Theoretical Study On Electronic Structure And Rectification Properties Of Lateral Heterojunction Base On Two-dimensional Materials

In recent years,two-dimensional materials,led by graphene,have received much attention due to their extraordinary physicochemical properties and attractive application prospects in the field of nanoelectronic devices.Rectifier diodes are commonly used in digital circuits,and researchers have conducted a series of researches on rectifier devices based on lateral heterojunctions of 2D materials,however,there are still many problems,such as the difference of rectification effect caused by lattice mismatch at the interface of different 2D materials and the rectification effect of current diodes based on lateral heterojunctions is not too good.In order to solve the above problems,this paper investigates the electronic structure properties of lateral heterojunctions based on MA₂Z₄ group materials and blue phosphorene using first-principles calculations,and designs diode devices with excellent rectification performance by modulating the length adjustment,adsorption,and doping,pointing out an effective way to design excellent rectifier diode devices.The main research contents and results of this paper are as follows:1.Electronic structure properties and rectification effects of TaSi₂N₄-WGe₂N₄/Mo-Ge₂N₄ lateral heterojunctionsThe lattice mismatch between two materials in lateral heterostructures leads to inhomogeneous stresses or defects at the interface and multiple bonding modes,resulting in different potential barriers and rectification effects,so it is important to find metal and semiconductor 2D materials with low lattice mismatch for designing high-performance diodes based on lateral heterojunctions.Based on the first principle calculations,we designed in-plane heterojunction diodes of metal TaSi₂N₄ and semiconductor WGe₂N₄/Mo Ge₂N₄,systematically calculated their electronic properties as well as electronic transport properties,and obtained devices with excellent rectification effect by length modulation.By tuning the length of the semiconductor part of the heterojunctions,ultrahigh rectification ratios of 10⁶ and 10⁷is obtained for the TaSi₂N₄–WGe₂N₄ and TaSi₂N₄–Mo Ge₂N₄ heterojunction devices,respectively.These results provide a guideline to the design in-plane heterojunction diodes with ultrahigh rectification.2.Schottky diodes based on blue phosphorene nanoribbonsBlue phosphorene behaves as a semiconductor with good stability and a band gap of more than 2 e V,and we consider the modulation of its electronic properties by adsorption and apply it in rectifier diodes.The electronic properties of blue phosphorus nanoribbons based on being adsorbed by 3d transition metal elements were investigated using density functional theory combined with nonequilibrium Green’s function.The adsorption of transition metal atoms Sc/Cr/Ti and Ni on top site of blue phosphorene nanoribbons leads to metallic and semiconducting properties,respectively.The devices consisting of the planar contact of the metallic and the semiconducting nanoribbons show rectifying behaviors due to the Schottky barriers of the homojunctions.The rectification ratio of the Sc-Ni device and the Cr-Ni device can reach up to 10⁸,much higher than that of traditional p-n junctions.The high rectification ratio at low bias regions together with the low threshold voltages and negligible reverse currents make the blue phosphorene nanoribbon homojunctions ideal rectifier diodes.The present work provides a reference for the adsorption modulation of the same material to form a heterojunction and obtain a rectifier diode with excellent performance.3.High-performance rectifier device based on MoSi₂N₄-WSiGeN₄ p-n junctionThe MA₂Z₄ family materials exhibit rich electronic properties,we have designed an in-plane heterojunction with small lattice mismatch by selecting a p-type semiconductor MoSi₂N₄ monolayer and an n-type semiconductor WSiGeN₄ monolayer of the MA₂Z₄ family,calculated their charge transfer and attempted penetration barriers,and doped the device electrodes accordingly.The calculations show that the MoSi₂N₄-WSiGeN₄ based heterojunction devices exhibit excellent single conductivity and exhibit ultra-high rectification ratios:the rectification ratios can reach more than 10⁶ at low biases of 0.2 V and the maximum rectification ratio can reach 10¹¹ at 1.0 V.This work provides further applications of MA₂Z₄ family materials in nano-electronic devices.This thesis consists of six chapters:Chapter one is the introduction,which briefly introduces the blue phosphorene and MA₂Z₄ materials,and the rectifier device based on the lateral heterojunction of 2D materials.The second chapter is a brief introduction of the theoretical calculation method.In Chapter 3,TaSi₂N₄,WGe₂N_4,and Mo Ge₂N₄ in the MA₂Z₄ group are selected to form lateral heterojunctions to study their electronic structure properties and rectification mechanism.In Chapter 4,Schottky diodes based on blue phosphorene nanoribbons adsorbed by transition metal elements are studied.In Chapter 5,the high-performance rectifier p-n junction device based on MoSi₂N₄-WSiGeN₄ is designed.The sixth chapter is the summary of the work and the prospect of the future development of lateral heterojunctions.