Disentangling the Impact of Point Defect Density and Carrier Localization-Enhanced Auger Recombination on Efficiency Droop in (In,Ga)N/GaN Quantum Wells.
Disentangling the Impact of Point Defect Density and Carrier Localization-Enhanced Auger Recombination on Efficiency Droop in (In,Ga)N/GaN Quantum Wells.
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DOI：
10.1021/acsphotonics.3c00355
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发表时间：
2023-08-16
期刊：
影响因子：
7
通讯作者：
Binks, D.
中科院分区：
文献类型：
--
作者：
Barrett, R. M.;McMahon, J. M.;Ahumada-Lazo, R.;Alanis, J. A.;Parkinson, P.;Schulz, S.;Kappers, M. J.;Oliver, R. A.;Binks, D.
在中等驱动电流密度下，（In,Ga）N/GaN量子阱的内部量子效率可以超过90%，但在较长的发射波长和较高的激发速率下，量子效率显著降低。后一种效应被称为效率“下降”，它限制了基于这种量子阱的发光二极管（led）的亮度。人们提出了几种解释效率下降的机制，包括固有和缺陷辅助的俄歇复合、载流子逃逸和局域态饱和。然而，目前尚不清楚这些机制中哪一个是最重要的，因为事实证明很难使理论计算与测量相一致。在这里，我们首先提出了在不同温度下生长的三个样品的三个数量级激发的实验光致发光测量，表明下垂行为不依赖于所研究的量子阱中的点缺陷密度。其次，我们使用原子紧密结合电子结构模型计算了局域增强的辐射率和俄热率，并表明相应的载流子密度依赖的内部量子效率和载流子密度衰减动力学与我们的实验测量结果非常吻合。此外，我们还发现点缺陷密度、俄歇复合以及极化场对复合速率的影响只会将共振激发的绿色发射量子阱的峰值内量子效率限制在70%左右。这表明，量子阱的外部因素，如载流子注入效率和均匀性，对绿色led的峰值外部量子效率显著降低有明显的贡献。
The internal quantum efficiency of (In,Ga)N/GaN quantum wells can surpass 90% for blue-emitting structures at moderate drive current densities but decreases significantly for longer emission wavelengths and at higher excitation rates. This latter effect is known as efficiency “droop” and limits the brightness of light-emitting diodes (LEDs) based on such quantum wells. Several mechanisms have been proposed to explain efficiency droop including Auger recombination, both intrinsic and defect-assisted, carrier escape, and the saturation of localized states. However, it remains unclear which of these mechanisms is most important because it has proven difficult to reconcile theoretical calculations of droop with measurements. Here, we first present experimental photoluminescence measurements extending over three orders of magnitude of excitation for three samples grown at different temperatures that indicate that droop behavior is not dependent on the point defect density in the quantum wells studied. Second, we use an atomistic tight-binding electronic structure model to calculate localization-enhanced radiative and Auger rates and show that both the corresponding carrier density-dependent internal quantum efficiency and the carrier density decay dynamics are in excellent agreement with our experimental measurements. Moreover, we show that point defect density, Auger recombination, and the effect of the polarization field on recombination rates only limit the peak internal quantum efficiency to about 70% in the resonantly excited green-emitting quantum wells studied. This suggests that factors external to the quantum wells, such as carrier injection efficiency and homogeneity, contribute appreciably to the significantly lower peak external quantum efficiency of green LEDs.
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