應用一維光子晶體的阻抗匹配增加發光二極體的發光效率

Abstract

在本論文中，我們首先由波動觀點來探討光正向及斜向入射至多層介質其等效折射率的變化，也由阻抗匹配的概念解釋說明可調式濾波器穿透頻率的漂移。此外我們利用一維光子晶體具有光子禁帶的特性以及等效阻抗的觀念來設計發光二極體(LED)在照明應用上所需的寬頻寬及寬角度的全內反射鏡，藉由此全內反射鏡將LED中向下發射至基板的損耗降到最低，進而提升發光效率。我們也藉由邊緣濾波器(edge filter)以及阻抗匹配(impedance match)觀念來設計一寬頻寬且寬角度的高穿透率結構，使得光可由發光層大量出射至空氣中，進而提升發光效率，在考慮LED有限大小的情況下，我們也以計算的方式估算了的出射效率及出光功率分布。

First, We discussed the variation of the effective refractive index for normal incidence and oblique incidence, and demonstrated the shift of transmission frequency for the tunable filter by the concept of impedance-matching. By the characteristic photonic band gap and the effective refractive index of photonic crystal, we also designed an omni-directional reflector (ODR) in LED for lighting applications, which has high reflection for broadband and wide incidence angle. With ODR, the loss in the substrate could be reduced so that the extraction efficiency could be improved. In addition, we used the edge filter and the concept of impedance-matching to design a high transmission structure for broadband and wide incidence angle. Therefore, light can extract from active layer through the high transmission structure to the air, so the extraction efficiency can be increased. To consider the finite size of LED, we theoretically calculated the extraction efficiency could increase to 74% with the high transmission structure.