Durham E-Theses Atmospheric pressure metal-organic vapour phase epitaxy of InP, (GaIn)as, and (GaIn)(AsP) alloys Butler, Barry R. How to cite: Butler, Barry R. (1989) Atmospheric pressure metal-organic vapour phase epitaxy of InP, (GaIn)as, and (GaIn)(AsP) alloys, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/6545/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk 2 Abstract Atmospheric Pressure Metal-Organic Vapour Phase Epitaxy of InP, (Galn)As, and (GaIn)(AsP) Alloys. Barry R. Butler An introduction to optical communications and opto-electronic devices is given, which demonstrates the motivation for research into III/V devices, and materials. Different epitaxial growth techniques are compared, an introduction to Metal-Organic Vapour Phase Epitaxy (MOVPE) is given, and the author's reactor is described. The reaction chemistry of MOVPE is discussed and results from studies of the passivation of p-type InP are used to confirm the surface nature of reactions. Results upon the background doping of MOVPE grown InP and the effect of growth conditions are discussed. High electron mobility results from InP layers are presented. The growth of epitaxial alloy layers of (Galn)As and (GaIn)(AsP) is described with particular reference to crystallinity, lattice matching and composition control. A novel method of monitoring the dynamic vapour pressure of metal alkyls is described, and theoretical and practical results upon the factors affecting gas mixing and alloy uniformity are presented. Results on the intentional doping of epitaxial layers with dimethylzinc, hydrogen selenide, and silane and the effect of varying the growth conditions are presented; and the use of other dopants is reviewed. The passivation of zinc acceptors by hydrogen in p-type InP is reported and discussed in detail. Results upon the use of ferrocene as a semi-insulating dopant are presented and the literature is reviewed. Photoluminescence and transmission electron microscopy results are presented upon the growth of low dimensional structures, containing layers of less than lOOA thickness. Systematic studies of growth conditions are reported which have led to an understanding of the factors affecting hetero-interface abruptness. Experimental results are reported upon distributed feedback lasers and all MOVPE double heterostructure and ridge waveguide lasers. A discussion on safety aspects of MOVPE is included, with particular reference to the toxicity of arsine and phosphine, and the prevention of environmental pollution. Atmospheric Pressure Metal-Organic Vapour Phase Epitaxy of InP, (Galn)As and (GaIn)(AsP) Alloys. Barry R. Butler This thesis was submitted to the Faculty of Science of the University of Durham, for the degree of Master of Science. 1989 The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. 2 6 J^N 1990 The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. Contents Page Abstract Preface Chapter 1: Introduction Optical Fibre Communications 1 Optical Fibres 2 Cost Advantages of Optical Fibres 3 Optical Fibre Communication Systems 4 Opto-Electronic Devices 8 III/V Semiconductors 10 Device Fabrication 11 Epitaxial Layer Growth 12 Liquid Phase Epitaxy 13 Vapour Phase Epitaxy 14 Metal Organic Vapour Phase Epitaxy 15 Molecular Beam Epitaxy 16 Metal Organic Molecular Beam Epitaxy 17 Summary 17 Chapter 2: MOVPE Chemistry Reaction Mechanism for MOVPE 18 Metal Organic Compounds 21 Group V Precursors 23 Preparation of Metal Organic Compounds 25 Chapter 3: InP Epitaxy Crystal Structure of InP 28 Epitaxial Crystal Growth 28 Substrates 30 Substrate Preparation 30 InP Growth Conditions 31 Background Doping of InP 32 Variation of InP Background Doping Level 33 with Growth Conditions Interface Carrier Concentration Spikes 34 Source of Background Doping 35 Single Epilayer Mobilities 37 Chapter 4: (GaIn)(AsP) Alloy Epitaxy III/V Alloy Systems 40 Lattice Matching of Alloys 41 (Galn)As 42 (GaIn)(AsP) 45 Alloy Uniformity 47 Non-Uniformity Due to Slow Arrival of Reactants 47 Ultrasonic Binary Gas Composition Monitoring 48 Trimethylindium Vapour Pressure Rise Time Measurements 51 Run to Run Vapour Pressure Stability 52 Trimethylindium Source Exhaustion Characteristics 53 Gas Mixing 54 Turbulent Mixing 56 Diffusion Mixing of Gases 58 Interface Abruptness: The Effect of Gas Diffusion 59 Interface Abruptness: Effect of Parabolic Velocity Profile 60 Entrance Effects 61 Longitudinal Compositional Uniformity 62 Thickness Uniformity 63 Chapter 5: Impurity Doping of InP and (Gain)As n-type Dopants 64 Silane 65 Disilane 67 Hydrogen