透過在{0001}基面上進行奈米壓痕測試，並且系統地研究了六方4H SiC單晶（能隙為3.26 eV）的奈米力學。 4H SiC單晶是由M. C. Chou教授實驗室製備的，透過X射線繞射分析（XRD）檢查生長的晶體，已確認4H六方結構，c軸平行於晶體生長方向並具有週期性ABCB堆疊順序，2θ = 35.5°處的 (0004) 峰是唯一出現的峰，保證了單晶生長良好且缺陷最少，透過XRD測量，確定晶格參數 a 和 c 分別為 0.3073 和 0.1006 nm，與文獻報告的數據非常一致，透過XRD Rocking curve分析，證實生長的單晶內部應該有最少的缺陷。
透過在4H SiC（0001）基面上進行多次奈米壓痕測試，使用鈍或尖的壓痕尖端，彈性模量和硬度分別約為480-500 GPa和39-42 GPa，透過 Tabor 假設（應力~硬度/2.5），4H SiC 晶體的降服應力為約 15-17 GPa，發現具有鈍的或尖銳的壓痕尖端的第一次pop-in所需的應力約為 13-16 GPa，接近上述 15-17 GPa 的降服應力。這表明 4H SiC 晶體中移動差排的活化應力 (13-16 GPa) 非常接近最終的飽和流動應力 (15-17 GPa)，因此，這種半導體 SiC 晶體的加工硬化程度最低。
為了更仔細地研究壓痕尖端應力集中效應，我們採用了三種具有不同尖端曲率半徑的尖端，鈍的尖端Rb~150 nm，中等的尖端Rb~50 nm，尖銳的尖端Rb~20 nm。Pop-in的應力確定為 16.1 GPa、14.8 GPa 和 13.2 GPa，證明了壓痕尖端下方的應力集中效應。尖端曲率半徑越尖銳，first pop-in的應力就會越低，測量到鈍頭或鋒利尖端下的first pop-in的位移約為 10 或 1 nm，可能是穿透式螺旋差排沿 [0001] 向下滑動約 10 或 1個 Burgers 向量（b = c 〜1 nm），透過對SiC晶體進行TEM表徵，我們發現了Burgers向量為b=c=[0001]的穿透式螺旋差排 （TSD）和Burgers向量為b=a1=的基底差排 （BPD） [121 ̅0 ]/3。

The nano-scaled mechanics for the hexagonal 4H SiC single crystals (with a bandgap of 3.26 eV) is examined systematically by using nanoindentation tests on the {0001} basal plane. The 4H SiC single crystal was prepared by Prof. M. C. Chou’s lab. The grown crystal has been examined carefully by X-Ray diffraction (XRD) to confirm the 4H hexagonal structure, with the basal plane lying on the horizon plane and the c-axis parallel to the crystal growth direction, with the periodical ABCB staking sequence. The (0004) peak at 2=35.5° is the only peak appeared, ensuring the well-grown single crystal orientation with minimum defects. From the XRD measurement, the lattice parameters, a and c, are determined to be 0.3073 and 0.1006 nm, respectively, well consistent with the reported data in literature. Through the analysis of XRD rocking curves, it is confirmed that there should be minimum defects inside the as-grown single crystal.
By using multiple nanoindentation tests on the 4H SiC (0001) basal plane, with a blunt or sharp indent tip, the elastic modulus and nano-scaled hardness were about 480-500 GPa and 39-42 GPa, respectively. By applying the Tabor’s assumption (stress~ hardness/2.5), the yield stress of this 4H SiC crystal is determined to be about 15-17 GPa. The stress required for first dislocation pop-in, with a blunt or sharp indent tip, is found to be about 13-16 GPa, close to the above yield stess of 15-17 GPa. This indicates that the stress for the first activation of moving dislocation in the 4H SiC crystal (13-16 GPa) is pretty close to the final saturated flow stress (15-17 GPa). There is minimum work hardening in this semiconductor SiC crystal.
To more closely examine the indent tip stress concentration effects, we adopted three tips with different tip radii of curvatures, the blunt one with Rb~150 nm, the medium one with Rb~50 nm, and the sharp one with Rb~20 nm. The stress for the first dislocation pop-in was determined to be 16.1 GPa, 14.8 GPa and 13.2 GPa, demonstrating the stress concentration effect beneath the indent tip. With a sharper tip radius of curvature, the stress for the first pop-in would be lower. The first pop-in displacement under the blunt or sharp indent tip was measured to be about 10 or 1 nm, likely a result of the threading screw dislocation along the vertical [0001] sliding downward by about 10 or 1 Burgers vector (b = c ~ 1 nm). Through TEM characterizations on the indented SiC crystal, we have found the vertical threading screw dislocations (TSD) with a Burgers vector of b=c=[0001], and the basal plane dislocations (BPD) with a Burgers vector of b=a1=[12 ̅10]/3.

論文審定書 i
Acknowledgements ii
中文摘要 iv
Abstract v
Table of Content vii
List of Figures x
List of Tables xv
Chapter 1 Preface 1
1.1 Brief introduction of various generation of semiconductors 1
1.2 N-type and P-type SiC semiconductors 5
1.3 Motive of this study 10
Chapter 2 Literature Review 12
2.1 Various crystal structures of SiC single crystals 12
2.2 Fabrication means for SiC single crystals or thin films 20
2.2.1 Physical vapor transport method 21
2.2.2 High temperature chemical vapor deposition 23
2.2.3 Solution growth 25
2.3 Mechanical properties of SiC 26
2.4 Defects in SiC 35
2.4.1 Generation of dislocations 37
2.4.2 Micropipe defects 41
2.4.3 Threading screw dislocations 44
2.4.4 Threading edge dislocations and basal plane dislocations 45
2.4.5 Defect reduction 48
2.5 Potential applications of SiC 50
2.5.1 High voltage SiC device applications 52
2.5.2 SiC solar inverter 53
2.5.3 Railway traction inverter 54
2.5.4 Electrical vehicle 55
Chapter 3 Experimental Methods 57
3.1 Sample pre-processing 57
3.2 Optical microscopy observation (OM) 60
3.3 X-ray diffraction (XRD) confirmation of crystal structures 61
3.4 Scanning electron microscopy (SEM) 64
3.5 Nanoindentation 64
3.6 Electron backscattered diffraction (EBSD) 65
3.7 Kernal average misorientation (KAM) 66
3.8 Transmission electron microscopy (TEM) 67
Chapter 4 Experimental Results 69
4.1 Sample preparation 69
4.2 OM observation 69
4.3 White light interferometer 71
4.4 XRD examination 75
4.5 EBSD examination on the as-grown surface 78
4.6 Nanoindentation testing 82
4.7 Minimum work hardening, distinctly different from metals 87
4.8 Stress concentration caused by different tip radii of curvatures 89
4.9 The possible activated dislocations 94
4.10 Extracting the TEM thin samples by FIB 96
4.11 Transmission electron microscopy (TEM) 97
4.11.1 The as-grown crystal without loading 97
4.11.2 The indented specimen using the blunt tip to 900 nm depth 99
4.11.3 The indentation using the sharp tip to a shallow depth of 300 nm 103
4.12 Closing remarks 107
Chapter 5 Discussion 108
5.1 The first dislocation pop-in phenomenon 108
5.2 Comparison between the mechanical response in SiC and GaN 110
Chapter 6 Conclusion 112
Chapter 7 Future Works 114
References 115

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