Gallium Oxide: Materials Properties, Crystal Growth, and Devices (Springer Series in Materials Science, 293)

Preface
	Part I
	Part II
	Part III
	Part IV
Contents
Contributors
1 Introduction
	1.1 Introduction
	1.2 Material Properties
		1.2.1 Crystal Structures of Ga2O3
		1.2.2 Physical Properties of β-Ga2O3
	1.3 Bulk Melt Growth
	1.4 Epitaxial Growth
	1.5 Electrical Devices
		1.5.1 Advantages and Disadvantages of Ga2O3 Power Devices
		1.5.2 Schottky Barrier Diodes (SBDs)
		1.5.3 FETs
	1.6 DUV Photodetectors
	1.7 Summary
	References
Bulk Growth
2 Czochralski Method
	Abstract
	2.1 Introduction
	2.2 Czochralski Growth Furnace for Oxides
	2.3 β-Ga2O3—Early Attempts with the Czochralski Method
	2.4 Thermodynamics of Ga2O3
	2.5 Crystal Growth
		2.5.1 Impact of the Free Carrier Absorption on the Growth Stability
	2.6 Structural Quality
		2.6.1 Intentional Doping and Residual Impurities
	2.7 Effect of Annealing
	2.8 Summary
	Acknowledgements
	References
3 Vertical Bridgman Growth Method
	Abstract
	3.1 Introduction
	3.2 VB Growth Method and Crucible Materials
		3.2.1 VB Method Using Pt–Rh Alloy Crucible
		3.2.2 Measurement of β-Ga2O3 Melting Temperature and Determination of Pt–Rh Alloy Crucible Composition
	3.3 Growth and Characterization of VB-β-Ga2O3 Crystals
		3.3.1 Directional Solidification of β-Ga2O3 Single Crystals in the VB Furnace
		3.3.2 VB-β-Ga2O3 Crystals and Their Characteristics
		3.3.3 Crystal Defects and Electrical Properties
			3.3.3.1 Structural Defects
			3.3.3.2 Geometric Shape and Formation Mechanism of Line-shaped Defects
			3.3.3.3 Electrical Properties
	3.4 Summary
	References
4 Floating Zone Method, Edge-Defined Film-Fed Growth Method, and Wafer Manufacturing
	Abstract
	4.1 Floating Zone Method
	4.2 Edge-Defined Film-Fed Growth Method
		4.2.1 Growth Sequence and Conditions of EFG
		4.2.2 Twin Boundaries
		4.2.3 Dislocations and Nanovoids
		4.2.4 Residual Impurities
		4.2.5 Intentional Doping
		4.2.6 Distribution of Dopants
	4.3 Wafer Manufacturing
		4.3.1 Wafer Manufacturing Process
		4.3.2 Effect of Annealing on Carrier Concentration
	References
Epitaxial Growth
5 Plasma-Assisted Molecular Beam Epitaxy 1
	Abstract
	5.1 Introduction
	5.2 Characterization
	5.3 β-Ga2O3 PAMBE Growth
	5.4 Doping
	5.5 Heterostructures
	References
6 Plasma-Assisted Molecular Beam Epitaxy 2
	Abstract
	6.1 Introduction
	6.2 MBE Growth Chamber and in Situ Analytics to Investigate Growth Kinetics
		6.2.1 Line-of-Sight Quadrupole Mass Spectrometry (QMS)
		6.2.2 Laser Reflectometry (LR)
		6.2.3 Quantifying the Metal-, Oxygen-, and Desorbing Fluxes
	6.3 Suboxide-Related Kinetics During Binary Growth
		6.3.1 Flux Stoichiometry and Growth Versus Etching
		6.3.2 Growth Temperature Dependence and Growth Window
		6.3.3 Suboxide-Mediated Two-Step Growth Mechanism a General Explanation
		6.3.4 Comparing Ga2O3, In2O3, and SnO2 Growth Oxidation Efficiency and Suboxide Vapor Pressure
	6.4 Thermodynamics Aspects
		6.4.1 (InxGa1-X)2O3 Growth: Ga–O Bonds Versus In–O Bonds
