Desired location doping in 2D semiconductors via bottom-patterned ultrathin nafion for stable and excessive hole-carrier supply

Abstract

Desired or intended location doping in two dimensional (2D) semiconductors has been a persistent issue for 2D semiconductor based electronics along with contact resistance (R_C) lowering. Such doping in 2D seems almost impossible unlike in 3D semiconductors, which use ion implantation. Furthermore, maintaining a stable doping state in 2D seems very difficult. Here, we report a strategy for intended location doping of 2D materials: hole carrier transfer from electron-beam-patterned sulfonated tetrafluoroethylene-based fluoropolymer-copolymer (Nafion) underlayer. Bottom-patterned ultrathin Nafion with a large work function excessively dopes p-type WSe₂, so that its sheet resistance may become compatible for integrated circuit. Top-gated WSe₂ field-effect transistor channel with Nafion support for ungated region demonstrates 7 times higher mobility than without Nafion. As bottom-patterned for contact area, Nafion directly lowers R_C to ∼6 kΩ$·$µm, which is maintained for 2 months in air ambient and survives N₂ anneal of 250 °C. Our Nafion approach for 2D doping and stable R_C seems advanced and practically useful.