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Optical and Material Characteristics of InAs/GaAs Quantum Dots and Ga2O3/GaAs Thin Film
No full text本論文主要研究熱退火處理之砷化銦/砷化鎵量子點與氧化鎵/砷化鎵薄膜的光學與材料特性，依其熱退火條件與環境的不同下做各種研究，內容大致分成三大部份：
(一) 在As4 環境下熱退火處理之砷化銦/砷化鎵量子點的研究：
砷化銦量子點是採用MBE製程生長在半絕緣的砷化鎵基板上，並在上以不同的熱退火溫度成長砷化鎵間隔層，使用原子力顯微鏡(AFM)、 變溫及變功率光激發螢光量測系統來做觀測比較與分析。由AFM實驗可知生長溫度較低者有較大的量子點產生及最小的密度，隨著溫度變高，量子點的尺寸變小密度變大；由光激發螢光(PL)實驗可知生長溫度較低者峰值有最高的能量與較高的強度，隨著溫度上升，峰值能量與強度皆變小。由此可知，量子點中的電子能量跟量子點的大小有極大的關係，越大的量子點會導致樣品有越小的能量。我們也藉由峰值位置、半高寬、峰值強度與溫度變化之間的關係，分別對各退火溫度之樣品做分析，發現到熱退火溫度為五百度C之樣品其光學特性較佳，活化能也最小，代表著此樣品其品質較佳，量子點的大小與密度也最均勻，而後由變功率光激發螢光實驗也證明此一論點。
(二) 在P2 環境下熱退火處理之砷化銦/砷化鎵量子點的研究：
此部份樣品其生長條件與之前量子點雷同，只是在不同的氣體環境下熱退火成長砷化鎵間隔層。由AFM實驗可知，隨著溫度變高，量子點的生長遭到破壞而消失，這跟磷原子與砷原子之間的化學鍵結有關係，當熱退火溫度越高其化學反應越劇烈，砷磷化銦的形成轉而取代砷化銦並造成量子點的減少。由光激發螢光(PL)實驗可知生長溫度較低者峰值有最高的能量，隨著溫度上升，峰值能量逐漸變小。而在熱退火溫度為五百度C的樣品中，我們在其變溫光激發螢光(PL)實驗中觀測到有趣的現象，其內部量子點所造成的大小峰值強度會隨著溫度增加而改變，此現象可以用來解釋量子點內部載子隨溫度變化的移動情形。
(三)熱退火處理之三氧化二鎵薄膜成長的研究：
三氧化二鎵薄膜以濺鍍方式成長在砷化鎵基板上，藉由X射線光電子能譜儀(XPS)分析，知道其不同熱退火條件下的樣品束縛能產生變化，推測熱退火溫度的不同造成樣品結構的改變。之後又經由掃瞄式電子顯微鏡(SEM)與X射線能量散佈分析儀(EDX)實驗，證實其氧原子與鎵原子的比例確實隨著熱退火溫度不同而改變。最後再藉由X射線繞射儀(XRD)分析，由其峰值改變以及半高寬的減少判定樣品的品質與熱退火溫度之間的關係。This thesis concerns with the studies on the optical properties and material characteristics of thermal annealing InAs/GaAs quantum dots and Ga2O3/GaAs. Many optical measurements are carried out to study the physical properties according to the conditions of thermal annealing. Many peculiar phenomena have been observed, which are very useful for understanding as well as application of these materials.
(1) Characterization of the InAs/GaAs quantum dots with spacer annealed under AS4：
InAs quantum dots were deposited onto GaAs layer with different growth temperature spacer layer by molecular beam epitaxy and compared using temperature dependence photoluminescence measurements, power dependence photoluminescence measurements and atomic force microscope (AFM).From the AFM measurement, we can know the sample annealed at lower temperature has lager size quantum dots and smaller density of quantum dots. And the size of quantum dots is getting smaller and the density of quantum dots is getting larger as the annealing temperature increase. The photoluminescence energy was considerably increased for samples grown in lower temperature. So the energy of quantum dots related with the size of quantum dots. We also analyzed samples by the peak positions, FWHMs, and PL integrated intensity as a function of temperature. The sample annealed at 500 has better optical properties and less activation energy and the density of quantum dots is most uniform. Power-dependent photoluminescence measurements also confirm the contention.