		6.4.2 Metal-Exchange Catalysis (MEXCAT) Enhances the Growth Window of Ga2O3: Kinetics Collaborating with Thermodynamics
		6.4.3 Stabilizing Different Phases
		6.4.4 Surface Faceting
	6.5 Open Questions
	Acknowledgements
	References
7 Ozone-Enhanced Molecular Beam Epitaxy
	Abstract
	7.1 Introduction
	7.2 Surface Orientation Dependence of β-Ga2O3 Homoepitaxial Growth by Ozone MBE
		7.2.1 Experimental Methodology
			7.2.1.1 Ozone MBE System
			7.2.1.2 Sample Preparation and Evaluation
		7.2.2 Orientation Dependence of Growth Rate
		7.2.3 Orientation Dependence of Surface Morphology
		7.2.4 Orientation Dependence of Crystal Quality
			7.2.4.1 Crystal Defect Generation Mechanism on the (\\overline{2} 01) Plane
			7.2.4.2 Crystal Defect Generation on the (101) Plane
	7.3 β-Ga2O3 Ozone MBE Growth on (010) Plane
		7.3.1 Experimental Methodology
		7.3.2 Growth Rate as a Function of VI/III Ratio
		7.3.3 Growth Temperature and VI/III Ratio Dependence of Surface Morphology of Unintentionally Doped β-Ga2O3 Homoepitaxial Films
		7.3.4 Growth Temperature and VI/III Ratio Dependence of Surface Morphology of Sn-Doped β-Ga2O3 Homoepitaxial Films
		7.3.5 Sn Doping of β-Ga2O3 Homoepitaxial Films
			7.3.5.1 Sn-Dopant Control
			7.3.5.2 Carrier Concentration and Electron Mobility of Sn-Doped β-Ga2O3 Films
	7.4 Summary
	References
8 Metalorganic Chemical Vapor Deposition 1
	Abstract
	8.1 Metalorganic Precursors and Oxygen Sources
	8.2 Homoepitaxial Ga2O3 Growth by MOCVD
		8.2.1 MOCVD Growth of β-Ga2O3/(100) β-Ga2O3
		8.2.2 MOCVD Growth of β-Ga2O3/(010) β-Ga2O3
	8.3 Doping and Background Impurities in an MOCVD-Grown Ga2O3 Thin Films
		8.3.1 Unintentional and N-Type Doping
		8.3.2 Deep Acceptor Doping
	8.4 β-(AlxGa1−x)2O3/β-Ga2O3 Heterostructures and Superlattices
		8.4.1 β-(AlxGa1−x)2O3/β-Ga2O3 Heterostructures
		8.4.2 β-(AlxGa1−x)2O3/β-Ga2O3 Superlattices
	8.5 Conclusions
	Acknowledgements
	References
9 Metal Organic Chemical Vapor Deposition 2
	9.1 Introduction
	9.2 Metalorganic Chemical Vapor Deposition (MOCVD)
	9.3 Heteroepitaxy of Ga2O3 Using MOCVD
		9.3.1 Growth of β-Ga2O3
		9.3.2 Growth of α- and ε-Ga2O3
		9.3.3 Effect of Growth Condition on Film Growth
	9.4 Doping in MOCVD-Grown Heteroepitaxial Ga2O3 Films
	9.5 Summary and Conclusions
	References
10 Halide Vapor Phase Epitaxy 1
	Abstract
	10.1 Introduction
	10.2 Thermodynamic Analysis of β-Ga2O3 Growth by HVPE
		10.2.1 Calculation Procedure
		10.2.2 Calculation Results
	10.3 Homoepitaxial Growth of UID β-Ga2O3 Layers by HVPE
	10.4 Growth of Intentionally Si-Doped β-Ga2O3 Layers by HVPE
	10.5 Summary
	Acknowledgements
	References
11 Halide Vapor Phase Epitaxy 2
	Abstract
	11.1 Introduction
	11.2 HVPE of α-Ga2O3
		11.2.1 Features of α-Ga2O3
		11.2.2 Growth Apparatus and Growth Conditions
		11.2.3 HVPE Growth Characteristics of α-Ga2O3
		11.2.4 Properties of HVPE-Grown α-Ga2O3
		11.2.5 n-Type Doping Control
			11.2.5.1 Motivation
			11.2.5.2 Experimental Methods
