臺灣博碩士論文加值系統

氧化鋅是一個寬能隙的半導體材料(3.37eV)，而且由於它擁有大的激子束縛能(60meV)，使之能夠穩定的存在於室溫當中，所以氧化鋅有絕對的潛力去發展藍光雷射和發光二極體。因此，增強氧化鋅近能帶發光和改善其發光效率是當前研究氧化鋅的重要議題。
在實驗當中，我們藉由溶膠凝膠法製備均一大小的氧化鋅球體，其球體尺寸為次微米級且由氧化鋅的奈米粒子團簇而成，接著我們將氧化鋅球體以不同的溫度進行退火。藉由掃描式電子顯微鏡和X光繞射儀的測量結果，我們發現在不同的退火條件下氧化鋅球體的形貌與晶體結構會產生很大的變化。進而，我們研究其光學激發下的發光特性和產生的雷射行為，得知氧化鋅球體在退火之後其光學特性也獲得了大幅的改善。而且，我們也由X射線光電子能譜的量測發現，經由退火過程可以移除大部分在氧化鋅球體表面的OH鍵結，而OH鍵結對於表面陷阱能態的產生扮演重要的角色。由此可見，經由高溫退火的氧化鋅球體確實擁有較卓越的光學特性。

Zinc oxide (ZnO) is a wide band gap semiconductor (3.37 eV) and its large exciton binding energy of 60 meV makes free excitons stable even at room temperature. Thus it has been suggested that ZnO has enormous potential for developing blue lasers and light emitting diodes. Therefore, the enhancement of the band gap emission and the improvement of the luminescence efficiency have become the vital issues in the research of ZnO.
We fabricated the monodisperse ZnO submicron spheres consisting of aggregated nanoparticles by sol-gel process, and annealed them at the different temperatures. According to the results, we found out that the various annealed temperature would influence the morphologies as well as the crystal structures of the ZnO spheres by scanning electron microscope (SEM) and X-ray diffraction measurement (XRD). We investigated both luminescence characteristics and lasing action by optical pumping. The optical properties of the ZnO spheres obtained great improvement via thermal treatment. Moreover, Using X-ray photoelectron spectroscopy (XPS), we found that the annealing process can mostly remove the OH bonds at the surface, which may play important roles for surface trapped state. As a result, the superior optical properties of high-annealing ZnO mainly could be achieved.

Abstract (in Chinese) I
Abstract (in English) II
Acknowledgements III
Contents IV
List of Tables VII
List of Figures VIII

1 Introduction 1
1.1 Preface 1
1.2 Motivation 4
2 Background Theory 5
2.1 Characteristics of Zinc Oxide 5
2.2 Material Properties of Nanostructure 7
2.2.1 Quantum Confinement Effect 7
2.2.2 Surface and Interface Effect 7
2.3 Optical Properties of Zinc Oxide 7
2.3.1 Spontaneous Emission 7
2.3.1.1 UV Emission 8
2.3.1.2 Defect Emissions 12
2.3.2 Stimulated Emission 15
2.3.2.1 Nanostructures as Cavities 15
2.3.2.2 Random Lasing 16
3 Experiment Process and Measurement Instrument 18
3.1 Experiment Process 18
3.1.1 Substrate Cleaning 18
3.1.2 Synthesis of Zinc Oxide Spheres by Sol-Gol Growth 18
3.1.3 Post Treatment 20
3.2 Measurement Instrument 22
3.2.1 X-ray Diffraction (XRD) 22
3.2.2 Field-Emission Scanning Electron Microscopy (FE-SEM)22
3.2.3 Photoluminescence (PL) 23
3.2.4 X-ray photoelectron Spectroscopy (XPS) 26
4 Experiment Results and Discussions 28
4.1 XRD and SEM Analysis 28
4.2 Continuous-wave (CW) PL Analysis 31
4.2.1 PL at Roomtemperature (RT) 31
4.2.2 Temperature-dependent PL 33
4.3 Pulsed laser pumped PL Analysis 41
4.4 XPS Analysis 48
5 Conclusion 52
Reference 53

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