Inspired by Photonics: Switching in Graphene Using Gate-Tunable Electron Optics

Graphene has established itself as a wonder material with a number of intriguing and record-setting properties, such as ultra-high mobility [~200,000 cm2/V-s on hexagonal Boron Nitride (h-BN) at room temperature], room temperature anomalous quantum Hall, and conductivity quantization. In addition, manipulation of ballistic electron trajectories across graphene junctions explains the photon-like behavior of electrons (electron optics); these electrons, however, are directly tunable with gate fields and can thus show highly unconventional analogs of Snell, Fresnel, and Malus' law. Electrons can be focused without a lens using a p-n junction by making the refractive index negative. The electrons at zero degrees of incidence cannot back-scatter because of symmetry rules, so they transmit through arbitrarily high voltage barriers (Klein tunneling). Using two angled junctions, we can turn back these electrons like a polarizer-analyzer (creating transport-gap). Moreover, this method allows us to control the degree of polarization precisely. All these attributes come together to help us design an electron optics based Klein tunnel switch in graphene [Graphene Klein Tunnel Field Effect Transistor (GKTFET)]. Such a switch (with ideal structure) can help us turn off graphene in the absence of a band-gap, thus making good use of the graphene's high transmission speed. As GKTFET utilizes the angular resolution of electrons, this kind of device is particularly susceptible to geometrical non-idealities. Among the non-idealities, edge roughness, junction roughness, and non-ideal potential (across the junctions) strongly affect the on-off ratio by creating states inside the transport gap. By comparing experimental data with simulation results, we characterized and benchmarked the edge and junction roughness. The results show that these non-idealities increase the floor value of the transport gap. Even in the presence of non-idealities, the pseudo gap in the transport window helps to obtain saturation in the output characteristics; this saturation is similar to that found in conventional logic devices. GKTFET is a suitable candidate for analog applications due to high output resistance as a route to increasing maximum oscillation frequency (f_{max}) without hurting mobility. Furthermore, bilayer graphene (BLG) provides more degrees of freedom for gate control at low scattering by utilizing anti-Klein tunneling. This opens the door for bilayer graphene's application in electron optics based devices.