Nanophononics. Zlatan Aksamija. Thermal Generation, Transport, and Conversion at the Nanoscale. edited by

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1 Nanophononics Thermal Generation, Transport, and Conversion at the Nanoscale edited by

3 Nanophononics

5 Nanophononics Thermal Generation, Transport, and Conversion at the Nanoscale edited by

6 Published by Pan Stanford Publishing Pte. Ltd. Penthouse Level, Suntec Tower 3 8 Temasek Boulevard Singapore editorial@panstanford.com Web: British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. Nanophononics: Thermal Generation, Transport, and Conversion at the Nanoscale Copyright 2018 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 (Hardcover) ISBN (ebook)

7 Contents Preface ix 1. Modeling Self-Heating Effects in Nanoscale Devices 1 Katerina Raleva, Abdul Rawoof Shaik, Suleman Sami Qazi, Robin Daugherty, Akash Laturia, Ben Kaczer, Eric Bury, and Dragica Vasileska 1.1 Introduction Self-Heating General Considerations Arizona State University Model Description Simulation Results Self-Heating Effects in FD-SOI Devices Basic findings Thermal boundary conditions and proper choice of the device simulation domain Can We Reduce Self-Heating? Single-gate versus dual-gate FD-SOI devices FD-SOI devices with diamond and AlN BOX Multiscale Modeling: Modeling of Circuits (CS and CD Configuration) Conclusions and Future Directions of Research Simulation of Charge and Thermal Transport Introduction The Boltzmann Transport Equation for Electrons Electron Scattering Rates The Phonon Boltzmann Transport Equation Phonon Scattering and Anharmonic Decay 37

8 vi Contents 3. Phonon Emission and Absorption Spectra in Silicon Introduction The Adiabatic Bond Charge Model for Phonons Numerical Computation of Phonon Spectra Results and Discussion Conclusions Device Simulation, Including the Full Phonon Dispersion Introduction Monte Carlo Device Simulation Thermal Properties of Silicon Results Conclusions Anharmonic Decay of Nonequilibrium Intervalley Phonons in Silicon Introduction Intervalley Phonon Emission Monte Carlo Simulation of Anharmonic Phonon Decay Scattering of Acoustic Phonons Results and Discussion Phonon Monte Carlo: Generating Random Variates for Thermal Transport Simulation 109 L. N. Maurer, S. Mei, and I. Knezevic 6.1 Introduction Generating Random Variates The Inversion Method The Rejection Method Overview of Phonon Monte Carlo Generating Phonon Attributes in PMC Thermal Phonons with Full Dispersion in 2D 119

9 Contents vii Thermal Phonons with an Isotropic Dispersion in 3D Diffuse Boundary Scattering Contacts D Internal Contacts D Boundary Contacts D Contacts Energy Conservation Conclusion Hybrid Photovoltaic-Thermoelectric Solar Cells: State of the Art and Challenges 139 Bruno Lorenzi and Dario Narducci 7.1 Introduction A Primer on Thermoelectricity Strategies of Thermoelectric Solar Energy Conversion Solar Thermoelectric Generators Hybrid Cogenerative Solar Thermoelectric Generators Hybrid Thermoelectric-Photovoltaic Generators Photovoltaic Generation Physical Principles The p-n Junction Single-Junction Solar Cells: Diode under Illumination Photovoltaic Technology PV Efficiency, Energy Gap, and Temperature Thermoelectric Hybridization of PV Cells Conditions for Enhanced Efficiency in HTEPV Devices Optimal Layout of the Thermoelectric Stage Optical and Thermal Concentration Summary and Concluding Remarks 174

