Graphite–metal composite electrodes with a tunable work function for use in optoelectronic devices

Abstract

In electronic devices, the work function (WF) of the electrodes must be tailored to achieve a well-aligned Ohmic or Schottky contact. Low- and high-WF electrodes are typically used to ensure effective injection/extraction of electrons and holes. In this study, composite graphite–aluminum (G : Al) and graphite–nickel (G : Ni) electrodes were deposited on a glass substrate using electron beam evaporation, and ambient pressure photoemission spectroscopy was conducted to evaluate the WF of the fabricated electrodes. The WF of the G : Al electrode was successfully tuned from 4.24 ± 0.047 eV to 5.10 ± 0.031 eV (a range of ∼0.9 eV) by increasing the graphite content. Similarly, the WF of the G : Ni composite electrode was tuned from 4.67 ± 0.041 eV to 5.11 ± 0.031 eV (a range of ∼0.4 eV). The shift in the WF in the composite graphite–metal electrodes could be explained by the formation of metal–metal (or semiconductor) junctions. The optical reflectance, sheet resistance, and morphology were also able to be tuned. The sheet resistance of the G : Al and G : Ni electrodes varied from 2.28 ± 0.03 Ω sq⁻¹ to 80.05 ± 9.1 Ω sq⁻¹ and from 4.92 ± 0.04 Ω sq⁻¹ to 166.30 ± 4.1 Ω sq⁻¹, respectively, while the total tunable reflectance was 53.77% and 45.70%, respectively. This research demonstrates a novel exploratory technique for tailoring the WF of hybrid graphite materials.