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，我們利用化學氣相沉積法去生成氧化鋅微米柱並與P型氮化鎵複合製作出發光二極體。
在實驗中，我們藉由簡單堆疊的方式去製作發光二極體。藉著掃描式電子顯微鏡和拉曼光譜系統的量測結果，我們發現利用化學氣相沉積法所成長的單根氧化鋅微米柱是表面光滑的六角柱，同時也是一個很好的單晶纖鋅礦結構。接著，我們便研究其氧化鋅與P型氮化鎵複合發光二極體的電性與電激發光特性與其機制。我們發現元件在正逆偏壓下皆會放光，特別在逆偏壓下所放出的光為較強的藍紫光。因此在對逆偏壓下操作的二極體做更深入的研究後，我們發現到放光的增強是由於電子穿隧效應的影響。藉著數學模型推導與理論的驗證可以證明元件當中的穿隧效應是由於氧化鋅的缺陷捕捉電子，讓電子更容易地穿隧到氧化鋅的價帶上增加氧化鋅近能帶放光的可能性。

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, we used a chemical vapor deposition method to produce zinc oxide microrod (MR) and combine with the P-type gallium nitride (p-GaN) thin film to form the hybrid light-emitting diode.
In the experiment, we fabricated the light-emitting diodes simply by a stacked manner. According to the results, we found out that the growth of a single ZnO microrod by chemical vapor deposition has the hexagonal cross section and smooth side facets, and also with single crystalline wurtzite ZnO structure by scanning electron microscope (SEM) and raman spectrum system. Then, we study the ZnO MR/p-GaN hybrid light-emitting diode to realize the current characteristics, optical properties and the electron transport mechanism. The emission from the device can be found under the both forward and reverse bias. Especially, the light emitted under reverse bias has a strong blue-violet light. Therefore doing more in-depth study on the device which was operated under the reverse bias, we found that the emission enhance is attributed to electron tunneling effect. By the theory and mathematical model, we can prove electron tunneling effect caused by the zinc oxide defects which can capture the electron into the deep-level states and make it easier for the electron can tunneling from the deep-level states to the conduction band in n-ZnO. This mechanism can increase the recombination in the ZnO and enhance its near band edge emission.

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 6
2 Background Theory 7
2-1 Characteristics of Zinc Oxide 7
2-2 The Spontaneous Emission of Zinc Oxide 9
2-2-1 Ultraviolet Emission 9
2-2-2 Green Emissions 11
2-3 P-N Heterojunction 12
2-3-1 Structure of A P-N Junction 12
2-3-2 Properties of A P-N junction 13
2-3-2-1 Equilibrium (zero bias) 13
2-3-2-2 Forward bias 14
2-3-2-3 Reverse bias 14
2-3-2-4 Depletion Layer and Band Diagram 15
2-4 The Parasitic Resistance Estimation 17
2-5 The CIE Chromatic Coordinate 19
3 Experiment Process 23
3-1 Experimental Procedure 23
3-2 Chemical and Consumable 24
3-3 The Growth System of ZnO Microrod 25
3-3-1 Chemical Vapor Transport System 25
3-3-2 Substrate Clean 28
3-3-3 The growth of ZnO Microrod 29
3-3-4 The Transfer of ZnO Microrod 30
3-4 The Preparation of PMMA Solution 31
3-5 Devices Fabrication 32
4 Measurement and Instrument 34
4-1 Raman Spectroscopy 34
4-2 Field-Emission Scanning Electron Microscopy 37
4-3 Photoluminescence 38
4-4 Electroluminescence 40
4-5 Semiconductor Characterization System 42
5 Experiment Results and Discussions 43
5-1 SEM and Raman Analysis 43
5-2 Continuous-wave PL Analysis 45
5-3 Electrical and Optical Characterization Analysis 47
5-3-1 IV Characteristic 47
5-3-2 Electroluminescence 49
5-3-3 Tunneling Effect Analysis 54
5-3-4 CIE chromaticity Diagram 56
5-3-5 Lifetime Time of the Device 59
6 Conclusion 60
7 Prospective Aspects 61
8 Reference 62

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