改善電洞傳導行為緩解Ⅲ族氮化物發光二極體效率下降特性之研究

Abstract

本論文中，我們針對為傳統氮化銦鎵發光二極體的磊晶結構進行改良，改善電洞傳導行為以緩解三族氮化物發光二極體效率隨外加電流提高而驟降之問題。 第一部分設計漸變鋁含量的氮化鋁鎵電子阻擋層，期待除了強化阻檔電子溢流外，更可增加電洞注入效率，藉以提升主動層載子複合發光效率，在以理論分析找得最佳化設計後，實作樣品利用電激發螢光(Electroluminescence, EL)量測，驗證其發光強度確實相較於使用傳統電子阻擋層之元件為佳，並且緩解了發光效率在高電流會產生效率驟降的情況。 再者，我們在使用氮化銦鎵作為主動層量子井的紫外光(UV) LED中，將位能障材料氮化鋁鎵替換成氮化鋁鎵銦，量測證實其與三元材料晶格常數和能隙相近的四元材料，有較好的磊晶品質外，EL量測結果也顯示其突出的電特性與發光效率。由於四元材料可以經由調整鋁和銦的含量而自由變動其晶格常數、能隙、應力、和載子侷限效果，因此在藉由理論模擬分析後，我們推論使用氮化鋁鎵銦作為位能障，可以提高量子井中電子的侷限、電洞的傳導與載子的遷移率，因而改善LED效率驟降的問題。

In this thesis, we designed the epitaxial structure of InGaN light-emitting diodes (LEDs) to improve the transportation of holes, which leads to reduction of efficiency droop. We first degined a graded-composition electron blocking layer (GEBL) for c-plane InGaN/GaN LEDs. The simulation results demonstrated that such GEBL can effectively enhance the capability of hole transportation across the EBL as well as the electron confinement. Consequently, the LED with GEBL grown by metal-organic chemical vapor deposition exhibited lower forward voltage and series resistance, and much higher output power at high current density, as compared to conventional LED. Second, we demonstrated InGaN-based UV LEDs with AlGaN and InAlGaN barrier. EL results indicate that the light output performance could be enhanced effectively when replacing the conventional AlGaN barriers by InAlGaN barriers. Furthermore, from numerical analysis, it is believed that InGaN/AlInGaN MQWs exhibit higher radiative recombination rate and low efficiency droop at a high injection current because of the better band-offset ratio and the higher hole mobility, which leads to the uniform distribution of holes in the active region.