Metalorganic Vapor Phase Epitaxy (MOVPE)

Wiley Series in Materials for Electronic & Optoelectronic Applications

www.wiley.com/go/meoa

Series Editors

Professor Arthur Willoughby, University of Southampton, Southampton, UK

Dr Peter Capper, Ex‐Leonardo MW Ltd, Southampton, UK

Professor Safa Kasap, University of Saskatchewan, Saskatoon, Canada

Published Titles

Bulk Crystal Growth of Electronic, Optical and Optoelectronic Materials, Edited by P. Capper Properties of Group‐IV. III–V and II–VI Semiconductors, S. Adachi

Charge Transport in Disordered Solids with Applications in Electronics, Edited by S. Baranovski

Optical Properties of Condensed Matter and Applications, Edited by J. Singh

Thin Film Solar Cells: Fabrication, Characterization, and Applications, Edited by J. Poortmans and V. Arkhipov

Dielectric Films for Advanced Microelectronics, Edited by M. R. Baklanov, M. Green, and K. Maex

Liquid Phase Epitaxy of Electronic, Optical and Optoelectronic Materials, Edited by P. Capper and M. Mauk

Molecular Electronics: From Principles to Practice, M. Petty

Luminescent Materials and Applications, A. Kitai

CVD Diamond for Electronic Devices and Sensors, Edited by R. S. Sussmann

Properties of Semiconductor Alloys: Group IV, III–V, and II–VI Semiconductors, S. Adachi

Mercury Cadmium Telluride, Edited by P. Capper and J. Garland

Zinc Oxide Materials for Electronic and Optoelectronic Device Applications, Edited by C. Litton, D. C. Reynolds, and T. C. Collins

Lead‐Free Solders: Materials Reliability for Electronics, Edited by K. N. Subramanian

Silicon Photonics: Fundamentals and Devices, M. Jamal Deen and P. K. Basu

Nanostructured and Subwavelength Waveguides: Fundamentals and Applications, M. Skorobogatiy

Photovoltaic Materials: From Crystalline Silicon to Third‐Generation Approaches, Edited by G. Conibeer and A. Willoughby

Glancing Angle Deposition of Thin Films: Engineering the Nanoscale, Matthew M. Hawkeye, Michael T. Taschuk, and Michael J. Brett

Physical Properties of High‐Temperature Superconductors, R. Wesche

Spintronics for Next Generation Innovative Devices, Edited by Katsuaki Sato and Eiji Saitoh

Inorganic Glasses for Photonics: Fundamentals, Engineering and Applications, Animesh Jha

Amorphous Semiconductors: Structural, Optical and Electronic Properties, Kazuo Morigaki, Sandor Kugler and Koichi Shimakawa

Microwave Materials and Applications 2 Vol sel, Edited by Mailadil T. Sebastian, Rick Ubic, and Heli Jantunen

Molecular Beam Epitaxy: Materials and Applications for Electronics and Optoelectronics, Edited by Hajime Asahi and Yoshiji Korikoshi

Metalorganic Vapor Phase Epitaxy (MOVPE)

Growth, Materials Properties, and Applications

Edited by

STUART IRVINECentre for Solar Energy Research, College of Engineering,

Swansea University, OpTIC Centre, St. Asaph, UK

PETER CAPPEREx‐Leonardo MW Ltd, Southampton, UK

This edition first published 2020© 2020 John Wiley & Sons Ltd

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.

The right of Stuart Irvine and Peter Capper to be identified as the authors of the editorial material in this work has been asserted in accordance with law.

Registered OfficesJohn Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USAJohn Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK

Editorial OfficeThe Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK

For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com.

Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some content that appears in standard print versions of this book may not be available in other formats.

Limit of Liability/Disclaimer of WarrantyIn view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of experimental reagents, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each chemical, piece of equipment, reagent, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

Library of Congress Cataloging‐in‐Publication DataNames: Irvine, Stuart, editor. | Capper, Peter, editor.Title: Metalorganic vapor phase epitaxy (MOVPE) : growth, materials properties, and applications / edited by Stuart

Irvine and Peter Capper.Description: First edition. | Hoboken, NJ : John Wiley & Sons, Inc., 2020. | Series: Wiley series in materials for electronic & optoelectronic applications ; 7593 | Includes bibliographical references

and index. | Identifiers: LCCN 2019017934 (print) | LCCN 2019019971 (ebook) | ISBN 9781119313045 (Adobe PDF) | ISBN

9781119313038 (ePub) | ISBN 9781119313014 (hardback)Subjects: LCSH: Metal organic chemical vapor deposition.Classification: LCC TS695 (ebook) | LCC TS695 .M478 2020 (print) | DDC 621.3815/2–dc23LC record available at https://lccn.loc.gov/2019017934

Cover Design: Dan JubbCover Image: © molekuul_be/Shutterstock

Set in 10/12pt Times by SPi Global, Pondicherry, India

10 9 8 7 6 5 4 3 2 1

Dedication

S.J.C.I. – This book is dedicated to my wife Fiona and our family for their patience and support in completing this project at a difficult time for our family. I also commit this book to the memory of Primrose.

P.C. – This book is dedicated to my wife Marian and our sons Samuel and Thomas for all their love and support. I also wish to dedicate it to the memory of my brother Ken.

