Disentangling the impact of point defect density and carrier localisation enhanced Auger recombination on efficiency droop in (In,Ga)N/GaN quantum wells

Rachel Barrett, Joshua Mcmahon, Ruben Ahumada-Lazo, Juan Arturo Alanis, Patrick Parkinson, Stefan Schulz, Menno J. Kappers, Rachel A. Oliver, David Binks

Research output: Contribution to journalArticlepeer-review


The internal quantum efficiency of (In,Ga)N/GaN quantum wells can surpass 90% for blue-emitting structures at moderate drive current densities but drops significantly for longer emission wavelengths and at higher rates of excitation. This latter effect is known as efficiency ‘droop’ and limits the brightness of light-emitting diodes (LEDs) based on such quantum wells. Several mechanisms have been proposed to explain efficiency droop including Auger recombination, both intrinsic and defect-assisted, carrier escape and the saturation of localised states. However, it remains unclear which of these mechanisms is most important because it has proven difficult to reconcile theoretical calculations of droop with measurements. Here, we first present experimental photoluminescence measurements extending over three orders of magnitude of excitation for three samples grown at different temperatures that indicate that droop behaviour is not dependent on the point defect density in the quantum wells studied. Secondly, we use an atomistic tight-binding electronic structure model to calculate localisation-enhanced radiative and Auger rates and show that both the corresponding carrier density dependent internal quantum efficiency and the carrier density decay dynamics are in excellent agreement with our experimental measurements. Moreover, we show that point defect density, Auger recombination and the effect of the polarisation field on recombination rates only limit the peak internal quantum efficiency to about 70% in the resonantly-excited green-emitting quantum wells studied. This suggests that factors external to the quantum wells, such as carrier injection efficiency and homogeneity, contribute appreciably to the significantly lower peak external quantum efficiency of green LEDs.
Original languageEnglish
JournalACS Photonics
Publication statusAccepted/In press - 5 Jul 2023


  • InGaN, efficiency droop
  • Auger recombination
  • localisation
  • point defect density
  • light-emitting diode


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