Size-Dependent Quantum Efficiency of Flip-Chip Light-Emitting Diodes at High Current Injection Conditions

Xingfei Zhang,Zhenlin Miao,Jinmin Li,Yiyun Zhang,Meng Liang,Zhicong Li,Guohong Wang,Yan Li,Xiaoyan Yi

doi:10.3390/photonics8040088

Abstract

Versatile applications call for InGaN-based light-emitting diodes (LEDs) to operate at ultra-high current densities with high quantum efficiency. In this work, we investigated the size-dependent effects of the electrical and optical performance of LEDs as increasing the current density up to 100 A/cm2, which demonstrated that mini-strip flip-chip LEDs were superior option to achieve better performance. In detail, at a current density of 100 A/cm2, the light output power density of these mini-strip LEDs was improved by about 6.1 W/cm2, leading to an improvement in the wall-plug efficiency by 4.23%, while the operating temperature was reduced by 11.3 °C, as compared with the large-sized LEDs. This could be attributed to the increase in the sidewall light extraction, alleviated current crowding effect, and improved heat dissipation. This work suggests an array of mini-strip LEDs would provide an option in achieving higher luminescent efficiency at ultrahigh current injection conditions for various applications.

Highlights

InGaN-based light-emitting diodes (LEDs) have emerged as vital building blocks in widespread applications like solid-state lighting [1,2,3], displays [4,5,6,7], and visible light communications [8,9,10]
Our results show that mini-strip LEDs exhibit more uniform light emission, greater light emission power density, higher wall-plug efficiency (WPE), and lower junction temperature, which suggests the use of mini-strip LED arrays as light sources would provide an option for achieving high quantum efficiency, which is more suitable especially at high current injection conditions
The epitaxial layers for the mini-strip LEDs in this study were grown on 4-inch patterned sapphire substrates (PSS) by MOCVD, with an emission wavelength centered at ~450 nm

Summary

Introduction

InGaN-based light-emitting diodes (LEDs) have emerged as vital building blocks in widespread applications like solid-state lighting [1,2,3], displays [4,5,6,7], and visible light communications [8,9,10]. This technical route has certain drawbacks, in which the yield and the costs during the production are the leading ones, as the sapphire substrates need to be removed by a laser lift-off process that would induce damages to the thin-films transferred Another technical route is to use ultra-large mesa thin-film LEDs (usually in several mm scale), which aims to push the working current density to the lower end, where the droop effect could be significantly alleviated, in order to achieve higher quantum efficiency even at high current injection conditions [33,34]. Our results show that mini-strip LEDs exhibit more uniform light emission, greater light emission power density, higher wall-plug efficiency (WPE), and lower junction temperature, which suggests the use of mini-strip LED arrays as light sources would provide an option for achieving high quantum efficiency, which is more suitable especially at high current injection conditions

Experiment

Discussion

Conclusions