The internal quantum efficiency (IQE) of InGaN/GaN quantum wells (QWs) can reach >90% at moderate current densities [1] but decreases significantly at higher excitation. Such behaviour is known as ‘droop’ and restricts LED efficiency for high brightness applications such as vehicle headlights. Intrinsic [2] and defect-assisted [3] Auger-Meitner recombination, and carrier escape [4] have each been proposed as the process underlying droop. It has also been suggested that the saturation of carrier localisation centres at large current densities enhances non-radiative recombination at defects due to the greater probability of delocalised carriers encountering them [5,6]. It has been challenging to establish which of these proposed mechanisms is most important due to the difficulty in accurately measuring carrier density experimentally and in calculating the effects of localisation. However, recent work [7] suggests that alloy-enhanced Auger-Meitner recombination is dominant at the high carrier densities at which droop is observed. This study extends the investigation by clarifying the role of the saturation of localisation centres in droop.

Power- and temperature-dependent photoluminescence spectroscopy was used to investigate how the saturation of localisation centres and emission efficiency are related in three InGaN/GaN QWs samples, grown to differ only in their point defect density. The saturation of localisation centres and the onset of droop occur was found to be produced by approximately the same carrier density. However, it was also found that as the carrier density was increased the relative contribution of defect-associated non-radiative recombination decreases. These results are explained using an atomistic model of recombination in InGaN/GaN QWs [7] which finds that radiative and Auger-Meitner recombination out-compete defect-related processes in the QW at the carrier densities required for saturation, indicating that the saturation of localisation centres does not significantly contribute to droop in these samples.

1.       Jpn J Appl Phys. 2013 May 31;52(8S):08JK09.

2.       J Appl Phys. 2013 Aug 21;114(7):071101

3.       Phys Rev Lett. 2013 Apr 25;110(17):177406

4.       Appl Phys Lett. 2009 Feb 23;94(8):081114

5.       Appl Phys Lett. 2007 Oct 29;91(18):181103

6.       J Appl Phys. 2008 Nov;104(9):093108

7.      ACS Photonics 2023, 10, 8, 2632–2640