title: Direct Observation of the Biaxial Stress Effect on Efficiency Droop in GaN-based Light-emitting Diode under Electrical Injection.
abstract: 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.
authors.affiliation: 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.
authors.forename: Jinjian
authors.initials: J
authors.lastname: Zheng
authors.affiliation: San'an Optoelectronics Co., Ltd., Xiamen, 361005, China.
authors.forename: Shuiqing
authors.initials: S
authors.lastname: Li
authors.affiliation: San'an Optoelectronics Co., Ltd., Xiamen, 361005, China.
authors.forename: Chilun
authors.initials: C
authors.lastname: Chou
authors.affiliation: Department of Physics, OSED, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Xiamen University, Xiamen, 361005, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Lin
authors.affiliation: San'an Optoelectronics Co., Ltd., Xiamen, 361005, China.
authors.forename: Feilin
authors.initials: F
authors.lastname: Xun
authors.affiliation: Department of Physics, OSED, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Xiamen University, Xiamen, 361005, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Guo
authors.affiliation: Department of Physics, OSED, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Xiamen University, Xiamen, 361005, China.
authors.forename: Tongchang
authors.initials: T
authors.lastname: Zheng
authors.affiliation: Department of Physics, OSED, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Xiamen University, Xiamen, 361005, China.
authors.forename: Shuping
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Physics, OSED, Fujian Provincial Key Laboratory of Semiconductor Materials and Applications, Xiamen University, Xiamen, 361005, China.
authors.forename: Junyong
authors.initials: J
authors.lastname: Kang