Negative Fermi-Level Pinning at Metal/GaAs Junction Occurring with Graphene Insertion Layer

Abstract

It is observed that the electric dipole layer due to the shift of bonding electrons (chemical interaction) at metal/graphene interface can induce the negative Fermi-level pinning effect in metal/graphene/n-GaAs(001) junction, supported by the Schottky barrier decreasing as metal work-function increasing in the current-voltage characteristics of junction. The chemical interaction dipole layer and the work-function difference between metal and graphene determine combinedly the profile of electrostatic potential across the metal/graphene interface. In particular, this combined effect is influential to the local Schottky barrier formed on the region of GaAs surface with low interface-trap density. The graphene insertion layer takes a role of diffusion barrier preventing the atomic intermixing at interface and preserving the low interface-trap density region. The electron transport through metal/graphene/n-GaAs(001) junction is dominated by the low Schottky barrier patches. Under the negative Fermi-level pinning, these low Schottky barrier patches will correspond to the low interface-trap density regions for metals with large work-functions. Our work provides an experimental method to form Schottky (metal/GaAs) and Ohmic (metal/graphene/GaAs) contacts simultaneously with one-time metal electrode deposition by covering the GaAs substrate partially with graphene.