Unanticipated Polarity Shift in Edge-Contacted Tungsten-Based 2D Transition Metal Dichalcogenide Transistors

Creating metal edge contacts in transition metal dichalcogenide (TMD) transistors is a promising path to advance transistor miniaturization for future technology nodes. Current experimental demonstrations nearly exclusively focus on MoS2 as the channel material. Here, we create edge-contacted WSe2 and WS2 transistors using a convergent Ar+ ion beam source integrated within an e-beam evaporator chamber for in-situ processing. An unanticipated polarity shift was observed compared to top-contact behavior for Ti-WS2 devices, which displayed p-type conduction. Meanwhile, three distinct metal contact materials yielded comparable p-branch-dominant performance on WSe2. Transmission electron microscope (TEM) imaging with energy dispersive spectroscopy (EDS) analysis indicated the existence of a residual layer of W (and chalcogen atoms to a lesser extent) beneath the metal contacts, even though the substrate was over-etched. The images presented a physically pure edge interface. This intriguing etching effect could carry significant implications for the design of tungsten-based, edge-contacted TMD transistors.