Review—Active Efficiency as a Key Parameter for Understanding the Efficiency Droop in InGaN-Based Light-Emitting Diodes

Abstract

In this paper, we aim to understand the interrelationships between current, voltage, radiant power, and eventually, the power efficiency (PE) of InGaN-based blue light-emitting diodes (LEDs) at high injection currents. For this purpose, we first summarize the terms and definitions of various LED efficiencies. It is essential to measure each efficiency to understand the physics behind the LED operation and improve the device performance further. Here, we show how to measure various LED efficiencies with physically measurable quantities of the radiant power, current, voltage, and spectrum of the LED device. Both the internal quantum efficiency (IQE) and the voltage efficiency (VE) are interrelated with the carrier recombination processes. The newly introduced active efficiency (AE) captures the effects of the active-layer quality on the IQE and the VE simultaneously. A novel method of measuring the IQE just at room temperature, so-called the room-temperature reference-point method, enables the measurement of the IQEs of many LED chips, highlighting the importance of the AE. Using the experimental IQE curve, it is possible to separate the total injection current into the radiative and nonradiative recombination currents. A trade-off relationship between the IQE and the VE and its common origins are revealed by this approach. © The Author(s) 2019. Published by ECS..