Contents Abstract Zusammenfassung Abbreviations and Acronyms Notations for Precursor Molecules xvi xviii xx xxi Chapter 1 Introduction 1 1.1 General aspect of group-iii nitrides and their application 3 1.2 Basics of semiconductors 5 1.2.1 Direct band gap and indirect band gap semiconductors 5 1.3 Gallium nitride 6 1.3.1 Crystal structure of gallium nitride 6 1.4 Substrates for gallium nitride 8 1.5 Synthetic approaches for gallium nitride 12 1.5.1 Gallium nitride using trimethyl gallium and ammonia 13 1.6 Basics of CVD process 15 1.6.1 General requirement of precursor for MOCVD/MOVPE 16 1.6.2 Fundamental processes underlying CVD 17 1.6.3 Nucleation and growth 18 1.6.4 Thermodynamics, kinetics and mass transport phenomena 19 1.6.4.1 Thermodynamics 19 1.6.4.2 Chemical kinetics 20 1.6.4.3 Mass transport phenomena 21 1.7 CVD models 22 1.8 A comment on atomic layer deposition of gallium nitride 24 1.9 The scope of the present work 25 1.10 References 26 Chapter 2 Synthesis of Intramolecularly Base Stabilized Dialkyl Gallium Amides and Their Use in GaN MOCVD 29 2.1 Precursor chemistry of gallium nitride: Present understanding 29 x
2.1.1 Amide type nitrogen 30 2.1.2 Hydrazido type nitrogen 30 2.1.3 Azide type nitrogen 31 2.2 Alternative nitrogen sources 32 2.3 Preamble to synthesis of the reported compound 33 2.4 Synthesis of ligand stabilized dialkyl gallium amides 33 2.5 Thermal characteristics of precursor 1 and 2 36 2.6 Deposition of GaN films using precursor 1 and 2 37 2.7 Effect of ammonia on precursor 1 and 2 with N 2 as carrier gas 38 2.8 Effect of ammonia on precursor 1 and 2 with H 2 as carrier gas 40 2.9 RBS Measurements on GaN films 41 2.10 Discussion 41 2.11 Conclusions 44 2.12 References 45 Chapter 3 Ligand Stabilized Dialkyl Aluminium Amide as New Precursor for Aluminium Nitride Thin Films 50 3.1 Introduction 50 3.2 Results 52 3.2.1 Synthesis and NMR spectroscopy 52 3.2.2 Thermal characteristic of the precursor 53 3.2.3 AlN film deposition and characterization 54 3.2.3.1 Single source characteristics 54 3.2.3.2 Deposition with ammonia 56 3.2.3.3 RBS of AlN films 59 3.3 Discussion 59 3.4 Conclusions 62 3.5 References 63 Chapter 4 Evaluation of Cyclic Gallium Amides as Precursors for Gallium Nitride Thin Films 65 4.1 Introduction 65 4.2 Synthesis of new cyclic gallium amides 66 xi
4.3 Crystal structure of [MeGa(NR(CH 2 ) 2 NR)] 2 67 4.4 Crystal structure of [EtN(CH 2 ) 2 NEtGa(CH 2 ) 3 NEt 2 ] 2 71 4.5 Thermal characterization of 5 and 6 72 4.6 Thermal characterization of 7 74 4.7 MOCVD of [MeGa(NEt(CH 2 ) 2 NEt)] 2 for GaN 75 4.7.1 Single source characteristics 75 4.7.2 Deposition with ammonia 76 4.8 Discussion 78 4.9 Conclusions 80 4.10 References 81 Chapter 5 MOCVD of Gallium Nitride nanostructures Using the Single Molecule Precursor Bisazidodiethylaminopropylgallium 83 5.1 Introduction 83 5.2 Applications of nanostructure 84 5.3 Nanostructures of group-iii nitrides 85 5.3.1 Aluminium nitride nanostructures 86 5.3.2 Indium nitride nanostructures 86 5.3.3 Gallium nitride nanostructures 87 5.3.3.1 Direct reaction of gallium with ammonia 87 5.3.3.2 Nanostructures from gallium, gallium nitride and ammonia 88 5.3.3.3 Nanostructures from Ga 2 O or Ga 2 O 3 and ammonia 88 5.3.3.4 Nanostructures from hydride/halide vapor phase epitaxy and sublimation 89 5.3.3.5 Nanostructures from metalorganic precursors 89 5.3.3.6 Nanostructures from other methods 90 5.4 Nanostructure growth mechanisms 90 5.5 SMPs as source for GaN nanostructures 91 5.6 Crystal structure of Bisazido(diethylaminopropyl)gallium 93 5.7 GaN nanostructure deposition conditions 93 5.8 Self-organized gallium nitride nanopillars 95 xii
