無應力GaAs/AlGaAs量子點光學異向性的理論研究

Abstract

本論文主要探討droplet-epitaxial GaAs/AlGaAs量子點的光學異向性(optical polarization anisotropy) 。相較大多數量子點系統，因為droplet-epitaxial量子點沒有應力效應，所以可以專注在量子點幾何大小對光學異向性的影響。 文章中使用k．p方法模擬激子系統的電子結構，透過對真實量子點形狀的模擬進而建立而量子點的三維拋物線模型，再使用費米黃金定理(Fermi’s Golden rule)計算電子由導電帶躍遷至價電帶的發光強度和偏振，當量子點越不對稱則偏振越強，而且量子點越高其偏振也越強，在量子點體積固定下，量子點越不對稱則高度越矮，使得偏振變弱。最後本文章使用部分組態交互作用計算偏振(DOP)，該理論結果顯示激子中電子和電洞間的關聯性的庫倫作用力導致DOP進一步微幅下修(<5%)。

This thesis theoretically investigates the optical anisotropy of GaAs/AlGaAs quantum dots grown by droplet epitaxy. The stress-free QD system allows as to focus on the geometry effects on optical anisotropy. First, the single particle spectra are separately calculated using the single-band effective mass model for conduction electron and four-band Luttinger-Kohn theory for valence hole using 3D finite difference method. For more analysis, we further build up three dimensional(3D) parabolic models for the quantum dots under study according to the numerically calculated electronic structures. Second, the photoluminescence (PL) intensity and the degree of optical polarization (DOP) for the recombination of e-h pairs are calculated using the Fermi’s Golden Rule. It is found that, besides the commonly know effect of lateral elongation, the height of QD is even more essential in the optical DOP of the droplet epitaxial dots. Finally, the influence of Coulomb interaction on polarization anisotropy is examined by using the partial configuration interaction (PCI) method. The calculated results show that Coulomb interactions in excitons make the DOPs slightly decreased (<5%).