Nanodevice Design Based On Strained Graphene

Since its discovery in 2004, graphene has always received increasing attention. The most fascinating advantage of graphene is its high mobility in electronic engineering. Graphene shows ballistic transmission characteristics with a scale of submicron at room temperature. Graphene's high mobility is even two orders higher than of the semiconductor. Thus it is regarded as a new semiconductor material to replace silicon. In Chapter 1, we give a brief introduction to these fields:graphene and its research status.There are two inequivalence of the Dirac points K and K at energy spectrum of the graphene. These two points are twofold valley degree of freedom. We previously put the electronic spin as information carrier. As a counterpart of this research method, we design a valley beam splitter. In Chapter 2, we investigate theoretically the lateral displacements of valley unpolarized electron beams in graphene after traversing a strained region. Valley double refraction occurs at the interface between the incident (unstrained) region and the strained region, in analogy with optical double refraction. It is shown that the exiting positions of K and K transmitted beams, together with their distance D, can be tuned by the strain strength and the inclusion of an electrostatic potential. In addition, D can be enhanced by the wave effect near the valley-dependent transmission resonances. The enhancement is remarkable for graphene n-p-n (or p-n-p) junctions. Thus the Goos-Hanchen effect of transmitted beams for a normal/strained/normal graphene junction can be utilized to design a valley beam splitter.The electronic properties of graphene can be tuned not only by external electric fields and mechanical strains, but also by magnetic barriers. In Chapter 3, we design a valley-filtering switch and a magnetoresistance device. We investigate valley-dependent transport through a graphene sheet modulated by both the substrate strain and the fringe field of two parallel ferromagnetic metal (FM) stripes. We find when the magnetizations of the two FM stripes are switched from the parallel to the antparallel alignment, the total conductance, valley polarization and valley conductance excess change greatly over a wide range of Fermi energy, which results from the dependence of the valley-related transmission suppression on the polarity configuration of inhomogeneous magnetic fields.