表面結構對太陽能電池與垂直式發光二極體之角度相依光學行為之效應

Abstract

諸多奈米粒子的應用(如奈米小球微影術)，一直被視為是一個製作表面奈米結構之快速且簡便的解決方案，而此製作於元件表面的奈米結構將可用以提昇如太陽能電池、發光二極體等光電元件的效能。然而，在這獲得改善的效能背後，卻仍有些議題與機制尚未獲得充分的研究與解釋。例如，針對太陽能電池而言，其入射光之反射率與光極化間的依存性；抑或針對發光二極體來說，已萃取的傳導模態其輻射行為與表面結構間的依存性等。 針對太陽能電池的第一個議題，我們對具有二氧化矽奈米小球鋪排於表面的太陽能電池與平面結構的太陽能電池進行探究與比較。我們發現到此奈米小球二維陣列對於電場垂直極化的光有較大的提升，而對磁場垂直極化的光幫助則較少，而這正好可以彌補電場垂直極化的光在光學上反射率較高的問題。 在本文的第二個段落中，除了經由單一表面圖案化製備的奈米柱之外，加上了截面微米圓頂結構的雙重表面圖案化亦於此處予以採用並研究之。結果顯示，發射光會因為與不同的單一表面結構作用，而發散至各種相對應之不同角度。而對於結合了奈米柱及微米圓頂的混合式結構來說，由於存在於半導體元件內部的各式的傳導模態，得以同時透過奈米柱抑或微米圓頂結構將其耦合出來，此種具混合式結構的發光二極體之光輸出增益，幾乎同等於具單一奈米柱結構以及單一微米圓頂結構的發光二極體之光輸出增益於特定方位上的線性疊加。藉由調變奈米柱與截面微米圓頂結構之相對蝕刻深度，本研究成果提供了一個操控光於不同方向上的增益強度之指導原則。

Various applications of nanoparticles, such like nanosphere lithography, is believed to be a fast and simple way to fabricate surface nanostructures and thus improve the performance of photonic device such as solar cell or LED. However, there’re still some issues and mechanisms behind not investigated or explained thoroughly, such like the polarization-dependent reflectivity of the incident light for solar cells or the texture-related radiation behaviors of the extracted guided light. With the focus on the first issue, for solar cells, investigations had been made by comparing the properties of cells with silica nanospheres coated to the one without any surface structure. We found that the silica nanosphere arrays can improve the TE polarized light more significant than TM polarized light, which is a good way to compensate the larger reflectivity in TE polarized light for oblique incidence. In the second part, for vertical-injection LED (VLED), besides one-step nanorod surface patterning, a two-step surface patterning with the addition of truncated microdome arrays is further employed and investigated. The results suggest that light will be radiated to various angles while interacting with different single-step textured surfaces. As for the hybrid structure, since separate guided modes in the semiconductor layers are diffracted by either nanorods or microdomes, the percentage increase of light extraction from it is found to be about the linear superposition of both types of single surface textures at certain corresponding angle domain. The result provides a guideline of manipulating light enhancement distribution by adjusting the relative etch depth between nanorod and truncated microdome structures.