臺灣博碩士論文加值系統

在本論文中，為了改善氮化鎵/氮化銦鎵系(GaN/InGaN)發光二極體之光萃取效率(light extraction efficiency)，吾人研製一系列具有短深度微米孔洞陣列及特殊圖案化邊牆之複合結構式高品質氮化鎵/氮化銦鎵系發光二極體。以此複合結構為主軸，進一步提出奈米材料應用及元件製程技術，其中包含利用快速對流沉積法(rapid convection deposition, RCD)製備混合式二氧化矽微奈米球抗反射保護層以及利用快速對流沉積法形成嵌入二氧化矽奈米球單層結構來形成反射鏡結構，有效提升氮化鎵系發光二極體之光電轉換效率(wall-plug efficiency, WPE)。本研究對複合結構式氮化鎵/氮化銦鎵系發光二極體之光電特性，及各種特定結構之製備方式皆有深入且詳細的研究及探討。
首先，吾人利用感應耦合電漿離子(inductively coupled plasma, ICP)蝕刻製程，製備出具有不同深度微米孔洞陣列及特殊邊牆結構之氮化鎵/氮化銦鎵系發光二極體，短深度微米孔洞陣列可在不影響電性特性之下，目的保留多重量子井(MQW)，有效增加發光面積且降低在氮化鎵/空氣介面之內部全反射(total internal reflection, TIR)，並增加光子散射(photons scattering)至元件外部的機會。另外，經由快速對流沉積法，塗佈混合式二氧化矽微奈米球抗反射保護層之氮化鎵/氮化銦鎵系發光二極體。在不影響順向電性特性下，有效抑制元件之逆向漏電流，並進一步提升元件表面粗糙度，使得光子有足夠的機會被導引至光逃離錐角(photon escape cones)，降低內部全反射效應。此外，二氧化矽保護層同時具備抗反射性質，抑制元件內部產生之Fresnel光損失(Fresnel loss)。相較於傳統平面式氮化鎵系發光二極體，在光輸出功率(light output power)、光通量(luminous flux)、光電轉換效率(wall-plug efficiency)及外部量子效率(external quantum efficiency)分別提升51.3%、 53.59%、54.55%及52.08%。
其次，為了有效改善高效率發光二極體之光萃取效率，吾人提出利用由快速對流沉積法嵌入二氧化矽奈米球單層結構來形成背鍍反射鏡結構，首先將具有自組裝偽六腳緊密堆積(pseudo-hexagonal close packing)陣列之奈米球單層結構塗佈在元件底部藍寶石基板，並蒸鍍鋁金屬反射鏡(aluminum metal mirror)，利用奈米球之圓球外型形成背鍍反射鏡，此結構改變反射光之光路徑可降低內部全反射(total internal reflection, TIR)；除此之外，由於奈米球單層結構於球與球之間會形成空氣孔洞(air voids) 陣列，利用空氣孔洞陣列導致減少元件底部之光吸收，有效地提升光子逃離錐角散射至元件外，且利用短深度微米孔洞陣列、特殊邊牆結構及二氧化矽保護層混合結構，此修飾結構大幅地改善光萃取效率。相較於傳統平面式氮化鎵/氮化銦鎵系發光二極體，在光輸出功率(light output power)、光通量(luminous flux)、光電轉換效率(wall-plug efficiency)及外部量子效率(external quantum efficiency)分別提升57.8%、47.2%、58.6%及58.1%。
最後，延續前章探討經由快速對流沉積法，塗佈不同尺寸二氧化矽抗反射保護層於具有短深度微米孔洞陣列及特殊邊牆結構之氮化鎵/氮化銦鎵系發光二極體。在不影響順向電性特性下，有效抑制元件之逆向漏電流，並改變元件表面粗糙度，不同表面粗糙度使得光子被導引至光逃離錐角(photon escape cones) 的機會不同。此外，二氧化矽保護層同時具備抗反射性質，抑制元件內部產生之Fresnel光損失(Fresnel loss)。相較於傳統平面式氮化鎵/氮化銦鎵系發光二極體，在光輸出功率、光通量、光電轉換效率及外部量子效率分別提升61.2%、39.9%、61.2%及62.0%。本研究論文中所研製之高品質氮化鎵/氮化銦鎵系發光二極體，皆有效提升光電轉換效率，在商業應用上相當具有潛力。

