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Efficiency and Electron Leakage Characteristics in
GaN-Based Light-Emitting Diodes Without AlGaN
Electron-Blocking-Layer Structures
Han-Youl Ryu, Jong-In Shim, Member, IEEE, Cheol-Hoi Kim,
Jin Hyoung Choi, Hyun Min Jung, Min-Soo Noh,
Jong-Moo Lee, and Eun-Soo Nam
IEEE PHOTONICS TECHNOLOGY LETTERS, VOL.
23, NO. 24, DECEMBER 15, 2011
報告者: T.Y. Huang
Outline
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Introduction
Simulation
Experiment
Conclusion
Introduction
The authors investigate efficiency and electron
leakage characteristics in GaN-based light-emitting diodes (LEDs)
without AlGaN electron-blocking-layer (EBL) structures.
Both simulation and electroluminescence (EL) measurement
results show that the internal quantum efficiency decreases
rapidly as the thickness of an undoped GaN interlayer between
active layers and a p-GaN layer increases, which is caused by
electron leakage from active layers to the p-GaN due to inefficient
hole injection.
However, photoluminescence (PL) measurement results show that
the quality of active layers deteriorates as the interlayer thickness
decreases. The EL and PL results imply that the optimization of
the undoped GaN interlayer thickness is important for achieving
high internal quantum efficiency in AlGaN-EBL-free LEDs.
Simulation
• 模擬能帶結構圖
Schematic diagram of the conduction band profile in the AlGaN-EBLfree
LED layer structure near the active region. Here, the thickness of an undoped
GaN (u-GaN) interlayer is varied in simulations and experiments.
Simulation
• 模擬結果
(a) Simulation result of internal
quantum efficiency (IQE) curves for
the interlayer thickness from 10 to 50
nm.
(b) Simulation result of electron current
density distribution at active layers, the
u-GaN, and the p-GaN layer when the
current density is 30 A cm .
Experiment
• 實驗結果: EL & PL data
EL efficiency normalized to the peak
value of LED B is shown as a function
of current for LED A, B, and C.
PL efficiency normalized to the peak
value of LED C is shown as a function of
LD pump power for LED A, B, and C.
Conclusion
We investigated the effect of the u-GaN interlayer between active
layers and the p-GaN layer on EL and PL efficiency characteristics in
the AlGaN-EBL-free LED structures.
The LED with a thick u-GaN interlayer showed greatly reduced EL
efficiency, which was attributed to large electron leakage from active
layers to the p-GaN by the poor hole injection.
This EL efficiency characteristic was also supported by device
simulations. On the contrary, the PL efficiency for the LED with a thick
GaN interlayer was higher than that with thin one possibly due to
reduced Mg diffusion into MQW layers.
Good control of the undoped layer thickness between MQWs and the pGaN was found to be important to realize high efficiency AlGaN-free
LEDs.
Thanks for your attention