Tunable transmission Gap in graphene p-n junction

For its unique electronic characteristics [1,2], graphene has been a material of great interest for scientists since its discovery. While its incredibly high mobility is attractive for high frequency field effect transistor realizations [3], the zero bandgap energy spectrum gives a modest transistor reliability for digital logic applications. And opening a bandgap with structural change or quantum confinement loses the advantage of high mobility. In this paper, we propose an efficient switching device using graphene p-n junction (GPNJ) by manipulating its the geometric optics like transport. Similarity between electronics and optics has been revitalized with GPNJ with recent theoretical [4] and experimental research [5]. By analytical and quantum simulation with atomistic Non-Equilibrium Green´s function Formalism (NEGF), we demonstrate that electron trajectories in graphene p-n junction are determined by analogous Snell´s law when electrons are injected with a point source. We also show that the ON-OFF ratio can be improved substantially by using an external barrier in the middle of the device, removing low angle, high longitudinal energy electrons responsible for high leakage current. The low longitudinal energy electrons are eliminated by total internal reflection (TIR) outside a critical angle which depends on gate voltages. This gate voltage dependence together with the external barrier leads to a tunable transmission gap and produces sub-thermal sub-threshold swing.