Abstract
We report the fabrication of ohmic van der Waals (vdW) contacts to nearly intrinsic WSe2 nanosheet-based channels in field-effect transistors (FETs) using degenerately p-doped MoS2 (p+-MoS2) as a contact metal. We demonstrate that accumulation-type ohmic contacts and the high device performance are achievable without electrostatically gating the drain/source contact regions despite the nearly intrinsic nature of WSe2. Back-gated WSe2 FETs with p+-MoS2 bottom contacts (which screen the back-gate electric field in the drain/source regions) exhibit linear output characteristics, a high on/off ratio of 108, and a high two-terminal field-effect mobility up to ∼200 cm2 V-1 s-1 at room temperature. Our theoretical modeling reveals that the p+-MoS2/WSe2 vdW junction behaves like a metal/semiconductor ohmic contact signified by a vanishingly thin space-charge region of ∼1 nm on the p+-MoS2 side and a substantial accumulation layer of free holes on the WSe2 side, which is further verified by additional temperature-dependent and dual-gated measurements of WSe2 FETs. We attribute the formation of accumulation-type ohmic contacts free of a Schottky barrier to the near absence of Fermi-level pinning at the vdW interface and the work function of p+-MoS2 being larger than the ionization energy of WSe2. This study represents an important step toward achieving low-resistance ohmic contacts to two-dimensional (2D) semiconductors by eliminating the Fermi-level pinning effects, which is expected to have significant implications for next-generation 2D semiconductor-based nanoelectronics.
Original language | English |
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Pages (from-to) | 5598-5610 |
Number of pages | 13 |
Journal | ACS Applied Nano Materials |
Volume | 4 |
Issue number | 5 |
DOIs | |
State | Published - May 28 2021 |
Keywords
- Fermi-level pinning
- MoS
- Schottky barrier
- WSe
- degenerately doped
- field-effect transistor
- ohmic contact
- two-dimensional