圖案化藍寶石基板對氮化鎵發光二極體發光效率影響之探討

Abstract

對於發光二極體(LED)來說,會影響光萃取效率的兩個最重要因素為全反射效應和材料本身的吸收.我們希望設計LED的結構減少這兩個效應的影響進而提升其效率.我們用Tracepro軟體,去分析各種不同的圖案化藍寶石基板(PSS) LED. 我們先建最基本的flat LED和圓錐型PSS LED的模型,從多重量子井提供100瓦,1000條亂數方向的光在LED內部追蹤,之後再外面設一個圓球型的檢測器(detector).並分為上半球,下半球來收LED的出光,進而算出光萃取效率. 我們從這flat LED和圓錐型PSS LED,先做效率的探討.可以發現,PSS在效率上遠高於flat LED,這是因為全反射的效應被減少的影響.因為各層折射率不同的關係,可能只有部份角度的入射光,可以克服折射率不同所造成的全反射效應並出光.但是在PSS LED,比較不容易受到限制因此出光量也會跟著變多. 接著,我們改變各種不同的PSS間距,高度,和形狀.當間距越小的時候,效率會越好,高度越高,效率也有變好的趨勢,接著在設計半球型還有其他形狀的PSS LED,可以發現半球型比原本圓錐型的PSS還要有更好的發光效率,因為光線會遇到的角度變多.之後再做一些奈米等級的p-GaN粗糙化,這個改變可以直接對p-GaN有更多的出光路徑改善一些全反射的問題進而直接提升LED的效率.最後再分析皇冠型的PSS LED,比對於同樣等級的圓錐型LED 的出光影響. 可以得知,皇冠型的PSS的出光,比一般圓錐型的PSS 佳.

For a common LED, two most important reasons to influence the light extraction efficiency are the effect of total internal reflection and material absorption. We hope we can design an LED chip to reduce those two factors to enhance light extraction efficiency. We use the Tracepro software to analyze different pattern sapphire substrate(PSS) design to increase light extraction efficiency. We build a model of flat LED and cone shape PSS LED. We give a flux of 100 watt with 1000 rays in random direction to trace in the LED. We use two hemisphere detectors to separately measure upper and lower power output of LED to study the light extraction efficiency. We analyze the model we built of flat LED and PSS LED first. We can see that, the PSS structure have enhanced the light extraction efficiency than flat LED. It is the elimination of total internal reflection. Then, we change different kinds of PSS in space, height, and shape. We also study the absorption of GaN to light extraction efficiency. When the spacing is smaller, the efficiency is higher. The efficiency have a trend to be higher when the height is higher. The light output power of dome shape PSS LED is better than cone shape. We also design the LED chip with p-GaN nano roughness. The LED with p-GaN roughness can also enhance the light extraction efficiency. At last, we design a crown shape PSS LED We can see that the crown-shape LED is better in efficiency than cone shape with same height, width, and space.