Genuine Ohmic van der Waals contact between indium and MoS2

Abstract

The formation of an ideal van der Waals (vdW) contacts at metal/transition-metal dichalcogenide (TMDC) interfaces is a critical step for the development of high-performance and energy-efficient electronic and optoelectronic applications based on the two-dimensional (2D) semiconductors. In overcoming the key chal-lenges of the conventional metal deposition process that leads to an uncontrol-lable Schottky barrier height and high contact resistance, notable advances were recently made by transferring atomically flat metal thin films or thermally evapo-rating indium/gold alloy. However, the realization of an ideal vdW contact be-tween an elemental metal and TMDC through the evaporation process is yet to be demonstrated, and particularly the evidence of an Ohmic contact between three-dimensional metallic electrodes and TMDCs is still unavailable. Herein, we report the fabrication of atomically clean metal/TMDC contacts by evaporating metals at a relatively low thermal energy and subsequently cooling the substrate holder down to 100 K by liquid nitrogen, achieving for the indium (In)/molybdenum disulfide (MoS2) case an accumulation-type Ohmic contact with a metal-induced electron doping density of 10$^{12}$/cm$^2$. We find that the transport at the In/MoS2 contact is dominated by the field-emission mechanism over a wide temperature range from 2.4 to 300 K, and the contact resistance reaches 600 Ohm um and 1,000 Ohm um at cryogenic temperatures for the few-layer and monolayer MoS2 cases, respectively. Based on first-principles calculations, we find that the na-ture of the ideal In/MoS2 vdW contact is characterized by the formation of in-gap states within TMDC together with the abrupt and rigid shift of the TMDC band.