High-Performance WS 2 MOSFETs with Bilayer WS 2 Contacts.

WS 2 is a promising transition-metal dichalcogenide (TMDC) for use as a channel material in extreme-scaled metal-oxide-semiconductor field-effect transistors (MOSFETs) due to its monolayer thickness, high carrier mobility, and its potential for symmetric n-type and p-type MOSFET performance. However, the formation of stable, low-barrier-height contacts to monolayer TMDCs continues to be a challenge. This study introduces an innovative approach to realize high-performance WS 2 MOSFETs by utilizing bilayer WS 2 (2L-WS 2 ) in the contact region grown through a two-step chemical vapor deposition process. The 2L-WS 2 devices demonstrate a high I ON / I OFF ratio of 10 8 and a saturated drain current, I D(SAT) , of 280 μA/μm (386 μA/μm) at room temperature (78 K), even while still using conventional metal (Pd or Ni) contacts. Devices featuring a 1L-WS 2 channel and 2L-WS 2 in the contact regions were also fabricated, and they exhibited performance comparable to that of 2L-WS 2 devices. The devices also exhibit good stability with nearly identical performance after storage over a 13 month period. The study highlights the benefits of a hybrid channel thickness approach for TMDC transistors.