氮化鎵發光二極體在固態照明中有許多重要應用已逐漸被重視。發光二極體由於電流分佈不均造成其晶片發光效率降低與熱能產生。此電流分佈不均的情形稱為電流擁塞，將影響晶片可靠度及光輸出的損耗。為了進一步了解晶片內部發光層電流擴散行為，本研究使用有限元素法建立數值模擬模型以計算發光二極體空間電流分佈。 為了達到發光二極體電流均勻性，須盡可能得讓晶片內部縱向擴散電流增加，而讓橫向擴散電流減少。在本研究中，使用數值模擬的方式針對各種不同形狀的n-電極進行了電流擴散分析比較。當n-電極迴圈圖案面積越小，其晶片電流均勻性較佳。晶片上不同的探針數目與位置均會影響電流分佈。另一方面，本模擬結果與實際製程比對，有一致性之趨勢，其模擬與實驗比對之準確率達90%。藉由垂直結構LED實際案例，在本研究中當目字型的n-電極圖案距離晶片邊緣為125μm長度時可以有0.2V的壓降改善，其晶片的活化區電流密度模擬結果與發光強度有一致性分佈。在有無電流阻障層之電流擴散效應分析，當有電流阻障層可明顯地使其效率增加。 GaN-based light-emitting diodes have attracted much attention due to their great applications to solid-state lighting. The non-uniform current spreading, which locally produces the light emission and the heat generation in the light-emitting diodes. It was reported that the non-uniform current spreading, the so-called current crowding effect, was strongly related to chip reliability in addition to local light emission. To further understand the current spreading behavior in the active region, a finite element method was used to simulate the electrical characteristic and current distribution of a GaN-based LEDs device in the study. It can be known that uniform current spreading can be achieved, the vertical current should be minimized, but the spreading current maximized. In this study, we designed several different shapes of n-electrode patterns in light emitting diodes, analyzed quantitatively the current spreading by numerical simulation method. At first, the current uniformity increases as the area inside n-electrode loop becomes small. The difference in the quantity and position of probe in the chips also affect current distribution. In second, simulation and experimental results for different n-electrode showed quite similar tendencies. Simulation results are accurate more than 90%.For real cases of vertical LEDs, the driving voltage for the distance 125μm between n-electrode patterns of 目 type and chip edge design considered in our thesis can be markedly reduced to around 0.2V. We obtained a good agreement between the measured light intensity distribution emitted from the surface of a fabricated device and that calculated with our current density distribution in the active layer of LED chip. In the other part of this thesis, comparison of some cases clearly shows that the use of the current blocking layer enhances the efficiency significantly.
