期刊
ACS APPLIED NANO MATERIALS
卷 4, 期 5, 页码 5598-5610出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsanm.1c01138
关键词
degenerately doped; MoS2; WSe2; two-dimensional; field-effect transistor; Schottky barrier; Fermi-level pinning; ohmic contact
资金
- NSF [2004445, 1849578]
- Kaskas Scholarship Funds
- U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division
This study demonstrates the successful fabrication of ohmic van der Waals contacts to nearly intrinsic WSe2 nanosheets without the need for electrostatic gating. By utilizing p(+)-MoS2 as contact metal, high device performance in back-gated FETs was achieved, showcasing linear output characteristics, high on/off ratio, and high field-effect mobility. The formation of accumulation-type ohmic contacts is attributed to the absence of Fermi-level pinning effects at the vdW interface and the appropriate work function of p(+)-MoS2. This research represents a significant advance towards low-resistance ohmic contacts in next-generation 2D semiconductor-based nanoelectronics.
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 similar to 200 cm(2) 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 similar to 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.
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