Tuning Electronic Properties Of Group-V 2D Materials By Isoelectronic Counterparts

In recent years,the group-V black phosphorus atomic layer material(also known as phosphorene)has attracted wide attention.With excellent physical properties such as non-zero band gap,high carrier mobility and in-plane anisotropy,and distinct from typical two-dimensional(2D)materials including graphene and transition metal dichalcogenides,black phosphorus is quite promising for nanoelectronics and optoelectronics applications.However,the drawback of black phosphorus including poor chemical stability in air hinders its prospects.At present,searching for alternatives from the V-group isoelectronic family may provide an effective solution.In this paper,based on the first-principles density functional calculations,we exploit the potential tunability of structural and electronic properties of 2D group-V materials and their isoelectronic compounds.This study consists the structural phase transition in antimony induced by charge doping,the structrual stability and stress control on the 2D ?-? indium iodide,and the heterostructural effect of isoelectronic systems on the electronic properties.The first chapter gives a detailed account of the historical background of 2D materials and some of the most representative materials.Chapter 2 briefly introduces the theoretical background of first-principles softwares used in the calculations and simulations worldwide.In chapter ?,the carrier-doping-induced phase transition in antimony--a group-V isoelectronic compound--is discussed.Our calculation predicts that a modest doping(?6×1012 hole/cm2)will greatly reduce the phase transition barrier and thus realize a structural phase transition of monolayer antimony from the hexagonal 3 phase to the orthogonal a phase.Thereby,the bandgap is optimized from indirect to direct type,and the carrier mobility is much enhanced.Further calculations show that there are many ways to achieve the structural phase transition by doping,including electrostatic charge doping,organic molecule functionalization or using graphene substrates.In chapter ?,we introduce a new isoelectronic system of black phosphorus,i.e.III-VII 2d indium iodide(InI).The results show that monolayer and few-layer InI structures have thermodynamic and dynamic stability comparable to their bulk counterpart existed in nature.Interlayer van der Waals stacking and external strain can be used to effectively tune its electronic properties.The band gap of the few-layer structure lies and is adjustable in the spectrum of visible light.Semiconductor-metal transition can be induced with modest stress.The result provides a good example for the strategy of expanding group-V semiconductors by searching for ?-? and other isoelectronic systems.In Chapter V,based on the conclusions drawn in Chapter ? and Chapter ?,we explore the relative stability of several structural phases of 2D antimony and its ?-?&?-? isoelectronic systems,as well as the electronic band characteristics of vertical heterostructures.It is found that there are three most stable structural phases(?,?,c)in SnTe and InI.Electron band gap has a direct relevance to the electronegativity difference between the elemental ions.The larger the electronegativity difference,the bigger the energy gap.The bandgap of the isoelectronic series cover the whole visible spectrum,which is potential for optoelectronic applications.Three types of band alignment can be achieved when forming isoelectronic vertical heterostructures.The abundance of electronic properties of group-V and its isoelectronic materials reveals promising prospects for more applications,by controlling the band gap through alloying or heterostructurization between different constituents.In Chapter ?,summary and prospect is made.