Design And Performance Study Of Electronic Devices Based On Two-dimensional Materials Van Der Waals Heterostructure

With the continuous miniaturization of devices,the size of silicon-based semiconductor devices has reached its physical limit.It is important to explore new materials and new structures for the continuous downscaling.Two-dimensional（2D）materials have been widely used in nanoelectronics and spintronics due to their properties such as atomic thickness,van der Waals interaction between layers,and no dangling bonds on the surface.By stacking 2D materials in an arbitrary order,van der Waals heterostructure with different functions can be realized.These heterostructures are bound by van der Waals forces between 2D materials,without consideration of lattice mismatches,providing opportunities for the development of novel desirable electronic and spintronic devices.In this thesis,the electronic properties of three kinds of 2D material van der Waals heterostructures were calculated using first principles,and electronic devices based on van der Waals heterostructures were designed.The electrical transport properties of these devices are calculated,and the potential applications of these devices in nanoelectronics and spintronics are demonstrated.The main research contents and results are as follows:1.Blue-phosphene-phase Ge Se van der Waals PN junction via molecular adsorptionThe adsorption of organic molecules on two-dimensional semiconductors can realize p/n-type doping to construct PN junction devices.In this work,F4-TCNQ,TTF and BV molecules were used to adsorb blue-phosphene-phase Ge Se semiconductor to design van der Waals heterostructure PN junction.The geometrical structure and electronic properties of the adsorption of three organic molecule on blue-phosphene-phase Ge Se were calculated and analyzed by first principles.The results show that the adsorption of F4-TCNQ and TTF（BV）molecule on blue-phosphene-phase Ge Se can provide local energy states near the Fermi level,realizing p-type and n-type doped semiconductors respectively.By simultaneously absorbing F4-TCNQ and TTF molecules on both sides of Ge Se,the doping concentration can be increased,which can design a van der Waals heterostructure PN junction.2.Graphene/VSi₂N₄/Graphene van der Waals magnetic tunneling junctionMagnetic tunneling junction uses spin as transmission signal,which has the advantages of high resistivity,small energy consumption and stable performance.It can be used as the basic element of magnetic random-access memory and magnetic head.New-type 2D material VSi₂N₄ is a magnetic material.In this work,we investigated the electronic properties of Graphene/VSi₂N₄/Graphene van der Waals heterostructure.Then,we designed a novel magnetic tunneling junction and calculated its spin transport properties.The results show that the tunnel magnetoresistance rate can reach 10⁶%at zero bias and low bias.3.VSi₂N₄/MSi₂N₄/VSi₂N₄（M=Cr,Mo,W）van der Waals magnetic tunneling junctionTransition metal silicon nitrides have abundant electronic and magnetic properties,which provide the possibility to design novel spintronic devices.In this work,we designed a series of van der Waals magnetic tunneling junctions formed by half-metallic VSi₂N₄ material as electrode and Mo Si₂N_4,Cr Si₂N₄and WSi₂N₄materials as tunneling barriers,respectively.Then,we investigated their spin transport properties.The results show that these magnetic tunneling junctions can achieve ultra-high tunnel magnetoresistance and 100%spin filtering effect at zero bias and low bias.This thesis consists of the following six chapters:Chapter 1 introduces the development of two-dimensional materials,the applications of van der Waals heterostructures;Chapter 2introduces the theoretical calculation methods,including density functional theory and non-equilibrium Green’s function method;In chapter 3,a van der Waals heterostructure PN junction based on blue-phosphene-phase Ge Se with molecular adsorption is studied.In chapter 4,the magnetic tunneling junction and spin transport properties of Graphene/VSi₂N₄/Graphene van der Waals heterostructure is studied.In chapter 5,a magnetic tunneling junction based on VSi₂N₄/MSi₂N₄/VSi₂N₄（M=Cr,Mo,W）van der Waals heterostructure and its spin transport properties are introduced on the basis of the previous chapter.Chapter 6 summarizes and looks forward to our work.