本論文利用有機金屬氣相磊晶(metal-organic vapor phase epitaxy, MOVPE)系統再成長倒置（p-side down）電極之氮化鎵系列發光二極體作相關研究。在元件特性方面，p-side down發光二極體之導通電壓偏大 ( > 4V) ，是由於高電阻的p型氮化鎵及p型氮化鋁鎵導致元件串聯電阻(series resistance) 過大 ( > 40 Ω)。由於電流擁擠(current crowding)效應的緣故使得電流注入效率不易，造成外部量子效率過低。此外，運用於p-side down發光二極體之上的透明導電層 (transparent conducting layer, TCL) 僅佔元件總面積的22%，與傳統 n-side down發光二極體其透明導電層將近78% 的覆蓋率相比差異極大，影響橫向電流散佈，造成發光效率不佳。另ㄧ方面，在發光二極體表面觀察到六角形缺陷造成漏電流路徑，導致元件在逆向偏壓20V時其漏電流為mA數量級，因電流注入效率不佳而影響到內部量子使得元件發光效率不高。因此，如何有效減少漏電流以及改善在p型氮化鎵層電流散佈不均問題，將是未來p-side down LEDs發展重點。

In this study, the p-side down GaN-based light emitting diodes (LEDs) were grown by metal-organic vapor phase epitaxy (MOVPE). These p-side down LEDs exhibited high operating voltage ( > 4V) and low efficiency. The high operating voltage could be attributed to the fact that high resistivity of p-GaN and p-AlGaN leads to high series resistance (> 40 Ω). In addition, the low external quantum efficiency (EQE) could be due to the severe current crowding effect and hence a poor injection efficiency of current. The covering percentage of transparent conducting layer (TCL) on p-side down and n-side down LEDs are 22% and 78% of the total device area, respectively. This covering rate of TCL influences the lateral current spreading. On the other hand, the leakage current under 20 V reverse bias could be as high as tens mA where the leakge path might be the hexagonal pyramid pits observed on the LEDs’ surfaces. The high leakage current would lead to a poor injection efficiency of current, thereby reducing internal QE. In addition to the fabrication and characterization of the p-side down LEDs, how to reduce leakage current and improve the current spreading in p-layer were also discussed in this thesis.

第一章
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