Atomically Thin p-doping Layer and Record High Hole Current on WSe 2

Two-dimensional transition metal dichalcogenide (TMD) thin films that can be exfoliated from bulk crystals or grown into wafer size have attracted a lot of attention due to their unique electrical, optical, and mechanical properties. In this article, we focus on field-effect transistor (FET) applications and chose tungsten diselenide (WSe 2 ) as the channel material since both electron and hole transport can be achieved, which is ideal for CMOS implementation. However, large contact resistance is often measured in WSe 2 FETs, which remains one of the major challenges to obtain good device performance. Although many chemical doping methods have been proposed to achieve p-type doping of the WSe 2 channels, such as ozone exposure [1], NO 2 chemisorption [2], and MoO 3 interfacial layer [3], the common problem for the above-mentioned methods is the lack of stability in air. To date, only [4] showed air stable p-doping of WSe 2 multilayer flakes by exposing to remote O 2 plasma. Here, we carry out comprehensive studies of the doping effects on monolayer WSe 2 by converting the top layer of a bilayer WSe 2 film to an atomically thin p-doping layer through direct O 2 plasma treatment at room temperature. Furthermore, a record high p-current (hole current) is also achieved in scaled devices with stronger doping effects introduced at an elevated temperature.