List of Contributors xvForeword xviiSeries Preface xixPreface xxiSafety and Environment Disclaimer xxiii

1 Introduction to Metalorganic Vapor Phase Epitaxy 1S.J.C. Irvine and P. Capper

1.1 Historical Background of MOVPE 11.2 Basic Reaction Mechanisms 41.3 Precursors 81.4 Types of Reactor Cell 91.5 Introduction to Applications of MOVPE 11

1.5.1 AlN for UV Emitters 111.5.2 GaAs/AlGaAs VCSELS 111.5.3 Multijunction Solar Cells 121.5.4 GaAs and InP Transistors for High‐Frequency Devices 131.5.5 Infrared Detectors 141.5.6 Photovoltaic and Thermophotovoltaic Devices 14

1.6 Health and Safety Considerations in MOVPE 151.7 Conclusions 16References 16

2 Fundamental Aspects of MOVPE 19G.B. Stringfellow

2.1 Introduction 192.2 Thermodynamics 20

2.2.1 Thermodynamics of MOVPE Growth 202.2.2 Solid Composition 242.2.3 Phase Separation 292.2.4 Ordering 31

2.3 Kinetics 352.3.1 Mass Transport 352.3.2 Precursor Pyrolysis 362.3.3 Control of Solid Composition 37

2.4 Surface Processes 402.4.1 Surface Reconstruction 412.4.2 Atomic‐Level Surface Processes 422.4.3 Effects of Surface Processes on Materials Properties 442.4.4 Surfactants 46

Contents

viii Contents

2.5 Specific Systems 522.5.1 AlGaInP 522.5.2 Group III Nitrides 532.5.3 Novel Alloys 56

2.6 Summary 59References 60

3 Column III: Phosphides, Arsenides, and Antimonides 71H. Hardtdegen and M. Mikulics

3.1 Introduction 713.2 Precursors for Column III Phosphides, Arsenides, and Antimonides 733.3 GaAs‐Based Materials 74

3.3.1 (AlGa)As/GaAs Properties and Deposition 743.3.2 GaInP, (AlGa)InP/GaAs Properties and Deposition 79

3.4 InP‐Based Materials 823.4.1 InP Properties and Deposition 823.4.2 AlInAs/GaInAs/AlGaInAs Properties and Deposition 833.4.3 AlInAs/GaInAs/InP Heterostructures 843.4.4 In

xGa

1–xAs

yP

1–y Properties and Deposition 84

3.5 Column III Antimonides Properties and Deposition 863.5.1 Deposition of InSb, GaSb, and AlSb 873.5.2 Deposition of Ternary Column III Alloys (AlGa)Sb and (GaIn)Sb 893.5.3 Deposition of Ternary Column V Alloys In(AsSb), GaAsSb 893.5.4 Deposition of Quaternary Alloys 903.5.5 Epitaxy of Electronic Device Structures 903.5.6 Epitaxy of Optoelectronic Device Structures 95

3.6 In Situ Optical Characterization/Growth Control 1003.7 Conclusions 100References 101

4 Nitride Semiconductors 109A. Dadgar and M. Weyers

4.1 Introduction 1094.2 Properties of III‐Nitrides 1104.3 Challenges in the Growth of III‐Nitrides 111

4.3.1 Lattice and Thermal Mismatch 1114.3.2 Ternary Alloys: Miscibility and Compositional Homogeneity 1134.3.3 Gas‐Phase Prereactions 1154.3.4 Doping of III‐Nitrides 117

4.4 Substrates 1204.4.1 Heteroepitaxy on Foreign Substrates 1224.4.2 GaN Growth on Sapphire 1254.4.3 III‐N Growth on SiC 1264.4.4 GaN Growth on Silicon 127

4.5 MOVPE Growth Technology 1304.5.1 Precursors 1304.5.2 Reactors and In Situ Monitoring 130

Contents ix

4.6 Economic Importance 1364.6.1 Optoelectronic Devices 1374.6.2 Electronic Devices 138

4.7 Conclusions 138References 138

5 Metamorphic Growth and Multijunction III‐V Solar Cells 149N.H. Karam, C.M. Fetzer, X.‐Q. Liu, M.A. Steiner, and K.L. Schulte

5.1 Introduction to MOVPE for Multijunction Solar Cells 1495.1.1 III‐V PV Solar Cell Opportunities and Applications 1495.1.2 Metamorphic Multijunction Solar Cells 1515.1.3 Reactor Technology for Metamorphic Epitaxy 154

5.2 Upright Metamorphic Multijunction (UMM) Solar Cells 1545.2.1 Introduction and History of Upright Metamorphic Multijunctions 1545.2.2 MOVPE Growth Considerations of UMM 1565.2.3 Growth and Device Results 1585.2.4 Challenges and Future Outlook 162

5.3 Inverted Metamorphic Multijunction (IMM) Solar Cells 1625.3.1 Introduction and History of Inverted Metamorphic Multijunctions 1625.3.2 MOVPE Growth Considerations of IMM 1645.3.3 Growth and Device Results 1675.3.4 Challenges and Future Outlook 169

5.4 Conclusions 169References 170

6 Quantum Dots 175E. Hulicius, A. Hospodková, and M. Zíková

6.1 General Introduction to the Topic 1756.1.1 Definition and History 1756.1.2 Paradigm of Quantum Dots 1766.1.3 QD Types 176

6.2 AIIIBV Materials and Structures 1786.2.1 QDs Embedded in the Structure 1786.2.2 Semiconductor Materials for Embedded QDs 180

6.3 Growth Procedures 1816.3.1 Comparison of MBE‐ and MOVPE‐Grown QDs 1816.3.2 Growth Parameters 1826.3.3 QD Surrounding Layers 185

6.4 In Situ Measurements 1936.4.1 Reflectance Anisotropy Spectroscopy of QD Growth 1936.4.2 Other Supporting In Situ Measurements 197

6.5 Structure Characterization 1986.5.1 Optical: Photo‐, Magnetophoto‐, Electro‐luminescence,

and Spin Detection 1986.5.2 Microscopies – AFM, TEM, XSTM, BEEM/BEES 2006.5.3 Electrical: Photocurrent, Capacitance Measurements 202

6.6 Applications 2036.6.1 QD Lasers, Optical Amplifiers, and LEDs 2046.6.2 QD Detectors, FETs, Photovoltaics, and Memories 205

x Contents

6.7 Summary 2086.8 Future Perspectives 208Acknowledgment 209References 209

7 III‐V Nanowires and Related Nanostructures: From Nitrides to Antimonides 217H.J. Joyce

7.1 Introduction to Nanowires and Related Nanostructures 2177.2 Geometric and Crystallographic Properties of III‐V Nanowires 219

