Enhancement of Light Extraction Efficiency for InGaN/GaN Light-Emitting Diodes Using Silver Nanoparticle Embedded ZnO Thin Films

Lattice Constant Effect on Diffracted Transmission of ITO Periodic Nanostructures and Improvement of the Light Extraction Efficiency of Light-Emitting Diodes

We studied the effects of the lattice pitch of indium-doped tin oxide (ITO) periodic nanostructures on the diffracted transmission to improve the light extraction efficiency of light-emitting diodes (LEDs). Periodic hexagonal ITO nanopillars with lattice constants of 600, 800, 1050, 1200, and 1600 nm were fabricated on ITO electrodes. We found that the light extraction efficiency strongly depended on the lattice constant. The LEDs with a lattice constant of 800 nm ITO nanopillars showed an increase in light extraction of 83%. In addition, their electrical properties were not degraded compared to conventional LEDs. The dependence of the extraction efficiency on the lattice constant was also calculated using a 3D finite-difference time-domain (FDTD) method, and this dependence was in good agreement with the experimental measurements. The transmission of each diffraction order and with the total transmission of ITO nanopillars with different lattice constants were calculated using the FDTD method to investigate the enhancement effect.

Self-Aligned Hierarchical ZnO Nanorod/NiO Nanosheet Arrays for High Photon Extraction Efficiency of GaN-Based Photonic Emitter

Advancements in nanotechnology have facilitated the increased use of ZnO nanostructures. In particular, hierarchical and core–shell nanostructures, providing a graded refractive index change, have recently been applied to enhance the photon extraction efficiency of photonic emitters. In this study, we demonstrate self-aligned hierarchical ZnO nanorod (ZNR)/NiO nanosheet arrays on a conventional photonic emitter (C-emitter) with a wavelength of 430 nm. These hierarchical nanostructures were synthesized through a two-step hydrothermal process at low temperature, and their optical output power was approximately 17% higher than that of ZNR arrays on a C-emitter and two times higher than that of a C-emitter. These results are due to the graded index change in refractive index from the GaN layer inside the device toward the outside as well as decreases in the total internal reflection and Fresnel reflection of the photonic emitter.

Surface/Interface Engineering for Constructing Advanced Nanostructured Light-Emitting Diodes with Improved Performance: A Brief Review

With the rise of nanoscience and nanotechnologies, especially the continuous deepening of research on low-dimensional materials and structures, various kinds of light-emitting devices based on nanometer-structured materials are gradually becoming the natural candidates for the next generation of advanced optoelectronic devices with improved performance through engineering their interface/surface properties. As dimensions of light-emitting devices are scaled down to the nanoscale, the plentitude of their surface/interface properties is one of the key factors for their dominating device performance. In this paper, firstly, the generation, classification, and influence of surface/interface states on nanometer optical devices will be given theoretically. Secondly, the relationship between the surface/interface properties and light-emitting diode device performance will be investigated, and the related physical mechanisms will be revealed by introducing classic examples. Especially, how to improve the performance of light-emitting diodes by using factors such as the surface/interface purification, quantum dots (QDs)-emitting layer, surface ligands, optimization of device architecture, and so on will be summarized. Finally, we explore the main influencing actors of research breakthroughs related to the surface/interface properties on the current and future applications for nanostructured light-emitting devices.

Enhanced Photon Emission Efficiency Using Surface Plasmon Effect of Pt Nanoparticles in Ultra-Violet Emitter

We demonstrate the surface plasmon (SP)-enhanced ultraviolet (UV) emitter using Pt nanoparticles (NPs). The UV emitter is hole-patterned on the p-AlGaN layer to consider the penetration depth of Pt NPs. The Pt NPs with sizes under 50 nm are required to realize the plasmonic absorption in UV wavelength. In this study, we confirm the average Pt NP sizes of 10 nm, 20 nm, and 25 nm, respectively, at an annealing temperature of 600 °C. The absorption of annealed Pt NPs is covered with the 365-nm wavelength. The electroluminescence intensity of SP-UV is 70% higher than that of reference UV emitter without hole-patterns and Pt NPs. This improvement can be attributed to the increase of spontaneous emission rate through resonance coupling between the excitons in multiple quantum wells and Pt NPs deposited on the p-AlGaN layer.