隨著發光二極體的晶片尺寸及輸入電流越來越大，此時發光層的電流分佈將明顯影響著整個晶片的光特性、電特性、及封裝散熱的效果。爲了更進ㄧ步了解LED晶片中發光層的電流擴散狀況，我們利用三維數值模擬的方式來進行目前氮化鎵發光二極體晶粒之電場模擬與電流擴散分析，以期提供未來相關研究人員在LED晶片設計上所需要的趨勢分析及參考依據。 從簡單的二維分析可知，側向形式的LED中，在p-GaN與發光層中的電流流向是垂直的，而電流擴散層與n-GaN層中的電流流向是水平的。因此，發光層中的電流會集中在p電極或n電極端，主要決定於電流擴散層與n-GaN層的阻值匹配的效果。同時，發光層中的電流分佈也會明顯影響LED晶片之取光效率及起始電壓值。 在三維實例分析方面，藉由side-view形式LED之適當p極及n極的電極佈置，在本論文討論的例子中，我們可以得到約有13 %的改善(0.45 V的壓降)。並且可知此LED型式之p電極圖形的改變對於電流分佈及壓降的改善會比n電極圖形的改變有較大的影響。另ㄧ方面，具有電流堵塞層的vertical 型式的LED也是被分析的，在這樣的例子中，可知LED晶片中的熱效應是應該被考慮進來及更為明顯的。 When the chip size of light emitting diodes (LEDs) and the input power become larger, current spreading in the active layer will obviously affect the optical, electrical, and thermal packaging performances of the LED chip. To further understand the current spreading behavior in the active layer, we use a three-dimensional numerical simulation to analyze the electrical characteristic and current distribution of a GaN LEDs device. The results and trends found could serve as useful references for researchers focusing on the design of an LED chip. Employing two-dimensional analysis, in lateral configuration LEDs, the current flows vertically in the p-GaN and active layers, and horizontally in the spreading and n-GaN layers. Therefore, that the current crowding in the active layer would be generated at p- or n-electrodes is mainly dependent on the effect of resistance match between the spreading and n-GaN layers. In addition, the current distribution in the active layer can also obviously affect light extraction efficiency (LEE) and driving voltage. Using three-dimensional analysis, for real cases of side-view LEDs, the driving voltage for the well-designed p- and n-electrode patterns considered in our study can be markedly reduced to around 0.45 V, which corresponds to about 13% decrease in magnitude. The influence of the change in p-electrode pattern on current spreading and voltage drop is more significant than that made by altering the n-electrode pattern for this type of LED. On the other hand, the vertical LEDs with a current blocking layer are also analyzed, it shows that thermal effect in the LED chip should be taken into account and is more obvious in such cases.