7.2.1 Crystal Phase 2197.2.2 Growth Direction, Morphology, and Side‐Facets 220

7.3 Particle‐Assisted MOVPE of Nanowires 2227.3.1 The Phase of the Particle 2227.3.2 The Role of the Particle 2247.3.3 Axial and Radial Growth Modes 2267.3.4 Self‐Assisted Growth 228

7.4 Selective‐Area MOVPE of Nanowires and Nanostructures 2287.4.1 The Role of the Mask 2297.4.2 Axial and Radial Growth Modes 230

7.5 Alternative Techniques for MOVPE of Nanowires 2317.6 Novel Applications of Nanowires 2317.7 Concluding Remarks 233References 234

8 Monolithic III/V integration on (001) Si substrate 241B. Kunert and K. Volz

8.1 Introduction 2418.2 III/V‐Si Interface 243

8.2.1 Si Surfaces 2438.2.2 Interface Formation in the Presence of Impurities and MO Precursors 2478.2.3 Atomic III/V on Si Interface Structure 2498.2.4 Antiphase Domains 2518.2.5 III/V Growth on Si(001) 252

8.3 Heteroepitaxy of Bulk Layers on Si 2558.3.1 Lattice‐Matched Growth on Si 2578.3.2 Metamorphic Growth on Blanket Si 2588.3.3 Selective‐Area Growth (SAG) on Si 264

8.4 Conclusions 282References 282

9 MOVPE Growth of Cadmium Mercury Telluride and Applications 293C.D. Maxey, P. Capper, and I.M. Baker

9.1 Requirement for Epitaxy 2939.2 History 2949.3 Substrate Choices 295

9.3.1 Orientation 2969.3.2 Substrate Material 296

9.4 Reactor Design 2979.4.1 Process Abatement Systems 298

Contents xi

9.5 Process Parameters 2999.6 Metalorganic Sources 2999.7 Uniformity 3009.8 Reproducibility 3029.9 Doping 3029.10 Defects 3049.11 Annealing 3079.12 In Situ Monitoring 3089.13 Background for Applications of MOVPE MCT 308

9.13.1 Introduction to Infrared Imaging and Atmospheric Windows 3089.13.2 MCT Infrared Detector Market in the Modern Era 309

9.14 Manufacturing Technology for MOVPE Photodiode Arrays 3119.14.1 Mesa Heterojunction Devices (MHJ) 3119.14.2 Wafer‐Scale Processing 312

9.15 Advanced MCT Technologies 3129.15.1 Small‐Pixel Technology 3139.15.2 Higher Operating Temperature (HOT) Device Structures 3139.15.3 Two‐Color Array Technology 3149.15.4 Nonequilibrium Device Structures 316

9.16 MOVPE MCT for Scientific Applications 3169.16.1 Linear‐Mode Avalanche Photodiode Arrays (LmAPDs) in MOVPE 316

9.17 Conclusions and Future Trends for MOVPE MCT Arrays 320Definitions 321References 322

10 Cadmium Telluride and Related II‐VI Materials 325G. Kartopu and S.J.C. Irvine

10.1 Introduction and Historical Background 32510.2 CdTe Homoepitaxy 32710.3 CdTe Heteroepitaxy 327

10.3.1 InSb 32710.3.2 Sapphire 32810.3.3 GaAs 32910.3.4 Silicon 330

10.4 Low‐Temperature Growth and Alternative Precursors 33010.5 Photoassisted MOVPE 33210.6 Plasma‐Assisted MOVPE 33310.7 Polycrystalline MOCVD 33310.8 In Situ Monitoring of CdTe 334

10.8.1 Mechanisms for Laser Reflectance (LR) Monitoring 33510.9 MOCVD of CdTe for Planar Solar Cells 337

10.9.1 CdS and CdZnS Window Layers 33810.9.2 CdTe Absorber Layer 33810.9.3 CdCl

2 Treatment Layer 342

10.9.4 Photovoltaic Planar Devices 34310.10 Core‐Shell Nanowire Photovoltaic Devices 34510.11 Inline MOCVD for Scaling of CdTe 34710.12 MOCVD of CdTe for Radiation Detectors 350References 351

xii Contents

11 ZnO and Related Materials 355V. Muñoz‐Sanjosé and S.J.C. Irvine

11.1 Introduction 35511.2 Sources for the MOCVD Growth of ZnO and Related Materials 356

11.2.1 Metalorganic Zinc Precursors 35611.2.2 Metalorganic Cadmium Precursors 36011.2.3 Metalorganic Magnesium Precursors 36011.2.4 Precursors for Oxygen 36111.2.5 Precursors for Doping 363

11.3 Substrates for the MOCVD Growth of ZnO and Related Materials 36411.3.1 ZnO Single Crystals and ZnO Templates as Substrates 36511.3.2 Sapphire (Al

2O

3) 367

11.3.3 Silicon 36911.3.4 Glass Substrates 372

11.4 Some Techniques for the MOCVD Growth of ZnO and Related Materials 37311.4.1 Atmospheric and Low‐Pressure Conditions in Conventional

MOCVD Systems 37411.4.2 MOCVD‐Assisted Processes 376

11.5 Crystal Growth of ZnO and Related Materials 38011.5.1 Crystal Growth by MOCVD of ZnO Layers 38011.5.2 Crystal Growth of ZnO Nanostructures 39311.5.3 Crystal Growth of ZnO‐Related Materials 39811.5.4 Doping of ZnO and Related Materials 400

11.6 Conclusions 405Acknowledgments 406References 406

12 Epitaxial Systems for III‐V and III‐Nitride MOVPE 423W. Lundin and R. Talalaev

12.1 Introduction 42312.2 Typical Engineering Solutions Inside MOVPE Tools 424

12.2.1 Gas‐Blending System 42412.2.2 Exhaust System 43312.2.3 Reactors 435

12.3 Reactors for MOVPE of III‐V Materials 43812.3.1 General Features of III‐V MOVPE 43812.3.2 From Simple Horizontal Flow to Planetary Reactors 43912.3.3 Close‐Coupled Showerhead (CCS) Reactors 44512.3.4 Rotating‐Disk Reactors 447

