In recent years, some methods or techniques that improve and increase the optical output intensity of LEDs have been published from many researches, including backside reflector, bettering the quality of emitting layers, lattice-match problems, and so on. One of effectively enhancing optical output intensity is coating reflector on the backside of the LED. In this thesis, the photonic crystal properties of colloidal crystal as the reflector are used to increase optical output intensity of GaN-based blue light LEDs. In order to understand the optical properties of colloidal crystal, the photonic band structure of fcc structure has been simulated by plane wave expansion (PWE) method due to colloidal spheres can close-packed themselves to fcc structure, and the calculated reflectivity spectrums of colloidal crystal with the different layers by using finite-difference time-domain simulated method. Then to the process for colloidal crystal, the optimum measured reflectivity spectrums can reach ~78% through tuning the temperature of hotplate and diameter size of o-ring, and compared with the simulated results. Then compared and combined the reflectivity of colloidal crystal with Al film, the highest measured reflectivity of the hybrid reflector (colloidal crystal + Al film) can reach ~94%. Finally we use colloidal crystal, Al film, and the hybrid reflector as the backside reflector of GaN-based blue light LEDs to increase optical output intensity, as compared to the GaN-based LEDs without reflector. The optical output enhancements of GaN-based LEDs with colloidal crystal and Al film at 20 mA current injection are around 120 ~ 140%, even the enhancement of LEDs with the hybrid reflector can reach 200 ~ 250% approximately. it was found that the optical output enhancement of GaN-based blue light LEDs with the colloidal crystal is close to the LEDs with Al film, combined these two reflector to form the hybrid reflector can increase much more optical intensity of GaN-based blue light LEDs as compared to only colloidal crystal or Al film.

近年來，許多文獻中關於LED光強度增加及相關品質改善之技術屢見不鮮，包括在LED背部鍍上反射鏡、改善發光層的品質、晶格匹配的問題…等，其中一種能有效增強LED光強度的技術就是在LED背面鍍上反射鏡。本論文裡，我們利用膠體晶體(colloidal crystal)的光子晶體(photonic crystal)特性作為反射鏡來提升氮化鎵型藍光LED的光輸出強度。實驗步驟主要分為兩個部份，首先從模擬過程中瞭解膠體晶體的光學特性，利用平面波展開(PWE)法來計算面心立方體(fcc)的光子能帶圖，是因為膠體小球會自組式排列成面心立方的結構，接著藉由有限差分時域(FDTD)法來模擬膠體晶體在不同層數的反射率。另一部份是製程方面，藉由加熱盤的溫度和o-ring的直徑大小為變數來成長膠體晶體，最佳化的反射率大約78%，然後和模擬比較結果。接著將膠體晶體與鋁鏡(Al film)作比較和結合，發現混合反射鏡(hybrid reflector)的反射率可以高達約94%。最後把膠體晶體、鋁鏡和混合反射鏡均鍍在氮化鎵型的藍光LEDs上，在輸入電流20mA下，以膠體晶體和鋁鏡為反射鏡的LEDs的光輸出強度提升率(optical output enhancement)約在120%至140%，甚至是有混合反射鏡的LEDs的光輸出提升率可以高達約200%到250%左右。這可以發現以膠體晶體為反射鏡的LEDs，光輸出提升率接近於以鋁鏡為反射鏡的LEDs，若結合這兩種反射鏡來形成混合反射鏡則可以增加更多的LEDs光輸出提升率。

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