Analysis of light extraction efficiency enhancement for thin-film-flip-chip InGaN quantum wells light-emitting diodes with GaN micro-domes

Peng Zhao,Hongping Zhao

doi:10.1364/oe.20.00a765

Abstract

The enhancement of light extraction efficiency for thin-film flip-chip (TFFC) InGaN quantum wells (QWs) light-emitting diodes (LEDs) with GaN micro-domes on n-GaN layer was studied. The light extraction efficiency of TFFC InGaN QWs LEDs with GaN micro-domes were calculated and compared to that of the conventional TFFC InGaN QWs LEDs with flat surface. The three dimensional finite difference time domain (3D-FDTD) method was used to calculate the light extraction efficiency for the InGaN QWs LEDs emitting at 460nm and 550 nm, respectively. The effects of the GaN micro-dome feature size and the p-GaN layer thickness on the light extraction efficiency were studied systematically. Studies indicate that the p-GaN layer thickness is critical for optimizing the TFFC LED light extraction efficiency. Significant enhancement of the light extraction efficiency (2.5-2.7 times for λ(peak) = 460nm and 2.7-2.8 times for λ(peak) = 550nm) is achievable from TFFC InGaN QWs LEDs with optimized GaN micro-dome diameter and height.

Highlights

As the promising candidate for the generation lighting technology, light-emitting diodes (LEDs) play an important role in solid state lighting [1,2,3,4]
Major challenges still exist for high performance InGaN quantum wells (QWs) LEDs, including 1) the existence of the spontaneous and piezoelectric polarizations in the III-nitride semiconductor materials [5] leads to the charge separation in the QWs, resulting in low radiative recombination rate of electrons and holes, and 2) low light extraction efficiency in InGaN QWs LEDs due to the total internal reflection at the semiconductor-air or semiconductor-encapsulant interface
We studied the light extraction efficiency for the thin film flip-chip (TFFC) LEDs based on three-dimensional finite difference time domain (3D-FDTD) method

Summary

Introduction

As the promising candidate for the generation lighting technology, light-emitting diodes (LEDs) play an important role in solid state lighting [1,2,3,4]. Several approaches have been proposed for enhancing the light extraction efficiency of III-nitride LEDs, including surface roughness [26, 27], photonic crystal [28], patterned sapphire substrate [29], nanopyramids [30], graded refractive index material [31] and SiO2/polystyrene microlens arrays [32, 33]. Potential issues such as non-uniformity, high cost, limited efficiency enhancement, material degradation and reliability are still required to be addressed in these approaches. Received 26 Jun 2012; revised 23 Aug 2012; accepted 27 Aug 2012; published 7 Sep 2012 10 September 2012 / Vol 20, No S5 / OPTICS EXPRESS A767

TFFC InGaN QWs LEDs with GaN micro-domes

Results and discussions

Conclusion