自組式量子點偏振螢光之理論研究

Abstract

本篇文章主要是探討激子(電子-電洞對)在自組式量子點中所釋放的旋光。文章中利用 多能帶理論以及波包近似法理解激子中電子和電洞的性質，接著將於系統中引入重電洞、輕電洞耦合並使用費米黃金定律了解其對激子所釋放出旋光的影響。而關於重電洞、輕電洞的耦合包含兩大因素：(1)Luttinger-Kohn Hamiltonian因為量子點得不對稱性(形狀、應力)而產生耦合 (2)激子間的交換能。結果發現其耦合效應的強弱會影響線性偏振光的能量劈裂大小，甚至可以發現有一個臨界點(能量簡併)會造成X、Y方向線偏振光能量反轉；量子點的不對稱性會造成光學的異相性；激子能量劈裂差距和光學異相性程度(極化率)具有成正比的關係。

This thesis presents a theoretical study of polarized photoluminescence spectrum of a single spin exciton confined in a strained self-assembled quantum dot (QD). The electronic structure of an exciton in QD is studied in the framework of four-band strain model. The time-dependent perturbation theory is employed to calculate the polarized emission spectrum of strained quantum dot. The study shows that the effect of heavy- and light-hole (HH and LH) mixing is especially pronounced in quantum dots with lateral shape deformation and is essential in the polarized photoluminescence spectrum of QD. The HH-LH mixing results in pronounced optical anisotropy and substantially renormalize the magnitude of fine structure splitting between the bright exciton states of deformed QD.