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Title Page

Abstracts

Contents

List of Abbreviations 18

Chapter 1. Introduction 20

1.1. Two-Dimensional (2D) Hexagonal Boron Nitride (hBN) 20

1.1.1. Types of Boron Nitride 22

1.1.2. Structural features of hBN 24

1.1.3. Properties of hBN 25

1.2. Applications of hBN 27

1.2.1. Encapsulation layer of other materials 27

1.2.2. Dielectric layer for 2D FET 29

1.2.3. Growth substrate for 2D materials 31

1.3. Growth method of 2D hBN 33

1.3.1. Top-down method 33

1.3.2. CVD growth on sapphire substrate 35

1.3.3. Metal catalyst assisted growth of hBN 37

Chapter 2. Experimental Details 45

2.1. Synthesis of Two-Dimensional hBN by MOCVD 45

2.1.1. Metal-Organic Chemical Vapor Deposition (MOCVD) 46

2.1.2. Precursor of hBN 49

2.2. Limitations of hBN growth on Sapphire substrate 51

2.2.1. Needs of catalytic metal substrate for hBN growth 53

2.3. Preparation of Ni (111) film 54

2.3.1. Orientation relationship of sapphire surface 54

2.3.2. Ni deposition by sputtering 56

2.3.3. Post-annealing of Ni film 60

2.4. Synthesis of hBN on Ni (111) film 63

2.4.1. Pulse mode growth 66

2.4.2. Control of growth cycles 70

2.4.3. Control of growth temperature 70

2.4.4. Control of precursor injection time 73

2.4.5. Control of interruption time 75

Chapter 3. Results and Discussion 77

3.1. Growth of single-crystalline hBN on Ni (111)/sapphire 77

3.1.1. Modulation for termination bonding of sapphire surface 78

3.1.2. Structural morphology of Ni surface 80

3.1.3. Fabrication of single aligned Ni (111) by annealing treatment 81

3.2. Growth procedure and mechanism of hBN on Ni (111) 85

3.2.1. Theoretical contents of hBN growth 85

3.2.2. Experimental contents (Structural characterizations of hBN on Ni (111)) 89

3.3. Characterizations of wafer-scale multi-layer single-crystalline hBN 92

3.3.1. Analysis of hBN properties 92

3.3.2. Electrical properties of hBN 100

3.3.3. Transfer method of hBN onto arbitrary substrate 102

Chapter 4. Conclusion 104

References 106

List of Figures

Figure 1. The types of boron nitride. 21

Figure 2. Atomic structure and configuration of hBN. 23

Figure 3. Schematic representation of typical properties of 2D hBN. 26

Figure 4. hBN as encapsulation layer of other materials to protect the damages. 28

Figure 5. hBN as a dielectric layer for 2D FET device. 30

Figure 6. hBN as a growth substrate for 2D materials. 32

Figure 7. Representative exfoliation method of hBN. 34

Figure 8. CVD growth of hBN on sapphire substrate. 36

Figure 9. hBN growth on metal catalyst of Ni, Cu. 38

Figure 10. hBN growth on metal catalyst of Au, Pt. 41

Figure 11. hBN growth on metal catalyst of Fe, Fe-Ni alloy. 43

Figure 12. Growth of hBN via MOCVD. 47

Figure 13. Experimental equipment of MOCVD for 2-inch wafer-scale hBN growth on Ni (111). 48

Figure 14. Atomic structure and chemical formula of typical precursor of hBN under MOCVD and CVD system. 50

Figure 15. Surface properties of hBN grown on sapphire substrates. 52

Figure 16. Orientation relationship between the metal film and sapphire substrate. 55

Figure 17. HRXRD data of Ni films deposited as a function of substrate temperature. 57

Figure 18. AFM images of Ni surface properties as a function of the working pressure. 58

Figure 19. Optical images of Ni surface properties working pressure of 10 mTorr to 2 mTorr, which shows the less existence of grain boundaries and the large grain size in low working pressure. 58

Figure 20. AFM images Ni surface properties as a function of the applied DC-power. 59

Figure 21. Ni deposition rate as a function of sputtering power. 59

Figure 22. Comparison of Ni film before and after annealing process. 61

Figure 23. Electron backscatter diffraction (EBSD) image of single crystal Ni (111) film. 62

Figure 24. Images of the chamber used for hBN growth and as-synthesized hBN on Ni (111). 64

