Electron Transport Properties Of Graphene-like Two-dimensional Heterostructures And Atomic Nanochains

With the miniaturizing of electronic componets,nanoelectronic devices are considered the bset condidates for the future electronic devices.Recently nano-heterostructures which are composed of at least two different nano-materials have attracted more attensions,because they can improve the performance of the material and get many new phenomena.Because of the deepening of research on nanoelectronic devices,getting a deep insight into the electron transport property is becoming more important.In this dissertation,non-equilibrium Green function together with the first-principles density functional theory are employed to systematically investigate the electron transport properties of the two dimensional nano-heterostructures and atomic chain heterojunctions,revealing the effect of doping and constructing heterostructures on their electron transport properties.The results of this dissertation are given as follows:(1)We have systematically investigated the electronic properties and spin magnetism of GNR doped with the triangular BN flak.It is found that under the nonmagnetic ground states,the devices show a metallic property and the electron transport is limited by the gradual increase of the size of the triangular BN flake.After considering the spin,the devices change to semiconductors and the spin polarization could be modulated by the size of the triangular BN flake.More importantly,bipolar magnetic semiconducting(BMS)is observed in TB15N21,which remains higher transport property and the SFE nearly reaches 100%.The rectangular BN flake with the same number of BN as TBi5N21 has not BMS and the transport property is constrained.Similar to the triangle BN flake doping,the triangular vacancies VB15N21 also present a bipolar magnetic semiconducting property with a higher SFE,but its transport property and the stability is no more than those of triangle BN flake.(2)We put forward two kinds of in-plane heterostructures composed of MoS2NRs and WS2NRs arranged in perpendicular and in parallel respectively which can be fabricated in practice,and investigate the electronic transport properties of these heterostructures.It is found that for all the heterostructures,they exhibit direct band gap semiconducting characteristics at ? point,which means that these heterostructures can be applied in optoelectronic devices and bandgap decreases slightly as the number of WS2NR unit cell increases,resulting in the rapid increase of the current and the higher current peak.In addition,for M(na),the NDR effect is enhanced little with the number of WS2NR unit cell increasing,while for M(nz),it exhibits an opposite trend but the current increases more quickly with a higher current peak,which indicates that the heterostructures arranged in perpendicular have a better application than those in parallel in logic transistor Especially for M(edge)with W atoms doping on the edge,it shows the best performance in the application of logic transistor,because it not only displays a notable NDR effect but also has a high current peak under low bias.(3)We investigate the electronic transport properties of these armchair and zigzag MoS2NRs/WS2NRS in-plane heterostructures.It is found that these armchair MoS2NRs/WS2NRs heterostructures all exhibit rectifying performance,which means that they can be applied in p-n junctions.The rectifying behavior is depressed as the number of WS2NR unit cell decreases,mainly from the reduction of the transmission peak at the positive bias.Owing to the quantum effect,the NDR effect is still observed at both positive and negative bias,which can be modulated with the changes of the WS2NR length.For all the zigzag heterostructures,spin filtering behavior and NDR effect are observed,making them potential application in spintronic devices.In addition,with the WS2NR length increasing,the spin-filtering efficiency at zero bias increases and almost reaches 60%for zMoS2-5zWS2NRs.Whether the spin is considered,the devices with the WS2 nanoribbbons electrode display a better electron transport property.(4)We investigate the electronic transport properties of the carbon and BN chains,and their heterojunctions.It is found that all the atomic chains exhibit even-odd behavior and the current rectifying effect is observed in even-numbered configurations except the pure carbon chains,which originates not only from the asymmetric electronic structure,but also the atomic structure.Importantly,the DOS of the chain channel determines the transmission spectrum and current-voltage characteristics of devices.Also the current-voltage characteristics are explained well by the equilibrium transmission spectrum,where the contribution of transmission spectrum around and away from the Femi level are consistent with the change of the initial current and the current under higher biases.Moreover,for the CBN chain heterojunctions,the electronic properties could be modulated by changing the number of C or BN atoms.The current rectifying ratio is similar to each other among the devices CnBNm,showing a forward and reverse rectifying behavior and with increase of the number of carbon atoms the current is doubled.Especially for the structures with the carbon atoms at the junction they show better electron transport properties,for example,the current and the rectification ratio are enhanced obviously.This dissertation is of great significance to deeply understand the electron transport properties of two-dimensional nano-heterostructures and provide theoretical guidance for the design and development of high performance nanoelectronic devices.