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GaN-based light-emitting diodes suffer from high-current loss mechanisms that lead to a significant decrease in internal quantum efficiency at high drive currents. This phenomenon, known as "efficiency droop," is a major problem for solid-state lighting applications, in which light-emitting diodes are driven at high currents to deliver large optical powers. Although substantial effort has been invested to uncover the physical origin and mitigate the effects of efficiency droop, there is still a lack of consensus on the dominant mechanism responsible. In this article, we review several mechanisms that have been proposed as explanations of efficiency droop, including junction heating, carrier delocalization, Auger recombination, and electron leakage from the active region. In addition, device structures intended to mitigate the droop-causing mechanism – (i) thick quantum wellsl, (ii) enhanced hole-injection efficiency structures, and (iii) polarization-matched active region – are discussed.

The efficiency droop in GaInN/GaN blue light-emitting diodes (LEDs) usually commences at current density around 10 A/cm² and the efficiency decreases monotonically after the droop onset. GaN-based LEDs suffer seriously, at typical operating current densities (10–100 A/cm²), by the efficiency droop. Efficiency re-climbing is observed in the typical droop regime at cryogenic temperatures below 125K. The “efficiency re-climbing” coincides with a distinct increase in device conductivity, which is mainly attributed to an enhancement in p-type conductivity due to field ionization of acceptors. The “efficiency re-climbing” phenomenon implies an approach of solving efficiency droop by enhancing hole injection by external electric field.

A new model for efficiency droop in InGaN/GaN light-emitting diodes (LEDs) is proposed, where the primary nonradiative recombination mechanisms, including Shockley–Read–Hall (SRH), Auger and carrier leakage, are considered. A room-temperature external quantum efficiency (EQE) measurement was performed on our designed samples and analyzed by the new model. Owing to advantages over the common “$ABC+f(n)$ model”, the “new model” is able to effectively extract recombination coefficients and calculate the leakage currents of the hole and electron. From this new model, we also found that hole leakage is distinct at low injection, while it disappears at high injection, which is contributed to the weak blocking effect of electron in quantum wells (QWs) at low injection.