			11.2.5.3 Properties of Ge-Doped α-Ga2O3
		11.2.6 Improvement of Crystal Quality by Epitaxial Lateral Overgrowth
			11.2.6.1 Motivation
			11.2.6.2 Experimental Methods
			11.2.6.3 Morphological Characterization of ELO-Grown α-Ga2O3
			11.2.6.4 Structural Characterization of ELO-Grown α-Ga2O3
	11.3 HVPE of ε-Ga2O3
		11.3.1 Features and Potential Applications of ε-Ga2O3
		11.3.2 Growth Methods and Conditions of ε-Ga2O3
		11.3.3 Properties of HVPE-Grown ε-Ga2O3
	11.4 Summary and Future Prospects
	Acknowledgements
	References
12 Mist Chemical Vapor Deposition 1
	Abstract
	12.1 Dawn of Corundum-Structured α-Ga2O3
		12.1.1 Semistable Phases of Ga2O3
		12.1.2 Mist Chemical Vapor Deposition for Oxide Growth
		12.1.3 Growth of α-Ga2O3 on Sapphire Substrates
	12.2 Fundamental Properties of α-Ga2O3
		12.2.1 Growth Characteristics
		12.2.2 Electrical Properties
		12.2.3 Defect Control
		12.2.4 Thermal Stability
	12.3 Growth and Properties of Corundum-Structured III-Oxide Alloys
		12.3.1 Bandgap Engineering
		12.3.2 Corundum-Structured p-Type Layers
	12.4 Future Prospects of α-Ga2O3
	References
13 Mist Chemical Vapor Deposition 2
	Abstract
	13.1 Introduction
	13.2 Mist CVD
	13.3 Crystal Structure
	13.4 Substrates
	13.5 Occurrence of Rotational Domains in Orthorhombic ε-Ga2O3
	13.6 Bandgap Engineering
	References
14 Pulsed Laser Deposition 1
	Abstract
	14.1 Introduction
	14.2 Unintentionally Doped β-Ga2O3 Homoepitaxial Films
	14.3 Impurity-Doped β-Ga2O3 Homoepitaxial Films
	14.4 β-Ga2O3 Heterostructures
	References
15 Pulsed Laser Deposition 2
	15.1 Short Introduction and History of Pulsed Laser Deposition
	15.2 The PLD Process
	15.3 Creation of Continuous Cation Composition Spreads by PLD
	15.4 Growth of (In, Ga, Al)2O3 by PLD
		15.4.1 Pseudomorphic Growth of α-(Al, Ga)2O3 Thin Films on R-Plane Sapphire
		15.4.2 Pulsed Laser Deposition of Heteroepitaxial Ga2O3 Thin Films
		15.4.3 Doping and Alloying of (In, Ga, Al)2O3 PLD Thin Films
	15.5 Summary and Outlook
	References
16 Low-Pressure Chemical Vapor Deposition
	Abstract
	16.1 Introduction
	16.2 LPCVD of β-Ga2O3 Thin Films on Off-Axis Sapphire Substrates
	16.3 LPCVD of β-Ga2O3 Thin Films on Native Ga2O3 Substrates
		16.3.1 Effects of Growth Temperature on Surface Morphology
		16.3.2 Growth of β-Ga2O3 on (001) and (010) Ga2O3 Substrates
		16.3.3 LPCVD β-Ga2O3-Based Schottky Barrier Diodes
	16.4 LPCVD of β-Ga2O3 Rod Structures
	16.5 Conclusion
	Acknowledgements
	References
Materials Properties
17 First-Principles Calculations 1
	17.1 Bulk Properties
		17.1.1 Crystal Structure
		17.1.2 Brillouin Zone
		17.1.3 First-Principles Methods
		17.1.4 Structural, Electronic, and Optical Properties of Bulk Ga2O3
	17.2 Alloys
		17.2.1 Ground-State Structures
		17.2.2 Lattice Constants
		17.2.3 Band Gaps and Optical Properties
		17.2.4 Crystal Structures
		17.2.5 Band Alignments
	17.3 Conclusions
	References
18 First-Principles Calculations 2
	18.1 Introduction
