The Electrical Transport Characteristics Of Graphene-nanoribbon-based Nanostructure

Graphene, a monolayer planar sheet of carbon atoms, is confirmed to have a very stable crystalstructure under ambient conditions and exhibits many unique electrochemical properties, whichinclude carrier mobility as high as15000cm2/Vs at room temperature, linear energy dispersionrelation, high thermal conductivity and good flexibility, indicate that graphene could be mostpotential new building blocks in future nanoelectronic devices. So the field-effect transistor (FET)fabricated by graphene ribbons can acheived more superior performance and scale-down prospectswith respected to conventional silicon-based devices.In this paper, based on the tight-binding approximation model within non-equilibrium Greenfunction formalism (NEGF), the energy band structure and electronic transport properties of somegraphene-nanoribbon-based nanostructures have been computed. The influences of defect anddoping on the electronic transport properties of graphene nanoribbon also have been investigated.Moreover, we study the electrical properties of transistor with a channel of armchair graphenenanoribbon (AGNR) for explored the major factors affecting on the performance of device. Theresearch work of this paper can be very useful to provide physical insights of electron transportmechanism in graphene-nanoribbon field-effect transistors (GNRFET) and some guidelines for theimprovement of its performance.The major works of this paper are given as follows:Firstly, we review the crystal of graphene and then, the band structure and electronic transportproperties of graphene-based nanostructure which include armchair and zigzag nanoribbon aresimulated, based on the tight-binding approximate model.Secondly, the effects of atom vacancy, Stone-Wales defect, and substituted doped with boron (B)or nitride (N) on the electronic transport properties of armchair graphene nanoribbon areinvestigated respectively. It is found that the introducing of defects and dopants lead to thetransmission suppressing effect of graphene nanoribbon, and result in the disappearance of itsquantum stepped characterized in the transport spectrum. Furthermore, the degree of impact onelectronic transport of GNR depends on the position of defects and dopants. And the differrent typeof impurity will cause the formation of different impurity level in GNR, then resulting in a differentconductivity type.Thirdly, two calculated models for describe the electronic transport properties of the device with a channel of graphene nanoribbon are built, one is a analytical model which based on the Büttikervirtual probe method, and the other one is the numerical method built in the real space based onNEGF formalism. And then the electrical characteristics of graphene nanoribbon transistor withdifferent types of contacting between intrinsic channel and source/drain reservoir of device aresimulated respectively by the two methods mentioned, and the effects of dissipation-limitedtransports are also investigated.Finally, the current-voltage (I-V) and sub-threshold charasticstics of a novel GNRFET withnon-symmetrical HALO-lightly doped drain (LDD) structure are simulated, and some comparisonsare made for electrical properties among the GNRFETs with different doped structure. Thesimulation results show that compared to others, the GNRFET with novel asymmetrical dopedstructure has a smaller leakage current, a higher on-off current ratio, a lower sub-threshold slopeand smaller threshold voltage drift.