Study On Charge Transport Properties Of Graphene And Silicene Nanoribbons

Graphene was successfully prepared in 2004,turning this theoretical material into a reality,which is the start of the golden age of graphene.With the deepening of research,two-dimensional materials show a variety of surprising properties,which stimulated the interest of scientific researchers,and scientists began to look for other graphene-like materials,phosphorene,borophene,germanene,silicene and other single-element two-dimensional materials.In this dissertation,graphene and silicene are chosen as our research objects,and we study their charge transport properties.In this thesis,the research model is constructed by tight binding approximation theory,using a quantum transport software Kwant.Green function is used to calculate the conductance of the system under consideration.We obtain visual results of band structures,conductance,density of states,etc.,which is conducive to the study of material transport properties.The dissertation contains three research contents:1.The charge transport properties of bilayer grapheneThe transport properties of zigzag and armchair bilayer graphene nanoribbons are both investigated in this dissertation.The energy band structure of zigzag bilayer graphene is significantly different from that of monolayer graphene.The band structure can be modulated by a perpendicular electric field.When no electric field is applied,the energy gap does not exist,so opening the band gap has become one of our research goal.It isfound that once the vertical electric field or off-resonant circularly polarized light is added to the double-layer graphene,the band gap can be opened,and the system then presents a topological edge state.The armchair bilayer graphene nanoribbons are also considered in this study,and no energy band gap is obtained without any external field effect in our proposed device.The electric field can open the energy gap in armchair bilayer graphene nanoribbons without generating topological edge states,but the off-resonant circularly polarized light can open a band gap with topological states found in the gap.2.The charge transport properties of siliceneSilicene is a graphene-like material,which also has a two-dimensional honeycomb structure.Unlike graphene,silicene has a buckled structure.This special structure offers silicene a stronger spin-orbit coupling effect than graphene,and this difference has attracted a lot of interest of researchers.In this dissertation,we mainly study the transport characteristics of armchair silicene.The off-resonant circularly polarized light and electric fields were applied to different areas of the silicene nanoribbon,and we study the electron tunneling of topological edge states in silicene.The research results are very useful in the design of electronic devices based on quantum tunneling.3.Graphene heterojunction field effect transistorAccording to the published experimental results,we build a theoretical model for graphene field effect transistors.We select the calculation parameters according to the experimentand compare the simulation results with the experimental results,and we find that the two results agree with each other.Our theoretical study can explain the experimental results.Graphene heterojunction is illuminated by off-resonant circularly polarized light,and it is found that the carrier concentration can be changed by the gate voltages,and the heterojunction junction can be changed,which can realize the"on/off" function of electronic devices.