Gallium Oxide-Based Devices: Electrical and Optical Characterization for High Performance

다국어 초록 (Multilingual Abstract)

This paper verifies the practical applicability of Ga2O3-based devices by establishing high-quality thin-film growth technologies and defect control strategies based on a systematic under-standing of the physical properties of Ga2O3, an ultra-wide-bandgap semiconductor material, and by applying them to extreme-environment sensor devices. Recently, the physical limitations of conventional Si and wide-bandgap semiconductor materials have become increasingly evident in the fields of high-voltage and high-power electronics, as well as in extreme-environment sensing applications such as ultraviolet (UVC) and X-ray detection. Consequently, Ga2O3 is attracting significant attention as a promising next-generation material capable of replacing existing semi-conductors. Ga2O3 offers excellent electrical and optical properties owing to its ultra-wide bandgap of approximately 4.5–5.3 eV and high breakdown field. In addition, its melt-growth ca-pability provides a distinct advantage in securing large-area bulk substrates and enabling low-cost mass production, further enhancing its technological and industrial potential.
Ga2O3 is a polymorphic material comprising various crystal phases, including α, β, γ, δ, ε, and κ, each of which exhibits distinct crystal structures as well as electrical and optical properties. In this study, the structural, electrical, and optical characteristics of each crystal phase were system-atically compared and analyzed to elucidate their respective application potentials. In particular, α -Ga2O3 enables high-quality heteroepitaxial growth owing to its excellent crystallographic com-patibility with sapphire substrates and exhibits properties well suited for UVC photodetectors due to its high selectivity in the ultraviolet region. In contrast, β-Ga2O3 is the most thermodynamical-ly stable phase and offers distinct advantages for radiation detection and high-reliability device applications, based on its superior electrical properties and thermal stability.
Furthermore, process technologies and defect control strategies for the growth of high-quality Ga2O3 thin films are established. By effectively suppressing the pre-reaction phenomenon during the α-Ga2O3 growth process, thin films with significantly improved crystal quality were achieved. For β-Ga2O3, a defect engineering approach based on a plasma nitridation process was introduced to precisely control oxygen vacancy concentrations. As a result, substantial improvements in electrical characteristics and device operational stability were observed, clearly demonstrating the critical impact of Ga2O3 growth technology and defect engineering on overall device perfor-mance.
Based on the material and process studies, a variety of Ga2O3-based devices were fabricated. A highly sensitive α-Ga2O3 UVC photodetector was fabricated to demonstrate its excellent ultravio-let detection performance, and a β-Ga2O3 UVC phototransistor exhibiting normally-off operation was fabricated to verify its practical feasibility. Furthermore, a β-Ga2O3-based X-ray detector ca-pable of stable operation even under high-temperature conditions was developed, experimentally demonstrating the applicability of Ga2O3 as an extreme-environment sensor material.
In summary, this study presents a systematic and integrated approach to Ga2O3-based device research by linking the phase-specific material properties of Ga2O3 with high-quality growth techniques, defect control strategies, and device fabrication. The findings of this paper provide valuable fundamental insights for utilizing Ga2O3 as a next-generation ultra-wide-bandgap semi-conductor material and are expected to establish a crucial academic and technological foundation for the development of high-performance and high-reliability power devices and extreme-environment sensors.

목차 (Table of Contents)

• CHAPTER I. Introduction 1
• 1.1 Necessity of Next-Generation Wide Bandgap Semiconductors 2
• 1.2 Limitations of Conventional Wide-Bandgap Semiconductors 4
• 1.3 Material and Processing Advantages of Ga2O3 5
• CHAPTER Ⅱ. Material Property Analysis of Ga2O3 10
• 2.1 Comparison of Material Properties in Crystalline Phases of Ga2O3 11
• 2.1.1 Introduction 11
• 2.1.2 Experimental methods 12
• 2.1.3 Results and discussion 14
• 2.1.4 Conclusion 21
• 2.1.5 Reference 22
• CHAPTER Ⅲ. High-Quality Ga2O3 Growth and Defect Engineering 24
• 3.1 Pre-Reaction Suppression in α-Ga2O3 HVPE Growth 25
• 3.1.1 Introduction 25
• 3.1.2 Experimental methods 27
• 3.1.3 Results and discussion 30
• 3.1.4 Conclusion 38
• 3.1.5 Reference 39
• 3.1.6 Supplementary information 42
• 3.2 Defect Engineering of β-Ga2O3 via Plasma Nitridation 47
• 3.2.1 Introduction 47
• 3.2.2 Experimental methods 48
• 3.2.3 Results and discussion 49
• 3.2.4 Conclusion 56
• 3.2.5 Reference 57
• CHAPTER Ⅳ. Ga2O3-Based UVC Photodetectors 59
• 4.1 High-Sensitivity α-Ga2O3 UVC Photodetector 60
• 4.1.1 Introduction 60
• 4.1.2 Experimental methods 61
• 4.1.3 Results and discussion 62
• 4.1.4 Conclusion 72
• 4.1.5 Reference 73
• 4.2 Normally-Off β-Ga₂O₃ UVC Phototransistor 76
• 4.2.1 Introduction 76
• 4.2.2 Experimental methods 78
• 4.2.3 Results and discussion 79
• 4.2.4 Conclusion 92
• 4.2.5 Reference 92
• 4.2.6 Supplementary information 99
• CHAPTER Ⅴ. Ga2O3-Based X-ray Detectors 104
• 5.1 Thermally Stable β-Ga2O3 X-ray Detector 105
• 5.1.1 Introduction 105
• 5.1.2 Experimental methods 106
• 5.1.3 Results and discussion 107
• 5.1.4 Conclusion 115
• 5.1.5 Reference 115
• 5.1.6 Supplementary information 118
• 5.2 Low-Dose X-ray Detection Using β-Ga2O3 Schottky Diode 123
• 5.2.1 Introduction 123
• 5.2.2 Experimental methods 125
• 5.2.3 Results and discussion 126
• 5.2.4 Conclusion 134
• 5.2.5 Reference 135
• CHAPTER Ⅵ. Conclusion 138
• 6.1 Summary 138