多邊形AlGaInP紅光發光二極體之研究

Abstract

本論文研究多邊形發光二極體之結構設計對光電特性的影響，當光在二維模式下， 入射角於何種範圍會造成全反射的發生，來探討出光的差異性 。以此方法簡易的分析， 結果顯示三角形會有最佳的出光。將此概念應用在 AlGaInP LED 上，我們期待在光性上 會有相似的趨勢, 此研究分為兩部分，首先透過模擬分析多邊形發光二極體之結構設計， 第二部分製作及探討多邊形發光二極體元件之光電特性。 第一部分，在模擬中我們設定了簡單的 LED 結構，分析 6 種圓形 LED 的光萃取效率。 由模擬結果可以得知，由於材料與空氣的折射率差異，對光萃取造成明顯的影響，但三 角形 LED 有最好的光萃取效率。進一步利用三種方法提升光萃取效率，第一種是增加 LED N 層厚度(8μm)，第二種是將 LED 側壁傾斜(30 度)，第三種是 LED 表面粗化，由結果得 知，表面粗化對光萃取效率有最佳的提升，且傾斜側壁又比增加 N 層厚度對光萃取效率 提升有效。 第二部分是實驗，我們設計了 3 種尺寸的晶粒(chip)分別是 16mil，22mil，31mil， 利用平臺蝕刻 (mesa etching) 製作出圖形化，並分別使用兩種蝕刻方式進而形成不同傾 斜程度的側壁，第一種是乾濕刻的感應耦合電漿離子蝕刻(ICP)，會造成不傾斜的側壁， 第二種是濕蝕刻，會造成傾斜的側壁。由實驗結果得知，ICP 較可以精準地控制 mesa 的形狀，所以有較好的光電特性。以 16mil 晶粒為例，ICP 蝕刻的三角形 mesa 在電流 10mA 下 η E ~16%且在電流 190mA 下效率下降約 54.4%。ICP 蝕刻的三角形平臺在電流 190mA 出光通量比傳統四邊形平臺多了 3.5%。且所有元件中，晶粒 22mil，ICP 蝕刻的 三角形平臺在電流 30mA 有最好的光電轉換效率(wall-plug efficiency)17.3% 。

In this thesis, we analyzed the structural design of polygonal LED which affected the optical & electrical properties. when the light in the two-dimensional mode, the range of incident angle(θ i ) for the TIR(total internal reflection) for the photons, further to exploration the difference of light output. By this simple analysis, triangle had the best light output. By application of this concept on the AlGaInP LED, we expected the optical properties had similar trend to this concept. First, we set up a simple LED structure in the simulation, then light extraction of 6 graphic LEDs were analyzed. From simulation result, the output flux was affected by the great difference of indices between semiconductor material and air. We use three methods to further enhance the light extraction efficiency of LEDs, for example, thicker n layer, inclined sidewall, rough surface. The result showed LED with rough surface had the greatest enhancement of extraction efficiency. And LED with inclined sidewall had superior enhancement of the extraction efficiency than the LED with thicker n layer Second was experiment. We designed three chip size including 16mil, 22mil and 31mil. We used the process of mesa etching to make graphic mesas including two methods in accordance with the different inclination of the side wall. Respectively, Inductively Coupled iv

Plasma etching made sidewall no inclined, and Wet etching made sidewall inclined. From experimental results, the mesa by ICP etching had better optical & electrical properties. For example, the wall-plug efficiency of triangular mesa was 16% at 10mA, and wall-plug efficiency droop was 54.4% at 190mA under 16mil chip. The triangular mesa had better output flux the tradition-quadrangular mesa by 3.5% under 16mil chip. In all devices, the triangular mesa had the best wall-plug efficiency 17.3% at 30mA under 22mil chip.