Defect-Assisted\nContact Property Enhancement in a\nMolybdenum Disulfide Monolayer

Abstract

Contact engineering\nfor two-dimensional (2D) transition metal dichalcogenides\n(TMDCs) is crucial for realizing high-performance 2D TMDC devices,\nand most studies on contact properties of 2D TMDCs have mainly focused\non Fermi level unpinning. Here, we investigated electrical and photoelectrical\nproperties of chemical vapor deposition (CVD)-grown molybdenum disulfide\n(MoS₂) monolayer devices depending on metal contacts, Ti/Pt,\nTi/Au, Ti, and Ag, and particularly demonstrated the essential role\nof defects in MoS₂ in contact properties. Remarkably, MoS₂ devices with Ag contacts show a field-effect mobility of\n12.2 cm² V^–1 s^–1, an\non/off current ratio of 7 × 10⁷, and a photoresponsivity\nof 1020 A W^–1, which are outstanding compared to\nsimilar devices with other metal contacts. These improvements are\nattributed to a reduced Schottky barrier height, thanks to the small\nwork function of Ag and Ag–MoS₂ orbital hybridization\nat the interface, which facilitates efficient charge transfer between\nMoS₂ and Ag. Interestingly, X-ray photoelectron spectroscopic\nanalysis reveals that Ag₂S was formed in our defect-containing\nCVD-grown MoS₂ monolayer, but such orbital hybridization\nis not observed in a nearly defect-free exfoliated MoS₂. This distinction shows that defects existing in MoS₂ enable Ag to effectively couple to MoS₂ and correspondingly\nenhance multiple electrical and photoelectrical properties.