Title Page
ABSTRACT
국문 초록
PREFACE
Contents
CHAPTER 1. INTRODUCTION 18
1.1. Introduction to III-nitrides 18
1.1.1. Physical Properties 18
1.1.2. History of GaN 25
1.1.3. Growth of GaN MOCVD 26
1.2. Introduction of GaN-based LED 32
1.2.1. History of GaN Metal-semiconductor Emitters 32
1.2.2. Thermal and Efficiency droop 34
1.3. Introduction Chemical Lift-off 38
1.3.1. Lift-off Technologies 38
1.3.2. Trend of CLO Technology 41
CHAPTER 2. THEORETICAL BACKGROUND 43
2.1. Introduction to III-nitrides 43
2.1.1. Home-made MOCVD System for GaN 43
2.1.2. PECVD System 48
2.1.3. Sputtering System for AlN Buffer 51
2.1.4. CMP System 56
2.2. Epitaxial Lateral Overgrowth of GaN 59
CHAPTER 3. EXPERIMENTAL 62
3.1. Trapezoid-shaped Patterned Sapphire Substrate Fabrication 62
3.2. Air Tunnel Formation 64
3.2.1. Carbonization of Photoresist process 64
3.2.2. SiO₂ Mask Process with LT-GaN Seed Layer 68
3.2.3. Photoresist Mask Process with AlN Sacrificial Layer 72
3.3. Chemical Lift-off of GaN with Air tunnel 75
CHAPTER 4. RESULTS AND DISCUSSION 77
4.1. Carbonization of Photoresist process 77
4.1.1. Photoresist Carbonization Process 77
4.1.2. GaN Growth Behavior Dependence on the Thickness of the Photoresist 79
4.1.3. Characteristics of GaN on Carbonization of Photoresist Process 82
4.2. SiO₂ Mask Process with LT-GaN Seed Layer 85
4.2.1. Epitaxial Growth of GaN on LT-GaN layer 85
4.2.2. GaN Crystallinity on LT-GaN/SiO₂/TPSS 88
4.3. Photoresist and SiO₂ Mask Process with AlN Sacrificial Layer 90
4.3.1. Epitaxial Growth of GaN on AlN Sacrificial layer 90
4.3.2. Characteristics of GaN on AlN Sacrificial layer 92
4.4. Chemical Lift-off of GaN with Air tunnel 96
CHAPTER 5. CONCLUSION 101
REFERENCES 102
Table 1.1. Material parameters for III-nitrides and other semiconductors of interest (SiC is considered in its 6H polytype). (a) and (b) correspond to theoretical and experimental... 24
Table 1.2. The thermal conductivity and lattice constants of materials. 37
Table 1.3. Development status of chemical lift-off technology by year 42
Table 3.1. Details of the deposition conditions for LT-GaN seed layer and GaN epi-layer. 71
Table 4.1. Comparison of CLO conditions and peeling rates. 100
Fig. 1.1. Energy bandgap vs. lattice constant for selected semiconductors. 20
Fig. 1.2. Energy bandgaps and lattice constant for III-V semiconductors. 21
Fig. 1.3. Ball and stick stacking model of crystal (a) with zincblende structure along the [111] direction and (b) with wurtzite structure along the [0001] direction. 22
Fig. 1.4. Structure of the (a) Ga-face and (b) N-face GaN. 23
Fig. 1.5. Possible chemical reactions and rate limiting steps in MOCVD growth of GaN using ammonia and TMGa. 30
Fig. 1.6. Schematic illustration of boundary layer in a horizontal MOCVD reactor. Note temperature and concentration profiles in the boundary layer. 31
Fig. 1.7. EQE of a commercial high-power LED as a function of driving current measured at several ambient temperatures. 36
Fig. 1.8. Laser Lift-Off process schematic diagram. 40
Fig. 2.1. Image of the home-made MOCVD system. 45
Fig. 2.2. Gas-line schematic of the home-made MOCVD system. 46
Fig. 2.3. schematic of reactor geometry used in this work. 47
Fig. 2.4. Image of the PECVD system. 49
Fig. 2.5. Gas-line schematic of the PECVD system. 50
