臺灣博碩士論文加值系統

本篇論文的主要研究為藍光發光二極體的調變頻寬、等效電路模型、資料傳輸表現之特性探討，探討元件尺寸、量子井數目以及單一式與陣列式結構對發光二極體直流特性、調變頻寬以及其資料傳輸速率之影響。由於小尺寸的元件能夠承受更高的電流密度以及較低的接面溫度，達到較高的調變頻寬。此外，相較於三個量子井的發光二極體，可以發現只有一個量子井的發光二極體能提升1.6倍的調變頻寬與2倍的資料傳輸速度，並透過TCAD模擬探討其物理機制，可以發現一個量子井的發光二極體相較於多個量子井的發光二極體擁有較高的載子濃度以致於較低的載子生命週期與較高的調變頻寬。透過改變發光二極體的量子井數目，除了直流的特性改變外，調變頻寬的增加更是劇烈，此研究結果將對設計適用於可見光通訊系統的發光二極體乃是一重大發現。相較於單一式發光二極體，陣列式發光二極體除了能提升光強度外，並不會損失調變速度，因此透過此結構，在元件尺寸縮小時，能維持相同的光強度，並增加元件的調變頻寬。另外，我們透過速率方程式推導出發光二極體的轉移方程式，以及建構發光二極體的小訊號電路模型，並萃取發光二極體的小訊號參數，發現當發光二極體尺寸縮小至微米等級後，寄生電容與電阻並不會影響調變頻寬。透過此微波萃取方式，更可以驗證微米發光二極體的調變頻寬主要決定於載子生命週期，因此如何降低載子生命週期將是設計高速發光二極體的一大關鍵。同時單一發光二極體的等效電路模型也能適用於陣列式發光二極體。
此外，我們成功製造出第一個藍光量子井(QW) 發光電晶體，探討其電、光、頻譜特性，除了特有的光電雙輸出特性外，電流增益也能達到4.9，從發光強度對注入基極電流的關係，可以觀察到藍光電晶體較沒有一般藍光發光二極體的Droop效應。此外，與一般藍光發光二極體不同，藍光發光電晶體隨著外加電流增加，發光波長並不會有明顯的藍移，意謂者藍光發光電晶體的發光波長穩定性更佳。量子井除了能提供光的輸出外，隨著溫度增加，逃脫出量子井的載子會被收集至集極，形成電流增益，透過此機制，發光電晶體可應用於溫度感測器，與一般紅外光的發光電晶體不同，藍光發光電晶體由於是可見光，將更容易被偵測與應用。藉由以上特性，藍光發光電晶體將是未來可見光通訊與光互連的關鍵元件。

This thesis presents the design and data transmission performance of high-speed blue micro-LEDs for visible light communication. The effect of device size, quantum well numbers, and different configuration (array) are discussed. Smaller area micro-LEDs can be operated at higher current density and hence a higher carrier density leading to higher modulation bandwidth (f-3dB) which can be attributed to a reduction in device self-heating. Nearly 1.6 times bandwidth and 2 times date rate enhancement can be achieved in single quantum well (SQW) micro-LEDs by comparison to triple quantum well (TQW) micro-LEDs. Combining the device size and quantum well numbers issue, we successfully demonstrated 752 MHz modulation bandwidth of blue single quantum well (SQW) micro-LEDs. Moreover, the high-speed blue micro-LEDs employed in a 2x2 integrated array configuration can achieve much higher light-output without sacrificing the speed. This work suggests that the micro-LEDs with fewer quantum well numbers and array configuration are suitable devices for future VLC application. Furthermore, we start from the rate equation analysis and develop a microwave extraction method based on a small-signal equivalent circuit model to determine the modulation response and recombination lifetime of high-speed LEDs. We find that in micro-LEDs the modulation bandwidth is not limited by parasitic RC and only determined by recombination lifetime. It is concluded that how to lower carrier lifetime is a critical issue to achieve higher modulation bandwidth. Moreover, we extend the equivalent physical circuit model of single micro-LED into a micro-LED array.
Furthermore, we extend the material system of quantum well heterojunction bipolar light emitting transistors (QW-HBLETs) into III-N material. By employing a quantum well into a base-InGaN layer, we successfully demonstrated the first blue QW-HBLETs with dual output modulation simultaneously. The InGaN/GaN QW-HBLETs achieve the current gain of ~5 and optical power of ~tens of µW. Owing to its unique structure inherited both advantages of LEDs and HBTs, the InGaN/GaN QW HBLET is the promising candidate for future application of optical interconnect, thermal sensor, and visible light communication (VLC).

口試委員審定書 I
誌謝 II
中文摘要 III
Abstract V
Table of Contents VII
List of Figures IX
List of Tables XVII
Chapter 1. Introduction 1
1.1. Motivation 1
1.2. From Light-Emitting Diodes to Light-Emitting Transistors 3
1.3. Organization of Work 4
Chapter 2. Design of High Speed Blue Micro-Light-Emitting Diodes 6
2.1. Preface 6
2.2. Device Fabrication and Experiment Set-up 6
2.3. The Effect of Device Size on Modulation Bandwidth 11
2.3.1. DC Characteristics 11
2.3.2. Microwave Characteristics 13
2.4. The Effect of Quantum Well Numbers on Modulation Bandwidth and Eye-Diagram Integrity 15
2.4.1. DC Characteristics 15
2.4.2. Microwave Characteristics 18
2.4.3. Data Transmission Performance: On-Off Keying (OOK) 21
2.5. TCAD Determination of Recombination Lifetime and Modulation Bandwidth 24
2.5.1. TCAD Simulation Flow 24
2.5.2. Recombination Lifetime and Modulation Bandwidth Extraction 28
2.6. Summary of Design Parameters on High-Speed Blue Micro-LEDs for Visible-Light Communication 32
Chapter 3. High-Speed 2x2 Integrated Micro-LED Array for Visible Light Communication 35
3.1. Preface 35
3.2. DC Characteristics 35
3.3. Microwave Characteristics 39
3.4. Data Transmission Performance: On-Off Keying (OOK) 40
Chapter 4. Microwave Characterization of Parasitic (RC), Recombination Lifetime, and Modulation Bandwidth on High-Speed Blue Micro-LEDs 43
4.1. Preface 43
4.2. Rate Equation Analysis 45
4.2.1. Coupled Carrier and Photon Rate Equations for LEDs 45
4.2.2. Differential Analysis 47
4.3. Equivalent Circuit Model and Parasitic Parameters Extraction 50
4.4. Microwave Determination of Recombination Lifetime Determination and Bandwidth 54
4.5. Equivalent Circuit Model of Four-LED Array 60
Chapter 5. Design, Fabrication, and Characterization of Blue InGaN/GaN Quantum-Well Heterojunction Bipolar Light Emitting Transistors 64
5.1. Preface 64
5.2. Layer Structure Design and Device Fabrication 65
5.3. Electrical and Optical DC Characteristics 70
5.4. Investigation of Emitter Size on Current Gain and Light Output Power 75
5.5. Investigation of Thermal Effect in Blue Light-Emitting Transistors 76
Chapter 6. Conclusion 82
References 84

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