混和型表面電漿模態對半導體量子點之自發輻射效率影響之研究

Abstract

一直以來，大家都在追求如何製造發光效率更高、耗能越低、體積越小的發光元 件，而調整發光材料的發光效率的關鍵之一是 Purcell factor，此值越大其自發輻 射效率(spontaneous emission rate)越高，而且和模態的體積(mode volume)成反比。 由兩個表面電漿模態藕合而成的混和模態正扮演了可以提供極小模態體積的角 色，除此之外它還能夠將電場侷限在很小的體積裡，意味存在著很強的能量密度。 在本篇論文裡面我們利用共軛聚焦顯微鏡系統、時間解析光譜研究鎘化砷膠狀半 導體量子點和由金薄膜和銀的奈米粒子所組成的混和型表面電漿模態耦合之下 所產生的交互作用，同時也針對量測的結果作深入的分析及討論。從我們的實驗 結果可以得知，量子點在混和型表面電漿模態的影響之下，可以加快自發輻射效 率約 70 倍左右，除此之外我們透過研究其反群聚效應之後，發現耦合的量子點 發光時還伴隨著雙激子的輻射。這個結果不僅間接為正在發展中的量子通訊工業 提供了一個新的方向，同時也為發展中的高效率光電元件提供了一個可行的發 展。

The modification of the radiative rate is a key to produce a higher efficiency optoelectronic device such as light emitting device or laser. Thus the coupling between two plasmonic modes play an important role due to its better field confinement, stronger field enhancement and smallest mode volume, which not on increase the Purcell factor but also enhance the fluorescence of coupled emitters. Here, we study the optical property of core/shell CdSe/ZnS nanocrystals coupling to the hybrid mode of localized surface plasmon and surface plasmon and it can be coupled well due to broadband performance of the plasmonic mode. In our case, a 70 times enhancement of radiative rate can be observed on coupled quantum dot, and the fluorescence enhancement is also shown in our result. In addition, from antibunching measurement, we can also find the existence of multiple exciton emission, including bi- and tri- exciton recombination, which enables the application of quantum information technology in the future.