近年來，雖然氮化鎵發光二極體的發光效率隨著磊晶及製程技術的發展而持續增加，但若與傳統照明系統比較可知，其發光強度和效率仍低了許多。在此研究中，我們利用水溶液沉積法製備氧化鋅奈米針且利用其折射率漸變的特性，以提高氮化鎵發光二極體之光取出效率。研究結果發現，氧化鋅奈米針經過熱處理過後可降低其氧化鋅缺陷，可增加其光取出。除了改善氧化鋅奈米針品質外，覆晶式發光二極體比傳統的發光二極體在垂直發射區（0角度）具有更高的光取出效率（1.25倍）。可得知若減少金屬的光吸收和菲涅耳的傳輸損耗即可增加二極體之發光強度。最後，依照上述之強調設計，我們製作一個高亮度發光二極體。其發光強度較傳統發光二極體提高了約 1.38倍。因此，我們可以製造一個發光二極體陣列與上述設計，以獲得較高的光輸出為未來的固態照明。

In recent years, even though the light output of GaN-related LED continues to increase, the brightness is still low compared to conventional lighting systems and it is necessary to further improve the light extraction of LEDs.
In this study, we utilize the ZnO nanotip with aqueous solution and flip-chip
technique to increase the light extraction of GaN LEDs. Electroluminescence (EL) and angular optical distribution are used to measure the light output intensity of LED.
In the results, ZnO nanotip after thermal annealing with N2O ambiance decrease the ZnO defects. Flip-chip LED has higher light intensity ( 1.25 times) than conventional one in vertical emitting area ( at 0 angles). The enhancement of light output is duo to the reduction of light absorption from the metal contact and Fresnel’s transmission losses.
Finally, we fabricate a high brightness LED with above light enhancement design. EL intensity of LED is increased about 1.38 times than conventional one. Therefore, we can manufacture a LEDs array with above designs to obtain high light output for future solid-state illumination.

Chapter 1 1
Introduction 1
1.1 Evolution and Applications of Light Emitting Diodes 1
1.1.1 Evolution of Light Emitting Diodes 2
1.1.2 Prospects of White LEDs Lighting 2
1.2 Structure and Problems of GaN-based Light Emitting Diodes 3
1.2.1 Structure of GaN-based Light Emitting Diodes 4
1.2.2 Problems of GaN-based Light Emitting Diodes 5
1.3 Motivations of ZnO on GaN blue LED 6
1.4 Synthesis of ZnO nanotip 7
1.5 Advantages of aqueous solution Deposition (ASD) 8
1.6 Enhancement of Light Extraction of GaN Light Emitting Diodes 9
1.7 Flip-Chip Technology 9
Reference 16
Chapter 2 20
Experiments 20
2.1 GaN Blue LED 20
2.2 ZnO buffer layer prepared by RF Sputtering 20
2.2.1 Sputtering mechanism 20
2.2.2 RF Sputtering 22
2.3 ZnO buffer layer prepared with ZnO Target by RF Sputtering 22
2.4 ASD System 23
2.5 ASD Processes 23
2.5.1 Substrate Cleaning Procedures 23
2.5.2 Preparation of Deposition Solution 24
2.5.3 Basic Mechanism for ZnO 24
2.5.4 Upside Down Process 25
2.6 Post-Annealing Treatment 25
2.7 Flip-Chip Technology 25
2.8 Characterization 26
2.8.1 Physical Properties 26
2.8.2 Optical and Electrical Properties 27
References 38
Chapter 3 39
Results and discussion 39
3-1 Characteristics of ZnO nanotip on GaN LED 39
3.1.1 Fresnel’s Loss 39
3.1.2 Buffer layer 40
3.1.3 FE-SEM Morphology 40
3.1.4 Crystal Structure 41
3.1.5 The Optical Properties of ASD-ZnO nanotip 42
3.1.6 Schematic ASD-ZnO nanotip on GaN LED 42
3.1.7 EL Spectrum 42
3.1.8 Angular Optical Distribution 43
3.2 Flip-Chip GaN LED 44
3.2.1 FE-SEM Morphology 44
3.2.2 EL Spectrum 45
3.2.3 Angular Optical Distribution 45
Reference 62
Chapter 4 63
Conclusions 63

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