12.4 Reactors for MOVPE of III‐N Materials 45112.4.1 Principal Differences between MOVPE of Classical III‐Vs and III‐Ns 45112.4.2 Rotating‐Disk Reactors 45412.4.3 Planetary Reactors 45512.4.4 CCS Reactors 45812.4.5 Horizontal Flow Reactors for III‐N MOVPE 459

12.5 Twenty‐Five Years of Commercially Available III‐N MOVPE Reactor Evolution 462References 464

Contents xiii

13 Ultrapure Metal‐Organic Precursors for MOVPE 467D.V. Shenai‐Khatkhate

13.1 Introduction 46713.1.1 MOVPE Precursor Classes and Impurities 468

13.2 Stringent Requirements for Suitable MOVPE Precursors 47213.3 Synthesis and Purification Strategies for Ultrapure MOVPE Precursors 472

13.3.1 Synthetic Strategies for Ultrapure MOVPE Precursors 47213.3.2 Purification Strategies for MOVPE Precursors 476

13.4 MOVPE Precursors for III‐V Compound Semiconductors 48313.4.1 Group III MOVPE Precursors 48313.4.2 Group V MOVPE Precursors 488

13.5 MOVPE Precursors for II‐VI Compound Semiconductors 49313.5.1 Group II MOVPE Precursors 49313.5.2 Group VI MOVPE Precursors 496

13.6 MOVPE Dopants for Compound Semiconductors 49913.7 Environment, Health, and Safety (EHS) Aspects of MOVPE Precursors 500

13.7.1 General Aspects and Considerations 50013.7.2 Employee and Environment Exposure Aspects 50113.7.3 Employee and Workplace Exposure Limits 502

13.8 Conclusions and Future Trends 502Acknowledgments 503References 503

14 Future Aspects of MOCVD Technology for Epitaxial Growth of Semiconductors 507T. Detchprohm, J.‐H. Ryou, X. Li, and R.D. Dupuis

14.1 Introduction – Looking Back 50714.2 Future Equipment Development 510

14.2.1 Production MOCVD 51014.2.2 R&D MOCVD 51114.2.3 MOCVD for Ultrawide‐Bandgap III‐Nitrides 51214.2.4 MOCVD for Emerging Materials 51314.2.5 Democratization of MOCVD 514

14.3 Future Applications for MOCVD Research in Semiconductor Materials 51514.3.1 Heteroepitaxy 51514.3.2 Nanostructural Materials 52714.3.3 Poly, Amorphous, and Other Materials 532

14.4 Past, Present, and Future Commercial Applications 53514.4.1 LEDs 53514.4.2 Lasers 53614.4.3 OEICs 53614.4.4 High‐Speed Electronics 53614.4.5 High‐Power Electronics 53714.4.6 Solar Cells 53714.4.7 Detectors 538

14.5 Summary and Conclusions 538Acknowledgments 539References 539

Index 549

I.M. Baker Leonardo MW Ltd, Southampton, UK

P. Capper Ex‐Leonardo MW Ltd, Southampton, UK

A. Dadgar Otto‐von‐Guericke Universität Magdeburg, Germany

T. Detchprohm Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, USA

R.D. Dupuis Georgia Institute of Technology, School of Electrical and Computing Engineering, Atlanta, USA

C.M. Fetzer Boeing‐Spectrolab, Sylmar, California, USA

H. Hardtdegen Ernst Ruska‐Centre, Forschungszentrum Jülich GmbH, Germany

A. Hospodková Department of Semiconductors, Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic

E. Hulicius Department of Semiconductors, Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic

S.J.C. Irvine Centre for Solar Energy Research, College of Engineering, Swansea University, OpTIC Centre, St. Asaph, UK

H.J. Joyce Department of Engineering, Cambridge University, UK

N.H. Karam Karamco USA Inc., La Cañada, California, USA

G. Kartopu Centre for Solar Energy Research, College of Engineering, Swansea University, OpTIC Centre, St. Asaph, UK

B. Kunert imec, Leuven, Belgium

X. Li Electrical Engineering Program, Computer, Electrical, Mathematical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Makkah, Saudi Arabia

X.‐Q. Liu Boeing‐Spectrolab, Sylmar, California, USA

List of Contributors

xvi List of Contributors

W. Lundin Ioffe Institute, Russia

C.D. Maxey Leonardo MW Ltd, Southampton, UK

M. Mikulics Peter Grünberg Institute, Forschungszentrum Jülich GmbH, Germany

V. Muñoz‐Sanjosé Dpto. Física Aplicada y Electromagnetismo, University of Valencia, Spain

D. Nelson IQEP, Cardiff, Wales

J.‐H. Ryou Department of Mechanical Engineering, The University of Houston, Texas, USA

K.L. Schulte National Renewable Energy Laboratory, Golden, Colorado, USA

D.V. Shenai‐Khatkhate Electronics & Imaging, DuPont de Nemours, Inc., Marlborough, Massachusetts, USA(Formerly known as Dow Electronic Materials, Rohm and Haas Company, and Morton Metalorganics)

M.A. Steiner National Renewable Energy Laboratory, Golden, Colorado, USA

G.B. Stringfellow The University of Utah, Salt Lake City, USA

R. Talalaev STR Group Ltd, Russia

K. Volz Material Sciences Center and Faculty of Physics, Philipps‐Universität Marburg, Germany

M. Weyers Ferdinand‐Braun‐Institute, Leibniz‐Institut für Höchstfrequenztechnik, Berlin, Germany

M. Zíková Department of Semiconductors, Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic

Foreword

It gives me immense pleasure to introduce this book on the technology of Metalorganic Vapor Phase Epitaxy (MOVPE), edited by Stuart Irvine and Peter Capper, and published by John Wiley. It is one of the most comprehensive books to have ever been published on the subject and will serve to educate, inform, train, and inspire a new generation of engineers and scientists of many disci-plines who become involved in the semiconductor industry in the coming years and decades ahead.