selenide 67 Hydrogen sulphide 68 Diethyltelluride 68 Tetraethyllead 68 p-type Dopants 69 Dimethylzinc and Diethylzinc 69 Dimethylcadmium 71 Magnesium Doping 72 Manganese Doping 72 Hydrogen Passivation of Acceptors in p-type InP 73 Hydrogen Incorporation in p-InP/p+(GaIn)As Structures 73 Hydrogen Incorporation into p-InP Layers 77 Relevance of Hydrogen Incorporation to Reaction Mechanism 78 Bonding Mechanism for Hydrogen in p-InP 79 Rare Earth Element Doping 80 Iron Doping of InP 80 Cobalt Doping 83 Chapter 6: Low Dimensional Structures Background 84 Device Applications 86 Growth on Mismatched Substrates 87 Growth of Low Dimensional Structures 88 Photoluminescence Studies of (GaIn)As/InP Quantum Wells 90 TEM Studies of (GaIn)As/InP Quantum Wells 92 Double Crystal X-ray Analysis of (GaIn)As/InP Quantum Wells 95 (GaIn)(AsP) Quantum Well Structures 95 Chapter 7: Semiconductor Lasers Grown by MOVPE History 97 Theory of Operation 98 Heterostructures 101 Double Heterostructure Lasers 102 Ideal Device Performance 104 Ridge-Waveguide Lasers 105 Distributed Feedback Lasers 106 Contact Layers 108 p and n-Type Doping of InP Confining Layers 108 Reliability of Lasers 109 Buried Heterostructure Lasers 110 The Use of Semi-Insulating Materials in Buried Heterostructure Lasers 112 Quantum Well InP Based Lasers 113 Chapter 8: MOVPE Safety Metal-Organic Chemicals 115 Phosphorus 116 Hydrogen 116 The Toxicity of Arsine and Phosphine 117 Safe Reactor Design and Operation 117 Gas Containment upon Equipment Failure 118 Cylinder Changing, Handling and Storage 119 Medical Aspects of Exposure to Arsine and Phosphine 120 Arsine and Phosphine Monitoring 120 Alternative Group V Sources 121 Environmental Protection 122 Charcoal Adsorption 122 Wet Scrubbers 123 Future Developments 124 Appendix 1: Atmospheric Pressure MOVPE Reactor B at STL Vent-Run Design 125 Pressure and Flow Balancing 125 Mass Flow Controllers and Reactant Lines 126 Metal-Organic Sources 126 Gaseous Sources 127 Reaction Chamber 127 Exhaust and Toxic Gas Monitoring 127 Computer Control and In-situ Monitoring 128 Leak Testing and Vacuum System 128 Acknowledgements 129 References Tables are incorporated within the text. References are denoted using square brackets: [n] Figures Figures are included at the end of each chapter. 1.1 Summary of telecommunication systems and opto-electronic components. 1.2 Attenuation in silica optical fibres. 1.3 Semiconductor laser fabrication steps. 3.1 Growth of InP upon a non-planar surface. 3.2 InP background doping level as a function of growth temperature. 3.3 SIMS profile through InP grown at different temperatures. 3.4 InP background doping level as a function of growth rate. 3.5 SIMS profile through InP grown at different rates. 3.6 InP background doping level as a function of V/III ratio. 3.7 SIMS profile through InP grown under different V/III ratios. 3.8 Electrochemical profile through high mobility InP. 3.9 Low temperature photoluminescence spectrum for high purity InP. 4.1 Lattice matching and band-gap contours for compositions of ternary and quaternary alloys. 4.2 Morphology of good and poor quality (Galn)As. 4.3 Morphology of (Galn)As grown using different arsine over-pressures. 4.4 77K photoluminescence from a 1.3)jm quaternary layer. 4.5 X-ray rocking curve for l.lSym quaternary material. 4.6 X-ray rocking curve for 1.3ym quaternary material. 4.7 Diagram of reactor trimethylindium line and ultrasonic reagent monitor. 4.8 Time response of trimethylindium vapour pressure at 50°C. 4.9 Time response of the ultrasonic reagent monitor. 4.10 Time response of trimethylindium vapour pressure at 40°C. 4.11 Run to run repeatability of trimethylindium vapour pressure. 4.12 Trimethylindium vapour pressure source exhaustion characteristics. 4.13 Lateral composition of epitaxial (Galn)As. 4.14 Lateral composition of epitaxial (Galn)As after reversal of the gas manifold inlet configuration. 4.15 Lateral composition of epitaxial (Galn)As grown with an increased trimethylgallium injection velocity. 4.16 Lateral composition of epitaxial (Galn)As grown using a protruding inlet gas switching manifold. 4.17 Lateral composition of epitaxial (Galn)As grown using a high impedance gas mixing nozzle. 4.18 Calculation for diffusion of trimethylgallium in hydrogen. 4.19 Photoluminescence map of (Galn)As grown using a dual line reactor. 4.20 Photoluminescence map of 1.55)jm quaternary material. 4.21 Variation of gallium content as a function of growth tube temperature. 4.22 Variation of arsenic content as a function of growth tube temperature.