Van der Waals contacts between three-dimensional metals and two-dimensional semiconductors

Yan Wang; Jong Chan Kim; Ryan J Wu; Jenny Martinez; Xiuju Song; Jieun Yang; Fang Zhao; Andre Mkhoyan; Hu Young Jeong; Manish Chhowalla

doi:10.1038/s41586-019-1052-3

Van der Waals contacts between three-dimensional metals and two-dimensional semiconductors

Nature. 2019 Apr;568(7750):70-74. doi: 10.1038/s41586-019-1052-3. Epub 2019 Mar 27.

Authors

Yan Wang^{1

2}, Jong Chan Kim³, Ryan J Wu⁴, Jenny Martinez⁵, Xiuju Song^{2

6}, Jieun Yang^{1

2}, Fang Zhao⁷, Andre Mkhoyan⁴, Hu Young Jeong³, Manish Chhowalla^{8

9

10}

Affiliations

¹ Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK.
² Materials Science and Engineering, Rutgers University, Piscataway, NJ, USA.
³ UNIST Central Research Facilities (UCRF) and School of Materials Science and Engineering, UNIST, Ulsan, South Korea.
⁴ Department of Chemical Engineering and Material Science, University of Minnesota, Minneapolis, MN, USA.
⁵ Mechanical Engineering, California State Polytechnic University, Pomona, Pomona, CA, USA.
⁶ International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology, Shenzhen University, Shenzhen, China.
⁷ Department of Physics, Princeton University, Princeton, NJ, USA.
⁸ Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK. mc209@cam.ac.uk.
⁹ Materials Science and Engineering, Rutgers University, Piscataway, NJ, USA. mc209@cam.ac.uk.
¹⁰ International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology, Shenzhen University, Shenzhen, China. mc209@cam.ac.uk.

PMID: 30918403
DOI: 10.1038/s41586-019-1052-3

Abstract

As the dimensions of the semiconducting channels in field-effect transistors decrease, the contact resistance of the metal-semiconductor interface at the source and drain electrodes increases, dominating the performance of devices^1-3. Two-dimensional (2D) transition-metal dichalcogenides such as molybdenum disulfide (MoS₂) have been demonstrated to be excellent semiconductors for ultrathin field-effect transistors^4,5. However, unusually high contact resistance has been observed across the interface between the metal and the 2D transition-metal dichalcogenide^3,5-9. Recent studies have shown that van der Waals contacts formed by transferred graphene^10,11 and metals¹² on few-layered transition-metal dichalcogenides produce good contact properties. However, van der Waals contacts between a three-dimensional metal and a monolayer 2D transition-metal dichalcogenide have yet to be demonstrated. Here we report the realization of ultraclean van der Waals contacts between 10-nanometre-thick indium metal capped with 100-nanometre-thick gold electrodes and monolayer MoS₂. Using scanning transmission electron microscopy imaging, we show that the indium and gold layers form a solid solution after annealing at 200 degrees Celsius and that the interface between the gold-capped indium and the MoS₂ is atomically sharp with no detectable chemical interaction between the metal and the 2D transition-metal dichalcogenide, suggesting van-der-Waals-type bonding between the gold-capped indium and monolayer MoS₂. The contact resistance of the indium/gold electrodes is 3,000 ± 300 ohm micrometres for monolayer MoS₂ and 800 ± 200 ohm micrometres for few-layered MoS₂. These values are among the lowest observed for three-dimensional metal electrodes evaporated onto MoS₂, enabling high-performance field-effect transistors with a mobility of 167 ± 20 square centimetres per volt per second. We also demonstrate a low contact resistance of 220 ± 50 ohm micrometres on ultrathin niobium disulfide (NbS₂) and near-ideal band offsets, indicative of defect-free interfaces, in tungsten disulfide (WS₂) and tungsten diselenide (WSe₂) contacted with indium alloy. Our work provides a simple method of making ultraclean van der Waals contacts using standard laboratory technology on monolayer 2D semiconductors.