Device perspective on 2D materials (invited)

Transition metal dichalcogenides (TMDs), typically MoS₂, show good potentials in device applications due to a satisfied band gap, thermal stability, carrier mobility, and compatibility to silicon based CMOS process. In order to realize high-performance MoS₂ MOSFETs, how to achieve a low-resistivity metal-semiconductor junction becomes very important. The 2D material cannot be effectively implanted due to the ultrathin nature, the contact resistance (R_c) is mostly determined by the Schottky barrier height (SBH) at the MoS₂/metal interface. Contact metal and doping engineering is needed to realize low resistivity contacts so that high-performance 2D FETs can be demonstrated. The third issue is related with transistor dimension, which determines the packing density for a single chip. For potential applications, the performance limitation of MoS₂ transistors associated with channel length/width scaling must be investigated. Due to the surphur vacancy or charge neutral level of metal/MoS₂ interface located near the conduction band edge, MoS₂ FETs perform as n-channel Schottky barrier transistors. Phosphorene, complementing to MoS₂, is a p-type channel material. It provides a good addition to the existing 2D family and provides great opportunities for 2D hetero-structures and hetero-integrations.