Zheng Jinjian, Li Shuiqing, Chou Chilun, Lin Wei, Xun Feilin, Guo Fei, Zheng Tongchang, Li Shuping, Kang Junyong
Department of Physics, OSED, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Xiamen University, Xiamen, 361005, China.
San'an Optoelectronics Co., Ltd., Xiamen, 361005, China.
Sci Rep. 2015 Dec 4;5:17227. doi: 10.1038/srep17227.
Light-emitting diode (LED) efficiency has attracted considerable interest because of the extended use of solid-state lighting. Owing to lack of direct measurement, identification of the reasons for efficiency droop has been restricted. A direct measurement technique is developed in this work for characterization of biaxial stress in GaN-based blue LEDs under electrical injection. The Raman shift of the GaN E2 mode evidently decreases by 4.4 cm(-1) as the driving current on GaN-based LEDs increases to 700 mA. Biaxial compressive stress is released initially and biaxial tensile stress builds up as the current increases with respect to the value of stress-free GaN. First-principles calculations reveal that electron accumulation is responsible for the stress variation in InxGa1-xN/GaN quantum wells, and then reduces the transition probability among quantum levels. This behavior is consistent with the measured current-dependent external quantum efficiency. The rule of biaxial stress-dependent efficiency is further validated by controlling the biaxial stress of GaN-based LEDs with different sapphire substrate thicknesses. This work provides a method for direct observation of the biaxial stress effect on efficiency droop in LEDs under electrical injection.
由于固态照明的广泛应用，发光二极管（LED）的效率引起了人们的极大关注。由于缺乏直接测量方法，对效率下降原因的识别受到了限制。在这项工作中，开发了一种直接测量技术，用于表征电注入下基于GaN的蓝色LED中的双轴应力。随着基于GaN的LED驱动电流增加到700 mA，GaN E2模式的拉曼位移明显下降了4.4 cm⁻¹。随着电流相对于无应力GaN的值增加，双轴压应力最初释放，双轴拉应力逐渐形成。第一性原理计算表明，电子积累是InxGa1-xN/GaN量子阱中应力变化的原因，进而降低了量子能级之间的跃迁概率。这种行为与测量的电流相关外部量子效率一致。通过控制不同蓝宝石衬底厚度的基于GaN的LED的双轴应力，进一步验证了双轴应力相关效率的规律。这项工作提供了一种直接观察电注入下双轴应力对LED效率下降影响的方法。
