Negative Fermi-level Pinning Effect Observed in Metal/GaAs Junction with Graphene Insertion Layer

Abstract

We report the direct observation revealing that the electric dipole layer due to the chemical interaction of metal/graphene contact 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. The chemical interaction dipole layer and the work-function difference between metal and graphene determine the change of electrostatic potential across metal/graphene interface combinedly. In particular, this combined effect is influential to the local Schottky barrier formed on the region of GaAs surface with low interface-trap. 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 which will be the low interface-trap density region for metals with large work functions. Our work provides an experimental method to form Schottky (metal/GaAs) and Ohmic (metal/graphene/GaAs) contacts simultaneously on a GaAs substrate covered partially with graphene by using identical metal electrodes.