(184c) Tuning the Electronic and Structural Properties of MoS2-Metal Interface through in-Silico Screening of Metal Contacts

Authors: 
Udyavara, S., University of Minnesota
Neurock, M., University of Minnesota
Wu, R., University of Minnesota
Mkhoyan, K. A., University of Minnesota
Koester, S., University of Minnesota
Chhowalla, M., University of Cambridge
Ma, R., University of Minnesota
Wang, Y., Rutgers University
Birol, T., University of Minnesota
Tuning the electronic and structural properties of MoS2-metal interface through in-silico screening of metal contacts

Sagar Udyavara1*, Ryan Wu1, Rui Ma2, Yan Wang3, Manish Chhowalla3,4, Turan Birol1, Steven J. Koester2, K.Andre Mkhoyan1 and Matthew Neurock1

1Dept. of Chemical Engineering and Material Science, University of Minnesota, Minneapolis, MN 55455

2Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455

3Department of Material Science and Engineering, Rutgers University, Piscataway, NJ 08854

4Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK

Abstract:

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently generated a lot of interest due to its unique tunable electronic properties that make it suitable for electronic applications. Of these, 2D molybdenum disulfide (MoS2) is of particular interest and acts as an excellent channel material for ultra-thin field effect transistors [1]. However, high contact resistance across the metal-MoS2 interface due to Fermi level pinning continues to limit its full realization [2]. This contact resistance is linked to the structure of the interface which remains poorly understood. While previous theoretical studies have looked at such metal-MoS2 contacts using the “metal-MoS2-slab” approach, they however have failed to consider the structural changes at the interface upon metal deposition and the influence of those changes on the electronic properties of the interface [3]. Here, using a different “single-atom-addition” approach, we are able to characterize the resultant structural changes occurring at the interface upon deposition of different metals and also the subsequent effect on its electronic properties [4]. We initially looked at the Ti-MoS2 interface which when characterized using atomic-resolution analytical scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) show a destruction of the pristine MoS2 layers, formation of void pockets and penetration of metal atoms into the deeper MoS2 layers. Calculations using the “single-atom-addition” approach validate these observations and show that early transition metals such as Ti and Sc, which have high affinity for sulfur react with the metal-MoS2 interface leading to release of S from Mo along the interface, formation of MxSy clusters and pores in the MoS2, which lead to the penetration of the metal atoms into the MoS2 layers. Further, calculations suggest that such interfaces would have many localized states in the band gap of MoS2 contributing into Fermi level pinning which show that the contact problem could be a fundamental limitation for such metals and cannot be overcome. We thus further looked into other different metal contacts and showed that this contact problem could be minimized by using metals like In which interact with the MoS2 surface via weaker van der Waal’s type interactions, thus keeping the surface pristine. DFT calculations further revealed that such systems do not have many localized states present in the band gap due to which Fermi level pinning would likely be avoided, leading to lower contact resistances [5].

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