Access Type

Open Access Dissertation

Date of Award

January 2021

Degree Type


Degree Name



Physics and Astronomy

First Advisor

Zhixian Zhou


We report the fabrication of ohmic van der Waals (vdW) contacts to WSe2 using degenerately p-doped MoS2 (p+-MoS2) as a contact-metal. We demonstrate in WSe2 field-effect transistors (FETs) that accumulation-type ohmic contacts and high device performance are achieved 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 cm2V-1s-1 at room temperature. Our theoretical modeling reveals that the p+-MoS2/WSe2 vdW contact behaves as a metal/semiconductor ohmic contact signified by a vanishingly thin space charge region of ~ 1nm in the p+-MoS2 side and a substantial accumulation layer of free holes in 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 the p+-MoS2 being larger than the ionization energy of WSe2.

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