Improvement of the light extraction efficiency of GaN-based LEDs using rolled-up nanotube arrays

Enhancing the light extraction efficiency of AlInN nanowire ultraviolet light-emitting diodes with photonic crystal structures

In this paper, AlInN nanowire ultraviolet light-emitting diodes (LEDs) with emission at ∼299 nm have been successfully demonstrated. We have further studied the light extraction properties of these nanowire LEDs using photonic crystal structures with square and hexagonal lattices of nanowires. The light extraction efficiency (LEE) of the periodic nanowire LED arrays was found to be significantly increased as compared to random nanowire LEDs. The LEEs reach ∼ 56%, and ∼ 63% for the square and hexagonal photonic crystal-based nanowire structures, respectively. Moreover, highly transverse-magnetic polarized emission was observed with dominant vertical light emission for the AlInN nanowire ultraviolet LEDs.

Analytic design of light extraction array for light guide plate based on extended sources

Light extraction array, comprised of millions of discrete scattering dots randomly distributed on edge-lit light guide plates (LGPs), determines both the light efficiency and spatial uniformity of liquid crystal displays. However, it is hard to define by a specific mathematical expression. Here, we propose a novel analytic design for light extraction array based on geometrical optical principles. This design method consists of three successive procedures evolving from point- and line-source approximations to extended surface-source computation. Three procedures are demonstrated via both simulation and experiment, and the key factors influencing the performance of the light extraction array are also discussed. Our approach with high accuracy and reduced complexity will have broad prospect for illumination design.

Enhanced light extraction efficiency of Eu-related emission from a nano-patterned GaN layer grown by MOCVD

Eu-doped GaN is a promising material for the active layer in red light emitting diodes. Although the output power of LEDs based on GaN:Eu has been increasing by a combination of structural and growth optimizations, there is still a significant limitation resulting from a poor light extraction efficiency, typical for high refractive index materials. Here we studied nanostructuring of the top of the optical active layer by nano-cubes for enhancement of the light extraction efficiency, and its effect on the optical emission characteristics. By etching nano-cubes into the active layer, we observed an increase in directional light output power of Eu³⁺ ions of up to 60%, as well as a grating effect. Simultaneously, the absorption of excitation light into the optical active layer was improved, leading to a 12.8 times increase of output power per available Eu³⁺ ion.

Whispering gallery mode lasing from InGaN/GaN quantum well microtube

In this work, we have successfully fabricated microtubes by strain-induced self-rolling of a InGaN/GaN quantum wells nanomembrane. Freestanding quantum wells microtubes, with a diameter of 6 µm and wall thickness of 50 nm, are formed when the coherently strained InGaN/GaN quantum wells heterostructure is selectively released from the hosting substrate. Periodic oscillations due to whispering-gallery modes resonance were found superimposed on photoluminescence spectra even at low optical excitation power. With increasing pumping power density, the microtube is characterized by a stimulated emission with a threshold as low as 415 kW/cm². Such emission shows predominant TM polarization parallel to the microtube axis.