The publication of such a comprehensive collection of chapters, covering the growth, materials properties, and applications enabled by MOVPE, and written by subject‐matter experts, could not be more timely. It is no exaggeration to say that MOVPE has changed the world we all live in and the way we work, live, and play.

The entire global communications network, from the devices that provide the light signalling, switching, and detection in high‐speed fiber optic systems and the optical infrastructure for dramatically increasing the information‐handling capacity of todays’ data centers, to the critical radio frequency (RF) components in handsets, base stations, and satellites that enable mobile communications in all its forms, would not be practically possible without MOVPE technology providing the manufacturing of the fundamental materials structures from which the key devices are made. Without MOVPE, we would have no high‐speed broadband, no internet as we know it, no global mobile communications as we know it.

MOVPE has enabled a global lighting revolution to take place over the last two decades, in the form of light‐emitting diodes (LEDs), which save enormous amounts of energy every year because they are up to 10 times more efficient at converting electrical energy into light energy than conven-tional incandescent light bulbs. Lighting accounts for around one‐third of all energy use on our planet, so the replacement of incandescent bulbs with LED equivalents is cutting down carbon emissions enormously by reducing the need for power stations. LEDs are also being used to trans-form whole industries. From the way in which retailers use light to promote their products – be they clothing, cars, or perishable foods – to the advent of hydroponic and vertical farming to grow plants more efficiently and closer to the point of use, thereby reducing transport needs, are all contributing to carbon‐emission reduction on our planet. The increasing production of electric vehicles is reliant upon materials made by MOVPE, as are the new wave of power‐efficient devices used for a myriad of electrical switching applications such as mobile phone chargers, motors, inverters for solar farms, and a host of other energy‐hungry applications.

All satellites launched today are powered in space by highly efficient solar cells made by MOVPE. Almost all large screens in stadiums, advertising hoardings, concert, and entertainment lighting use high‐brightness LEDs made by MOVPE. High‐power laser welding used in the auto-motive, aerospace, and other industrial sectors use materials made by MOVPE. 3D sensing now appearing on mobile handsets, gesture recognition in cars, and LiDaR (Light Detection and Ranging, the fundamental sensing technology for autonomous drive vehicles) all rely on MOVPE.

Looking forward, MOVPE will be used for many more applications and is now poised to enable the increasingly rapid adoption of compound semiconductors within the overall semiconductor industry. This is a $400 billion business spanning the entire globe and providing almost half of all

xviii Foreword

global GDP growth directly and through its impact on information and communications technology (ICT). In other words, MOVPE is an absolutely core enabling technology for future global growth.

The MOVPE industry is growing rapidly but continues to require significant numbers of engi-neers, scientists, physicists, chemists, chemical engineers, operators, managers, and leaders. They all need to be well informed, well trained, knowledgeable, and inspired and motivated to help further develop the technology. By doing so, they will play a significant role, not only in bringing more efficient, more powerful, higher‐speed, lower‐cost products to market, thus enhancing the way we live our lives, how we work, and how we spend our leisure time; but also contributing to the reduction of greenhouse‐gas emissions, to the benefit of our planet.

This book provides a comprehensive overview of MOVPE and should be used to train, inform, educate, and inspire this new generation of industrial and academic participants. I am proud to be associated with it, and I commend it wholeheartedly to the semiconductor community. No self‐respecting technology bookshelf should be without it.

Drew NelsonIQEP

Cardiff, Wales

Wiley Series in Materials for Electronic & Optoelectronic Applications

This book series is devoted to the rapidly developing class of materials used for electronic and optoelectronic applications. It is designed to provide much‐needed information on the fundamental scientific principles of these materials, together with how these are employed in technological applications. The books are aimed at (postgraduate) students, researchers, and technologists, engaged in research, development, and the study of materials in electronics and photonics, and industrial scientists developing new materials, devices, and circuits for the electronic, optoelec-tronic and, communications industries.

The development of new electronic and optoelectronic materials depends not only on materials engineering at a practical level, but also on a clear understanding of the properties of materials, and the fundamental science behind these properties. It is the properties of a material that eventually determine its usefulness in an application. The series therefore also includes such titles as electrical conduction in solids, optical properties, thermal properties, and so on, all with applications and examples of materials in electronics and optoelectronics. The characterization of materials is also covered within the series in as much as it is impossible to develop new materials without the proper characterization of their structure and properties. Structure–property relationships have always been fundamentally and intrinsically important to materials science and engineering.

Materials science is well known for being one of the most interdisciplinary sciences. It is the interdisciplinary aspect of materials science that has led to many exciting discoveries, new materi-als and new applications. It is not unusual to find scientists with a chemical engineering back-ground working on materials projects with applications in electronics. In selecting titles for the series, we have tried to maintain the interdisciplinary aspect of the field, and hence its excitement to researchers in this field.

Arthur WilloughbyPeter Capper

Safa Kasap

Series Preface

Whole industries currently rely on metalorganic vapor phase epitaxially (MOVPE) grown layers of a wide variety of materials. These industries range from lighting, based on light‐emitting diodes made from III‐V compounds (currently worth over $26Bn), to UV emitters, solid‐state laser diodes, multijunction solar cells, high‐frequency devices, and photovoltaic/thermovoltaic devices, again all mainly based on III‐V compounds, to infrared imaging, based on mercury cadmium tel-luride. In addition, much MOVPE R&D activity is taking place in many III‐V and II‐VI compound systems as well as oxide materials systems throughout the world.

This book is an attempt to summarize the position in a number of these areas where MOVPE‐grown layers are central to particular industries. The book is aimed at senior under‐ and post‐graduates in physics, chemistry, materials science, electrical engineering, and optical engineering disciplines, as well as those employed in the various fields of thin‐film crystal growth within the relevant industries. It is hoped that the former group will find the book readable both as an intro-ductory text and as a useful guide to the literature. Workers in industry will hopefully find the book useful in bringing them up‐to‐date information in both their own and other areas of interest. To both groups of readers, we trust that the book will prove interesting and a spur to further progress in this key area of technology.

