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Enhancement in Light Extraction Efficiency of AlGaInP Light-Emitting Diodes (Amber)
Pattern with mirror
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|摘要:||發光二極體的亮度由其輻射發光效率(Radiant Efficiency)決定，而輻射發光效率為內部量子效率(Internal Quantum Efficiency)與外部量子效率(External Quantum Efficiency)兩者的乘積。一般而言，具有多重雙異質量子井結構且成膜品質良好之發光二極體，其內部量子效率已可達99%，但截至目前，外部量子效率卻仍很難超過10%。本論文探討提升磷化鋁銦鎵(AlGaInP)發光二極體外部量子效率之可能方法，包含窗口層粗化及反射鏡圖案化；而圖案化部分又區分為無序粗糙化、有序陣列化、以及傳統平面反射鏡等。實驗數據顯示，經窗口層粗化及反射鏡圖案化處理後之發光二極體，其光強度的角度分佈相較於窗口未粗化且為平面反射鏡之傳統發光二極體會有減小12°至增大14°不等的半高全寬角度變化。在輻射發光效率方面，窗口層粗化並搭配平面反射鏡可使輻射發光效率之統計平均值提升為傳統發光二極體的1.45倍，但窗口層粗化並搭配圖案化反射鏡之發光效率最多只能提升至1.38倍。由此結果得知，反射鏡的圖案化確能改變外部量子效率，惟本實驗所使用的圖案對增加發光二極體的輻射發光效率並無助益，其原因可能為尚未找到最優化的幾何圖案或蝕刻減損了圖案的表面平整度造成光子被漫射並受困於晶粒中而被吸收。若能進一步藉由理論模擬並設計製作出最優化且表面平整之幾何圖案，發光二極體的輻射發光效率應有機會獲得提升。|
The brightness of a LED is determined by its radiant efficiency, i.e. the multiplication of the internal quantum efficiency and the external quantum efficiency. Even though the internal quantum efficiency of high quality LEDs with double hetero junction can reach as high as 99%, it is still very difficult to achieve an external quantum efficiency higher than 10%. This thesis studies the potential methods for increasing the external quantum efficiency of LEDs, including the roughening of the window layer and applying various patterns on the mirror layer; the patterns applied on the mirror layer are disordered roughening, ordered array, and regular flat surfaces, respectively. The experimental data show that the light emitting angle measured in full width half maximum (FWHM) of these specially-treated AlGaInP LEDs can vary from 12 reduction to 14 enhancement as compared to that of the traditional LEDs with flat window layer and flat mirror. The statistically averaged radiant efficiency of LEDs with rough window layer and flat mirror is 1.45 times that of traditional LEDs. However, the statistically-averaged radiant efficiency of LEDs with rough window layer and patterned mirror can only reach up to 1.38 times that of traditional LEDs. These results demonstrate that the patterned mirror can indeed change the radiant efficiency, but the patterns used in this study are not effective enough to increase the LED radiant efficiency. This might be due to the facts that an optimal mirror pattern has not been found or the itching process has reduced the mirror surface flatness, causing diffused scattering, trapping and absorption of the photons within the LEDs. If an optimal and higher quality patterned mirror can be designed and fabricated with the assistance of theoretical simulations, it should be possible to raise the radiant efficiency of LEDs.
|Appears in Collections:||精密工程研究所|
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