	18.2 Defect Formation Energies and Computational Methodology
		18.2.1 Defect Charge-State Transition Levels
		18.2.2 Evaluating Formation Energies
	18.3 Results and Discussion
		18.3.1 Oxygen Vacancies
		18.3.2 Donor Impurities and Dopants
		18.3.3 Gallium Vacancies and Compensation
		18.3.4 Acceptor Impurities
		18.3.5 Fundamental Barriers to p-Type Dopability
		18.3.6 Conclusions
	References
19 Structural Properties 1
	Abstract
	19.1 Introduction
	19.2 Experimental Procedure
	19.3 Results and Discussion
		19.3.1 Arrays of Edge Dislocations
		19.3.2 Platelike Nanovoids
		19.3.3 Twins and Twin Lamellae
	19.4 Conclusions
	References
20 Structural Properties 2
	20.1 Introduction
	20.2 Crystal Structure and Slip System
	20.3 Dislocations and SFs Observed by XRT
		20.3.1 Experiments
		20.3.2 Dislocations
		20.3.3 SFs
	20.4 Summary
	References
21 Structural Properties 3
	Abstract
	21.1 Introduction
	21.2 Positron Annihilation Spectroscopy
	21.3 Positrons in Solids: Physical Background
		21.3.1 Experimental Methods
	21.4 Findings in β-Ga2O3
		21.4.1 Ga2O3 Reference Material
		21.4.2 Vacancy Defects and Electrical Compensation
		21.4.3 Vacancy Formation in (InxGa1−x)2O3 Alloys
	21.5 Conclusions
	References
22 Electrical Properties 1
	Abstract
	22.1 Introduction
	22.2 Shallow Donors
	22.3 Deep Acceptors
	22.4 Unintentional Donors and Acceptors
	22.5 Conclusion
	References
23 Electrical Properties 2
	Abstract
	23.1 Introduction
	23.2 Overview on Mobility and Velocity-Field Curves in β-Ga2O3
	23.3 Impact Ionization Rates
	23.4 Transport Under Very High Field
	23.5 Avalanche Breakdown and Implication on Devices
	23.6 Conclusions
	Acknowledgements
	References
24 Electrical Properties 3
	Abstract
	24.1 Introduction
	24.2 Materials Characterization Approach for Deep Level Defects in β-Ga2O3
	24.3 Deep Levels in β-Ga2O3
	24.4 Trap Identification in β-Ga2O3 Transistors and Their Influence on Device Instabilities
		24.4.1 MESFET Experimental Details and Terminal Characteristics
		24.4.2 Isothermal Constant Drain Current Deep Level Transient Spectroscopy
		24.4.3 Identifying the Traps Responsible for Threshold Voltage Instability
	24.5 Summary of Traps and Potential Sources
	24.6 Conclusions
	Acknowledgements
	References
25 Electrical Properties 4
	Abstract
	25.1 Introduction
	25.2 Characterization of Dielectric-Semiconductor Interfaces
		25.2.1 Band Offsets
		25.2.2 Capacitance-Voltage Characterization of HfO2/Ga2O3 and ZrO2/Ga2O3 Interfaces
		25.2.3 Interface State Density Analysis
	25.3 Summary
	Acknowledgements
	References
26 Electrical Properties 5
	Abstract
	26.1 Introduction
	26.2 β-Ga2O3 Crystal Structure
	26.3 Experimental Procedure
	26.4 Defect Observations
		26.4.1 Unetched Pits on (010)
		26.4.2 Void-Related and Dislocation-Related Etch Pits on the (010) Plane
		26.4.3 ( \\mathit{\\bar{\\bi 2}{\\bi 01}} ) Orientation Etch Pits and Pattern
		26.4.4 The (001) Surface
		26.4.5 The (100) Surface Orientation
	26.5 Relation with SBD Characteristics