The first chapter is an introductory chapter covering historical background, basic reaction mech-anisms, chemical precursors, growth substrates, reactors, main applications areas, and finally some health and safety considerations of MOVPE. The next chapter discusses the fundamental aspects of MOVPE in some detail. Areas covered include thermodynamics, kinetics, surfaces, and a wide range of specific materials systems.

Chapter 3 outlines the current situation with regard to the growth, properties, and applications of a range of Group III phosphides, arsenides, and antimonides. Topics covered include relevant precursors, doping issues, heterojunctions, and devices in a wide range of binary, ternary, and quaternary compounds. In situ optical characterization as a means to control growth is also dis-cussed. The next chapter deals with the nitride semiconductors, a family of materials that has received much attention recently. After describing the properties of these materials, the main chal-lenges in the growth of such materials are outlined. Doping is once again a key area in the growth and applications of these material as is the issue of suitable substrates, and these two topics are discussed at length. These materials are used for short‐wavelength optoelectronic devices and for high‐power, high‐temperature electronic devices.

Chapter 5 deals with multijunction III‐V solar cells. Various types of metamorphic solar cells are described, and details of the growth, properties, and applications of each are given. The next chap-ter describes the current position in the field of quantum dots (QDs) grown by MOVPE. The vari-ous types of QDs, e.g. embedded, are outlined in the various material systems. A comparison is given between MOVPE and molecular beam epitaxy (MBE) grown QDs. The importance of in situ measurements is stressed. The range of devices made in materials produced by MOVPE is outlined and some comparisons made to their MBE‐produced counterparts. A brief list of future possibili-ties is also given.

Preface

xxii Preface

Chapter 7 deals with the area of III‐V nanowires and related nanostructures made by MOVPE. The crucial crystallographic properties are discussed in some detail before a description of the particle‐assisted growth of nanowires is covered. Selective‐area growth and the various relevant growth modes are outlined. Potential applications for these structures range from photovoltaics to topological quantum computing. Chapter 8 deals with the fascinating topic of integrating III‐V compounds onto silicon substrates in monolithic structures. This combination would open up new device opportunities benefiting from optoelectronic properties of III‐Vs and mature, cost‐effective silicon‐based integrated circuit process technology. Integration methods that have been recently researched are the focus – particularly, but not exclusively, those based on MOVPE. A range of devices has been made in such material, and some details are given in the chapter.

There is a change of focus in the next three chapters away from III‐V compounds to several II–VI compound systems.

Chapter  9 deals with the pre‐eminent infrared material, mercury cadmium telluride (MCT). Details of the growth process, including precursors, substrates, reactor design, and in situ monitor-ing are given, together with a discussion of doping and uniformity issues of heterostructures. Various device structures/types are discussed, including advanced technologies, such as small pixel sizes, higher operating temperature, two‐color, and nonequilibrium devices. Recent work on avalanche photodiode arrays in astronomical applications ends the chapter. Chapter 10 describes the growth of CdTe and related materials for use in solar cells and radiation detectors. A variety of substrate types have been employed in this system, as has low‐temperature and photo‐/plasma‐assisted growth. Another family of II–VI materials, those based on ZnO, is the subject of the next chapter. The potential uses of these materials range from photonic to piezoelectric applications. Details of the numerous precursor varieties and substrate types, together with their pretreatments, are given. As in the previous chapter, several variants of MOVPE growth techniques, such as low‐temperature and photo‐/plasma‐assisted growth, have been applied to this material system. Growth of various nanostructures has also been demonstrated.

Chapter 12 goes into the details of MOVPE reactor design and its evolution over the past 25 years or so. Areas covered include MO sources (precursors), gas‐handling systems, reactor designs, and exhaust systems. A range of reactor designs from horizontal flow, showerhead, and rotating disc to planetary reactors are discussed for III‐V systems. In addition, the differences needed in reactor design for III‐N systems are detailed.

Precursors are the subject of Chapter 13. The requirements, synthesis, and purification strategies for these starting chemicals is outlined. This is followed by details of Group III, V, II, and VI pre-cursors, together with various dopant precursors. This chapter concludes with some comments on the important field of environmental, health, and safety aspects.

The final chapter of the book looks to the future of MOVPE as a technology. One example used is that of production reactor design for III‐N growth. Another example used is that of growth of Ga

2O

3 and its alloys for a range of device types. Two‐dimensional materials, such as graphene but

also binary systems such as BN, are being researched by MOVPE. Other nanopatterned materials, poly‐ and amorphous materials, various oxide systems, high‐temperature superconductors, and silicides are also outlined. The future of various device types, such as light‐emitting diodes, lasers, optoelectronic integrated circuits, high‐speed electronics, high‐power electronics, solar cells, and detectors (both radiation and particle varieties) is also discussed.

Finally, we would like to sincerely thank all the contributors to the book, as well as Jenny Cossham, Emma Strickland, and Elsie Merlin of John Wiley & Sons Ltd, for their help in various forms and their patience throughout the course of the book preparation and production stages.

Stuart Irvine, Swansea University, UKPeter Capper, Southampton, UK

April 2019

In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of experimental reagents, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each chemical, piece of equipment, reagent, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials, or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the informa-tion or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, conse-quential, or other damages.

Safety and Environment Disclaimer

Metalorganic Vapor Phase Epitaxy (MOVPE): Growth, Materials Properties, and Applications, First Edition. Edited by Stuart Irvine and Peter Capper. © 2020 John Wiley & Sons Ltd. Published 2020 by John Wiley & Sons Ltd.

