High-Performance WS2 MOSFETs with Bilayer WS2 Contacts

• Published in: ACS omega Vol. 9; no. 29; pp. 32159 - 32166
• Main Authors: Jin, Lun, Wen, Jiaxuan, Odlyzko, Michael, Seaton, Nicholas, Li, Ruixue, Haratipour, Nazila, Koester, Steven J.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23.07.2024
• ISSN: 2470-1343; 2470-1343
• DOI: 10.1021/acsomega.4c04431

WS2 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 WS2 MOSFETs by utilizing bilayer WS2 (2L-WS2) in the contact region grown through a two-step chemical vapor deposition process. The 2L-WS2 devices demonstrate a high I ON/I OFF ratio of 108 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-WS2 channel and 2L-WS2 in the contact regions were also fabricated, and they exhibited performance comparable to that of 2L-WS2 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.