		26.5.1 The (010) Surface
		26.5.2 The ( \\mathit{\\bar{\\bi 2}{\\bi 01}} ) and (001) Orientations
	26.6 Summary
	Acknowledgements
	References
27 Optical Properties
	Abstract
	27.1 Introduction
	27.2 Experimental Procedure
	27.3 Valence Band Ordering of β-Ga2O3
	27.4 Temperature-Dependent Exciton Resonance Energies and Their Correlation with IR-Active Optical Phonon Modes
	27.5 Emission Properties of β-Ga2O3
	27.6 Summary
	Acknowledgements
	References
28 Phonon Properties
	28.1 Introduction
	28.2 Methods
		28.2.1 Density Functional Theory
		28.2.2 Generalized Ellipsometry
	28.3 Phonon Mode Properties in β-Ga2O3
		28.3.1 Unit Cell and Brillouin Zone Center Modes
		28.3.2 TO and LO Mode Frequency and Orientation Parameters
		28.3.3 The Eigendielectric Summation Approaches
		28.3.4 Mode Multiplicity in β-Ga2O3 Without Free Charge Carriers
		28.3.5 Inner and Outer Phonon Modes and Phonon Mode Order in Monoclinic Plane of β-Ga2O3
	28.4 Phonon and Free Charge Carrier Properties  in β-Ga2O3
		28.4.1 LO-Phonon-Plasmon Coupling in β-Ga2O3
		28.4.2 Mode Multiplicity in β-Ga2O3 with Free Charge Carriers
		28.4.3 LPP Mode Parameters as a Function of the Plasma Frequency Parameter
		28.4.4 LPP Modes for Polarization Along b
		28.4.5 The Optical Hall Effect in β-Ga2O3
	28.5 Outlook
	28.6 Summary
	28.7 Note Added in Proof
	References
29 Thermal Properties
	Abstract
	References
30 Scintillation Properties
	Abstract
	30.1 Scintillators and Scintillation Detectors
	30.2 Methodology of R&D of Ga2O3 Scintillators
	30.3 Results
	30.4 Summary and Conclusion
	References
Devices
31 Field-Effect Transistors 1
	Abstract
	31.1 Introduction
	31.2 Exploiting Critical Electric Field Strength for Low-Loss Devices
		31.2.1 Minimizing Channel Resistance for a Target Breakdown Voltage
		31.2.2 Removing Parasitic Resistance for Minimal RON
	31.3 Unipolar Operation
	31.4 State-of-the-Art RF Devices
	31.5 Thermal Analysis and Solutions
	31.6 Summary and Conclusion
	References
32 Field-Effect Transistors 2
	Abstract
	32.1 Introduction
	32.2 Lateral Depletion-Mode Ga2O3 FETs
		32.2.1 MESFET
		32.2.2 MOSFET with Si-Ion-Implanted Source/Drain Contacts
		32.2.3 MOSFET with Si-Ion-Implanted Channel and Contacts
		32.2.4 Field-Plated MOSFETs
		32.2.5 MOSFET with Ge-Doped Channel
		32.2.6 Critical Field Strength in Ga2O3 MOSFETs
	32.3 Thermal Characteristics of Ga2O3 MOSFETs
	32.4 Ga2O3 MOSFETs for Radiation-Hard Electronics
	32.5 Lateral Enhancement-Mode Ga2O3 FETs
		32.5.1 Overview
		32.5.2 Planar MOSFETs
		32.5.3 Fin-Array MOSFETs
	32.6 Current Aperture Vertical Ga2O3 MOSFET
	32.7 Summary and Conclusions
	Acknowledgements
	References
33 Field-Effect Transistors 3
	Abstract
	33.1 Introduction
	33.2 Electrical Transport in (AlGa)2O3/Ga2O3 MODFETs
	33.3 Modulation-Doped Field-Effect Transistors
	33.4 Summary
	References
34 Field-Effect Transistors 4
	Abstract
	34.1 Back-Gated Depletion/Enhancement Modes GOOI FETs on SiO2/Si Substrate with Record Drain Current Density of 1.5/1 A/mm
