title: Bridging the "green gap" of LEDs: giant light output enhancement and directional control of LEDs via embedded nano-void photonic crystals.
abstract: 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.
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw and Computer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia. jrhau.he@kaust.edu.sa.
authors.forename: Yu-Lin
authors.initials: YL
authors.lastname: Tsai
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw.
authors.forename: Che-Yu
authors.initials: CY
authors.lastname: Liu
authors.affiliation: School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK.
authors.forename: Chirenjeevi
authors.initials: C
authors.lastname: Krishnan
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw.
authors.forename: Da-Wei
authors.initials: DW
authors.lastname: Lin
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw.
authors.forename: You-Chen
authors.initials: YC
authors.lastname: Chu
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw.
authors.forename: Tzu-Pei
authors.initials: TP
authors.lastname: Chen
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw.
authors.forename: Tien-Lin
authors.initials: TL
authors.lastname: Shen
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw.
authors.forename: Tsung-Sheng
authors.initials: TS
authors.lastname: Kao
authors.affiliation: School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK.
authors.forename: Martin D B
authors.initials: MD
authors.lastname: Charlton
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw.
authors.forename: Peichen
authors.initials: P
authors.lastname: Yu
authors.affiliation: Institute of Photonic System, National Chiao Tung University, Tainan 711, Taiwan, Republic of China. chienchunglin@faculty.nctu.edu.tw.
authors.forename: Chien-Chung
authors.initials: CC
authors.lastname: Lin
authors.affiliation: Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China. hckuo@faculty.nctu.edu.tw.
authors.forename: Hao-Chung
authors.initials: HC
authors.lastname: Kuo
authors.affiliation: Computer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia. jrhau.he@kaust.edu.sa.
authors.forename: Jr-Hau
authors.initials: JH
authors.lastname: He