10 viii Contents 8. Phonon Transport Effects in Ultranarrow, Edge-Roughened Graphene Nanoribbons 183 Neophytos Neophytou and Hossein Karamitaheri 8.1 Introduction Methods Phonon Dispersion Phonon Dispersion Features Phonon Transport within NEGF Influence of Roughness on Phonon Transport Influence of Roughness on Phonon Transmission Influence of Roughness on Different Phonon Modes Ballistic, Diffusive, and Localized Phonon Modes Transmission Effects in Width-Modulated GNRs Influence of Width Modulation on Acoustic Modes Influence of Width Modulation on Optical Modes Influence of Width Modulation on Low-Density-Mode Regions Influence of Width Modulation on Quasi-Acoustic Modes General Discussion of Width- Modulated Features Thermal Conductance Characteristic Scattering Length Scales Mean Free Path for Scattering Localization Length Thermal Conductivity Conclusions 213 Index 223

11 Contents ix Preface As the title implies, this book merges phonons, quantized packets of lattice vibrations that are the primary carriers of heat in most semiconductors, with nanoscale phenomena. The goal of this combination is to explore what happens to heat as we scale our nanoelectronic, optoelectronic, and energy devices down to feature sizes in the hundreds of, tens of, and even single nanometers. At such extreme scales, the thermal energy stored in and carried by phonons takes on new and emerging properties, such as ballistic transport and confinement, while modulating the coupling between electronic and thermal transport. Dissipation at the nanoscale, thus, becomes a new challenge but one rife with opportunities for discovery and improvement via nanoengineering. This book grew out of a special session on nanophononics that I organized at the IEEE Nano conference in Rome, Italy. The session brought together speakers who were studying phonons in nanostructures, with a particular focus on those individuals who are at the cusp between electrical engineering, a core area traditionally represented at the IEEE Nano conference; mechanical engineering, as it has historically encompassed heat transfer; and materials science for its contributions to first-principle materials modeling. While research in all three of these areas was affected by dissipation and phonons, they were infrequently brought together in conferences. After the conference, the authors of the chapters in this volume built off the work they presented at IEEE Nano and incorporated their most up-to-date findings and results. The fruit of their labors is this edited volume on nanophononics, which focuses on thermal effects in nanostructures, including the generation, transport, and conversion of heat at the nanoscale level. It covers semiconductor nanostructures, including the traditional group IV elements (e.g., Si, Ge, diamond), carbon allotropes (graphene and graphene nanoribbons), and emerging new materials like transition metal dichalcogenides (TMDCs). The volume could be roughly divided into four segments focusing on the main themes of this book: (i) phonon generation or heat dissipation, (ii) nanoscale phonon transport,

12 x Preface (iii) applications and devices (including thermoelectrics), and (iv) emerging materials (graphene or two-dimensional). In the first theme, phonon generation through interactions with electrons in out-of-equilibrium conditions and devices and light (photovoltaics) is covered. Nanoscale phonon transport, ranging from diffusive to ballistic, and anharmonic decay are covered in the second theme, comprising Chapters 4 and 5. In addition, theoretical and numerical simulation methods, such as phonon Monte Carlo and first-principle calculations, feature prominently in the second part of the book. The third theme, applications and devices, focuses on heat dissipation and self-heating in nanoelectronics and thermoelectric energy conversion. The fourth theme focuses on emerging issues such as tandem photovoltaic thermoelectric converters and ultranarrow graphene ribbons. Overall, this book will provide researchers, graduate students, and practitioners with a solid reference on the role of phonon transport at the nanoscale and in a variety of applications. I extend my sincere gratitude to all the chapter authors for their generous contributions to this book and their patience while the book came together. This volume, however, is by no means comprehensive: nanophononics remains an active area of research where numerous scientists and engineers continue to make breakthroughs by understanding, designing, building, and testing new phononic crystals, thermal diodes, and a slew of other materials and devices that take advantage of the unique thermal properties of nanostructures. It is my hope that the book will spark many deep conversations across disciplinary boundaries, between theorists and experimentalists, and between materials scientists and device engineers. University of Massachusetts Amherst 2017

Hydrophobic and Superhydrophobic Organic-Inorganic Nanohybrids. Chang-Sik Ha Saravanan Nagappan

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