| Due to the pursuit of miniaturization,convenience,and low energy consumption in the research of nanoelectronic devices,nanoscience has been attracting a large number of researchers to push the limits in theory and experiment in recent years.Especially in 2004,two famous physicists Konstantin Novoselov and Andre Geim from the University of Manchester successfully peeled off a graphene sample from graphite for the first time in the experiment.They also won the Nobel Prize in Physics in 2010.The successful preparation of graphene has opened the door to the research of two-dimensional(2D)materials.In recent years,more and more new 2D materials have been discovered and explored.Because of their unique properties,they have been widely used in the research and preparation of nanoelectronic devices,such as field effect transistors(FET),sensors,memories,spin valves,spin diode,spin current generator,etc.In this thesis,the quantum transport properties of nanoelectronic devices based on black phosphorus(BP)and spintronic devices based on 2D carbon materials are studied based on the first-principles calculation method combining non-equilibrium Green’s function and density functional theory(NEGF-DFT).Among them,gate voltage is the most important control method in the study of quantum transport characteristics of related nanoelectronic devices in this thesis.Besides,there are many other control approaches such as bias voltage and light.The main research contents and innovations of this thesis include:(1)Research on quantum transport characteristics of a novel volatile memory device based on few-layer BP.Using the giant Stark effect induced by few-layer BP under the applied voltage,the BP is gradually transformed from a semiconductor to metal.A two-probe metal-semiconductor-metal structure model based on pure BP with two electrodes applying a voltage(innovation point)perpendicular to the layer of BP and no voltage applied in the central scattering region is constructed.The applied vertical voltage makes the density of states of the electrode region mainly distributed in the upper or lower layer of few-layer BP and the intra-layer tunneling and inter-layer tunneling of the BP are realized by adjusting the sign of the voltage of the two electrodes.Due to the inter-layer tunneling is more difficult than intra-layer tunneling,it can be regarded as the on and off states of the circuit,respectively,thus realizing the characteristics of volatile memory.Along the zigzag direction,the on/off current ratio can be over 5000 %.(2)Research on quantum transport properties of spintronic devices based on few-layer black phosphorus-nickel(BP-Ni).Utilizing the giant Stark effect induced by few-layer BP under the applied voltage replaces the spin-orbit coupling(SOC)effect induced by the applied gate voltage in the previous spintronic device research(innovation point),we study the spin-dependent transport properties of a spintronic device based on few-layer BP-Ni(100).In the linear response region,the spin polarization of the system is largely varied from 0.0181 %-73.2 % in parallel configuration(PC)and 0.0077 %-62.84 %in anti-parallel configuration(APC).In the non-equilibrium state,both bias and gate voltages can be used to tune the spin polarization of the system.A large turn on/off ratio can be realized by the gate voltage(6761 for spin up current and 5828 for spin down current)when the bias voltage is fixed at 0.01 V.(3)Research on quantum transport properties of spin diode devices base on graphyne nanoribbon.In the lateral heterojunction structure composed of 6,6,12-graphyne nanoribbon and γ-graphyne nanoribbon,the parallel configuration(PC)and anti-parallel configuration(APC)is obtained by adjusting the magnetization direction of the two electrodes.It is found that within a certain bias voltage range,the APC can produce the dual-spin filtering effect,while the PC has a spin polarization of almost 0 in the corresponding bias voltage range,which results in giant magnetoresistance in the low bias voltage range.Finally,by applying a gate voltage at the interface of the heterojunction,it is found that the dual-spin filtering effect can also be produced in the PC.(4)Research on quantum transport characteristics of spin photocurrent generator based on graphene nanoribbons.The spin photocurrent can be generated in zigzag graphene nanoribbon(ZGNR)via photogalvanic effect(PGE)(innovative point).By adjusting the sign of the voltage applied to the two electrodes of the device,the pure spin current with opposite signs and fully spin polarized photocurrent with different spin components can be generated.Besides,photon energy,polarization angle and incident angle of polarized light,and width of the nanoribbon can all be used to effectively adjust the generation of spin photocurrent.Compared with the previous method,such as from ferromagnetic materials inject spin into graphene,our proposed method avoids spin-dependent scattering at the interface caused by the contact of different materials with graphene and can noninvasively inject spin into the spintronic devices based on graphene(innovation point). |
