Currently, the internal quantum efficiency (IQE) of GaInN-based green light-emitting diodes (LEDs) is still low. To overcome this problem, surface plasmon (SP)-enhanced LEDs have been intensively studied for the last 15 years. For an SP effect in green LEDs, Au and Ag are typically employed as the plasmonic materials. However, the resonance wavelength is determined by their material constants, which are theoretically fixed at ~537 nm for Au and ~437 nm for Ag. In this study, we aimed to tune the SP resonant wavelength using double-metallic nanoparticles (NPs) composed of Au and Ag to match the SP resonance wavelength to the LED emission wavelength to consequently improve the IQE of green LEDs. To form double-metallic NPs, Au/Ag multilayers were deposited on a GaN layer and then thermally annealed. We changed the thicknesses of the multilayers to control the Ag/Au ratio in the NPs. We show that the SP resonant wavelength could be tuned using our approach. We also demonstrate that the enhancement of the IQE in SP-enhanced LEDs was strongly dependent on the SP resonant wavelength. Finally, the highest IQE was achieved by matching the SP resonant wavelength to the LED emission wavelength.

The role and effect of surface defects (SDs) on the efficiency degradation of GaInN-based green LEDs was investigated. Two types of green LED samples having the same structure were prepared; an additional underlying layer was introduced in one sample to artificially reduce SDs in the multiple quantum well active region. Then, various characteristics were analyzed for both samples. Based on these analyses, schematic models including those of SD dynamics during growth and potential fluctuation induced by SDs in green LEDs were proposed. Results show that SDs play a crucial role in efficiency degradation.

Surface-plasmon (SP)-enhanced light-emitting diodes (LEDs) covering self-assembled Ag nanoparticles (NPs) on top of a p-GaN layer are broadly studied to improve luminescence efficiency in green LEDs. However, the enhancement factor of SP-enhanced LEDs is reduced under electrical injection compared to that under external optical pumping. For current injection, indium tin oxide (ITO) is typically deposited on top of a p-GaN layer for current spreading and ohmic contact. In this paper, we investigate the effect of the ITO layer on the performance of SP-enhanced green LEDs. We prepared samples with varying ITO thicknesses, from 30 nm to 200 nm, and investigated their optical and electrical characteristics. From the ITO thickness-dependent measurements, we show ITO thickness has a significant impact on electroluminescence intensity and current–voltage characteristics. Finally, we propose the optimized ITO thickness for SP-enhanced LEDs.

In this study, we compared the device performance of GaInN-based green LEDs grown on c-plane sapphire substrates with a conventional low temperature GaN buffer layer to those with a sputtered-AlN buffer layer. The light output power and leakage current characteristics were significantly improved by just replacing the buffer layer with a sputtered-AlN layer. To understand the origin of the improvement in performance, the electrical and optical properties were compared by means of electro-reflectance spectroscopy, I–V curves, electroluminescence spectra, L–I curves, and internal quantum efficiencies. From the analysis of the results, we concluded that the improvement is mainly due to the mitigation of strain and reduction of the piezoelectric field in the multiple quantum wells active region.

To investigate the mechanism of efficiency enhancement achieved by introducing underlying layers (ULs) in green light–emitting diodes (LEDs), this study compares green GaInN‐based LEDs with an identical epitaxial structure and chip structure comprising different types of ULs, i.e., without an UL or with a GaInN or AlInN UL. To this end, the samples are analyzed with respect to several characteristics, such as their electroluminescence spectra, internal quantum efficiency, recombination coefficients, joint density of states, localized state, and Stokes shift. Based on these analyses and considerations, a mechanism of efficiency enhancement achieved by introducing ULs is proposed, and the degradation mechanisms responsible for the green gap, efficiency droop, and electrical potential drop in green LEDs are also discussed. The results show that the piezoelectric field in the In‐clustering region and the nonradiative recombination center simultaneously play crucial roles in the degradation mechanisms for green LEDs.

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