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16 February 2009 Reduction of efficiency droop in InGaN-based blue LEDs
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We have investigated the efficiency droop in InGaN based multiple-quantum light-emitting diodes (MQWs-LEDs) and double hetero-structure light-emitting diodes (DH-LEDs) by changing the barrier (both thickness and barrier height) within quantum wells. Our results show that for MQW-LEDs, with the decrease of barrier width from 12nm In0.01Ga0.99N to 3nm In0.01Ga0.99N, the external quantum efficiency (EQE) droop point is increased from 350 Acm-2 to >1000 Acm-2, and the slope of EQE drop is also greatly reduced. When the barrier height of the MQW-LEDs is decreased, i.e. barriers changed from In0.01Ga0.99N (3nm) to In0.06Ga0.94N (3nm), the EL intensity is reduced to half. In the case of DH-LEDs, 6nm DH-LED shows the highest EL intensity and no EQE droop up to 1000 Acm-2. When the active region of the DHLED is increased from 6nm to 12nm, the electroluminescence (EL) intensity is reduced to 70% of that of the 6nm DHLED, and the EQE shows negligible droop compared to the 6nm DH-LED due to both enhanced hole injection and reduced electron overflow. These results suggest that heavy effective mass of holes and low hole injection efficiency (due to relatively lower p-doping) leading to severe electron leakage are responsible for the efficiency droop.
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X. Ni, X. Li, J. Xie, Q. Fan, R. Shimada, Ü. Özgür, and H. Morkoç "Reduction of efficiency droop in InGaN-based blue LEDs", Proc. SPIE 7216, Gallium Nitride Materials and Devices IV, 72161W (16 February 2009); doi: 10.1117/12.809877;

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