本論文中，我們提出兩項關於氮化鎵(GaN)系發光二極體(LEDs)之電流分佈性質的改善方法及製程，量測並深入討論其光電特性之改善結果，另外，並針對磷化鋁鎵銦(AlGaInP)材料系統為基礎的的發光二極體，提出改進其電流分佈性質之有效方法及製程，並深入討論其光電特性之改善結果。
於氮化鎵發光二極體的研究中，首先我們提出以直接歐姆接觸在p型氮化鎵層與氧化銦錫(ITO)界面的製程方法。此研究是利用金(Au)金屬藉由熱退火和蝕刻過程，使其金顆粒在p型氮化鎵表面形成具金屬特性之接觸層，且由於熱退火和蝕刻的過程使得p型氮化鎵表面的鎵(Ga)空缺變多，以至於p型氮化鎵表面的電洞濃度提升，因此在p型氮化鎵層與氧化銦錫透明導電層界面可能會有能帶窄化效應或是穿隧效應的產生。在電性和光性的分析中，我們可以發現順向導通電壓下降且輸出功率明顯提升。另外，在可靠度的分析中，在電流為20毫安培測試下，光衰退的趨勢和未經過金熱退火處理過程所製作出來的元件是一樣的，因此二極體的結構在經過熱退火和蝕刻過程後並未被破壞或是改變。
之後，我們利用階梯型(stair-like)氧化銦錫電流擴散層和p型電流擴散電極(在傳統圓形電極兩旁各拉出一條分支線的電極)來增加電流分佈的面積，此階梯型結構可利用其厚度的差異而造成不同電阻的特性，來提升發光層邊緣流入的電流量，再利用電流走最短路徑之特性，使得流入發光層邊緣的電流直接注入到主動層，減少電流流向電極下方的區域，也因此增加了電流分佈的區域。在電性和光性的分析中，我們可以發現順向導通電壓有明顯的下降，且輸出功率提升也非常明顯。外部量子效率在導通電流(20毫安培)和高電流下皆有明顯的提升。最後，在可靠度分析中，在電流為20毫安培測試下，元件的可靠度衰減程度亦不明顯。
另外，本文並針對磷化鋁鎵銦(AlGaInP)材料為基礎的的發光二極體做電流分佈之研究。我們研究不同種類表面歐姆接觸層對氧化銦錫透明導電層於磷化鎵窗層上的影響，研究發現經由碳摻雜磷化鎵歐姆接觸層相較於習知p型砷化鎵歐姆接觸層，於20毫安培操作下，元件輸出功率可提升11%。

In this thesis, two approaches related to how to promote the current spreading effect and process method improved for GaN-based light-emitting diodes (LEDs) are presented and discussed. In addition, the approach relate to how to promote the current spreading effect and process method improved for AlGaInP-based LEDs are also investigated and discussed.
In respect of research on GaN-based LEDs, we have proposed a good and direct Ohmic contact between ITO and p-type GaN by Au diffused process. After the Au diffused process, the Au atoms layer is exhibited on the surface of p-type GaN. The gallium vacancies are also increased, resulting in an increased free acceptors concentration and reduced resistivity on the p-GaN surface. Therefore, the high hole concentration and formation of metallic surface on the p-GaN surface may result in bandgap narrowing or tunneling effects at p-GaN/ITO interface. It is found that the turn-on voltage and light output power are improved of our studied LED. In addition, the brightness reliability of our studied LED is found to be comparable to the conventional LED.
Then, we increase the current spreading area by using the stair-like ITO transparent layer and current spreading electrode (the circular electrode with two branches). we adjust a uniform ITO current-spreading layer into the stair-like structure where each step exhibits different series resistance, so that the whole current-spreading area could be improved. In addition, the stair-like structure also helps blocking current. We can find out the light output power is significantly increased of our studied LED. Our studied LED also shows 25% improvement on EQE at 20 mA and over 40% enhancement at a higher current region, as compared with conventional LED does. Moreover, the brightness reliability of our studied LED is found to be comparable to the conventional LED.
Finally, we investigated the effect of different Ohmic contact layer structure applied to ITO-assisted on GaP window layer of AlGaInP LEDs. By selecting the C-doped GaP layer as Ohmic contact layer, the light-output power is significantly increased by a factor of 11% than conventional p-GaAs contact layer structure under DC 20-mA operation.

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