Optical And Electronic Transport Properties Of Two-Dimensional Material

Since the discovery of graphene in 2004,new two-dimensional materials have been the focus of academic research.Following the graphene,MoS2,Silicene and black phosphorus and other two-dimensional materials because of its excellent performance has been the researchers attention.In this paper,the transport properties of graphene heterojunctions under magnetic field and the photoelectric properties of black phosphorus under polarized light are discussed.Although graphene has been prepared for more than a decade,the problem of graphene is still a hot issue.In this paper,Green's function method is used to study the transport properties of graphene: For the general quantum transport problem,because the system is in a non-equilibrium state,even after a long period of evolution can not return to the initial state,so the traditional equilibrium Green Function is more difficult to deal with such problems,non-equilibrium Green's function is to solve the problem of quantum transport the main method.In Chapter 2,Klein tunneling of graphene sheets in the magnetic field region is calculated by the non-equilibrium Green's method.When there is no magnetic field,Klein tunneling(perpendicular to the incident electron transmittance of 1)is characterized by the existence.However,when a magnetic field is applied,the Lorentz force is generated.The existence of the Lorentz force affects the incident angle of the electron,and the incident angle affects the transmission curve and thus the overall conductance.From the numerical results of conductivity,we know that when the potential barrier is equal to the Fermi level,the conductance tends to zero.This result shows that one can change the conductance of graphene by adjusting the intensity of the external magnetic field and the size of the barrier in the middle region.Graphene-like material silicene is a kind of excellent two-dimensional materials,it has a larger energy gap,can make up for graphene gap without control of the shortcomings.However,the preparation of silicene is still a difficult point,and light response speed of silicene is relatively slow,can not meet the performance requirements of certain optoelectronic devices.Black phosphorus as a popular two-dimensional material,which has been researched in recent years,has attracted the attention of many researchers because of its good photoelectric properties.Black phosphorus is a direct narrow bandgap semiconductor material,with better light response than silicene.In the third chapter,the low-energy Dirac theory is used to study the photoelectric properties of black phosphorus,and the band splitting of black phosphorus is considered under Rashba spin-orbit interaction.After applying the circularly polarized light,we found that the external electric field almost does not affect the transition from the valence band to the conduction band of the same valence band,but mainly affects the spin transition from the valence band to the conduction band,and the transition of the photoelectron The probability increases with increasing electric field.When the external electric field is relatively large,the probability of spin transition near the transition is much lower than other positions;and the applied electric field is relatively small,the probability of nearby transition is much larger than other positions.In the future,one can adjust the size of the external electric field,change the intensity of Rashba spin orbit coupling intensity,thus effectively regulating the photoelectron transition,the preparation of high performance optoelectronic devices.