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

摘要

Due to the chemical inertness of 2D hexagonal-Boron Nitride (h-BN), fewatomic-layer h-BN is often used to encapsulate air-sensitive 2D crystals suchas Black Phosphorus (BP). However, the effects of h-BN on Schottky barrierheight, doping and contact resistance are not well known. Here, we investigatethese effects by fabricating h-BN encapsulated BP transistors with cobalt (Co)contacts. In sharp contrast to directly Co contacted p-type BP devices, weobserve strong n-type conduction upon insertion of the h-BN at the Co/BPinterface. First principles calculations show that this difference arises fromthe much larger interface dipole at the Co/h-BN interface compared to the Co/BPinterface, which reduces the work function of the Co/h-BN contact. The Co/h-BNcontacts exhibit low contact resistances (~ 4.5 k-ohm), and are Schottkybarrier free. This allows us to probe high electron mobilities (4,200 cm2/Vs)and observe insulator-metal transitions even under two-terminal measurementgeometry.