1. 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

2. Outline Introduction Introduction Simulation Simulation Experiment Experiment Conclusion Conclusion

3. 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.

4. Simulation 模擬能帶結構圖 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.

5. Simulation 模擬結果 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.

6. Experiment 實驗結果 : EL & PL data 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.

7. 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 p- GaN was found to be important to realize high efficiency AlGaN-free LEDs.

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