短波紫外光氮化鋁鎵發光二極體中的載子傳輸與量子效率之數值模擬探討

The Simulation of Carrier Transport and Quantum Efficiency in Ultra-Violet Band-C AlGaN-Based Light Emitting Diode

陳弘翔(Hung-Hsiang Chen)

指導教授 ： 吳育任

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201803021

摘要

短波紫外光發光二極體日漸變成重要的光源，可以廣泛用在殺菌等用途。在這篇研究中，我們使用三維模擬軟體去研究合金擾動對於載子傳輸和量子效率的影響。我們知道由於短波紫外光發光二極體的結構全是由氮化鋁鎵合金所構成，這使得合金擾動的問題更加嚴重。我們發現，合金的擾動使得位能也跟隨出現擾動。這直接地讓量子障和電子阻擋層的阻擋能力下降，然後造成大量的載子外溢問題。同時，位能擾動也導致量子井的載子局限能力衰弱，讓電子可以擴散到周圍的量子障中，並發出較強的TM 光。不僅如此，在有鎂摻雜的區域中，我們發現鎂提供了額外的能階，使得載子有較短的壽命並放傾向發出非複合發光。此外，擴散到量子障中的載子，亦會放出較多的非複合發光。我們也透過計算k.p 理論，發現合金擾動不只影響了量子效率，也導致了TM 偏振光的增強。
另外，為了解決p 型氮化鎵的吸光問題，我們也對p 型氮化鋁鎵的超晶格結構做了研究，並嘗試以此取代p 型氮化鎵。相較於純氮化鎵電洞傳導層，p 型氮化鋁鎵的超晶格結構提供了較好的出光效率。而跟p 型純氮化鋁鎵相比，超晶格結構擁有較低的阻抗。我們利用二維的柏松－飄移方程式和蒙地卡羅光跡法去分別研究紫外光發光二極體的電性和光性。結果顯示p 型超晶格結構能有效的減少吸光量。此外，我們在p 型超晶格結構中，於其底部添加粗糙的表面來改善出光。總結而言，p 型氮化鋁鎵的超晶格結構是個改善元件效能的選項之一。

關鍵字

短波紫外光發光二極體 ； 合金擾動 ； 量子井 ； 量子效率 ； 超 晶格結構 ； 氮化鎵 ； 氮化鋁鎵

並列摘要

Ultra-violet band-C light emitting diodes (UVC-LEDs) becomes an important light sources for sterilization. To understand the limiting factor for the efficiency of UVC LEDs, we applied 3D simulation tools to understand the influence of random alloys to the carrier transport and efficiency. UVCLEDs face stronger alloy fluctuation effects since the whole structure is made by AlGaN alloy. Due to potential fluctuation caused by alloy fluctuation, the quantum barrier and the electron blocking layer have a weak blocking ability. It leads to a stronger carrier overflow. In addition, carriers in the quantum well has a poor confinement, which leads carriers diffusing to the quantum barrier and a stronger TM polarized light emission. Besides, carriers in the Mg doped region has a shorter nonradiative lifetime, and the carrier leakage into QB may also lead to a stronger nonradiative recombination. Further calculation using k.p method shows that TM polarization will be enhanced under the fluctuated potential.
Besides the modeling of random alloys, we also work on p-type AlGaN super lattice structures to understand its potential to replace the p-GaN hole transportation layer. The p-type AlGaN super lattice (p-SL)structure could provide a higher light extraction efficiency (LEE) than the p-GaN hole transport layer and with a lower contact resistance than the p-AlGaN hole transport layer. We studied the electrical property of UVC-LEDs by solving 2D Poisson and drift-diffusion solver and the optical property by Monte Carlo ray-tracing solver. The result shows that p-type SL will reduce the light absorption. The patterned rough surface in the emitting plane will improve the light extraction especially in the condition without the p-GaN layer. In conclusion, the p-type AlGaN SL could be a possible solution to improve the device performance.

並列關鍵字

UVC-LED ； alloy fluctuation ； multiple quantum well ； quantum efficiency ； super lattice structure ； GaN ； AlGaN

參考文獻

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