披覆銻砷化鎵層之砷化銦量子點的載子動力學及能帶排列

Abstract

論文第一部分利用光激螢光光譜研究不同 GaAs0.8Sb0.2 披覆厚度對於 InAs 量子點的發光特性影響。發現披覆層厚度的增加將造成發光能量紅移、載子生命期變長及出現能帶彎曲效應。透過八能帶k.p理論分析發光紅移及生命期延長的主因是來自於第二型能帶的形成及電洞量子侷限的降低，另外披覆層厚度增加造成量子點尺寸的擴大也是紅移因素之一。論文第二部分利用變功率光激螢光光譜以及時間解析光譜研究不同注入載子濃度對於 type-II InAs/GaAs0.84Sb0.16 QDs 發光特性的影響。不同的載子注入濃度將造成不同的庫倫作用力強度，因而改變了量子點的躍遷型態。透過改變注入濃度，我們可以調變量子點的發光能量及輻射復合生命期。論文第三部分為研究PIN結構下 type-II QDs 之光電特性。我們藉由光電流實驗來研究 type-II QDs 的吸收，並透過變溫實驗觀察載子脫逃的行為。另外我們也討論了外加電場對於 type-II QDs 發光特性的影響。

The optical properties of GaAsSb-capped InAs quantum dots (QDs) with different capping layer thickness are investigated. Both the emission energy and the recombination lifetime of the QDs are found to be correlated with the capping layer thickness. Theoretical calculations based on eight-band model indicates that the quantum confinement of hole states and their wave function distributions are sensitive to the GaAsSb capping layer thickness. The Sb induced structural changes in QDs are also found to play a significant role in the optical properties of GaAsSb-capped QDs. We show that controlling the GaAsSb capping layer thickness is a feasible way to tailor the InAs QDs for long-wavelength applications. Then, we study the recombination dynamics in the InAs/GaAs0.84Sb0.16 QDs. In this type-II QDs system, the radiative transitions are strong affected by the band-bending effect induced by the carriers accumulated at the type-II InAs/GaAs0.84Sb0.16 interface. After the laser pulse excitation, the QD emission exhibits strong transition rate variations and large energy redshifts. Here we use the energy dependent TRPL to map the whole QD emission spectrum. After analysis the time evolution of peak energy and peak intensity, we can get the time evolution of the intensity and the energy shift. We report up to 2.1 times transition rate enhancement in the annealed type-II InAs/GaAs0.84Sb0.16 QDs could be achieved by high injection power. We find that the transition energy shows a linear dependence with the 2/3th power of the total emission intensity, indicating the QD emission obeys the type-II transition. Consequently, we can control the transition type in the InAs/GaAs0.84Sb0.16 QDs by the different injection levels. Finally, we study the electro-optical characteristics of type-II QDs embedded in PIN structure. We use photocurrent experiment to study the absorption spectra and the carrier escape processes in the type-II QDs. Then we study the effect of applied electric field on the emission properties of type-II QDs.