Functional hybrid indium-tin-oxide transparent conductive electrodes for light-emitters

Recently, new types of nano-materials such as carbon nanotubes, graphene, and silver nanowires have been demonstrated as next-generation transparent conductive electrodes (TCEs) in organic and inorganic light-emitting devices owing to their unique functional features such as mechanical flexibility, improved electrical conductivity, high optical transmittance across the entire wavelength range, and surface plasmonic effects. Functional TCEs fabricated with indium-tin-oxide (ITO) materials were developed in this research to maximize the output efficiency of III-nitride light-emitting diodes (LEDs). The functional ITO TCE consists of a small area portion (∼2%) of e-beam evaporated ITO (acting as an Ohmic patch) and a sputtered ITO over-layer (acting as a current spreader). They yield excellent optical transmittance of 93.1% at 450 nm, sheet resistance of 24.2 Ω/sq, and specific contact resistance of 1.5 × 10⁻³ Ωcm². More strikingly, LEDs fabricated with functional hybrid ITO show 62% greater output power than the reference LEDs fabricated with conventional ITO. This was due to the functional feature of hybrid ITO, i.e., a significant vertical out-coupling of laterally guided modes at near the e-beam evaporated Ohmic patch (because of the generated trapezoidal cylindrical surface textures on the ITO surface), enhanced uniform current spreading as well as to the improved TCE performances.