S “This book contains a collection of the most recent studies written by highly recognized and ilicon authors in the field. The book is valuable especially for young scientists seeking inspiration from the most fascinating discoveries in the field. The book can also serve an excellent reference for experts.” Prof. Vassilios Vargiamidis Concordia University, Montreal, Canada Nanoscale materials are showing great promise in various electronic, optoelectronic, and energy applications. Silicon (Si) has especially captured great attention as the leading material for microelectronic and nanoscale device applications. Recently, various silicides have garnered special attention for their pivotal role in Si device engineering and for the vast potential they possess in fields such as thermoelectricity and magnetism. The fundamental understanding of Si and silicide material processes at nanoscale plays a key role in achieving device structures and performance that meet S real-world requirements and, therefore, demands investigation and exploration of nanoscale device applications. This book comprises the theoretical and experimental ilicide analysis of various properties of silicon nanocrystals, research methods and techniques to prepare them, and some of their promising applications. Yu Huang is a faculty member in the Department of Materials Sciences and Engineering at the University of California, Los Angeles (UCLA), USA. She received her PhD in physical chemistry from Harvard University, USA. Her research focuses on the fundamental principles governing nanoscale material synthesis and assembly at the molecular N edited by level, which can be utilized to design nanostructures and nanodevices with unique functions and properties to address critical challenges in anowires Yu Huang electronics, energy science, and biomedicine. She has received several recognitions King-Ning Tu including MRS student award, the Grant Prize Winner of Collegiate Inventors’ Competition, the IUPAC Young Chemist Prize, Lawrence Postdoctoral Fellowship, MIT Technology Review World’s Top 100 Young Innovator Award, NASA Nanotech Brief Nano 50 Innovator award, the Kavli Fellowship, the Sloan Fellowship, the PECASE, DARPA Young Faculty Award and, the NIH Director’s New Innovator Award. King-Ning Tu received his PhD in applied physics from Harvard University in 1968 and was associated with IBM T. J. Watson Research Center for 25 years before joining the UCLA, USA, in 1993. He is distinguished professor in the Department of Materials Science and SILICON AND Engineering and the Department of Electrical Engineering at the UCLA. He has over 500 journal publications with citations over 18,000 and h-factor of 74. He received the TMS John Bardeen Award in 2013. He has ILICIDE Huang S co-authored the textbook Electronic Thin Film Science and authored the books Solder Joint Technology: Materials, Properties, and Reliability and Electronic Thin-Film Reliability. Tu His research interests are focused on metal–silicon reactions, solder joint reactions, NANOWIRES point-contact reactions in nanowires, polarity effect of electromigration on interfacial reactions, and kinetic theories of interfacial reactions. applications, fabrication, and properties V159 ISBN 978-981-4303-46-0 SILICON AND SILICIDE NANOWIRES 1BO4UBOGPSE4FSJFTPO3FOFXBCMF&OFSHZ7PMVNF edited by Yu Huang King-Ning Tu SILICON AND SILICIDE NANOWIRES applications, fabrication, editors and properties Preben Maegaard Anna Krenz Wolfgang Palz The Rise of Modern Wind Energy Wind Power for the World Published by Pan Stanford Publishing Pte. Ltd. Penthouse Level, Suntec Tower 3 8 Temasek Boulevard Singapore 038988 Email: [email protected] Web: www.panstanford.com British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. Silicon and Silicide Nanowires: Applications, Fabrication, and Properties Copyright © 2014 by Pan Stanford Publishing Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the publisher. For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. ISBN 978-981-4303-46-0 (Hardcover) ISBN 978-981-4303-47-7 (eBook) Printed in the USA Contents Preface xv 1. In situ Observations of Vapor–Liquid–Solid Growth of Silicon Nanowires 1 S. Kodambaka 1.1 Introduction 1 1.2 Experimental 4 1.3 Silicon Nanowire Nucleation Kinetics 6 1.4 Silicon Nanowire Growth Kinetics 11 1.5 Summary and Outlook 14 2. Growth of Germanium, Silicon, and Ge–Si Heterostructured Nanowires 23 Shadi A. Dayeh and S. Thomas Picraux 2.1 Introduction 23 2.2 The VLS Growth Mechanism 24 2.3 Size Effects in Nanowire