Schottky Barrier Height Engineering for Electrical Contacts of Multilayered MoS2 Transistors with Reduction of Metal-Induced Gap States

Abstract

The difficulty in Schottky barrier height (SBH) control arising from Fermi-level pinning (FLP) at electrical contacts is a bottleneck in designing high-performance nanoscale electronics and optoelectronics based on molybdenum disulfide (MoS₂). For electrical contacts of multi-layered MoS₂, the Fermi level on the metal side is strongly pinned near the conduction-band edge of MoS₂, which makes most MoS₂-channel field-effect transistors (MoS₂ FETs) exhibit n-type transfer characteristics regardless of their source/drain (S/D) contact metals. In this work, SBH engineering is conducted to control the SBH of electrical top contacts of multi-layered MoS₂ by introducing a metal–interlayer–semiconductor (MIS) structure which induces the Fermi-level unpinning by a reduction of metal-induced gap states (MIGS). An ultra-thin titanium dioxide (TiO₂) interlayer is inserted between the metal contact and the multi-layered MoS₂ to alleviate FLP and tune the SBH at the S/D contacts of multi-layered MoS₂ FETs. A significant alleviation of FLP is demonstrated as MIS structures with 1-nm-thick TiO₂ interlayers are introduced into the S/D contacts. Consequently, the pinning factor (S) increases from 0.02 for metal–semiconductor (MS) contacts to 0.24 for MIS contacts, and the controllable SBH range is widened from 37 meV (50 – 87 meV) to 344 meV (107 – 451 meV). Furthermore, the Fermi-level unpinning effect is reinforced as the interlayer becomes thicker. This work widens the room for modifying electrical characteristics of contacts by providing a platform to control the SBH through a simple process as well as understandings of the FLP at the electrical top contacts of multi-layered MoS₂.