外加垂直電場下砷化鎵/砷化鋁鎵量子點的精細結構

Abstract

糾纏光子對在量子光學、量子通訊以及量子密碼中扮演著重要的角色，半導體量子點光源因有三維侷限性，能階高度量化，被認為是理想的糾纏光子對發射器。 在本篇論文中利用數值方法，研究利用droplet epitaxy方式生成的GaAs/AlGaAs無應變(strain-free)量子點在垂直方向外加電場下的電子結構、光偏振特性與精細結構，比起InAs/GaAs自組式量子點，droplet epitaxy量子點的體積通常較大，預期輕重電洞混合(valence band mixing)也較明顯且對光學性質有重要影響。 數值方法是利用多能帶k∙p理論並搭配有限差分法計算電子結構，利用繪圖處理器(graphics processing units(GPU)平行運算可計算電子電洞交換能並得到精細結構匹裂(fine structure splitting)，利用費米黃金定律(Fermi’s Golden rule)計算發光強度與光偏振，討論輕重電洞混合對光學特性及精細結構匹裂的影響。

Generation of entangled photon pairs is a key element in quantum optics, communication and cryptography. Semiconductor quantum dots (QDs) are considered as an ideal entangled photon pair emitter due to their three-dimensional confinement of electrons and holes. In this thesis I theoretically investigate the energy spectra, optical polarizations and fine structure splittings of GaAs/AlGaAs quantum dots grown by droplet epitaxy (DE) under external vertical electric fields. We build up a theory for electron-hole exchange in the framework of multi band k.p theory. Compared with the widely studied InAs/GaAs self-assembled QDs, the sizes of DE-QDs are so large that the valence band mixing (VBM) is significant in the optical properties. The VBM effects on fine structure splittings (FSS), intensities and degrees of polarizations of the emitted photon pairs from the biased QDs are investigated.