Growth 30 2.4 Temperature Effects on Nanowire Growth 36 2.5 Pressure Effects on Nanowire Growth 38 Nanowire Growth 40 2.72.6 Defects Dopant Precursorduring VLS Influence Growth of on Semiconductor Nanowires 42 2.8 Ge Core/Si Shell Heterostructured Nanowires 47 2.9 Unique Opportunities for Bandgap Engineering in Semiconductor Nanowires 50 2.10 Conclusions 52 3. Transition Metal Silicide Nanowires: Synthetic Methods and Applications 59 Jeremy M. Higgins, Andrew L. Schmitt, and Song Jin 3.1 Introduction 59 3.2 Formation of Bulk and Thin-Film Metal Silicides in Diffusion Couples 66 3.2.1 Basic Description 67 vi Contents 3.2.2 Diffusion, Thermodynamics, and Nucleation in Silicide Reactive Phase Formation 67 3.2.2.1 Diffusion and the dominant diffusing species 67 3.2.2.2 Thermodynamics of silicide reactions in binary diffusion couples 69 3.2.2.3 Basics of nucleation 70 3.2.3 Kinetics of Silicide Layer Growth 70 3.2.3.1 Nucleation-controlled kinetics 71 3.2.3.2 Diffusion-controlled kinetics 71 3.2.3.3 Reaction rate–controlled kinetics 73 3.2.3.4 Bulk versus thin-film diffusion couples 74 3.2.4 Phase Formation 77 3.2.4.1 Walser–Bene first phase rule 77 3.2.4.2 Effective heat of formation approach 78 3.2.5 Modern Developments 79 3.3 Silicide Nanowire Growth Techniques 80 3.3.1 Silicidation of Silicon Nanowires 81 3.3.2 Delivery of Silicon to Metal Films 84 3.3.3 Reactions of Transition Metal Sources with Silicon Substrates 86 3.3.3.1 Metal vapor 86 3.3.3.2 Metal halides 87 3.3.4 Simultaneous Metal and Silicon Delivery 88 3.3.4.1 Chemical vapor transport 88 3.3.4.2 Chemical vapor deposition 90 3.3.5 Vapor-Phase Technique Comparison 94 3.4 Applications of Silicide Nanowires 100 3.4.1 Nanoelectronics 100 3.4.2 Nanoscale Field Emitters 102 3.4.3 Spintronics 102 3.4.4 Thermoelectrics 103 3.4.5 Solar Energy Conversion 104 3.5 Conclusion 105 Contents vii 4. Metal Silicide Nanowires: Growth and Properties 121 L. J. Chen and W. W. Wu 4.1 Introduction 121 4.2 Epitaxial Growth of Silicide Nanowires on Si Substrate 122 4.2.1 Epitaxial NiSi2 Nanowires 123 2 Nanowires with Length Tunability 126 4.2.34.2.2 Growth Epitaxial of α-FeSi High-Density Titanium Silicide Nanowires in a Single Direction on a Silicon Surface 130 4.3 Growth of Free-Standing Silicide Nanowires and Their Properties 133 4.3.1 Growth of Single-Crystal Nickel Silicide Nanowires with Excellent Electrical Transport and Field-Emission Properties 133 4.3.1.1 Well-aligned epitaxial Ni31Si12 nanowire arrays 134 4.3.1.2 Growth of free-standing single-crystal NiSi2 nanowires 139 4.3.2 Cobalt Silicide Nanostructures: Synthesis, Electron Transport, and Field-Emission Properties 145 4.3.3 Synthesis and Properties of the Low- Resistivity TiSi2 Nanowires Grown with Metal Fluoride Precursor 151 4.3.4 Ti5Si4 Nanobats with Excellent Field-Emission Properties 157 4.4 Formation of Silicide/Si/Silicide Nano- Heterostructures from Si Nanowires 163 4.4.1 Controlled Growth of Atomic-Scale Si Layer with Huge Strain in the Nano- Heterostructure NiSi/Si/NiSi through Point-Contact Reaction between Nanowires of Si and Ni and Reactive Epitaxial Growth 163 4.4.2 Repeating Events of Nucleation in Epitaxial Growth of Nano CoSi2 and NiSi in Nanowires of Si 170 viii Contents 4.4.3 Reactions between Si Nanowires and Pt Pads 173 4.4.3.1 Formation of PtSi nanowire and PtSi/Si/PtSi nanoheterostructures 173 4.4.3.2 Epitaxial relationship of PtSi formation within a silicon nanowire 175 4.4.3.3 PtSi/i–Si/PtSi nanowire heterostructures as high- performance p-channel enhancement mode transistors 177 4.5 Conclusions 178 5. Formation of Epitaxial Silicide in Silicon Nanowires 187 Yi-Chia Chou, Kuo-Chang Lu, and King-Ning Tu 5.1 Introduction 187 5.1.1 Overview of Contacts in Microelectronics and Nanoelectronics 187 5.1.2 Introduction to Contacts in Nanoscale Electronics 188 5.1.2.1 Transition-metal silicides 188 5.1.2.2 One-dimensional nanostructures 189 5.1.2.3 Si-based nanocircuits in Si nanowires 191 5.1.3 Introduction to Solid-State Phase Transformations 192 5.2 Introduction to Solid-State Phase Transformation in Thin Film 195 5.2.1 Thin Film Metal Silicide Formation 195 5.2.1.1 Phase sequence 195 5.2.1.2 Growth kinetics 197 5.2.2 Examples of Silicides Formation on Si Wafers 199 5.2.2.1 Ni silicides formation 199 5.2.2.2 Co silicides formation 200 5.2.3 Summary 201 5.2.3.1 Metal-rich silicides 202 Contents ix 5.2.3.2 Monosilicides 202 5.2.3.3 Disilicides 202 5.3 Nanoscale Silicide Formation by Point Contact Reaction between Ni/Co and Si Nanowires 206 5.3.1 Introduction 206 5.3.2