Improved Light Extraction Efficiency of Nonpolar a-Plane GaN-Based LEDs Based on Embedded Pyramid-Shape Air-Gap Structure

Author

Park, M.J. ; Hwang, S.J. ; Kim, H.J. ; Jung, Sanghyuk ; Bang, K.H. ; Kim, H.G. ; Chang, Yuan-Chih ; Choi, Yang-Kyu ; Kwak, Joon Seop

Author_Institution

Dept. of Printed Electron. Eng., Sunchon Nat. Univ., Sunchon, South Korea

Volume

9

Issue

5

fYear

2013

fDate

May-13

Firstpage

346

Lastpage

352

Abstract

A significant improvement of output power and external quantum efficiency (EQE) for nonpolar a-plane (11-20) GaN light-emitting diodes (LEDs) on r-plane sapphire substrates has been demonstrated by using embedded pyramid-shape air-gap arrays on hexagonally patterned SiO₂ layer. The air-gap structure was realized based on asymmetrical growth behavior of a-plane epitaxial lateral overgrowth (ELO) GaN along +c-axis and -c-axis. The output power and EQE of the a-plane LEDs with the air-gaps on patterned SiO₂ have increased by more than 50% when compared to those of the conventional a-plane LEDs. Theoretical fit to the measured EQE suggested that the significant improvement of EQE was mainly attributed to the increase in light extraction efficiency (EXE). Light emission pattern analysis and ray-tracing simulation revealed that the air-gap arrays on top of patterned SiO₂ enlarged the guided-light scattering at the air-gap surface due to the significant refractive index contrast with the GaN layer, followed by the improvement of EXE of nonpolar a-plane LEDs.

Keywords

III-V semiconductors; air gaps; epitaxial growth; gallium compounds; light emitting diodes; refractive index; silicon compounds; ELO; EQE; EXE; GaN; SiO₂; a-plane epitaxial lateral overgrowth; asymmetrical growth behavior; embedded pyramid-shape air-gap structure; external quantum efficiency; light emission pattern analysis; light extraction efficiency; nonpolar a-plane light-emitting diode; nonpolar a-plane-based LED; r-plane sapphire substrates; ray-tracing simulation; refractive index contrast; Air gaps; Current measurement; Gallium nitride; Light emitting diodes; Power generation; Refractive index; Substrates; Air-gap; light extraction efficiency; light-emitting diode (LED); nonpolar a-plane GaN;

fLanguage

English

Journal_Title

Display Technology, Journal of

Publisher

ieee

ISSN

1551-319X

Type

jour

DOI

10.1109/JDT.2012.2225597

Filename

6416082