Semiconductor Device Physics and Simulation

Semiconductor Device Physics and Simulation

MICRODEVICES Physics and Fabrication Technologies Series Editors: Ivor Brodie and Arden Sher SRI International Menlo Park, California Recent volumes in the series: COMPOUND AND JOSEPHSON HIGH-SPEED DEVICES Edited by Takahiko Misugi and Akihiro Shibatomi ELECTRON AND ION OPTICS Miklos Szilagyi ELECTRON BEAM TESTING TECHNOLOGY Edited by John T. L. Thong ORIENTED CRYSTALLIZATION ON AMORPHOUS SUBSTRATES E. I. Givargizov PHYSICS OF HIGH-SPEED TRANSISTORS Juras Pozela THE PHYSICS OF MICRO/NANO-FABRICATION Ivor Brodie and Julius J. Muray PHYSICS OF SUBMICRON DEVICES David K. Ferry and Robert O. Grondin THE PHYSICS OF SUBMICRON LITHOGRAPHY Kamil A. Valiev RAPID THERMAL PROCESSING OF SEMICONDUCTORS Victor E. Borisenko and Peter J. Hesketh SEMICONDUCTOR ALLOYS Physics and Materials Engineering An-Ban Chen and Arden Sher SEMICONDUCTOR DEVICE PHYSICS AND SIMULATION J. S. Yuan and J. J. Liou SEMICONDUCTOR LITHOGRAPHY Principles, Practices, and Materials Wayne M. Moreau SEMICONDUCTOR PHYSICAL ELECTRONICS Sheng S. Li A Continuation Order Plan is available for this series. A continuation order will bring delivery of each new volume immediately upon publication. Volumes are billed only upon actual shipment. For further information please contact the publisher.

Semiconductor Device Physics and Simulation J. S. Yuan and J. J. Liou University of Central Florida Orlando, Florida Springer Science+Business Media, LLC

Library of Congress Cataloging-in-Publication Data Yuan, J. S. Semiconductor device physics and simulation / J.S. Yuan and J.J. Liou. p. cm. (Microdevices) Includes bibliographical references and index. ISBN 978-1-4899-1906-9 1. Semiconductors Computer simulation. 2. Junction transistors- -Computer simulation. I. Liou, Juin J. II. Title. III. Series. TK7871.85.Y83 1998 621.3815'2'0113--dc21 98-18553 CIP ISBN 978-1-4899-1906-9 ISBN 978-1-4899-1904-5 (ebook) DOI 10.1007/978-1-4899-1904-5 Springer Science+Business Media New York 1998 Originally published by Plenum Press, New York in 1998 Softcover reprint of the hardcover 1st edition 1998 http://www.plenum.com 10987654321 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher

To my late father and my mother -J. S. Yuan

Preface The advent of the microelectronics technology has made ever-increasing numbers of small devices on a same chip. The rapid emergence of ultra-large-scaled-integrated (ULSI) technology has moved device dimension into the sub-quarter-micron regime and put more than 10 million transistors on a single chip. While traditional closed-form analytical models furnish useful intuition into how semiconductor devices behave, they no longer provide consistently accurate results for all modes of operation of these very small devices. The reason is that, in such devices, various physical mechanisms affect the device performance in a complex manner, and the conventional assumptions (i.e., one-dimensional treatment, low-level injection, quasi-static approximation, etc.) employed in developing analytical models become questionable. Thus, the use of numerical device simulation becomes important in device modeling. Researchers and engineers will rely even more on device simulation for device design and analysis in the future. This book provides comprehensive coverage of device simulation and analysis for various modem semiconductor devices. It will serve as a reference for researchers, engineers, and students who require in-depth, up-to-date information and understanding of semiconductor device physics and characteristics. The materials of the book are limited to conventional and mainstream semiconductor devices; photonic devices such as lightemitting and laser diodes are not included, nor does the book cover device modeling, device fabrication, and circuit applications. It is assumed that the reader has already acquired a basic understanding of device structures and operations, such as those given in Solid-State Electronic Devices, 4th ed. (Prentice-Hall, 1995) or Device Electronics/or Integrated Circuits, 2nd ed. (Wiley, 1986). A two-dimensional device simulator called MEDICI, originally developed by Stanford University (PISCES II) and supported by Technology Modeling Associates, Inc., CA, is used to perform the analysis and to generate the simulation results. Basically, MEDICI solves numerically the fi ve classical semiconductor device equations: Poisson's equation, electron and hole continuity equations, and electron and hole drift-diffusion current equations. Relevant device physics, such as heavy doping effects, concentration, and field-dependent free-carrier mobilities, and concentration-dependent free-carrier lifetimes, are incorporated in the program. The capability of MEDICI goes beyond the traditional device simulator, however, in that it also contains two optional modules which vii

