Schottky barrier height engineering on MoS2 field-effect transistors using a polymer surface modifier on a contact electrode

Two-dimensional (2D) materials are highly sought after for their superior semiconducting properties, making them promising candidates for next-generation electronic and optoelectronic devices. Transition-metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS₂) and tungsten diselenide (WSe₂), are promising alternative 2D materials. However, the devices based on these materials experience performance deterioration due to the formation of a Schottky barrier between metal contacts and semiconducting TMDCs. Here, we performed experiments to reduce the Schottky barrier height of MoS₂ field-effect transistors (FETs) by lowering the work function (Ф_m = E_vacuum − E_F,metal) of the contact metal. We chose polyethylenimine (PEI), a polymer containing simple aliphatic amine groups (–NH₂), as a surface modifier of the Au (Ф_Au = 5.10 eV) contact metal. PEI is a well-known surface modifier that lowers the work function of various conductors such as metals and conducting polymers. Such surface modifiers have thus far been utilized in organic-based devices, including organic light-emitting diodes, organic solar cells, and organic thin-film transistors. In this study, we used the simple PEI coating to tune the work function of the contact electrodes of MoS₂ FETs. The proposed method is rapid, easy to implement under ambient conditions, and effectively reduces the Schottky barrier height. We expect this simple and effective method to be widely used in large-area electronics and optoelectronics due to its numerous advantages.