Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China.
School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK.
Nanoscale. 2016 Jan 14;8(2):1192-9. doi: 10.1039/c5nr05555e.
Green LEDs do not show the same level of performance as their blue and red cousins, greatly hindering the solid-state lighting development, which is the so-called "green gap". In this work, nano-void photonic crystals (NVPCs) were fabricated to embed within the GaN/InGaN green LEDs by using epitaxial lateral overgrowth (ELO) and nano-sphere lithography techniques. The NVPCs act as an efficient scattering back-reflector to outcouple the guided and downward photons, which not only boost the light extraction efficiency of LEDs with an enhancement of 78% but also collimate the view angle of LEDs from 131.5° to 114.0°. This could be because of the highly scattering nature of NVPCs which reduce the interference giving rise to Fabry-Perot resonance. Moreover, due to the threading dislocation suppression and strain relief by the NVPCs, the internal quantum efficiency was increased by 25% and droop behavior was reduced from 37.4% to 25.9%. The enhancement of light output power can be achieved as high as 151% at a driving current of 350 mA. Giant light output enhancement and directional control via NVPCs point the way towards a promising avenue of solid-state lighting.
绿光 LED 的性能不如其蓝色和红色同类产品，这极大地阻碍了固态照明的发展，这就是所谓的“绿光差距”。在这项工作中，通过外延侧向过生长（ELO）和纳米球光刻技术，在 GaN/InGaN 绿光 LED 中制造了纳米空穴光子晶体（NVPCs）。NVPCs 充当有效的散射背反射器，将导光和向下的光子取出，这不仅将 LED 的光提取效率提高了 78%，而且将 LED 的视角从 131.5°准直到 114.0°。这可能是因为 NVPCs 的高度散射性质减少了干涉，从而产生了法布里-珀罗共振。此外，由于 NVPCs 抑制了位错和缓解了应变，内部量子效率提高了 25%，下降行为从 37.4%降低到 25.9%。在 350 mA 的驱动电流下，光输出功率的增强可高达 151%。通过 NVPCs 实现的巨大光输出增强和方向控制为固态照明开辟了一条有前途的途径。
