title: Coherent vertical beaming using Bragg mirrors for high-efficiency GaN light-emitting diodes.
abstract: We propose a dielectric Bragg mirror that utilizes coherent coupling with multiple quantum wells (MQWs) to significantly enhance light extraction from GaN light-emitting diode (LED). Full vectorial electromagnetic simulation showed that, under constructive interference conditions, the Bragg mirror consisting of two dielectric (SiO(2)/TiO(2)) stacks and a silver layer led to >30% enhancement in light extraction, as compared to a single silver mirror. Such significant enhancement by a pre-designed Bragg/metal mirror was ascribed to the vertically oriented radiation pattern and reduced plasmonic metal loss. In addition, the gap distance between the MQWs and a Bragg mirror at which the constructive interference takes place could be controlled by modulating the thickness of the first low-refractive-index layer. Moreover, a two-dimensional periodic pattern was incorporated into an upper GaN layer with the designed Bragg mirror and it was shown that a lattice constant of ~800 nm was optimal for light extraction. We believe that tailoring the radiation profile of light emitters by coherent coupling with designed high-reflectivity mirrors will be a promising route to overcome the efficiency limit of current semiconductor LED devices.
authors.affiliation: Department of Applied Physics, Kyung Hee University, Gyeonggi-do 446-701, South Korea.
authors.forename: Sun-Kyung
authors.initials: SK
authors.lastname: Kim
authors.forename: Hong-Gyu
authors.initials: HG
authors.lastname: Park
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005708:Gallium / Q000737:chemistry*; D007909:Lenses; D008029:Lighting / Q000295:instrumentation*; D012031:Refractometry / Q000295:instrumentation*; D012666:Semiconductors
chemical_list: C473348:gallium nitride; D005708:Gallium