van der Waals Bonded Co/h-BN Contacts to Ultrathin Black Phosphorus Devices

5 years ago

van der Waals Bonded Co/h-BN Contacts to Ultrathin Black Phosphorus Devices

Ahmet Avsar, Su Ying Quek, Khoong Hong Khoo, Jun Y. Tan, Yuting Yeo, Barbaros Özyilmaz, Takashi Taniguchi, Kenji Watanabe, Xin Luo

Because of the chemical inertness of two dimensional (2D) hexagonal-boron nitride (h-BN), few atomic-layer h-BN is often used to encapsulate air-sensitive 2D crystals such as black phosphorus (BP). However, the effects of h-BN on Schottky barrier height, doping, and contact resistance are not well-known. Here, we investigate these effects by fabricating h-BN encapsulated BP transistors with cobalt (Co) contacts. In sharp contrast to directly Co contacted p-type BP devices, we observe strong n-type conduction upon insertion of the h-BN at the Co/BP interface. First-principles calculations show that this difference arises from the much larger interface dipole at the Co/h-BN interface compared to the Co/BP interface, which reduces the work function of the Co/h-BN contact. The Co/h-BN contacts exhibit low contact resistances (∼4.5 kΩ) and are Schottky barrier-free. This allows us to probe high electron mobilities (4,200 cm²/(V s)) and observe insulator–metal transitions even under two-terminal measurement geometry.

Publisher URL: http://dx.doi.org/10.1021/acs.nanolett.7b01817

DOI: 10.1021/acs.nanolett.7b01817