(2) Characterization of the InAs/GaAs quantum dots with spacer annealed under P2：
The samples had the same growth conditions just annealed under P2. From the AFM charts, the amount of quantum dots is destroyed and decreased. It rely on the bonding of phosphorus atoms and arsenic atoms. When the annealing temperature is getting higher, the chemical reaction is getting violent, so the alloy of InPxAs1-x was grown instead of InAs. The photoluminescence energy was decreased for samples grown in higher temperature. And we find an interesting phenomenon in the temperature-dependent photoluminescence measurement of the sample annealed at 500 . The two broad peaks are attributed to the combined size distribution of the bimodal quantum dots. The change of peak intensity between them can be explained the movement of the carriers in the quantum dots as the temperature increased.
(3) Characterization of thermal annealing Ga2O3 thin films：
Ga2O3 thin films were deposited onto GaAs substrate with different annealing temperature. We can know the change in binding energy as the different annealing temperature and suppose the composition of samples is changed by X-ray Photoelectron Spectroscopy (XPS) measurement. Subsequently, we confirmed the increase of ratio of oxygen to gallium assuredly as the annealing temperature increased by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) measurement. Finally, from the X-ray diffraction (XRD) measurement analysis, we can identify the relations between the quality of the interface and annealing temperature by the increased peak positions and decreased FWHMs in the spectra.口試委員審定書......................................I
誌謝...............................................II
中文摘要…………………………………………………..…...III
Abstract…………………………………………………..…..…V
Contents….………………………………………………......VIII
Last of Figure and Table..........................................................XII
Chapter 1
Introduction………………………………………………...…...1
1.1 Nature and Applications of InAs Quantum Dots…………....….....1
1.2 Nature and Applications of gallium oxide materials………….…...4
Reference…………...…………………………………………….……6
Chapter 2
Experimental Principle、Set Up and Measuring Method ...10
2.1 Atomic Force Microscopy (AFM)…………………………..……10
2.2 Photoluminescence………..………………………………….…..14
2.2.1 The Principle of Photoluminescence…..........................…..14
2.2.2 Measurement System Set Up of Photoluminescence….......20
2.3 X-ray Photoelectron Spectroscopy (XPS)…..............................…21
2.4 X-ray diffraction (XRD)…………………………………………25
Reference…………………………………………………….………30
Chapter 3
Design, Growth, and Characterization of InAs/GaAs Quantum Dots….........................................................................33
3.1 Introduction of Quantum Dot…………………………..………...33
3.2 Optical Transitions in Self-Assembled Quantum Dots………..…42
3.3 Annealing Experiments…….........................................……… …45
3.4 Characterization of the Samples with Spacer Annealed under AS4.................................................................................................48
3.4.1 Low Temperature Photoluminescence measurements results and analysis…......................................................................50
3.4.2 Temperature-dependent Photoluminescence measurements results and analysis.........................................................….51
3.4.3 Power-dependent Photoluminescence measurements results and analysis….................................................................….64
3.5 Characterization of the Samples with Spacer Annealed Under P2…...............................................................................................66
3.5.1 Low Temperature Photoluminescence measurements results and analysis…..........................................................70
3.5.2 Temperature-dependent Photoluminescence measurements results and analysis…..........................................................71
3.6 Summary……………………………………………………….....79
Reference…………………………………………………..…………83
Chapter 4
Optical Characterization in Ga2O3 Thin Film...................…..87
4.1 Introduction of Ga2O3 ……............................................................87
4.2 Structural and Optical Properties of Ga2O3 Thin Film.............….88
4.2.1 X-ray Photoelectron Spectroscopy (XPS) measurement results and analysis...............................................................89
4.2.2 Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray spectroscopy (EDX) measurement results and analysis..........................................................................92
4.2.3 X-ray diffraction (XRD) measurement results and analysis.97
4.3 Summary…....................................................................................99
Chapter 5
Conclusion…........................................…………………….…103
Appendix A
Optical Studies of YAG Crystals ............................................106
A.1 Introduction¬ of YAG Crystals.............................................................106
A.2 Experimental Methods…………………………..…..............………109
A.3 Results and Discussion…………………….……...…………...……110
A.3.1 Room temperature photoluminescence measurements results and analysis of YAG crystals ………………...……………….110
A.3.2 Room temperature optical transmission measurements results and analysis of YAG crystals…………...………...……………111
A.3.3 Raman scattering measurements results and analysis of YAG crystal……………...………...………………………….……..113
A.4 Conclusion..........................................................................................120
Reference………………………………………...………………………121
Appendix B
X-ray diffraction (XRD) Spectra of Ga2O3 / GaAs Thin Film…………………………………………………………....122
Appendix C
Fourier Transform Infrared Spectroscopy (FTIR) Spectra of Ga2O3 / GaAs Thin Film……………….......12
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