Conductance Anisotropy In Phosphorene Tuned With External Electric Field

The phosphorene has been widely paid attentions because of its special structure and excellent properties,since it had been fabricated successfully in 2014.Phosphorene has a direct band gap,and its band gap strongly depends on the number of layers.The phosphorene has not only a high on/off ratio up to 105,but also relatively high carrier mobility up to 1000 cm2V-1s-1 at room temperature.Because of these superior properties,the phosphorene has a high application prospect in nano-electronic and opto-electronic devices.In particular,phosphorene has a high carrier mobility and a strong in-plane anisotropy.The conductance anisotropy of phosphorene has been observed experimentally.Although the intensity of conductance anisotropy is basically the same,the direction of maximum conductance is different in various experiments,located between-5° and 50°.In the theoretical studies,the magnitude of conductance anisotropy is 10 times larger than the experimental measurements,while the maximum conductance is located only at the armchair direction of orientation index(0,n),different from the experimental observation.The physical mechanism of the conductance anisotropy of phosphorene is still unclear and needs to be explored in depth.In this paper,based on the non-equilibrium Green's function method,the conductance anisotropy of phosphorene has been studied under chemical potential and/or external field.The main research content is divided into the following parts:1.The conductance anisotropy of monolayer phosphorene and its electric field tuning.(1)Based on the four-band tight-binding model and the Green's function method,the conductance anisotropy of monolayer phosphorene and its physical mechanism have been studied.The results show that the anisotropy of conductance strongly depend on the chemical potential.The ratio of maximum to minimum conductance and the direction of maximum conductance are all significantly changed with the chemical potential,which is in good agreement with experimental observations.The related results can well explain that the various observation of conductance anisotropy by several groups,which can be caused by the experimental conditions such as the chemical potential and external fields and so on.(2)The tuning of electric field on the conductance anisotropy of monolayer phosphorene has been investigated.It is found that the conductance anisotropy can be largely modulated by external field.Under certain conditions,the magnitude of conductance anisotropy can be increased by one order of magnitude,and the direction of the maximum and minimum conductance can be even reversed.It is of guiding significance to design and improve the performance of phosphorene microelectronic devices.2.The conductance anisotropy of bilayer phosphorene and its interlayer coupling effect.The conductance anisotropy and the interlayer coupling effect of bilayer phosphorene has been studied under chemical potential and/or external field.The results show that the anisotropy of conductance is not only related to the chemical potential,but also modulated by interlayer coupling.