1Introduction to Metalorganic Vapor

Phase Epitaxy

S.J.C. Irvine1 and P. Capper2

1Centre for Solar Energy Research, College of Engineering, Swansea University, OpTIC Centre, St. Asaph, UK

2Ex‐Leonardo MW Ltd, Southampton, UK

1.1 Historical Background of MOVPE

The technique of metalorganic chemical vapor deposition (MOCVD) was first introduced in the late 1960s for the deposition of compound semiconductors from the vapor phase, a variant of chemical vapor deposition (CVD) but with the advantage over the then‐existing methods for compound semiconductor epitaxy of only requiring a single temperature for reaction and film deposition. The pioneers of the techniques, Manasevit and Simpson [1], were seeking a method for depositing optoelectronic semiconductors such as GaAs onto different, nonlattice‐matched substrates, including spinel and sapphire. The near‐equilibrium techniques such as liquid phase epitaxy (LPE) and chloride vapor phase epitaxy (VPE) were not suitable for nucleation onto a chemically very different surface than the compound being deposited. The first paper [2] reported on the single‐crystal growth of GaAs on various oxide substrates. The process was based on a combination of a volatile alkyl organometallic for the Group III element and a hydride gas for the Group V element. This basic approach has remained for all the III‐V compounds, with a few exceptions where arsine or phosphine are replaced by liquid sources, tertiarybutylyarsine (TBAs) and tertiarybutylphosphine (TBP) [3]. For the Group II‐VI compounds, the hydrides were less useful where low‐temperature growth was considered to be important to control native defect concentrations. However, early work using H

2Se and H

2S for sources to grow ZnSe and ZnS was

successful at higher temperatures [4]. For the tellurides, the hydride route was not practical as H2Te

is not stable under ambient conditions, so alkyl tellurium was used from the outset.It was more than a decade after the first reports of MOCVD that the international conference

series started with the conference in Ajaccio in 1981, when the “father” of MOCVD, Hal Manasevit

2 Metalorganic Vapor Phase Epitaxy (MOVPE)

gave an invited talk that covered a wide range of compound semiconductor materials that had been successfully grown by MOCVD, including III‐V, II‐VI, IV‐VI, and II‐IV‐V

2 [5]. Perhaps the most

significant developments over that first decade, represented at that conference, were the progress with improved purity of the organometallic precursors and low‐defect‐density, lattice‐matched epitaxy, which led to the first demonstration of electron mobility >100 000 cm2/V s [6]. This made MOCVD competitive with other epitaxial techniques for GaAs, such as the emerging molecular beam epitaxy (MBE), and paved the way for high‐performance optoelectronic devices, including quantum‐well lasers and high‐mobility transistors. The issues of purity of the early organometal-lics is addressed again in Section 14.1, which takes a historical perspective before looking forward to future prospects for MOCVD. The improved purity of the organometallic sources led to the demonstration of low‐threshold lasers that opened the way for commercialization of MOCVD. Purification of precursors is covered in more detail in Chapter 13, where the challenges with tradi-tional distillation methods were overcome using adduct purification.

The high‐quality epitaxial nature of the films was emphasized by more commonly adopting the name of the growth method to be metalorganic vapor phase epitaxy (MOVPE) or organometallic VPE (OMVPE). There was some debate at the first international conference on what it should be called, which may seem strange now; but in those formative years, even the name was a point of discussion. The title of the conference was “IC‐MOVPE I,” which settled the issue. For the benefit of newcomers to MOVPE, all of these variants of the name can be found in the literature and, in most cases, can be used interchangeably. MOCVD can be considered broader, as it includes polycrystalline growth that is appropriate to the photovoltaic thin films covered in Chapter 10. The early niche applications of MOVPE were with GaAs photocathodes [7], GaAs heterojunction bipolar transistor (HBT) lasers [8], and GaInAsP lasers and detectors for 1.3‐μm optical fibre-optic communications [9].

The ease with which GaAs could be grown using trimethylgallium (TMG) and arsine was not readily replicated by all the semiconductor materials of interest. Indium phosphide had proved to be particularly challenging due to a polymerization prereaction that occurred between trimethylindium (TMI) and phosphine [10]. This was overcome, initially, by going to low‐pressure MOVPE and replacing TMI with triethylindium (TEI). Later improvements in the purity of TMI and in overcom-ing issues with it being a solid source at room temperature have led to TMI now being the precursor of choice. Atmospheric‐pressure MOVPE of InP was achieved by Moss [11] using an elegant solu-tion that took advantage of the adduct formation of In alkyls. A room‐temperature stable adduct, TMIn.TEP (where TEP is triethylphosphine), was formed that prevented the polymerization reaction with PH

3 but the adduct decomposed over the hot substrate to yield TMIn and TEP. The TEP was

stable and was exhausted from the reactor without further decomposition, while the TMIn and PH3

or AsH3 for the arsenic compounds reacted to form the compound semiconductor on the substrate.

Adducts have also been used in the purification of the organometallic precursors, as will be described in Chapter 13, and for preventing prereactions with ZnO, as described in Chapter 11. The significance of growing InP was to be able to then grow ternaries and quaternaries for infrared lasers and detec-tors, lattice matched to InP. This enabled access to the growing market for 1.5‐μm wavelength devices for long‐range optic fibre-optic communications [12]. The purification of Group III precursors is discussed in Chapter 3 with regard to the device application of these materials. The decomposition chemistry and role of the Group V hydride is important to minimize the incorporation of carbon. In some devices, this is now used as an intentional P‐type dopant, substituting on the Group V site.

The antimonides (InSb, GaSb, AlSb) are an important class of narrow‐bandgap semiconductors for infrared detectors, long‐wavelength lasers, and thermoelectric devices. Unlike GaAs‐ and InP‐based semiconductors, where hydrides are normally used as the Group V source, for the antimon-ides it is necessary to use alkyl sources such as TMSb. The growth of the antimonides is described in Section 3.5.

Introduction to Metalorganic Vapor Phase Epitaxy 3

The II‐VI alloy mercury cadmium telluride (MCT) had also proved to be difficult to produce by MOVPE, and the growth in the interest in MCT for long‐wavelength thermal imagers (operating around 10 μm) was stimulating research in different epitaxial techniques, including LPE, MBE, and MOVPE, all of which are used in production today. The challenge was from the very‐high‐equilibrium vapor pressure of mercury in MCT at growth temperatures ranging from 200 °C to 500 °C. Early success in the 1980s with an MOVPE approach using a liquid Hg source ensured a very fertile two decades of research that will be described in more detail in Chapter 9 [13]. This helped to demonstrate at an early stage that MOVPE can be a very versatile technique that has been proven again many times for different compound semiconductors over the intervening years.