		34.1.1 Back-Gate GOOI FET Fabrication
		34.1.2 D/E-Mode GOOI FETs with Record High Drain Current Densities
		34.1.3 VT Dependence on the β-Ga2O3 Nano-membrane Thickness
		34.1.4 Interface Characterization of β-Ga2O3 Nano-membrane on Conventional Dielectrics
	34.2 Minimized Self-heating Effect of Top-Gate GOOI FETs on High Thermal Conductivity Substrates
		34.2.1 Top-Gate GOOI FET Fabrication
		34.2.2 I–V Electrical Characterization
		34.2.3 Suppression of Self-heating Effects by High Thermal Conductivity Substrates
	34.3 β-Ga2O3 Nano-membrane NC-FET with Steep SS for Wide Bandgap Logic Application
		34.3.1 β-Ga2O3 Nano-membrane NC-FET Structure and Fabrication
		34.3.2 β-Ga2O3 NC-FET with Bidirectional SS lessthan 60 mV/dec and Small Hysteresis
	Acknowledgements
	References
35 Field-Effect Transistors 5
	Abstract
	35.1 Brief Introduction of Vertical FinFET Device Concept
	35.2 Ga2O3 Vertical FinFET Structure Design
		35.2.1 Ga2O3 Vertical FinFET Device Structure
		35.2.2 Ga2O3 Vertical FinFET Device Operation
		35.2.3 Ga2O3 Vertical FinFET Device Fabrication
		35.2.4 Design for High Breakdown Voltages
	35.3 Current–Voltage Characteristics of Ga2O3 Vertical FinFETs
		35.3.1 Device Characteristics
		35.3.2 Threshold Voltage Control and Normally-on Versus Normally-off FinFETs
		35.3.3 Voltage Blocking Gain and Drain-Induced Barrier Lowering Effects
	35.4 Summary of Vertical Power FinFETs and Brief Mention of Trench SBDs
	References
36 Diodes 1
	Abstract
	36.1 Introduction
	36.2 Applications
	36.3 Reverse Breakdown Voltage
	36.4 On-State Resistance
	36.5 Edge Termination Design
	36.6 Summary of Literature on Ga2O3 Rectifiers
	36.7 Summary
	Acknowledgements
	References
37 Diodes 2
	37.1 Introduction
	37.2 Suitable p-Type Materials
		37.2.1 Nickel(II) Oxide
		37.2.2 Copper(I) Oxide
		37.2.3 Zinc Cobalt Oxide
	37.3 Diode Properties
		37.3.1 Device Layout and Junction Symmetry
		37.3.2 Current-Voltage Characteristics
		37.3.3 Capacitance Voltage Measurements and Built-In Potential
		37.3.4 Breakdown of the Diodes
	37.4 Summary and Outlook
	References
38 Photodetectors
	Abstract
	38.1 Introduction
	38.2 Types of Photodetectors
	38.3 Film-Based Photoconductors and MSM Photodetectors
	38.4 Photodetectors Based on (AlxGa1−x)2O3 and (InxGa1−x)2O3 Alloy Films
	38.5 Schottky Photodiodes Using β-Ga2O3 Single-Crystal Substrates
	38.6 Heterojunction Photodetectors
	38.7 Photodetectors Based on β-Ga2O3 Nanostructures
	38.8 Conclusion
	References
39 Image Sensors
	Abstract
	39.1 Introduction
	39.2 Theory
		39.2.1 Stacked Image Sensor
		39.2.2 Ga2O3/Se Photodiode
	39.3 Fabrication of Photodiode
	39.4 Results and Discussion
		39.4.1 Characteristics of Ga2O3/Se Photodiode
		39.4.2 Improving Characteristics via Crystallization of Ga2O3
	39.5 Conclusion
	References
Special Contribution
40 Gallium Oxide Materials and Devices
	40.1 Pre–2008
	40.2 2008–2012
	40.3 2013–2014
	40.4 2015–2017
	40.5 2018–Future
	References
Index