Study On Charge And Spin Transport Properties Of Phosphoene Nanoribbons

The discovery of phosphorene in 2014,due to its direct band gap,high carrier mobility,and high on/off ratio,it has been regarded as a good candidate for field effect transistors,and it also promotes the development of spintronics.In order explore its applications in spintronic devices,in this dissertation,take the phosphorene nanoribbons as our research object.The research method used in this dissertation is nonequilibrium Green’s function with tight-binding model,which is employed to study the spin-dependent transport properties of the phosphorene nanoribbons.First,in chapter one,we introduced background of phosphorene,including the discovery,preparation technology,properties and research status,then we briefly introduce its development history and application of spintronics,which can help us understand the research background.In chapter two,we mainly introduce the theory of quantum transport used in the research of this paper,which includes the nonequilibrium Green function and the generalized Landauer-Büttiker formula that we will use.Then we introduced the Kwant software used in the calculation of this paper,including its advantages and applications.In chapter three,we mainly study the energy band structure and spin polarized transport properties of the phosphorene nanoribbons with a single ferromagnetic layer and an external voltage.We find that the energy bands of the phosphorene nanoribbons are separated when a ferromagnetic layer is considered,which will cause the difference between the conductance for up and down spin electrons,which may have potential applications in phosphorene-based spintronics devices.We also found that the spin polarization oscillates periodically when the gate voltage is increased,and the value of the spin polarization is changed between-100% to 100%.This tunable spin transport may have important applications in the future.In chapter four,we study the tunneling magnetoresistance effect of armchair phosphene nanoribbons with two ferromagnetic layers.By changing the direction of the magnetic field,we find that a large tunneling magnetoresistance effect can be obtained when an external electric field is applied.At the same time,we also found that during the process of increasing voltage,the tunneling magnetoresistance will change from positive to negative.This discovery can help us realize the phosphorene spin nanodevices,and will also promote the development of low energy spintronic devices.In chapter five,we study the transport of zigzag phosphene nanoribbons with metal leads.We study the control of edge transport in zigzag phosphorene nanoribbons,and we found that applying voltage to both edges and deleting some phosphorus atoms can both manipulate the transport properties on the edges,which can be recognized as a switch or transistor.This provides us a theoretical basis for the application and development of spintronic devices.Finally,we summarize the main results of this dissertation and put forward our own views on the future work.Through the research in this dissertation,we can find that the phosphorene nanoribbons are one of the two dimensional materials with unique properties.Due to their unique properties,they will have a good prospect in spintronic devices applications.