Thus, the technique of MOVPE was born, but it was not until the late 1980s that MOVPE became a production technique of any significance. This success depended on painstaking work on improving the impurity of the organometallic precursors and development of MOVPE equipment to improve uniformity and deposit onto multiple substrates in the reaction chamber. The emergence of commercial equipment suppliers took over from the “home‐built” reactors and provided much‐needed standards to which production of epi‐wafers could be benchmarked. By this time, the focus was on high‐quality epitaxial layers on lattice‐matched substrates, in contrast with the early work. One exception was the growth of CdTe epitaxial layers onto C‐plane sapphire as a substrate for LPE growth of MCT for mid‐wave infrared (MWIR) detectors. Ironically this was manufactured by Rockwell International, where Hal Manasevit carried out his original research. The topic of homoepitaxy versus heteroepitaxy has been a continual balance between achieving very high‐quality epitaxial layers and materials functionality. To this day, the growth of high‐quality epitaxy on silicon substrates has remained the ultimate challenge, through not only providing a ready supply of high‐quality and cheap substrates but also the integration of optoelectronic and electronic devices. By the late 1980s and early 1990s, there was a commercial supply of GaAs on Si substrates to be used as a substitute for GaAs substrates. Improvements in the quality and size of GaAs substrates made this approach uncompetitive. Today, this is attracting a new generation of research activity; the topic of monolithic III‐V integration on Si(001) substrates is covered in Chapter 8. New understanding of epitaxial processes and new applications are driving this resurgence of activity.

The characteristics of MOVPE that have taken it from a research curiosity to production have been in the simplicity of delivery of the reactive vapors and the versatility of selecting different alloy compositions, dopants, and layer thicknesses. These basic attributes have enabled the same basic technique to be used for narrow‐bandgap semiconductors such as the infrared detector mate-rials MCT and GaInSb and now for wide‐bandgap semiconductors such as GaN and ZnO. Indeed, the success of GaInN in the 1990s for high‐brightness blue light‐emitting diodes (LEDs) has now led to this being the most commonly produced MOVPE material with the growth of the market for high‐brightness white‐light LEDs for displays and lighting [14]. A new set of challenges for MOVPE equipment has led to a generation of commercial reactors designed to cope with the higher temperatures of GaN and AlN epitaxy. For AlN, the temperature required for growth is over 1200 °C, and reactors capable of over 1400 °C are now being manufactured. Prereaction is also more of an issue than with GaAs. The nitrides now represent over half the total commercial output of MOVPE, and research on AlN is pushing emitters to shorter wavelengths, into the UV, where they could eventually replace mercury lamps as a source of UV radiation for sterilization [15]. The nitrides are discussed in Chapter 4 in some depth, covering GaInN, AlGaN, and substrates for nitride epitaxy.

The early strength of MOVPE was its ability to grow onto different substrates, but this was later abandoned in favor of the more conventional homoepitaxy; however, the nitrides rely on heteroepi-taxy onto sapphire and SiC substrates, bringing MOVPE back to its roots with the early work of Manasevit. The goal of more recent work has been to achieve a reduced density of dislocations in the GaN layer using patterned substrates [16]. Heteroepitaxial growth onto silicon substrates has

4 Metalorganic Vapor Phase Epitaxy (MOVPE)

been widely studied and is of growing importance for optoelectronic device integration with silicon devices. The challenge is not only lattice mismatch but also the fundamental issue of growing a polar material onto a nonpolar substrate. If this is not properly understood and controlled, it will lead to antiphase domain boundaries. The fundamental considerations of MOVPE growth of III‐V materials onto silicon substrates is discussed in Chapter 8. There is also a growing realization that some of the lattice‐mismatch problems can be overcome by growing nanowires, which has been an intensive topic of research across all the material systems over the past 10 years and will be dis-cussed in Chapter 7 [17]. The versatility of substrate materials presents MOVPE with the ultimate challenge of mating high‐performance optoelectronic materials with silicon substrates to combine the best of optoelectronic and electronic performance.

1.2 Basic Reaction Mechanisms

The early progress of MOVPE was based on the availability of room‐temperature volatile but ther-mally stable precursors for the Group II source and trihydrides for the Group V source. Both have the essential properties of being volatile in a suitable carrier gas stream (usually hydrogen) and being chemically stable at ambient temperature. The temperatures of the organometallic precur-sors are carefully controlled, normally below ambient temperature to avoid condensation in the lines, to provide a fixed saturated vapor pressure (SVP). This is combined with a measured volu-metric flow of the carrier gas through the liquid organometallic source (contained in a stainless‐steel bubbler) to yield a known molar flow as shown in Eq. (1.1):

F

p

p

vm

svp

STP

b

22 4. (1.1)

where Fm is the molar flow, p

svp is the saturated vapor pressure in the bubbler, v

b is the flow of

carrier gas through the bubbler in l/min, and pSTP

is the pressure at STP.The organometallic precursors and hydrides are normally mixed outside the reaction chamber

where additional dilution of the carrier gas is carried out and then introduced into the reaction chamber through a suitable injector arrangement and directed onto a hot substrate. This is shown schematically in Figure 1.1. The alternative design of reactors will be discussed later in this chap-ter. The reaction of the precursors to yield the III‐V compound on the substrate can occur either in the hot vapor above the surface or on the hot surface. The stoichiometric reaction for GaAs growth is given as follows:

CH Ga AsH GaAs CH3 3 3 43 (1.2)

Gas phasereactions

Diffusion ofproducts tosurface

Diffusion tosurface ofprecursors

Hydridestream

Organometallicstream

PushflowDesorption of

organicproducts

Mixing

Parasitic reactions on reactor wall

Surface heterogeneousreactions

Figure 1.1 Schematic of MOVPE gas transport and reaction process.