無應變GaAs/AlGaAs量子點在[111]成長方向的光學異向性

Abstract

糾纏光子對在量子資訊領域為一個關鍵的要素，而能否形成糾纏光子對的條件為精細結構匹裂要遠小於線寬(約1μeV)，然而實際上因為形狀、應變、原子擴散……等原因會使精細結構匹裂變大，而無應變GaAs/AlGaAs量子點可以單純研究形狀的影響。 價電帶混成(輕重電洞混成)對光偏振、精細結構匹裂扮演著一個重要的角色。本篇論文使用簡單模型研究量子點不同晶面方向、暗激子亮激子耦合如何影響輕重電洞混成，而進一步改變光偏振。結果顯示在[111]晶面方向的光偏振小於[001]方向；在零磁場之下暗激子亮激子耦合效應極小。

Polarization-entangled pairs are a key element in the field of quantum information. The condition for generating polarization-entangled pairs is that fine structure splitting (FSS) must be smaller than the linewidth(~1μeV); however, many factors like shape, strain, atomic diffusion may increase FSS. And unstrained GaAs/AlGaAs quantum dots (QDs) is an excellent candidate easy to study due to nearly pure shape effect. Valence band mixing (VBM) plays a crucial role on optical polarization (DOP) and FSS. In this thesis, studying by using simple model how growth directions or bright-exciton (BX) and dark-exciton (DX) coupling affect component of light-hole (LH) of QDs, further changing DOP. The results show DOP in the [111] direction is smaller than the one in the [001] direction and BX-DX coupling is weak without magnetic field.