Novel switching mechanism with angle dependent transmission through graphene based pn junction

Graphene's exceptional electronic properties [1] have sparked tremendous amount of interest in the scientific community in the past decade. The linear energy dispersion leads to very low effective mass and ultra high mobility. This advantage of high mobility becomes useless due to lack of bandgap for digital logic applications[2] and any attempt to open bandgap degrades the mobility substantially. Among other exotic electronic properties, a unique facet of graphene electronics is its analogy with optics. At a graphene pn junction (GPNJ), the electron trajectories resemble optical refraction [3]. For graphene, the gate voltage plays the role of refractive index and this can be made negative easily leading to negative angle of refraction, similar to Veselago lens in optics with negative refractive index metamaterials. Another important analogy is total internal reflection (TIR), which occurs when carriers are unable to conserve the transverse wave-vector component due to lower gate voltage on the refracted side. We show that such electronic refraction governed by analogous Snell's law can be manipulated to modulate current with multiple pn junctions. Our calculations show that we can modulate current by many orders of magnitude without degrading mobility. We vary the number, shape and orientation of gates to introduce a transport gap in the graphene bandstructure similar to what was predicted in a different geometry with external tunnel barrier [5]. Atomistic Non-equilibrium Green's function (NEGF) calculation in experimentally relevant size range (~100nm) shows the current modulation from source to drain by changing gate voltage ratio across the junctions. The aforementioned effects require ballistic transport and suppressed edge scattering [4]. Recent experiment [6] indicates that such manipulation of carriers in graphene is possible (Fig 2).