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Omnidirectional Reflector with Total Internal Reflective Interface for Light Extraction Enhancement of Solid‐State Light Source
Author(s) -
Yamae Kazuyuki,
Fukshima Hiroshi,
Fujimoto Kozo
Publication year - 2019
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201700775
Subject(s) - reflector (photography) , materials science , optics , optoelectronics , light emitting diode , total internal reflection , wavelength , refractive index , layer (electronics) , diode , light source , physics , composite material
Light extraction efficiency is key to the performance of solid‐state light sources such as the light‐emitting diode. The reflectance of the bottom mirror has a significant impact on the light extraction efficiency because a large difference in the refractive index between the light source and air leads to multiple internal reflections and optical loss. Therefore, efficiency can be drastically improved with even a slight increase in the bottom mirror reflectance. This paper focuses on wide angular light incidences. An omnidirectional reflector (ODR) is then designed that included a low‐index thick layer (MgF 2 ), a pair of quarter‐wavelength‐thick layers (Ta 2 O 5 /MgF 2 ), and a metal layer (Ag) on a solid‐state light source with n = 2.4. The first thick layer works as a perfect reflector for wide angular and broadband incident light since total internal reflection (TIR) occurs at the interface. In the simulations, the angular integrated reflectance for our designed reflector (TI‐ODR) reaches 99.7%. The reflectance is higher than the typical ODR that is composed of a quarter‐wavelength‐thick layer and Ag (98.6%) or an Ag reflector alone (97.9%). The TI‐ODR is then fabricated onto a gallium nitride (GaN)‐based light‐emitting diode and obtained a light extraction efficiency enhancement factor of approximately 1.1.