A study on the Cu and Graphene/Cu nanowire for transparent conducting electrode

Abstract

The copper nanowires(Cu NWs) have been noted as the next generation of transparent conducting electrode(TCE) due to its high transmittance and excellent electrical conductivity. Comparing to transmission and conductivity of indium tin oxide (ITO) electrode, those of Cu NWs show similar performance. However, as a transparent electrode, oxidation issue of Cu NWs is demerit to be practically used, and this disadvantage must be compensated. In order to improve the oxidation issue of Cu NWs, the studies on the formation of passivation layer on Cu NWs have been tried using polymer, metal and carbon based materials. Among these materials, graphene has merits as a capping material because graphene is easily grown on Cu surface and has excellent transmittance, low sheet resistance and high thermal conductivity. In this paper, Cu NWs with high aspect ratio were synthesized by controlling the amount of capping agent. And then, graphene coating process was conducted on the Cu NWs using low temperature thermal chemical vapor deposition(CVD) system to overcome the oxidation problem of Cu NWs. The optimized graphene/Cu shell/core NWs has high transparency (88.85 %) and low sheet resistance (36.91 Ω/sq), which are comparable to those of ITO. Three types of light emitting diodes(LEDs) are fabricated with (Gr/)Cu NWs in order to investigate the application as a TCE. Firstly, the synthesized Gr/Cu NWs were applied to GaN based blue LED as a current spreading layer. The GaN based LED with Gr/Cu NWs spreading layer shows 2.36 times increased electroluminescence(EL) intensity comparing to EL intensity of conventional LED. In addition, the In(OH)3/p-Si LED was fabricated with wide surface area(10 x 10 mm2) by forming Cu NWs on the surface of In(OH)3 nanorods. Finally, green light emission of In2O3 NRs/p-GaN heterojunction was studied by formation of Cu NWs on the surface of In2O3 NRs. In this study, proposed (Gr/)Cu NWs can be applied to various opto-electronic applications and show possibility to adopt as a next generation transparent conductive electrode.