In this thesis, in order to enhance light extraction efficiency (LEE), GaN/InGaN-based light-emitting diodes (LEDs) with specific sidewalls are fabricated and studied. The device fabrication process and nanomaterials applications, including a shallower depth of a microhole array, textured sidewalls, nanospheres (NSs) backside reflector via rapid convection deposition (RCD), and an appropriate SiO2 passivation layer via a RCD approach are proposed to further improve wall-plug efficiency (WPE) of the studied devices. The optical and electrical properties of these multi-structured GaN/InGaN-based LEDs are studied and discussed in detail. In addition, the related fabrication processes of these specific structures are also explained in detail.
A hybrid structure, including 45° sidewalls, a microhole array, and an SiO2 nanoparticle (NP)/microsphere (MS) passivation layer, is used to produce GaN/InGaN-based light-emitting diodes (LEDs). The influences of the microhole depth and SiO2 NP/MS passivation layer on the LED performance are studied. A shallower depth (0.25 µm) of a microhole array shows better optical properties due to the complete preservation of the GaN/InGaN multiple quantum well (MQW) region. In addition, the use of a thin SiO2 NP/MS passivation layer gives a remarkably reduced reverse-biased leakage current and improved optical performance. Experimentally, under an injection current of 400 mA, the studied device, with a proper hybrid structure, shows enhancements of 51.3%, 53.59%, 54.55%, and 52.08% in light output power (LOP), luminous flux, wall-plug efficiency, and external quantum efficiency (EQE), respectively, as compared to a conventional LED device. These improvements are mainly caused by the reduced total internal reflection and Fresnel reflection which increase scattering probability and the opportunity to find photon escape cones. So, the studied hybrid structure in this work is a promising route to fabricate high-performance GaN/InGaN-based LEDs.
An approach to improve light extraction efficiency of high power GaN/InGaN-based LEDs by use of the nanospheres backside reflector is studied. A backside reflector is taken shape by depositing a self-assembled SiO2 nanosprere monolayer via a RCD approach between Al metal mirror and backside of sapphire substrate. Due to the use of inserting SiO2 nanospheres, hemispherical patterns could be transferred to the deposited reflector. However, photons could be redirected into arbitrary angles for light extraction by the transferred concave surface. In addition, the air void is formed due to the presence of gap between SiO2 nanospheres. It could effectively improve light scattering effect. Hence, a hybrid structure, including backside reflector, 45° sidewalls, a microhole array, and an SiO2 nanoparticle (NP)/microsphere (MS) passivation layer, is used to produce GaN/InGaN-based light-emitting diodes (LEDs). This assuredly gives photons more opportunities to find the escape cone. Experimentally, as compared to a conventional LED device under an injection current of 400 mA, the studied device, with a proper hybrid structure, shows enhancements of 57.8%, 47.2%, 58.6%, and 58.1% in light output power (LOP), luminous flux, wall-plug efficiency, and external quantum efficiency (EQE), respectively, Therefore, these results reveal that use of the proper hybrid structure could effectively improve the optical performance of high-performance GaN/InGaN-based LED applications.
Finally, the characteristics of GaN/InGaN-based light emitting diodes (LEDs) with a hybrid structure, including a shallower depth of a microhole array, 45° sidewalls, and an appropriate SiO2 passivation layer, were fabricated and studied. The use of the different size of passivation layer, formed via RCD method, causes an effective reduction in reverse-biased leakage current. The employment of the different size of SiO2 with a smaller size (30 nm) yields improved optical properties due to the highest roughened surface. In addition, the employment of hybrid structures of SiO2 NP/MS passivation layer improved optical properties due to increase surface roughness. Experimentally, as compared to a conventional LED device under an injection current of 400 mA, the studied device, with a proper hybrid structure, shows enhancements of 61.2%, 39.9%, 62.0%, and 61.2% in light output power (LOP), luminous flux, wall-plug efficiency, and external quantum efficiency (EQE), respectively, Therefore, these results reveal that use of the proper hybrid structure could effectively improve the optical performance of high-performance GaN/InGaN-based LED applications.
These proposed hybrid specific structures, which were employed in GaN/InGaN-based LED, indeed improve the total light output performance and reduce the power consumption. Therefore, the high-performance GaN/InGaN-based LEDs possesses commercial potential to compete with traditional light sources for practical applications in solid-state lighting.

Chapter 1
Introduction
1-1. History of GaN/InGaN-based LEDs 1
1-2. Problems of GaN/InGaN-based LEDs 4
1-3. Review of Microhole Array Structures 5
1-4. Review of Textured Sidewall Structures 5
1-5. Review of Micro-/Nano-sphere Structures 6
1-6. Thesis Organizations 6
Chapter 2
Influences of Microhole Depth and SiO2Nanoparticle/Microsphere Passivation Layer on the Performance of GaN/InGaN -Based Light-Emitting Diodes
2-1. Introduction 8
2-1-1. Introduction 8
2-1-2. Formation of Microhole Arrays with Different Microhole Depth 9
2-1-3. Rapid Convection Deposition 10
2-1-4. Mechanisms of Anti-reflection 11
2-2. Fabrication Processes of LED Devices 13
2-2-1. LED Wafer Cleaning Process 13
2-2-2. Devices Structure and Fabrication 13
2-3. Experimental Results and Discussion 15
2-3-1. Surface Morphology 15
2-3-2. Transmittance and Atom Force Microscope 17
2-3-3. Electrical Properties 17
2-3-4. Optical Properties 19
2-3-5. Near-field Light Emission Mapping 22
2-3-6. Far-filed Radiation Pattern 23
2-4. Summary 24
Chapter 3
Applications of Nanospheres (NSs) Backside Reflector for GaN/InGaN-based LEDs
3-1. Introduction 25
3-1-1. Introduction 25
3-1-2. Backside reflector 26
3-2. Fabrication Processes of LED Devices 27
3-2-1. LED Wafer Cleaning Process 27
3-2-2. Devices Structure and Fabrication 28
3-3. Experimental Results and Discussion 30
3-3-1. Surface Morphology 30
3-3-2. Atom Force Microscope 31
3-3-3. Electrical Properties 32
3-3-4. Optical Properties 33
3-3-5. Near-field Light Emission Mapping 36
3-3-6. Far-filed Radiation Pattern 37
3-4. Summary 38
Chapter 4
Influences of SiO2 Nanoparticle size of SiO2 Passivation Layer on the Performance of GaN/InGaN-based Light-Emitting Diodes
4-1. Introduction 39
4-1-1. Introduction 39
4-2. Fabrication Processes of LED Devices 41
4-2-1. LED Wafer Cleaning Process 41
4-2-2. Devices Structure and Fabrication 41
4-3. Experimental Results and Discussion 43
4-3-1. Surface Morphology 43
4-3-2. Atom Force Microscope 45
4-3-3. Electrical Properties 45
4-3-4. Optical Properties 47
4-3-5. Near-field Light Emission Mapping 50
4-3-6. Far-filed Radiation Pattern 51
4-4. Summary 52
Chapter 5
Conclusion and Prospects
5-1. Conclusion 53
5-2. Prospects 56
References 57
Figures

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