砷化銦鎵自聚性量子點的單光子輻射特性; Single photon emission properties of InGaAs self-assembled dots

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/7360

Title:	砷化銦鎵自聚性量子點的單光子輻射特性;Single photon emission properties of InGaAs self-assembled dots
Authors:	張翔思;Hsiang-Szu Chang
Contributors:	物理研究所
Keywords:	單光子輻射;單一半導體量子點;semiconductor single quantum dots;single photon emission
Date:	2009-06-23
Issue Date:	2009-09-22 10:56:20 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本論文旨於研究三種砷化銦鎵自聚性量子點的單光子輻射特性 - 量子點埋在平的砷化鎵中，量子點成長於類角錐狀多面體結構的頂端平台上以及量子點埋在光子晶體共振腔中。首先，自聚性量子點的電子能態特性和量子點中的侷限能階將理論性地被介紹。量子點具有數個能階而且每個能階有其簡併態使得數個電子與電洞可以填入量子點中。電子與電洞在量子點中體驗著很強的庫倫作用力，這使得量子點的輻射具有多重激子的細微結構。本工作的第二個部分將研究量子點埋在平的砷化鎵中的多重激子細微結構。單一量子點的輻射線，有關於激子，雙激子和帶電激子，利用微螢光光譜解析以及確認。其帶電激子的形成機制亦被研究。光子時間相關的實驗展示了激子輻射具有光子反成束特性，代表著在試片表面製作奈米孔洞可以有效的隔離出單一量子點的輻射。剩下的問題可能是這些量子點的光萃取效率會被全內反射的臨界角所限制。這問題可以藉由接下來兩部份討論的方法來克服。本工作的第三部份將研究量子點成長於多面體結構的頂端平台上的數目隨不同圖案化的平台面積變化。多面體結構的表面型態以及量子點的數目變化將以電子束掃描顯微鏡來研究。量子點被發現喜歡成長於多面體結構的頂端的平台。微螢光光譜顯示這是因為頂端平台的磊晶速率比旁邊斜面的磊晶速率快所致。個別量子點的輻射線也被加以檢測。這些研究的結果顯示控制量子點成長於縮小面積的頂端平台上不只可以限制量子點的數目還可以改善其單光子的萃取效率，其效果可比得上將量子點引進到光子晶體奈米共振腔中。在本工作的最後一個部份，我們將討論單一量子點埋入光子晶體共振腔中的單光子和多重光子輻射。首先，光子晶體奈米共振腔將先被簡介而它們的共振模態亦將被研究。個別量子點輻射的研究顯示當量子點輻射與共振腔模態共振時其光輻射強度比量子點埋在平的砷化鎵中強。這個光強度的增強歸因於較高的光萃取效率以及增加的自發性輻射速率。這個光強度的增強使得我們可以利用脈衝激發來產生單光子輻射，同時其多重光子輻射的機率也比量子點在平的砷化鎵中和量子點在多面體結構上來的小。然而，一些多重光子輻射的事件仍被觀察到。最後，量子點非零多重光子輻射的機率的來源將藉由不同的激發能量將激子注入到砷化鎵位障或是量子點的激發態來研究。所量測到的多重光子輻射機率被確認係來自於激子再捕捉以及濕潤層能態的背景輻射。激子再捕捉則以速率方程式模型計算加以分析討論，這結果顯示激子再捕捉效應為主要的多重光子輻射的來源。 This thesis investigates the single photon emission properties of three kinds of InxGa1-xAs self-assembled quantum dots - quantum dots embedded in planar GaAs, quantum dots grown on apex plane of a pyramid-like multifaceted structure and quantum dots embedded in photonic crystal nancavities. First, the electronic properties of self-assembled quantum dots as well as the confined energy states in the self-assembled quantum dots are theoretically introduced. Quantum dots have several confined energy levels and each level has its own degeneracy so that several electrons and holes can be populated in them. Electrons and holes in the quantum dots experience strong Coulomb interaction, resulting in quantum-dot emission exhibits multiexciton fine structure. The second part of this work discusses light emission from the multiexciton fine structures of quantum dots in planar GaAs. The emission lines of single quantum dots, those associated with excitons, biexcitons and charged excitons, are resolved and identified by using microphotoluminescence. The mechanism of formation of charged excitons is investigated. Photon correlation measurements demonstrated that exciton emission exhibits photon antibunching behavior, revealing that fabrication of nanoapertures on sample surface can effective isolate single quantum-dot emissions. The remainder may be the extraction efficiency of these quantum dots is limited by the critical angle of total internal reflection. This problem can be overcome by using the other approaches that discussed in the next two parts. The third part of this work investigates the number variation of quantum dots grown on the apex plane of a pyramid-like multifaceted structure at various patterning mesa areas. The surface morphology of the multifaceted structure and the number variation of quantum dots are examined using scanning electron microscopy. The quantum dots were found to grow preferentially on the apex plane. Microphotoluminescence studies reveal that this preference follows the fact that the growth rate of apex plane exceeds that of side wall facets. The emission lines of individual quantum dots are also examined. This study demonstrates that control of quantum dots grown on a reduced apex plane area not only limits the number of quantum dots but also improves the single photon extraction efficiency, which is comparable to that obtained when the QDs are introduced in photonic crystal nanocavities. In the last part of this work, we discussed the single and multiple photon emission from single quantum dots that are embedded in photonic crystal nanocavities. An introduction of photonic crystal nanocavities is presented and their cavity modes are studied first. A study of individual quantum-dot emission reveals that the intensity of quantum-dot emission is stronger than that of quantum dots in planar GaAs when its emission resonates with the cavity mode. This increasing intensity is attributable to the improvement in higher extraction efficiency and an enhanced spontaneous emission rate. Such intensity enhancement allows us to generate single photon with pulsed excitations and reduces the probability of multiphoton emission considerably comparing with quantum dots in planar GaAs and quantum dots on multifaceted structure. However, some multiphoton events are still detected herein. Finally, the origins of the nonzero probability of multiple photon emission from quantum dots are studied by using different excitation energies to inject excitons into either the GaAs barrier or the quantum-dot excited state. The detected multiphoton events are established to arise from both the recapture of excitons and background emissions from the wetting layer tail states. The recapture of excitons is analyzed using rate-equation-model calculations, which suggest that the multiphoton emission is dominated by the recapture effect.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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