Technologies | Light Generation | Light Extraction | LEDs | Flip-Chip LED | SSL-Research | Oct 25, 2019

Chinese Researchers Propose Method to Overcome Low Efficiency of High-Power Flip-Chip LEDs

Chinese scientists from different research centers recently published a co-authored paper on "Highly Efficient GaN-based High-Power Flip-Chip LEDs" in Optics Express Vol. 27, Issue 12, pp. A669-A692 (2019)under the terms of the OSA Open Access Publishing Agreement. High-power flip-chip light-emitting diodes (FCLEDs) suffer from low efficiencies because of poor p-type reflective ohmic contact and severe current crowding, they propose an improvement by using an Ag film.


In this paper, the authors show that it is possible to improve both the light extraction efficiency (LEE) and current spreading of an FCLED by incorporating a highly reflective metallic reflector made from silver (Ag). The reflector, which consists of an Ag film covered by three pairs of TiW/Pt multilayers, demonstrates high reflectance of 95.0% at 460 nm at arbitrary angles of incidence.

The numerical simulation and experimental results reveal that the FCLED with Ag-based reflector exhibits higher LEE and better current spreading than the FCLED with indium-tin oxide (ITO)/distributed Bragg reflector (DBR). As a result, the external quantum efficiency (EQE) of FCLED with Ag-based reflector was 6.0% higher than that of FCLED with ITO/DBR at 750 mA injection current.

The work also suggests that the EQE of FCLED with the Ag-based reflector could be further enhanced 5.2% by replacing the finger-like n-electrodes with three-dimensional (3D) vias n-electrodes, which spread the injection current uniformly over the entire light-emitting active region. This study paves the way towards higher-performance LED technology.


The originl paper is published and under copyright of © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement and can be downloaded at


Shengjun Zhou, Xingtong Liu, Han Yan, Zhiwen Chen, Yingce Liu, and Sheng Liu, "Highly efficient GaN-based high-power flip-chip light-emitting diodes," Opt. Express 27, A669-A692 (2019)