Two-dimensional electric-double-layer Esaki diode

Abstract

Two-dimensional van der Waals materials offer unique advantages for the development of band-to-band tunneling devices given their lack of dangling bonds, atomically flat thickness and steep band edges. Here, we present the experimental demonstration of an electric double layer (EDL) Esaki junction in synthetic WSe2 thin films. A Si-compatible process is developed for the fabrication of nanoscale FETs utilizing molecular beam epitaxy of WSe2 performed directly on top of a high-κ dielectric at back-end-of-line-friendly temperatures (<550 °C). Degenerate and abrupt doping profiles are obtained by modulating the electron/cation and hole/anion EDLs formed at the interface between a tens-of-nanometer long WSe2 channel and a solid polymer electrolyte, polyethylene oxide:cesium perchlorate (PEO:CsClO4). Numerical simulations are used to determine the bias dependence of the equilibrium ion and carrier density profiles. The EDL-doped tunnel diode exhibits repeatable, gate-tunable band-to-band tunneling with negative differential resistance in the forward bias regime at temperatures up to 140 K, and strong conduction in reverse bias. A maximum peak-to-valley current ratio of 3.5 is measured at 110 K.