圖案化二氧化矽奈米柱結構應用於氮化鎵發光二極體之研究

Efficiency enhancement of GaN-based Light Emitting Diode prepared on SiO2 nanorod patterned GaN template

李建勳(Chien-hsun Lee)

指導教授 ： 郭政煌

國立中央大學/理學院/照明與顯示科技研究所/碩士(2011年)

摘要

本論文主要研究以有機金屬氣相沉積機台(Organometallic Vapor Phase Epitaxy, OMVPE)成長氮化鎵發光二極體於微米與奈米尺度的圖案化二氧化矽於氮化鎵薄膜/藍寶石基板。實驗中探討微米與奈米尺度的圖案化二氧化矽對氮化鎵發光二極體的影響，因基板運用磊晶側向成長技術(Epitaxial Lateral Overgrowth；ELOG)，將能降低缺陷密度，且圖案化二氧化矽結構包覆於氮化鎵薄膜中，而二氧化矽之幾何結構與折射率的差異，增加了光被散射的機率，更進一步因奈米級圖樣化二氧化矽相較於微米級圖樣化二氧化矽有著較多的光散射中心，增強了發光二極體之光萃取率。
成長氮化鎵發光二極體在微米與奈米級圖樣化二氧化矽排列於氮化鎵薄膜(un-doped GaN )/藍寶石基板，以及氮化鎵薄膜(un-doped GaN )/藍寶石基板為實驗對照組。由光電特性量測結果顯示出，在操作電流 20 mA注入下，各自具有大約相同的順向偏壓3.4V，實驗對照組LED C1、微米級LED M1、奈米級LED N1的光輸出功率分別為3.53mW、4.37mW、5.02mW，而光輸出功率LED M1 與LED N1 相對於LED C1 元件各提升23 與42 %。
在二維光強度影像量測中，操作電流 100 mA注入下，可觀察到具有奈米與微米級圖樣化二氧化矽排列於氮化鎵薄膜/藍寶石基板皆優於氮化鎵薄膜/藍寶石基板。且光學顯微鏡下拍攝到氮化鎵發光二極體之奈米與微米級之條狀圖樣化二氧化矽排列形貌，呼應於二維光強度影像分佈，驗證了氮化鎵發光二極體基板上的圖案會增加光的折射和反射會提升元件的光取出效率。為了釐清光輸出功率的提高，以有限時域差分法（FDTD）分析模擬，研究光線在發光二極體的散射路徑。

關鍵字

氮化鎵 ； 二氧化矽奈米結構 ； 發光二極體

並列摘要

GaN have emerged as important semiconductor materials for light-emitting diodes (LEDs). However, It was well known that light-extraction efficiency (LEE) of LED is limited mainly by the large difference in refractive index between GaN film and the surrounding air. Since the refractive indexes of GaN and the air are 2.5 and 1. Critical angle is crucially important for the light extraction efficiency of LEDs. It has been shown that one can enhance light output by light scattering layer (e.g., patterned substrate.), photons generated in the active layer will have multiple opportunities to find the escape cone.
In the study, the LED device with the embedded micro-size SiO2 stripe was fabricated. We labeled the LED as LED M1. In order to clarify the light scattering in different scale, we fabricate the LED device with the embedded nano-size SiO2 nanorods stripe. We labeled the LED as LED N1. For comparison, convention LED was also prepared, we labeled as LED C1.
With 20 mA current injection, it was found that output power of LED C1, LED M1 and LED N1 was 3.15mW, 4.37 mW, and 5.07 mW, respectively. To clarify the enhancement in light output power, the finite-difference time-domain (FDTD) analysis is used to study the irradiance behavior of the proposed LED with SiO2 patterned structure. Shows the simulated light emission of proposed LED with SiO2 patterned structure. We can found in this figure, the photon density in nano-size structure was larger than micro-size structure. The result shows that nano sized structure could provide more light scattering center than micro size structure.
In conclusion, we can enhance the 20 mA LED output power by 42% from the LED N1 compared with the conventional LED. The increasing of light scattering centers could reduce the probability of photons restricted in GaN epitaxial layers.

並列關鍵字

GaN ； LED ； SiO2 nanorod patterned

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