Origins of Fermi Level Pinning for Ni and Ag Metal Contacts on Tungsten Dichalcogenides

• Published in: ACS nano Vol. 17; no. 20; pp. 20353 - 20365
• Main Authors: Wang, Xinglu, Hu, Yaoqiao, Kim, Seong Yeoul, Addou, Rafik, Cho, Kyeongjae, Wallace, Robert M.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 24.10.2023
• Subjects: interface chemistry; transition metal dichalcogenides; Fermi level pinning; metal contact; imperfections; density functional theory; band alignment
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.3c06494

Tungsten transition metal dichalcogenides (W-TMDs) are intriguing due to their properties and potential for application in next-generation electronic devices. However, strong Fermi level (EF) pinning manifests at the metal/W-TMD interfaces, which could tremendously restrain the carrier injection into the channel. In this work, we illustrate the origins of EF pinning for Ni and Ag contacts on W-TMDs by considering interface chemistry, band alignment, impurities, and imperfections of W-TMDs, contact metal adsorption mechanism, and the resultant electronic structure. We conclude that the origins of EF pinning at a covalent contact metal/W-TMD interface, such as Ni/W-TMDs, can be attributed to defects, impurities, and interface reaction products. In contrast, for a van der Waals contact metal/TMD system such as Ag/W-TMDs, the primary factor responsible for EF pinning is the electronic modification of the TMDs resulting from the defects and impurities with the minor impact of metal-induced gap states. The potential strategies for carefully engineering the metal deposition approach are also discussed. This work unveils the origins of EF pinning at metal/TMD interfaces experimentally and theoretically and provides guidance on further enhancing and improving the device performance.