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# ナノ凹凸構造によるLEDの光取り出し効率改善

## Abstract

Simulation of the improvement of light extraction efficiency of LED by nano-uneven structure was carried out by using the electromagnetic analysis software KeyFDTD. Compared to conventional incandescent light bulbs, LEDs are superior in terms of durability and luminous efficiency. The improvement of LED luminous efficiency includes internal quantum efficiency, which indicates the ratio of the number of photons generated in the LED to the current flowing through the LED, light out-coupling efficiency, which indicates the ratio of the generated light going out of the LED, and other improvements in the substrate, etc. A technique to improve the light out-coupling efficiency is to add sub-wavelength nanostructures to the surface of visible light. In this report, the FDTD method was applied to simulate the nano-uneven structure of multiple shapes and the improvement of the light out-coupling efficiency was confirmed.

## １. 解析概要

LEDの発光効率改善には内部量子効率、光の取り出し効率、その他基板等の改善の3つが挙げられている [1] 。光取り出し効率を向上させる技術にナノ構造を表面に付与する手法がある。本報告書ではナノ凹凸構造付与する場合と付与しない場合をFDTD 法によりシミュレートして比較し、ナノ凹凸構造による光取り出し効率の改善効果を報告する。

There are three types of improvements in the luminous efficiency of LEDs: internal quantum efficiency, light extraction efficiency, and other improvements such as the substrate [1]. One of the technologies to improve the light out-coupling efficiency is to add nanostructures to the surface. In this report, the FDTD method is simulated and compared with and without the nano-convex structure, and the effect of the nano-convex structure on the light out-coupling efficiency is reported.

## 2. 解析条件

Fig.1 Simulation model

## 3. 解析結果

3．解析結果 Fig2.に波長350～750nmにおける3形状のナノ凹凸構造による光取り出し効率の改善率を示す。各形状で改善率は最大約1.5倍、改善率のピーク波長は1倍で500nm、1.16倍で600nm、1.33倍で750nmであった。3形状の改善率ピーク波長におけるナノ凹凸構造断面部の電界分布をFig3～5.に示す。ナノ凹凸構造内の定在波は3形状で類似していることからナノ凹凸構造の形状、配置によりFig3～5.に類似した定在波となる周波数範囲で高い改善率を示すと考えられる。また、ナノ凹凸構造とピーク波長の比率の不一致は点源の位置が構造に比例していないため、点源から界面までの距離を比例させることで異なるピーク波長を示すと考えられる。

## 4.まとめ

The improvement rate of light out-coupling efficiency by nano-uneven structure was investigated by using the electromagnetic wave analysis software KeyFDTD. It was confirmed in the simulation that the extraction efficiency was improved by a maximum of 1.5 times by the nano-uneven structure and that the peak wavelength of the improvement rate varied with the structure and period.

Fig.2 Improvement rate of Light extraction efficiency

Fig.3 Electric field distribution(×1 : λ=500[nm])

Fig.4 Electric field distribution(×1.16 : λ=600[nm])

Fig.5 Electric field distribution(×1.33 : λ=750[nm])

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