Study On The Modulation Of Electronics Transport Properties Of Phosphorene And Phosphorene Nanoribbons

Different from graphene with zero-gap band,phosphorene is semiconductor material with tunable direct band gap,which depends on its number of layers.Phosphorene exhibits anisotropic physics properties in electrical and optical field.These interesting properties make it be concerned by experimental and theoretical researchers.Phosphorene is also a candidate material in future nanoelectronic devices.The design and application of phosphorene-based devices relies on the studies of properties and control methods of phosphorene.In this dissertation,by using the first principles calculation in combination with the non-equilibrium Green's function,we have investigated the electronic structure and anisotropic transport properties of doped monolayer phosphornene and phsophorene nanoribbons.Firstly,the effect on the electronic structure and transport properties of monolayer phosphorene doped with B,Al,Ga,C,Si,Ge,N,As,O,S,Se atoms was studied based on the first principles calculation in combination with non-equilibrium Green's function.We find that the monolayer phosphorene doped with B,Al,Ga,N,As atoms still retains the properties of semiconductor,while the monolayer phosphorene doped with C,Si,Ge,O,S,Se atoms changes to be metal from the semiconductor.In addition,the study on the transport properties of doped monolayer phosphorene with C,Si,Ge,O,S,Se atoms shows that the transport properties of monolayer phosphorene is still anisotropic,but the anisotropic transport properties of monolayer phosphorene can be modulated by changing the impurity elements.For example,the doping of Al and Ga atoms reduces the anisotropy of transport properties of momolayer phosphine,and the negative differential resistance effect(NDR)appears in C,Si,Ge,O,S,Se-doped monolayer phosphorene models.Considering the effect of boundary,the influence on the electronic structure and transportproperties of phosphoene nanoribbons doped with C,Si,Ge atoms was further studied.We find that the armchair phosphorene nanoribbon by hydrogen terminated is semiconductor,while the doping of C,Si,Ge atoms can transform the armchair phosphorene nanoribbons into metal.Negative differential resistance effect can be found in I-V curves of these doped armchair phosphorene nanoribbons.Moreover,the transport properties of doped armchair phosphorene nanoribbons can be regulated by adjusting the concentration of doped atoms.As the doping concentration gradually decreases,the bias range of the negative differential resistance effect also gradually decreases.Based on the theoretical analysis,it is concluded that the negative differential resistance is induced by the change of the level matching of the both electrodes in two probes model.These results will contribute to the design of novel phosphorene-based electronic devices.Thirdly,the electronic structure and transport properties of the cliff-edge phosphorene nanoribbons terminated by H,F,Cl and O atoms were studied.We find that the edge saturation can not only improve the stability of the cliff-edge phosphorene nanoribbon,but also induce its transformation from metal to semiconductor.cliff-edge phosphorene nanoribbons passivated by H and F atoms is semiconductor with a direct band gap,while the cliff-edge phosphorene nanoribbons passivated by O and Cl atoms is semiconductor with an indirect band gap.Further studies on its transport properties show that the electrons on the edge of cliff-edge phosphorene nanoribbon were more sensitive to F and Cl atoms.Moreover,the effect on the stability and the electronic transport properties of the armchair phosphorene nanoribbons,conserdering all the substitution doping positions of C and O atoms was discussed.We find that the doping of C and O atoms lead to the transformation of the armchair-edge phosphorene nanoribbons into metal properties,and the armchair phosphorene nanoriibon doped with C and O atoms at the edge is most stable,this independent of the width of nanoribbons.However,the performance of the negativedifferential resistance effect variates as the width of nanoribbon changes.Finally,the transport properties of the field effect transistors based on the doped armchair phosphoene nanoribbons were studied.We find that the negative differential resistance effect appears in the transistor and the effect can be controlled by adjusting the length of gate and dielectric layer materials.The larger the dielectric constant of the material,the smaller the drain current.This result provides a feasible method for the design of novel phosphorene based electronic devices.