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 similar to 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 similar to 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 omega sq(-1) to 80.05 +/- 9.1 omega sq(-1) and from 4.92 +/- 0.04 omega sq(-1) to 166.30 +/- 4.1 omega 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.