(Invited) Spatially Resolved Study of the EQE Droop in InGaN QW LEDs: Interplay of Point Defects, Extended Defects, and Carrier Localization

Spatially-resolved electroluminescence (as a function of injection current) and spatially-resolved photoluminescence (as a function of excitation power) are used to investigate the external quantum efficiency (EQE) droop in InGaN QWs based blue LEDs. The spatially-resolved EL mapping allows us to study two most commonly observed but distinctly different droop behaviors on a single device, minimizing the ambiguity trying to compare independently fabricated devices. We conclude that the EQE ~ current curve reflects the interplay of three effects: nonradiative recombination through point defects, carrier localization due to either In composition or well width fluctuation, and nonradiative recombination of the extended defects, which is in fact common to various optoelectronic devices.[1] By comparing EL and PL mapping data, we show that individual singular sites exhibiting either particularly strong or weak emission in PL do not usually play any significant and direct role in the EQE droop. We introduce a two-level model that can capture the basic physical processes that dictate the EQE ~ current dependence and describe the whole operating range of the device from 0.01 – 100 A/cm².

[1] Y. Lin, Y. Zhang, Z. Q. Liu, L. Q. Su, J. H. Zhang, T. B. Wei, and Z. Chen, Appl. Phys. Lett. 101, 252103 (2012).

In collaboration with Yue Lin, Zhiqiang Liu, Liqin Su, Jihong Zhang, Tongbo Wei, and Zhong Chen.