We proposed a method to determine the internal quantum efficiency (IQE) of GaInN-based light-emitting diode (LED). For the accurate determination thereof, we carefully reviewed a conventional carrier rate equation and then proposed a set of advanced formulae, which can comprehensively explain the carrier dynamics in a modern GaInN-based LED. Based on our proposed formula, this convenient method to determine the IQE is presented. Next, to identify the proposed carrier rate equations and recombination dynamics, we investigated carrier lifetime. We also discuss the physical origins of IQE degradation in a modern GaInN-based LED such as efficiency droop and green gap.
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.
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