Fig. 2.6. Schematic diagram of sputtering deposition 53
Fig. 2.7. Image of the DC/RF sputtering system. 54
Fig. 2.8. Schematic of sputtering system in this work 55
Fig. 2.9. Image of the CMP system 57
Fig. 2.10. Schematic of sputtering system in this work 58
Fig. 2.11. Morphological changes in ELO GaN for different reactor pressures and growth temperatures. Growth time was 0.5 h. 60
Fig. 2.12. Changes in crystal quality of AlN (Graph) and morphological changes in ELO GaN (SEM image) for different RF power by RF sputtering. 61
Fig. 3.1. (a), (b) Patterned Sapphire substrate (PSS) and (c), (d) Trapezoid-shaped patterned sapphire substrate (TPSS). 63
Fig. 3.2. Schematic of the formation of air tunnel structure using carbonization of photoresist. 65
Fig. 3.3. Process time chart for MOCVD used for deposition of epitaxial GaN and carbonization. 66
Fig. 3.4. Formed air tunnel and Carbonization layer on TPSS. 67
Fig. 3.5. Schematic of the formation of air tunnel structure using SiO₂ mask. 69
Fig. 3.6. Process time chart for MOCVD used for deposition of epitaxial GaN on SiO₂/sapphire. 70
Fig. 3.7. Schematic of the formation of air tunnel structure using photoresist mask AlN sacrificial layer. 73
Fig. 3.8. Process time chart for MOCVD used for deposition of epitaxial GaN on AlN/SiO₂/Sapphire. 74
Fig. 3.9. Schematic of the formation of air tunnel structure using photoresist mask AlN sacrificial layer. 76
Fig. 4.1. Cross-sectional FE-SEM images of the coated photoresist thickness on TPSS: (a)-(c) and carbonized photoresist for 5 min by MOCVD; (d)-(f). 78
Fig. 4.2. Top and cross-sectional FE-SEM images of the GaN growth for 10 min by MOCVD. 80
Fig. 4.3. Top and cross-sectional FE-SEM images of GaN growth on a substrate using photoresist coated at 3700 rpm: (a) 10 min, (b) 20 min and (c) 60 min. 81
Fig. 4.4. X-ray diffraction pattern of GaN template with air tunnel structure. 83
Fig. 4.5. Photoluminescence spectrum of GaN with air tunnel at room temperature. 84
Fig. 4.6. FE-SEM images of the surface of TPSS with the SiO₂ mask applied (a) and LT-GaN deposited and annealed at 1020°C for 1 min (b). 86
Fig. 4.7. FE-SEM images of GaN growth by various time. 87
Fig. 4.8. Top and cross-sectional FE-SEM images of GaN epitaxial layer on LT-GaN/SiO₂/TPSS 88
Fig. 4.9. X-ray diffraction pattern of GaN epitaxial layer on LT-GaN/SiO₂/TPSS. 89
Fig. 4.10. Top and cross-sectional FE-SEM images of the GaN growth process: (a), (b) AlN sacrificial layer/TPSS structure with air tunnel before GaN growth; (c), (d) 1st step of growth... 91
Fig. 4.11. X-ray diffraction pattern of GaN template with air tunnel structure. 93
Fig. 4.12. Photoluminescence spectrum of GaN with air tunnels and normal GaN at room temperature. 94
Fig. 4.13. AFM image of GaN surface. Scan size was 10 × 10 µm². (a) 2D image, (b) 3D image, and (c) line scanning. 95
Fig. 4.14. Schematic of chemical lift-off (CLO) process. 98
Fig. 4.15. FE-SEM images of the backplane of the detached GaN: (a) Carbonization process, (b) SiO₂ mask process on LT-GaN seed layer, (c) Photoresist & SiO₂ mask process on AlN... 98
Fig. 4.16. (a) Schematic of CLO, (a) low-magnification FE-SEM image of the backplane of the detached GaN, and (b)–(d) high-magnification FE-SEM image by position on backplane... 99