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A wide-narrow well design for understanding the efficiency droop in InGaN/GaN light-emitting diodes K. Ding, Y.P. Zeng, X.C.Wei, Z.C. Li, J.X. Wang, H.X. Lu, P.P. Cong, X.Y. Yi, G.H.Wang，J.M. Li APPLIED PHYSICS B-LASERS AND OPTICS J.K. Lee Outline Introduction Experiment and Results Discussions Conclusion References Introduction A major problem that hinders the application of InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes (LED) is the so-called “efficiency droop”. Experiment P ITO GaN:Mg 150 nm MQW 4 period In0.16Ga0.84N N GaN:Si 3μm buffer Sapphire Chip Size ： 500 * 2500 μm2 Experiment 5 nm 12 nm 3 nm 12 nm 12 nm 3 nm 3 nm 1.5 nm Fig. 1 Schematic diagram of the wide-narrow-well MQWs LED. The thicknesses of the wide wells and barriers are 3 and 12 nm, and the thicknesses of the narrow well and barrier are 1.5 and 5 nm. Experiment and Results RT 15K 15K時會有些許藍移， 在低溫時因為載子的移 動率下降，不容易移動 較容易侷限住、而載子 會 開 始 堆 積 、 像 band filling effect狀況。所以 會有些許的藍移出現。 Fig. 2 EL spectra of the wide-narrow-well MQWs LED at RT (a) and at 15 K (b). Experiment and Results Experiment and Results RT 15K Fig. 3 Integrated EL intensity and normalized relative EQE as functions of current density for the narrow and wide wells from multi-Gaussian peak fitting at RT (a, b) and at 15 K (c, d). Discussions Efficiency droop : 1. high density of threading dislocations 2. misfit defects 3. capture of delocalized carriers 4. effective mass of holes in GaN 5. carrier leakage Resolve: 1. With thinner QBs must be due to an enhanced hole distribution 2. lower carrier density in the QWs 3. subsequently a reduced Auger nonradiative recombination Conclusion Increasing the thickness of the QWs will reduce the droop, since the carrier density is reduced. But at the same time making the QWs too thick will also reduce the overall luminescence efficiency. Thus, other approaches improving the hole injection such as thin QBs or low indium containing InGaN barriers may reduce the efficiency droop. References Ding K, Zeng YP, Wei XC, Li ZC, Wang JX, Lu HX, Cong PP, Yi XY, Wang GH, Li JM, “A wide-narrow well design for understanding the efficiency droop in InGaN/GaN light-emitting diodes,” APPLIED PHYSICS B-LASERS AND OPTICS, Vol. 97, pp465-468, OCT 2009.