Figure 25. Schematic of the hBN growth sequence under MOCVD system. 65

Figure 26. Schematic illustration of a typical film formation process and the creation of byproduct caused by parasitic reactions effect in conventional MOCVD systems. 67

Figure 27. Comparison of pulsed growth and one-step growth under MOCVD. 68

Figure 28. Schematic diagram of procedure for pulse mode grown hBN in our MOCVD system. The sequence is consisting of 4 steps: TEB injection, Interruption (IB), NH₃ injection, Interruption (IN)[이미지참조] 69

Figure 29. SEM images of the hBN growth results as the number of growth cycles increases. 71

Figure 30. SEM images of hBN growth results as a function of growth temperature. 72

Figure 31. SEM images of the hBN growth results as a function of TEB injection time. 74

Figure 32. SEM images of the hBN growth results as a function of NH₃ injection time. 74

Figure 33. SEM images of the hBN growth results as a function of Interruption (IB) time.[이미지참조] 76

Figure 34. SEM images of the hBN growth results as a function of Interruption (IN) time.[이미지참조] 76

Figure 35. AFM images of sapphire surface after oxidation and piranha treatment process. 79

Figure 36. XPS measurement of sapphire substrate. 79

Figure 37. Configuration of Ni (111) after post-annealing. 82

Figure 38. Orientation of Cu on sapphire substrate. 83

Figure 39. Characterization of single crystal Ni (111) film on sapphire substrate. 84

Figure 40. Growth mechanism of hBN on Cu substrate. 87

Figure 41. Growth mechanism of hBN on Ni substrate. 88

Figure 42. AFM height sensor and phase images of hBN on Ni (111). 90

Figure 43. SEM images of hBN on Ni (111). 91

Figure 44. SEM images of fully grown hBN on Ni (111) at 2-inch wafer-scale. 94

Figure 45. Selected Area Electron Diffraction (SAED) pattern images of 9 points in large-area hBN. The orientation of 6 symmetrical hexagonal patterns with the same angle. It shows that all... 95

Figure 46. LEED patterns of single-crystalline hBN on Ni (111). The hexagonal pattern at 9 different locations has the same rotation angle. 96

Figure 47. Thickness data of transferred hBN on SiO₂/Si substrate. 97

Figure 48. Thickness data of transferred hBN on SiO₂/Si substrate. AFM images of the transferred hBN is measured at 9 points and exhibits similar thickness values between the hBN... 98

Figure 49. Raman measurement of transferred hBN on SiO₂/Si substrate. 99

Figure 50. Results for XPS spectrum of hBN. 99

Figure 51. Leakage current measurement of multi-layer hBN. 101

Figure 52. Electrochemical bubbling transfer method of hBN on Ni (111). 103

Figure 53. SEM images of hBN before and after transfer. 103

초록보기

 Two-dimensional (2D) hexagonal boron nitride (hBN) has the potential to be used in various electronics and optoelectronics owing to its unique properties, such as electrical insulation, chemical stability, mechanical inertness, and high thermal conductivity. The layered structure of hBN has dangling bond free structure, atomically flat surface, which prevents charge scattering and electron doping from the substrate. It also suppresses the formation of oxide trap sites. hBN is the only 2D material with insulation properties and wide bandgap (~6 eV). When the thickness of hBN decreases, it becomes susceptible to charge tunneling and poses a significant problem by generating leakage currents in the device. Moreover, the insulation properties change depending on the number of layers; the tunneling current can be controlled when hBN has more than ten layers. Using multi-layer hBN can prevent the degradation of intrinsic properties of 2D materials and improve the performance of the device. Although large-area growth of single-layer hBN has been reported, there is a need for studies on multi-layer hBN synthesis while controlling the number of layers on a large scale.

In this dissertation, a method for epitaxial growth of wafer-scale multi-layer hBN on Ni (111) using triethylborane (TEB) and NH3 by metal-organic chemical vapor deposition (MOCVD) is demonstrated. The Ni (111) film facilitated an epitaxial growth of high crystalline multi-layer hBN at high temperatures. The sapphire surface was modified with the same bonding orientation relationship, and a Ni film was deposited. High-temperature annealing was performed to produce single crystal Ni on the sapphire surface. This process can serve as a substrate for hBN to grow on Ni (111) epitaxially. By controlling the number of growth cycles in MOCVD, a growth condition is provided for the B and N precursors to react sufficiently on the Ni (111) surface. The synthesized 2D hBN can be applied as a dielectric layer and as an interlayer that protects the channels in the structure of the device.

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