Interfacial Elemental Analysis of Slanted Edge-Contacted Monolayer MoS Transistors via Directionally Angled Etching.

Edge contacts offer a significant advantage for enhancing the performance of semiconducting transition metal dichalcogenide (TMDC) devices by interfacing with the metallic contacts on the lateral side, which allows the encapsulation of all of the channel material. However, despite intense research, the fabrication of feasible electrical edge contacts to TMDCs to improve device performance remains a great challenge, as interfacial chemical characterization via conventional methods is lacking. A major bottleneck in explicitly understanding the chemical and electronic properties of the edge contact at the metal-two-dimensional (2D) semiconductor interface is the small cross section when characterizing nominally one-dimensional edge contacts. Here, we demonstrate a directional angled etching technique that enables the characterization of the interfacial chemistry at the metal-MoS junction when in an edge-contact configuration. The slanted edge structure provides a substantial cross section for elemental analysis of the edge contact by conventional X-ray photoemission spectroscopy, in which a simple chemical environment and sharp interface were revealed. Facilitated by the well-characterized contact interface, we realized slanted edge-contacted monolayer MoS transistors encapsulated by hexagonal boron nitride. The transport characteristics and photoluminescence of these transistors allowed us to attribute the efficient carrier injection to direct and Fowler-Nordheim tunneling, validating the distinct Au-MoS interface. The established method represents a viable approach to fabricating edge contacts with encapsulated 2D material devices, which is crucial for both the fundamental study of 2D materials and high-performance electronic applications.