Chemical trends of Schottky barrier behavior on monolayer hexagonal B, Al, and Ga nitrides

Abstract

The Schottky Barrier Heights (SBH) of metal layers on top of monolayer hexagonal Xnitrides (X=B, Al, Ga, h-XN) are calculated using supercells and density functional theory so as to understand the chemical trends of contact formation on graphene and the 2D layered semiconductors such as the transition metal dichalcogenides. The Fermi level pinning factor S of SBHs on h-BN is calculated to be near 1, indicating no pinning. For h-AlN and h-GaN, the calculated pinning factor is about 0.63, less than for h-BN. We attribute this to the formation of stronger, chemisorptive bonds between the nitrides and the contact metal layer. Generally the h-BN layer remains in a planar sp² geometry and has weak physisorptive bonds to the metals, whereas h-AlN and h-GaN buckle out of their planar geometry which enables them to form the chemisorbtive bonds to the metals.