Current saturation and steep switching in graphene PN junctions using angle-dependent scattering

Graphene's ultra-high carrier mobility (200,000cm2/Vs on hBN) [1] makes it promising for high speed applications; however the absence of a band-gap makes it hard to design logic elements out of graphene. It is possible to open a bandgap in graphene by applying strain [2] or by confining it in one direction into nanoribbons [3], but in the process bandstructure gets distorted near Dirac point and the carrier mobility decreases [4]. A recent set of papers have exploited instead the angle dependent transmission across graphene pn junctions (GPNJ) [5-9]. Since the opening angle is gate tunable, a sequence of angled junctions can turn off the electrons [10,11] using gateable momentum filtering in the absence of a band-gap (instead, the ideas use a transmission gap). In the absence of edge scattering, momentum filtering is predicted to give large ON, low OFF current and a steep subthreshold swing (SS). In this paper, we calculate the transfer (ID-VG) and output (ID-VD) characteristics of a GPNJ switch [11] and show current saturation using gate geometry alone.