We review recent advances in the understanding of the green gap phenomenon, the drastic reduction of quantum efficiency of c-plane InGaN/GaN light-emitting diodes (LEDs) towards the green spectral region. In particular, we have decoupled the contributions of Shockley-Read-Hall recombination, quantum-confined Stark effect and hole localization in the random alloy. We show that the latter, significantly increasing with Indium content, plays a crucial role in the reduction of efficiency, as localized holes do not only possess lower overlap with delocalized electrons in the quantum well, but also appear to enhance Auger recombination.
For our study we use an electro-optical pump and probe scheme, which is most suitable to obtain differential carrier lifetimes in device operating conditions. In combination with conventional pulsed electroluminescence measurements, the internal quantum efficiency and recombination rates of the different processes can be determined. Temperature-dependent analyses then allow to assign recombination losses to the different underlying limitations (i.e. random alloying, polarity, defect density).
 F. Nippert et al., Japanese Journal of Applied Physics 55, 05FJ01 (2016)
 F. Nippert et al., Applied Physics Letters 109, 161103 (2016)
Felix Nippert, Sergey Yu. Karpov, Markus R. Wagner, Gordon Callsen, Thomas Kure, Bastian Galler, Hans-Jürgen Lugauer, Martin Strassburg, and Axel Hoffmann, "Carrier localization in InGaN-based light-emitting diodes (Conference Presentation)," Proc. SPIE 10554, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXII, 105540D (Presented at SPIE OPTO: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2292437.5751488554001.
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