臺灣博碩士論文加值系統

本論文的主要內容在於使用PL的量測技術研究1.3 μm In0.5Ga0.5As/GaAs 量子點（Quantum Dot, QD）的光學特性，尋找最佳的In0.5Ga0.5As/GaAs量子點成長厚度。
論文中所有In0.5Ga0.5As/GaAs的量子點樣本，均由氣態源分子束磊晶機在溫度480 oC成長一系列不同量子點厚度的樣本。藉由PL的量測研究，尋找出成長高品質In0.5Ga0.5As/GaAs量子點最佳的條件。研究中發現不同的量子點厚度，會造成其發光波長及量子點的密度的變化，而過量的量子點厚度則可能會造成量子點結構開始產生缺陷或是鬆弛。
在PL變溫的量測中，經由Arrhenius的方程式去擬合PL的數據，發現當量子點厚度為8 ML時，有最大的活化能103.8 meV及淬滅能 15.4 meV，且在溫度為9 K的PL頻譜中，明顯地看到8 ML厚度的量子點有三個在不同能階的訊號放光，其相鄰的能階間距約為56 meV呈現簡諧震盪的特性，顯示此厚度的量子點具有拋物線（parabolic）的位障。並經由量子點發光的半寬對溫度的變化中，探討量子點中電荷載子的遷移情形。在論文中也將討論聲子瓶頸效應（phonon bottleneck effect）對量子點的影響並使用速率方程式（rate equation）模型來擬合PL實驗數據，估算量子點的本質鬆弛時間（intrinsic relaxation time）及探討不同的成長方式對量子點的影響。

This work is concentrated on In0.5Ga0.5As/GaAs quantum dots (QDs) optical properties by using Photoluminescence technology and find out optimum thickness of In0.5Ga0.5As/GaAs quantum dots.
All of QDs with different thickness were deposited in gas source molecular beam epitaxy system by using migration enhanced epitaxy technology at growth temperature of 480 0C. By using photoluminescence technology to get optimum growth condition of In0.5Ga0.5As/GaAs quantum dots are our main purposes. Wavelength of luminescence, density and volume are affected by different thickness of quantum dots affect in our research. Defects, dislocations and relax in Quantum dots are induced while we deposit too much material of In0.5Ga0.5As whose thickness of quantum dots exceeds critical thickness. Carrier transfer in quantum dots is observed during temperature-dependent Photoluminescence measurement. Activation energy and thermal quenching of quantum dots are also obtained by fitting the curve with following Arrhenius equation. Activation and quenching energy has maximum value 103.8 meV and 15.4 meV respectively when QDs's thickness is 8 ML.
In their 9K PL spectra, three peaks can be clearly resolved. The energy spacing between neighboring peaks are all equal and the value is about 56 meV. It indicates that the QDs are with harmonic-oscillator-type potentials. We will discuss the influence of phonon bottleneck in QDs and estimate intrinsic relaxation time of QDs by using rough rate equation. In finally, we also discuss the effect of different growth methods on QDs.

第1章 緒論……………………………………………6
第2章 理 論…………………………………………12
2.1 量子點形成之機制12
2.2 能階密度15
2.3 載子之鬆弛17
第3章 實驗設置與量測方法24
3.1 結構設計及磊晶24
3.2 光激螢光量測系統25
第4章 結果與討論29
4.1 量子點厚度之影響29
4.1.1 量子點厚度與PL的關係29
4.1.2 量子點的活化能及淬滅能30
4.2 量子點內的能階32
4.3 量子點中的電荷載子34
4.3.1 溫度的影響34
4.3.2 電荷載子的遷移35
4.3.3 聲子瓶頸效應的影響37
4.4 強化遷移的成長方式38
第5章 結 論62
參 考 文 獻63

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