半導體發光二極體具有成為新世代高發光效率固態照明的特定必須條件，包含可調變發光頻譜以及材料磊晶特質…等等，其中三族氮化物可以磊晶形成具有藍光或紫外發光波段的多重量子井結構，而這正式實現白光固態照明所必需的光源。然而依據現有磊晶以及元件製程技術，依舊無法克服三族氮化物材料特性—非對稱晶體結構—所引發的特殊效應：量子侷限史塔克效應。此效應導致極性面三族氮化物材料中的電子電洞分佈機率最大值錯位，意即導電帶與價帶傾斜，使得電子電洞複合發光機率大幅下降，並間接導致低水平的「內部量子效益」。此外，如何有效將電子電洞複合產生的光子萃取出元件結構外，以直接對「照明」做出貢獻是另一項課題，因為此「光萃取效率」所影響的是「外部量子效益」，或者可通稱為半導體發光二極體的「發光效益」。

本篇論文包含了如何在溝渠圖形化的m面藍寶石基板上、溝渠圖形化的無極性a面氮化鎵模板上(磊晶於r面藍寶石基板上)利用有機金屬化學氣相沉積方法磊晶出高結晶品質的無極性a面氮化鎵。利用在溝渠圖形化的m面藍寶石基板上成長高結晶品質無極性a面氮化鎵所得到的磊晶經驗，並將之應用到溝渠圖形化的無極性a面氮化鎵模板上，使用「溝渠圖形化側向磊晶成長方式」，可以得到高結晶品質、平坦的無極性a面氮化鎵於r面藍寶石基板上。在這一高品質的無極性a面氮化鎵基板上，無極性氮化銦鎵/氮化鎵多重量子井結構可以成功實現，並具有藍光440nm的發光波段。

此一有機金屬化學氣相沉積方法所依賴的實驗關鍵在於較低的五族/三族原子比例，其值大約100。而成長模式主要依靠正c方向的快速成長面以達到側向完全癒合平坦的目標。使用「溝渠圖形化側向磊晶成長方式」所得到的高結晶品質、平坦的無極性a面氮化鎵，其差排密度可由初始r面藍寶石基板上的a面氮化鎵的1E10cm-2大幅降低到在側向成長區域的1E8cm-2。本論文中並針對利用此兩種方式：「溝渠圖形化的m面藍寶石基板上磊晶」、「溝渠圖形化的無極性a面氮化鎵模板上磊晶」所得到的高結晶品質無極性a面氮化鎵進行分析，並搭配掃描式電子顯微鏡、穿透式電子顯微鏡進一步針對缺陷分布以及形成原因進行探究。

由於使用「溝渠圖形化側向磊晶成長方式」所得到的高結晶品質、平坦的無極性a面氮化鎵其存在特殊的孔洞於氮化鎵/r面藍寶石基板介面，因此本文中利用氫氧化鉀溶液針對這些因溝渠圖形化設計以及磊晶限制所留下的孔洞進行蝕刻處理。蝕刻處理所選定的試片包含了完整磊晶的無極性氮化銦鎵/氮化鎵多重量子井結構，以針對蝕刻分析是否對發光性質造成影響。氫氧化鉀溶液蝕刻條件控制在100°C、120°C、140°C;濃度條件維持在5 wt. %、10 wt. %以及20 wt. %；蝕刻時間則選擇10min、20min、40min、80min以及160min。藉由調整不同條件組合的蝕刻條件發現在低溫低濃度的狀況下，氫氧化鉀溶液對於存在高結晶品質、平坦的無極性a面氮化鎵/r面藍寶石基板介面的孔洞無顯著的蝕刻效果，蝕刻速率約為2.35±1.67nm/min，速率慢且蝕刻差異大；高溫高濃度的狀況下則可以得到有效的蝕刻效果，蝕刻速率約為26.0±1.90nm/min，速率雖快但蝕刻差異大。而中間溫度120°C以及10 wt. %的組合提供了13.6±0.90nm/min的蝕刻速率，具有可接受的蝕刻速率且蝕刻差異降低到1nm/min以下。

