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標題: 提升氮化鎵系列外部量子效率之研究
Improvement in external quantum efficiency of GaN-based LEDs
作者: 楊喬智
Yang, Chiao-Chih
關鍵字: GaN;氮化鎵;Surface texture;ITO;Polystyrene sphere;表面粗化;氧化銦錫;聚苯乙稀
出版社: 精密工程研究所
本論文將研究藉由表面粗化提升氮化鎵(GaN)發光二極體出光機率,進而增加發光二極體外部量子效率。因為在傳統的氮化鎵發光二極體,當光在內部產生的發光效率及射出至外部的發光效率有顯著的差異,其中差異是由於光是由高折射率介質的半導體介質GaN(n ~ 2.5)射出至外部低折射率之空氣介質(n ~ 1),即造成光在出射時之臨界角小。在本論文中我們探討選用不同高穿透率(氧化銦錫(ITO)、氧化矽、Polyimide、光阻1、光阻2)薄膜做為發光二極體之出光窗口及蝕刻層。再將聚苯乙烯小球塗佈在此層薄膜表面並使用感應式電漿蝕刻系統(ICP)對此層進行蝕刻,經由控制乾蝕刻時間、及蝕刻功率將對此薄膜表面粗糙之情形進行探討。
最後量測元件之光電特性及封裝後之出輸功率及以掃描式電子顯顯鏡及原子力顯微鏡圖證明實驗中粗糙之表面將對光出射機率增加。在最佳蝕刻條件下,ITO表面粗糙度可達143 nm,此時所使用之聚苯乙烯小球大小(250 nm ~ 300 nm)經由量測原始ITO/GaN發光二極體及表面粗糙之ITO/GaN發光二極體之輸出功率@20 mA下分別為7 mW及9.1 mW,可得粗化的表面可使輸出功率增加30 %,且同理可證外部量子效率亦增約30 %。

In this thesis, we use surface-textured to increase light extraction to improve the external quantum efficiency of GaN-based LEDs . There is a significant gap between the internal and external efficiencies of conventional GaN light-emitting diodes (LEDs). The reason for this shortfall is the narrow escape cone for light in high refractive index GaN (n~2.5) to the air (n~1). In this paper, we choose five transparent film (ITO, SiO2, Polyimide, Photoresist 1, Photoresist 2) as the ITO/GaN LEDs widow layers and etching layers. Then we drop polystyrene spheres (PS) as the ICP etching mask under different etching time and etching power. Finally, we use SEM and AFM analyze the film's surface and measure the optic-electrical characteristic.
Under optimum etching conditions, the surface roughness of the ITO film can reach 140 nm while the polystyrene sphere on the textured ITO surface is maintained at about 250-300 nm in diameter. The output power of the ITO/GaN LED with and without surface texturing is respectively 9.1, and 7 mW at 20 mA. The LEDs fabricated using the surface-textured ITO produced an output power that exceeded that of the planar-surface LED by about 30 % at 20 mA. Also prove the light extraction increase about 30 %.
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