Contact Engineering High-Performance n-Type MoTe2 Transistors

Michal J Mleczko; Andrew C Yu; Christopher M Smyth; Victoria Chen; Yong Cheol Shin; Sukti Chatterjee; Yi-Chia Tsai; Yoshio Nishi; Robert M Wallace; Eric Pop

doi:10.1021/acs.nanolett.9b02497

Contact Engineering High-Performance n-Type MoTe₂ Transistors

Nano Lett. 2019 Sep 11;19(9):6352-6362. doi: 10.1021/acs.nanolett.9b02497. Epub 2019 Aug 13.

Authors

Affiliations

¹ Department of Electrical Engineering , Stanford University , Stanford , California 94305 , United States.
² Department of Materials Science and Engineering , University of Texas at Dallas , Richardson , Texas 75083 , United States.
³ Applied Materials, Inc. , Santa Clara , California 95054 , United States.
⁴ Department of Electrical and Computer Engineering , National Chiao Tung University , Hsinchu 300 , Taiwan.
⁵ Department of Materials Science and Engineering , Stanford University , Stanford , California 94305 , United States.

PMID: 31314531
DOI: 10.1021/acs.nanolett.9b02497

Abstract

Semiconducting MoTe₂ is one of the few two-dimensional (2D) materials with a moderate band gap, similar to silicon. However, this material remains underexplored for 2D electronics due to ambient instability and predominantly p-type Fermi level pinning at contacts. Here, we demonstrate unipolar n-type MoTe₂ transistors with the highest performance to date, including high saturation current (>400 μA/μm at 80 K and >200 μA/μm at 300 K) and relatively low contact resistance (1.2 to 2 kΩ·μm from 80 to 300 K), achieved with Ag contacts and AlO_x encapsulation. We also investigate other contact metals (Sc, Ti, Cr, Au, Ni, Pt), extracting their Schottky barrier heights using an analytic subthreshold model. High-resolution X-ray photoelectron spectroscopy reveals that interfacial metal-Te compounds dominate the contact resistance. Among the metals studied, Sc has the lowest work function but is the most reactive, which we counter by inserting monolayer hexagonal boron nitride between MoTe₂ and Sc. These metal-insulator-semiconductor (MIS) contacts partly depin the metal Fermi level and lead to the smallest Schottky barrier for electron injection. Overall, this work improves our understanding of n-type contacts to 2D materials, an important advance for low-power electronics.

Keywords: MoTe; Two-dimensional materials; X-ray photoelectron spectroscopy; hexagonal boron nitride; metal-insulator-semiconductor contacts; scandium; silver; unipolar transport.