Open Access Dissertation
Date of Award
Physics and Astronomy
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.
Rijal, Upendra, "Accumulation-Type Ohmic Van Der Waals Contacts To Nearly Intrinsic Wse2" (2021). Wayne State University Dissertations. 3430.