Modulation Of The Properties Of Two-Dimensional Van Der Waals Heterojunction

After the successful preparation of monolayer graphene,2D materials have also been used in various scientific fields due to their special optoelectronic properties,such as diodes,field effect transistors,sensors,detectors,photocatalysis,solar cells,etc.Although 2D materials have shown properties that distinguish them from bulk materials,such as the confinement of electrons to a 2D plane,which is the reason for the prominent electronic properties of 2D materials;the flat surface and the absence of chemically suspended bonds,which results in higher carrier mobility;the thickness at the atomic level and the covalent bonds that are stably connected within the face,so that 2D materials exhibit excellent optical transparency and have a certain mechanical strength and flexibility The large specific surface area of 2D materials can facilitate the research on the specific surface area,such as supercapacitors;because the surface atoms of 2D materials are exposed,doping,defects and strain can be used to regulate the properties of the materials.However,with the improvement of science and technology,the demand for integrated circuit technology is getting higher and higher,and the devices must be considered for high-efficiency performance when the volume is decreasing,therefore,higher demand for two-dimensional materials is also put forward,which can ensure high-efficiency performance and then require a smaller and smaller volume of materials,therefore,it is more and more difficult for a single two-dimensional material to meet people’s demand for high-performance devices.In the process of research and development of 2D materials,researchers have discovered van der Waals heterojunctions,which combine the properties of monolayer materials while creating richer and more exotic properties,and are an effective way to develop materials with specific properties,and have become a hot topic of research in recent years.In this paper,the optoelectronic properties of van der Waals heterojunctions and their applications in optoelectronic devices are investigated based on the first principal density functional theory in combination with nonequilibrium Green’s functions.The main research achievements of this paper are as follows:1.The lattice parameters and band gap of monolayer germanium sulfide（Ge S）,indium selenide（In Se）,and hexagonal lattice boron nitride（h-BN）were calculated.Three kinds of heterojunctions,Ge S/In Se,Ge S/h-BN/In Se and Ge S/TB/In Se,were constructed,and the stability of the heterostructures was demonstrated by calculating the binding energy and molecular dynamics simultaneously.The effects of different layers of h-BN on Ge S/In Se heterojunctions were investigated by calculating the projected energy band,the projected density of states,and the charge difference density of the heterojunctions.The effect of the applied electric field on the modulation of electronic and optical properties of the heterojunction is also investigated.This study shows that the introduction of h-BN makes the heterojunction more sensitive to the regulation of the external electric field,which is expected to be applied to highly sensitive grid-controlled optoelectronic devices.2.The lattice parameters and band gaps of the new Janus transition metal dichalcogenides materials（JTMDs）Hf Se S,Zr Se S,and tin disulfide（Sn S₂）with the same electronic structure were calculated,and the lattice parameters of the three materials were similar,and the lattice mismatch rate of the heterojunctions were small.MSe S（M=Hf,Zr）and Sn S₂ heterojunctions were constructed.Since MSe S（M=Hf,Zr）is an asymmetric structure,various stacking forms were considered,and by comparing the binding energy,the Hf Se S/Sn S₂ and Zr Se S/Sn S₂heterojunctions were found to be the most stable,and the devices were built with the most stable heterojunctions.The heterojunction device is constructed by doping the left and right electrodes to study its Ids-Vds characteristics,and the device exhibits a unique reverse rectification effect,which is demonstrated synergistically by calculating the transmission spectrum and transmission eigenstates of the device.Finally,the modulation effect on the rectification effect is investigated by the additional gate voltage and compared with previous heterojunction reverse rectification ratios.This study provides an important theoretical basis for the application of new Janus Hf Se S and Zr Se S materials in optoelectronic devices.3.A new Janus Ⅲ-Ⅵ chalcogenide monolayer was selected to construct heterojunction excitonic solar cells.The lattice parameters,band gaps,sideband positions,and light absorption coefficients of the nine Janus monomolecular layers were first calculated.Then,type II heterojunctions conforming to the two main criteria for high-performance excitonic solar cells were constructed in the nine materials,and the type II band gap arrangement of the heterojunctions was verified by calculating the projected band structures and projected density of states of the heterojunctions.The light absorption coefficients of the most stable heterojunction in terms of binding energy are calculated and compared with monolayer materials,and the power conversion efficiency as a solar cell was calculated and finally compared with the power conversion efficiency of heterojunctions that have been published in research.This study provides theoretical support for the application of Janus Ⅲ-Ⅵ chalcogenide materials in photovoltaic devices.