Enhanced Performance of WS2 Field‐Effect Transistor through Mono and Bilayer h‐BN Tunneling Contacts

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 18; no. 13; pp. e2105753 - n/a
• Main Authors: Phan, Nhat Anh Nguyen, Noh, Hamin, Kim, Jihoon, Kim, Yewon, Kim, Hanul, Whang, Dongmok, Aoki, Nobuyuki, Watanabe, Kenji, Taniguchi, Takashi, Kim, Gil‐Ho
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-04-2022
• Subjects: 2D transition metal dichalcogenides; Bilayers; Boron nitride; Chromium; Contact resistance; Electric contacts; Electron mobility; Field effect transistors; MIS (semiconductors); mono and bilayer h‐BN; Monolayers; Nanotechnology; Performance enhancement; Schottky barrier; Semiconductor devices; Transistors; Transition metal compounds; Tungsten disulfide; tunneling barrier; Work functions
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202105753

Transition metal dichalcogenides (TMDs) are of great interest owing to their unique properties. However, TMD materials face two major challenges that limit their practical applications: contact resistance and surface contamination. Herein, a strategy to overcome these problems by inserting a monolayer of hexagonal boron nitride (h‐BN) at the chromium (Cr) and tungsten disulfide (WS2) interface is introduced. Electrical behaviors of direct metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) contacts with mono‐ and bilayer h‐BN in a four‐layer WS2 field‐effect transistor (FET) are evaluated under vacuum from 77 to 300 K. The performance of the MIS contacts differs based on the metal work function when using Cr and indium (In). The contact resistance is significantly reduced by approximately ten times with MIS contacts compared with that for MS contacts. An electron mobility up to ≈115 cm2 V‐1 s‐1 at 300 K is achieved with the insertion of monolayer h‐BN, which is approximately ten times higher than that with MS contacts. The mobility and contact resistance enhancement are attributed to Schottky barrier reduction when h‐BN is introduced between Cr and WS2. The dependence of the tunneling mechanisms on the h‐BN thickness is investigated by extracting the tunneling barrier parameters.
Inserting an atomic hexagonal boron nitride layer at the interface of metal and WS2 to form a metal–insulator–semiconductor (MIS) contact is a practical method to improve mobility and contact resistance of four‐layer WS2 transistors. This study provides an opportunity to understand the impact of the metal work‐function and the mechanism of the Schottky barrier reduction of the MIS‐structured WS2 transistors.