此一蝕刻方式可以將存在高結晶品質、平坦的無極性a面氮化鎵/r面藍寶石基板介面的孔洞蝕刻成由{11-22}面以及+c面所構成的等腰三角形、梯形或者因缺陷導致的混合形。這些蝕刻行為可歸類為「極性選擇蝕刻行為」以及「缺陷選擇蝕刻行為」。

進一步由變角度光激發光光譜量測可得知這些條狀的幾何形狀孔洞對於光萃取效率有顯著的提升，在垂直等腰三角孔洞側邊的方向上(約偏離法向量自30°到60°)可以得到3倍以上的光取出強度改善。藉由組合不同的蝕刻條件以及優化不同的孔洞幾何形狀，大角度範圍(自法向量到60°以上)的光取出效率改善可被預期。

本論文成功整合高結晶品質、平坦的無極性a面氮化鎵的磊晶製程以及氫氧化鉀溶液的蝕刻製程以產生特殊形狀的孔洞，達到了同時針對內部量子效益(無極性材料性質)以及光萃取效益(蝕刻產生空氣孔洞)兩大影響半導體發光二極體發光效益的因素改善的目的。

Based on semiconductor light-emitting diodes, solid state lighting is a promising approach for the realization of highly efficient white light sources. The Group-III nitrides materials provide a great potential of constructing the multiple quantum wells which can emit light in blue and UV region and be used as important sources of white lighting. However the asymmetry of the Group-III nitrides materials crystalline structure leads to an undesirable Quantum-Confined Stark Effect (QCSE) which is a barrier of the recombination of electrons and holes. Besides, guiding the emission light out of the devices is one another important issue for it determining the total lighting efficiency by light extraction efficiency.

In this thesis, the epitaxial growth of nonpolar a-plane GaN on trench-patterned m-plane sapphire and on trench-patterned a-plane GaN template with r-plane sapphire by MOCVD was performed. The experimental knowledge was first constructed on the growth mode of a-plane GaN on trench-patterned m-plane sapphire and then applied to a modified technique, trench epitaxial lateral overgrowth (TELOG) on trench-patterned a-plane GaN template with r-plane sapphire, and successfully gain the planar a-plane GaN and the corresponding InGaN/GaN MQWs on it. The critical growth methods, i.e. the low level of V/III ratio of ~100, growth mode, i.e. the +c-direction-dominated growth fronts, crystalline quality, i.e. dislocation density decreasing from 1E10cm-2 to 1E8cm-2 at lateral wing region, optical properties including photoluminescence (PL) and cathodoluminescence (CL) are observed in this thesis.

A chemical etching technique based on the KOH solution was applied to the TELOG a-plane GaN and InGaN/GaN MQWs. The etching conditions including the temperature between 100°C and 140°C, the concentration of KOH between 5 wt. % and 20 wt. % and the etching times: 10min, 20min, 40min, 80min and 160min. This integration provides air-voids with specific geometries, i.e. the isosceles triangle or trapezoid or the mixed one, in the nonpolar a-plane GaN. Under investigations, it provides great improvement of the light extraction ability at a wide range of direction. Based on the varied-angle PL measurement, an approximately 3 times enhancement of the PL intensity was achieved at the angle from 25° to 50° with respect to the normal direction of the sample surface. Furthermore, by the combination of the etching mechanisms and the techniques of substrate engineering, a possible chemical lift-off process is expected to be established.

The thesis provides an integrated process includes the fabrications of nonpolar a-plane GaN materials by TELOG and the etching procedures by KOH solution without extra damages, which would be a powerful solution to enhance the total lighting efficiency from the factors of internal quantum efficiency and the light extraction efficiency at a same time.

