自組式量子點中電子-電洞交換作用理論研究

Abstract

在這篇論文中，我說明了一個在自組式量子點中的電子-電洞交換作用的理論研究，它是量子點中光極化特徵的關鍵。我們研究量子點中應變的效應對單激子的自旋結構的影響。根據J. H. Davises的理論，我們用數值的方法計算了一個矩形盒(InAs/GaAs量子點)的應變分佈，並分別計算應變對導電帶、重電洞與輕電洞的等效位能的修正，量子點中的電洞可被認為類”重電洞”的。我們利用純重電洞為基底的激子，去推導在半導體系統中的電子-電洞交換作用的公式，期望提供一個基礎去研究不同奈米結構中激子的精細結構：從三維侷限的奈米晶體到準二維的自組式量子點等。最後，我們應用這個理論在InAs/GaAs的自組式量子點中，並且完成輻射光的極化方向。根據這個分析，我們可以把極化光光譜連結到激子的自旋結構與量子點的幾何形狀。

In this thesis, I present a theoretical study of electron-hole exchange interaction in self-assembled quantum dots, a key element in the spin-characteristics polarized optical spectra and the spin dynamics of dots. We start with exploring the strain effects in self-assembled quantum dots on the spin structure of single exciton in dots. By taking the theory by J. H. Davies, we carry out the numerical calculation for the strain distribution in a box-like InAs/GaAs quantum dot and calculate the strain-modified effective potential profile for conduction electrons, heavy-holes, and light-holes, respectively. The hole carriers bounded in dots are confirmed to be heavy-hole-like. In the basis of pure heavy-hole exciton, we derive the generalized formulation of e-h exchange interaction in semiconductors, providing a base for the studies of the fine structure of excitons in a variety of nanostructures, from 3D confining nanocrystals to quasi-2D self-assembled quantum dots. At last, we apply the theory to InAs/GaAs self-assembled quantum dots and carry out the analysis of the polarized emission spectrum directly. According to the analysis, we can relate the polarized spectrum feature to the spin structure of excitons and dot geometry.