Quantum Transport In Graphene And Phosphorene Junctions

With the development of semiconductor and engineering manufacturing technology,electronic devices become smaller,faster and highly integrated.Nowadays,building more transistors on the chip by transistor scaling can effectively reduce the manufacturing cost of electronic devices.The trends in developing electronic devices are realizing chips,which makes devices with low manufacturing cost,high integration rate,and high working efficiency.For now,people have gained the ability to engineer materials and atomic-level materials.Notice that when the size of the electronic device is small to a certain extent,including mesoscopic-scale or nano-scale,the classical electromagnetic theory is no longer suitable for describing the transport characteristics of the device.At this time,the properties of electronic devices,especially the transport properties,can only be understood using quantum mechanics.In addition to technology process,people's research on new materials and materials in different dimensions are ongoing.Among them,single-element two-dimensional materials,including graphene and black phosphorene,are making a big shot in this area.These emerging two-dimensional materials have outstanding properties,which make them promising in application prospects in new electronic devices,optoelectronic devices,mechanical nano-devices,etc.This dissertation focuses on the study of two-dimensional materials,that is,the quantum transport properties of junctions based on graphene and phosphorene.The dissertation is mainly divided into seven chaptersIn Chapter 1,we firstly explains the research background of quantum transport in two-dimensional materials;After that,we introduce the applicable conditions of quantum transport,which means that the phase free length of electrons in the material must be longer than the size of materials;Finally,we focuses on the manufacturing method and electronic structure properties of graphene and phosphorene.In Chapter 2,we introduce some basic concepts of quantum transport,including current,transmission and reflection,and how to calculate these physical quantities numerically.We also introduced on two different numerical calculation methods:mode matching method and Green's function method.Eventhough the original ideas of the two calculation methods are different,there is no essential difference between them because they were dealing with Schrodinger's equation.In Chapter 3,we introduce the valley transport and valley polarization phenomenon in graphene nanoribbon crossed junction.The cross-shaped junction includes two single-layer armchair-shaped electrodes and two single-layer zigzag electrodes.When electrons are injected to the double-layer region from one of the armchair electrodes,they are modulated by the scattering area and derived to other electrodes.The valley conductance were formed and the valley polarization can be calculated at the same time,where electrons were scattered into two different valleys of the zigzag electrodes.In Chapter 4,we discuss the valley transport phenomenon in the graphene-based monolayer-bilayer-monolayer nanoribbon junction,the transport phenomenon is affected by the Fano resonance effect in the structure.Fano resonance effect makes the inter-valley scattering is much larger than the intra-valley scattering under a certain Fermi energy.Based on this phenomenon,we propose that such graphene junction can be used for building valley converters.In Chapter 5,we discuss the transport properties of black phosphorene in different transport directions,and the Goos Hanchen shift in different transport directions under the same model is also addressed.Because the excitations in the armchair and zigzag directions of phosphorene are similar to Dirac quasiparticles and Schrodinger quasiparticles respectively,the properties of junctions in different directions are quite different.In Chapter 6,we firstly introduce some basic knowledges of BCS theory and the pseudo-parity properties of hexagonal two-dimensional materials.Base on these,we further discussed the Andreev reflection in the normal-superconducting junction based on phosphone nanoribbons.In Chapter 7,we summarize this dissertation.