摘 要 II
ABSTRACT V
誌 謝 VIII
ACKNOWLEDGEMENT X
CONTENTS XII
TABLE CAPTIONS XV
FIGURE CAPTIONS XVI

CHAPTER 1 INTRODUCTION 1
1.1 PERSPECTIVES OF GROUP-III NITRIDES AND LIGHT-EMITTING DIODES (LED) 1
1.2 SPECIFIC PROPERTIES OF GROUP-III NITRIDE (GAN) AND LED APPLICATION 3
1.3 MOTIVATION AND ORGANIZATION OF THE THESIS 6
1.4 REFERENCES 8

CHAPTER 2 EXPERIMENTAL APPARATUS 12
2.1 SAPPHIRE SUBSTRATE 12
2.2 METALORGANIC CHEMICAL VAPOR DEPOSITION (MOCVD) 14
2.3 INDUCTIVELY COUPLED PLASMA REACTIVE ION ETCHING (ICP-RIE) 17
2.4 POTASSIUM HYDROXIDE (KOH)-ETHYLENE GLYCOL SOLUTION 19
2.5 SCANNING ELECTRON MICROSCOPY (SEM) 20
2.6 SCANNING TRANSMISSION ELECTRON MICROSCOPY (STEM) 22
2.7 TRANSMISSION ELECTRON MICROSCOPY (TEM) 24
2.8 PHOTOLUMINESCENCE SPECTROSCOPY (PL) AND CATHODOLUMINESCENCE SPECTROSCOPY (CL) 26
2.9 X-RAY DIFFRACTION (XRD) 32
2.10 REFERENCES 34

CHAPTER 3 EXPERIMENTAL PROCEDURES 47
3.1 EPITAXIAL RELATIONSHIP OF GALLIUM NITRIDE ON SAPPHIRE HETEROSUBSTRATE 47
3.2 NONPOLAR A-PLANE GAN ON M-PLANE SAPPHIRE 50
3.3 NONPOLAR A-PLANE GAN ON Γ-PLANE SAPPHIRE 51
3.4 KOH ETCHING PROCEDURES 53
3.5 MEASUREMENT AND CHARACTERIZATION 55
3.6 REFERENCES 56

CHAPTER 4 RESULT I – NONPOLAR A-PLANE GAN ON PATTERNED M-PLANE SAPPHIRE 66
4.1 THE EPITAXIAL MODE AND MORPHOLOGY UNDER DIFFERENT LEVEL OF V/III RATIO 66
4.2 DEFECTS DISTRIBUTION AND CLARIFICATION 68
4.3 SUMMARY 70
4.4 REFERENCES 71

CHAPTER 5 RESULT II –TRENCHED EPITAXIAL LATERAL OVERGROWTH (TELOG) A-PLANE GAN LED ON Γ-PLANE SAPPHIRE 81
5.1 THE EPITAXIAL MODE AND MORPHOLOGY 81
5.2 CRYSTALLINE QUALITY OF TELOG A-PLANE GAN AND INGAN/GAN MQWS 84
5.3 OPTICAL PROPERTIES OF TELOG A-PLANE GAN AND INGAN/GAN MQWS 86
5.4 SUMMARY 88
5.5 REFERENCES 90

CHAPTER 6 RESULT III – ETCHING OF TELOG A-PLANE GAN IN KOH-ETHYLENE GLYCOL SOLUTION 100
6.1 REVIEW OF ETCHING MECHANISM OF GAN IN KOH-ETHYLENE GLYCOL SOLUTION 100
6.2 CONCENTRATION, TEMPERATURE AND TIME DEPENDENCY OF KOH ETCHING TENDENCY 103
6.3 IDENTIFICATION OF CHEMICAL ETCHING BEHAVIORS AND RATE CHARACTERIZATION OF TELOG A-PLANE GAN IN KOH-ETHYLENE GLYCOL SOLUTION 106
6.4 OPTICAL PROPERTIES OF TELOG A-PLANE INGAN/GAN MQWS AFTER KOH-ETHYLENE GLYCOL SOLUTION ETCHING 112
6.5 SUMMARY 115
6.6 REFERENCES 115

CHAPTER 7 CONCLUSION AND PROSPECTS 132
7.1 THE ACQUIREMENT OF NONPOLAR A-PLANE GAN ON M-PLANE AND Γ-PLANE SAPPHIRE SUBSTRATE 132
7.2 THE OUTCOME OF KOH-ETHYLENE GLYCOL-SOLUTION-ETCHED TELOG NONPOLAR A-PLANE GAN AND MQWS 133
7.3 FUTURE WORKS AND PROSPECTS 133

PUBLICATION LIST 135

CURRICULUM VITAE 136

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