Photocurrent of Graphene/Au-Nanopillar: Near-Unity Degree of Linear Polarization

Abstract

The integration of metal nanostructures and graphene (Gr) layers has gained growing attention for novel optoelectronic device applications. The intriguing physical phenomena observed in Gr-metal systems originate from the unique features of Gr and the plasmonic contributions of the metal. In this work, we fabricate heterojunctions consisting of Gr monolayers and Au nanopillar (AuNP) arrays, denoted as Gr/AuNP, and investigate their photocurrent characteristics. The periodic AuNP arrays are prepared by evaporation of Au thin films on SiO2 nanopattern templates. The angle- and polarization-dependent optical reflectance spectra of AuNP indicated surface plasmon polariton (SPP) excitation in the near-infrared wavelength range, resulting in enhanced light–matter interaction in the Gr monolayers. The combined use of Kelvin probe force microscopy and conductive atomic force microscopy allows us to visualize the light-induced doping in the Gr monolayers and provide local current–voltage characteristics of Gr/AuNP, respectively. Without the requirement of complicated electrode fabrication, these scanning probe approaches clearly show how SPP excitation affects the generation and transport of photocarriers in Gr/AuNP. Applying a negative bias to AuNP can achieve almost a 100% degree of linear polarization, which can be attributed to the SPP-enhanced absorption and hot electron injection from Au to Gr.