5.8.1 Photoluminescence of gallium nitride nanopillars 98 5.9 Autocatalytic VLS mechanism for GaN nanopillars 99 5.10 Preferentially ordered gallium nitride nanorods 101 5.11 Randomly oriented gallium nitride nanowires 105 5.11.1 XPS of GaN nanowires 108 5.11.2 UV-VIS spectra of GaN nanowires 109 5.12 Effect of substrate on GaN nanowire growth 111 5.13 Effect of temperature on the GaN nanowire growth 111 5.14 Effect of pressure on gallium nitride nanowire growth 112 5.15 Possible growth mechanism of GaN nanowires and nanorods 112 5.16 AFM study on GaN nanowires 114 5.17 A comparison of nanostructure grown using BAZIGA and E-BAZIGA 116 5.18 Conclusions 118 5.19 References 119 Chapter 6 MOCVD Boundary Conditions in a Vertical Stagnation Flow Reactor for GaN Deposition from a Single Molecule Precursor - A Multiscale Simulation Study 126 6.1 Introduction 126 6.2 What is multiscale simulation/modeling of CVD? 128 6.3 Classical CVD versus Simulation CVD 130 6.3.1 Classical CVD 130 6.3.2 Simulation CVD 130 6.4 Definition of boundary conditions 131 6.5 Measurement of boundary conditions in vertical reactor 131 6.5.1 Mass flow of BAZIGA 132 6.5.2 Temperature distribution in the vertical reactor 135 6.5.3 Growth rate determination 143 6.6 The new reactor setup 147 6.7 Summary of the theoretical and CFD results 148 6.8 Conclusions 150 6.9 References 151 xiii
Chapter 7 Experimental 153 7.1 Starting material 153 7.2 General techniques in synthesis 153 7.3 Solvent drying procedure 154 7.4 Precursor characterization techniques 154 7.4.1 Melting point 154 7.4.2 Nuclear magnetic resonance spectroscopy 154 7.4.3 Mass spectrometry 154 7.4.4 Infrared spectroscopy 155 7.4.5 Elemental analysis 155 7.4.6 Atomic absorption spectroscopy 155 7.4.7 Thermogravimetry and differential thermal analysis 155 7.4.8 Single crystal X- ray structure analysis 155 7.5 Precursor Synthesis 156 7.5.1 Synthesis of Me 2 Ga[NEt(CH 2 ) 2 NMe 2 ] 156 7.5.2 Synthesis of Et 2 Ga[NEt(CH 2 ) 2 NMe 2 ] 156 7.5.3 Synthesis of MeClGa [NEt(CH 2 ) 2 NMe 2 ] 157 7.5.4 Synthesis of Me 2 Al[NEtCH 2 )NMe 2 ] 157 7.5.5 Synthesis of [MeN(CH 2 ) 2 NMeGaMe] 2 158 7.5.6 Synthesis of [EtN(CH 2 ) 2 NEtGaMe] 2 158 7.5.7 Synthesis of [EtN(CH 2 ) 2 NEtGa(CH 2 ) 3 NEt 2 ] 2 159 7.5.8 Synthesis of BAZIGA and E-BAZIGA 159 7.6 GaN and AlN thin film and GaN nanostructure deposition 167 7.6.1 Description of vertical stagnation flow reactor 167 7.6.2 Substrate preparation 169 7.6.3 Deposition experiments 169 7.7 Film and nanostructure characterization 169 7.7.1 X- ray diffraction 169 7.7.2 Ultra-violet visible spectroscopy 170 7.7.3 X-ray photoelectron spectroscopy 170 7.7.4 Scanning electron microscopy (SEM) and energy dispersive X-ray analysis 170 xiv
7.7.5 Transmission electron microscopy 170 7.7.6 Rutherford backscattering spectroscopy 171 7.7.7 Photoluminescence 171 7.8 Nanostructure dispersion technique 171 7.9 Determination of CVD boundary conditions for CFD simulations 171 7.9.1 Determination of precursor mass flow 171 7.9.2 New Evaporator system 172 7.9.3 Determination of temperature boundary condition 174 7.9.4 Determination of the growth rate and growth profile 174 7.10 References 177 Chapter 8 Summary and Conclusions 178 8.1 Precursor chemistry of group-iii nitrides 178 8.2 GaN nanostructures 180 8.3 CVD boundary conditions of a single molecule precursor for CFD 182 Chapter 9 Research publications and Presentations 185 9.1 Publications 185 9.1.1 Peer reviewed journals 185 9.1.2 Reviewed conference proceedings 185 9.2 Conference and workshop contributions 186 9.3 Collaborative work 187 Curriculum vitae 188 xv