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

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 multilayered 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 multilayered 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 ultrathin titanium dioxide (TiO2) interlayer is inserted between the metal contact and the multilayered MoS2 to alleviate FLP and tune the SBH at the S/D contacts of multilayered 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 scope for modifying electrical characteristics of contacts by providing a platform to control the SBH through a simple process as well as understanding of the FLP at the electrical top contacts of multilayered MoS2.