High efficiency switching using graphene based electron 'optics'

Abstract

The absence of a band-gap in graphene limits the gate modulation of its electron conductivity, both in regular graphene as well as in PN junctions, where electrostatic barriers prove transparent to Klein tunneling. We demonstrate a novel way to directly open a gate-tunable transmission gap across graphene PN junctions (GPNJ) by introducing an additional barrier in the middle that replaces Klein tunneling with regular tunneling, allowing us to electrostatically modulate the current by several orders of magnitude. The gap arises by angularly sorting electrons by their longitudinal energy and filtering out the hottest, normally incident electrons with the tunnel barrier, and the rest through total internal reflection. Using analytical and atomistic numerical studies of quantum transport, we show that the complete filtering of all incident electrons causes the GPNJ to act as a novel metamaterial with a unique gate-tunable transmission-gap that generates a sharp non-thermal switching of electrons. In fact, the transmission gap gradually diminishes to zero as we electrostatically reduce the voltage gradient across the junction towards the homogeneous doping limit. The resulting gate tunable metal-insulator transition enables the electrons to overcome the classic room temperature switching limit of kTln10/q = 60mV/decade for subthreshold conduction