This work demonstrates a large-scale batch fabrication of GaN light-emitting diodes (LEDs) with patterned multi-layer graphene (MLG) as transparent conducting electrodes. MLG films were synthesized using a chemical vapor deposition (CVD) technique on nickel films and showed typical CVD-synthesized MLG film properties, possessing a sheet resistance of [Formula: see text] with a transparency of more than 85% in the 400-800 nm wavelength range. The MLG was applied as the transparent conducting electrodes of GaN-based blue LEDs, and the light output performance was compared to that of conventional GaN LEDs with indium tin oxide electrodes. Our results present a potential development toward future practical application of graphene electrodes in optoelectronic devices.

The effect of an electron blocking layer (EBL) on the efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes (LEDs) is investigated. At low current density, the LEDs with a p-AlGaN EBL show a higher external quantum efficiency (EQE) than LEDs without an EBL. However, the EQE of LEDs without an EBL is higher than LEDs with an EBL as injection current density is increased. The improved EQE of LEDs without an EBL at high current density is attributed to the increased hole injection efficiency.

We demonstrate the surface plasmon ͑SP͒ enhanced green light-emitting diodes ͑LEDs͒. The Au nanoparticles were embedded in the p-GaN of LEDs. The photoluminescence and electroluminescence measurements showed improved optical properties of LEDs with Au nanoparticles due to an increase in the spontaneous emission rate by resonance coupling between the excitons in multiple quantum wells and localized surface plasmons in Au nanoparticles. The optical output power of SP-enhanced green LEDs with Au nanoparticles was increased by 86% without showing degradation of the electrical characteristics of LEDs compared to LEDs without Au nanoparticles.

We demonstrate the surface plasmon-enhanced blue light-emitting diodes (LEDs) using Ag nanoparticles embedded in p-GaN. A large increase in optical output power of 38% is achieved at an injection current of 20 mA due to an improved internal quantum efficiency of the LEDs. The enhancement of optical output power is dependent on the density of the Ag nanoparticles. This improvement can be attributed to an increase in the spontaneous emission rate through resonance coupling between the excitons in multiple quantum wells and localized surface plasmons in Ag nanoparticles embedded in p-GaN.

We demonstrate localized surface plasmon (LSP)-enhanced nearultraviolet light-emitting diodes (NUV-LEDs) using silver (Ag) and platinum (Pt) nanoparticles (NPs). The optical output power of NUV-LEDs with metal NPs is higher by 20.1% for NUV-LEDs with Ag NPs and 57.9% for NUV-LEDs with Pt NPs at 20 mA than that of NUV-LEDs without metal NPs. The time-resolved photoluminescence (TR-PL) spectra shows that the decay times of NUV-LEDs with Ag and Pt NPs are faster than that of NUV-LEDs without metal NPs. The TR-PL and absorbance spectra of metal NPs indicate that the spontaneous emission rate is increased by resonance coupling between excitons in the multiple quantum wells and LSPs in the metal NPs.