A Review on Experimental Measurements for Understanding Efficiency Droop in InGaN-Based Light-Emitting Diodes

Abstract

Efficiency droop in GaN-based light emitting diodes (LEDs) under high injection current density perplexes the development of high-power solid-state lighting. Although the relevant study has lasted for about 10 years, its mechanism is still not thoroughly clear, and consequently its solution is also unsatisfactory up to now. Some emerging applications, e.g., high-speed visible light communication, requiring LED working under extremely high current density, makes the influence of efficiency droop become more serious. This paper reviews the experimental measurements on LED to explain the origins of droop in recent years, especially some new results reported after 2013. Particularly, the carrier lifetime of LED is analyzed intensively and its effects on LED droop behaviors are uncovered. Finally, possible solutions to overcome LED droop are discussed.

Evaluation of Light Extraction Efficiency of GaN-Based Nanorod Light-Emitting Diodes by Averaging over Source Positions and Polarizations

“…For example, the emission efficiency of blue LEDs decreases significantly with increasing injection current. This "efficiency droop" phenomenon results in limited light output power at high current densities [6][7][8][9]. In addition, the EQE of GaN-based yellow-green LEDs with emission wavelengths from 530 to 600 nm has been reported to be <30%, which has been termed the "green gap" problem [10][11][12].…”

Abnormal Stranski–Krastanov Mode Growth of Green InGaN Quantum Dots: Morphology, Optical Properties, and Applications in Light-Emitting Devices

“…GaN-based light-emitting devices suffer from two obstacles for a long time. One is the “green gap” ,, and the other is the “droop” issue (the “droop” refers to the phenomenon that the efficiency of InGaN QW LEDs deteriorates dramatically as the injection current increases, for which one of the most widely known reasons is the leakage current). , In traditional c-plane long-wavelength InGaN QWs, strong polarization field causes severe QCSE effect which seriously constrains the IQE. In addition, high crystal quality epitaxy for high In-component InGaN QWs has always been a major road blocker.…”

Progress in External Quantum Efficiency for III‐Nitride Based Deep Ultraviolet Light‐Emitting Diodes

“…Therefore, the semipolar or the nonpolar AlGaN/AlGaN quantum well structures provide another design freedom to high‐efficiency DUV LEDs. Methods for suppressing the QCSE have been reported for InGaN/GaN visible LEDs, and we believe most of the approaches are also doable for DUV LEDs. However, when designing nonpolar and semipolar AlGaN based active region, one shall avoid using the p‐AlGaN/p‐GaN hole injection layer.…”