Abstract
Step graded-refractive index (SGRI)
(ZnO)<sub><i>x</i></sub>(SiO<sub>2</sub>)<sub>1-<i>x</i></sub> micropillar
multilayers have been introduced and demonstrated on GaN-based LEDs combined with the
mesh ITO. The SGRI (ZnO)<sub><i>x</i></sub>(SiO<sub>2</sub>)<sub>1-<i>x</i></sub> micropillars were
produced by controlling the Zn/Zn+Si ratio of co-sputtered
ZnO and SiO<sub>2</sub>. The introduced three-layered SGRI
(ZnO)<sub><i>x</i></sub>(SiO<sub>2</sub>)<sub>1-<i>x</i></sub> micropillars improved both critical angle
inside GaN LEDs and Fresnel transmittance coefficient (<i>η</i><sub>Fr</sub>) as well as had
better light coupling into the micropillars. Moreover, a high number of layers of the
SGRI micropillars would aid the light coupled in the pillars to escape from the side
wall of the pillar. LEDs with three-layered SGRI
(ZnO)<sub><i>x</i></sub>(SiO<sub>2</sub>)<sub>1-<i>x</i></sub> micropillars exhibited output power
enhancements of 12.2% with a 20 mA <i>V<sub>f</sub></i> of 3.19 V. The output power of the mesh
ITO LEDs with SGRI (ZnO)<sub><i>x</i></sub>(SiO<sub>2</sub>)<sub>1-<i>x</i></sub> micropillars was further
enhanced to 15.3% by improving the current spreading.
© 2012 IEEE
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