the chemical structure and morphological size of the prepared MoS₂ crystals.The long and moderately wide boat-shaped crucible can provide relatively stable gas flow and deposition pressure for the progress of chemical reactions,and then grow layered MoS₂ crystals with regular shapes and uniform surfaces.The short crucible is not conducive to the carrier gas carrying evaporated sulfur atoms into the reaction zone.We analyzed that the change in the size of the ship-shaped crucible can change the gas flow rate in the crucible to a large extent,which cause the change of the deposition pressure,and directly affect the growth of the crystal surface morphology and the growth of multiple layers.This work provides a feasible and simple method based on CVD to produce high-quality single-layer MoS₂ crystals for scientific research in the fields of single-layer,multilayer or heterojunction transistors,optoelectronic devices and sensors.2.Electronic and optical properties of stacked heterojunction based on borophene and MoS₂ are studied by density functional theory.It is found that the different stack of 1/6vacancy borophene?₁₂ and MoS₂ can induce different electronic properties through interlayer Van der Waals force.The external electric field can tune the Schottky contact types of the heterojunction.The stacked heterojunction enlarges the range of light response compared with MoS₂.It suggests that the stack changes the electronic and optical properties of sing layer MoS₂ and external electric field induces the changed Schottky contact type,providing a way to design optoelectronic device with tunable Schottky contact and good optical properties.3.We studied the electronic structure and optical properties of four Van der Waals heterojunctions constructed by?₆-borene,MoS₂ and WSe₂ based on the density functional theory.It is found that the difference in Van der Waals forces of atoms between layers caused by different stacking methods of the same material has a significant difference in the distance between layers.The interaction between electrons and slight hybridization also make their band structure,projected state density and Schottky contact type different.The Van der Waals heterojunction of the same stacking mode formed by?₆ and MoS₂ and WSe₂ behaves similarly in interlayer distance,band structure,electronic hybridization area and Schottky contact.The electronic structure they exhibit indicates the possibility of their application in electronic devices.In terms of optical properties,we found that the optical conductivity of the four Van der Waals heterojunctions all shifted to low energy compared to the single-layer transition metal sulfide,and the response range and intensity were enhanced.This work provides some of their electrical and optical properties through first-principles calculations,which are useful for experiments.The preparation provides a theoretical reference.