Low\nContact Resistance on Monolayer MoS₂ Field-Effect Transistors\nAchieved by CMOS-Compatible Metal Contacts

Abstract

Contact engineering on monolayer\nlayer (ML) semiconducting transition\nmetal dichalcogenides (TMDs) is considered the most challenging problem\ntoward using these materials as a transistor channel in future advanced\ntechnology nodes. The typically observed strong Fermi-level pinning\ninduced in part by the reaction of the source/drain contact metal\nand the ML TMD frequently results in a large Schottky barrier height,\nwhich limits the electrical performance of ML TMD field-effect transistors\n(FETs). However, at a microscopic level, little is known about how\ninterface defects or reaction sites impact the electrical performance\nof ML TMD FETs. In this work, we have performed statistically meaningful\nelectrical measurements on at least 120 FETs combined with careful\nsurface analysis to unveil contact resistance dependence on interface\nchemistry. In particular, we achieved a low contact resistance for\nML MoS₂ FETs with ultrahigh-vacuum (UHV, 3 × 10^–11 mbar) deposited Ni contacts, ∼500 Ω·μm,\nwhich is 5 times lower than the contact resistance achieved when deposited\nunder high-vacuum (HV, 3 × 10^–6 mbar) conditions.\nThese electrical results strongly correlate with our surface analysis\nobservations. X-ray photoelectron spectroscopy (XPS) revealed significant\nbonding species between Ni and MoS₂ under UHV conditions\ncompared to that under HV. We also studied the Bi/MoS₂ interface\nunder UHV and HV deposition conditions. Different from the case of\nNi, we do not observe a difference in contact resistance or interface\nchemistry between contacts deposited under UHV and HV. Finally, this\narticle also explores the thermal stability and reliability of the\ntwo contact metals employed here.