viii PREFACE allow one to simulate the device performance, including the effects of lattice heating and heterostructure. A detailed description of MEDICI is given in Chapter 1. The book is organized into nine chapters. Except for the first chapter, which discusses semiconductor fundamentals and the capabilities and features of device simulators, each chapter covers a semiconductor device, providing dc, ac, and transient simulation results, discussions of relevant device physics, and their implications to device design and analysis. The devices covered, in the same order as the chapters, are p-n junction, bipolar junction transistors, junction field-effect transistors, metal-oxide-semiconductor fieldeffect transistors, bipolar/cmos devices, metal-semiconductor field-effect transistors, heterojunction bipolar transistors, and photoconductive diodes. All chapters contain useful figures to illustrate the physical mechanisms and characteristics of the semiconductor devices simulated by MEDICI and, in some cases, those observed in measurements. Extensive references have also been given as an aid to the reader who wishes to carry out an in-depth study on a particular topic. J. S. Yuan and J. J. Liou Department of Electrical and Computer Engineering University of Central Florida

Contents CHAPTER 1. Introduction 1.1. Semiconductor Device Fundamentals.... 1.1.1. Mobility and Carrier Scattering.............. 1.1.2. Carrier Transport by Diffusion and the Einstein Relation. 1.1.3. Recombination and Generation.... 1.1.4. Heavy Doping Effects and Band-Gap Narrowing 1.1.5. Carrier Concentration in Semiconductors and Fermi-Dirac Statistics.... 1.2. Basic Semiconductor Equations Used in Device Simulators. 1.3. Numerical Techniques Used in Device Simulators. 1.4. Capability and Limitations of Device Simulators 1.5. Applications of Device Simulation References............. CHAPTER 2. P-N Junction 2.1. Device Physics of p-n Junction............ 2.2. DC Characteristics of a p-n Junction Diode..... 2.2.1. Forward-Bias Current-Voltage Characteristics 2.2.2. Reverse-Bias and Low-Forward-Bias Current-Voltage Characteristics........ 2.2.3. Junction Avalanche Breakdown.... 2.2.4. Temperature Dependence of Steady-State Current 2.2.5. Two-Dimensional Effect... 2.3. AC Parameters of a p-n Junction Diode... 2.3.1. Junction Capacitance........... 2.3.2. Diffusion Capacitance and Conductance. 2.4. Transient Behavior of a p-n Junction Diode 2.4.1. Open-Circuit Voltage Decay. 2.4.2. Short-Circuit Current Decay 2.4.3. Reverse Recovery Transient 2.5. Schottky Diodes........ 1 2 4 5 5 7 8 11 15 17 20 23 26 26 29 31 32 33 35 35 36 37 39 41 44 45 ix

x CONTENTS 2.6. Heterojunction References.. 45 51 CHAPTER 3. Bipolar Junction Transistors 3.1. Device Physics... 53 3.1.1. Collector Current 54 3.1.2. Base Current... 57 3.1.3. Current Gain... 58 3.2. DC Characteristics and Simulation 59 3.2.1. Current-Voltage Characteristics for Forward-Active and Saturation Operation..................... 59 3.2.2. C u r r ~ n t -Characteristics V o l t a g e for Reverse-Active Operation. 63 3.2.3. Current-Voltage Characteristics at Different Temperatures 64 3.2.4. Emitter Crowding and Sidewall Injection 66 3.2.5. Base Pushout and Collector Spreading 70 3.2.6. Current-Dependent Base Resistance 76 3.2.7. Avalanche Multiplication.... 78 3.3. AC Operation and Device Simulation. 82 3.3.1. Small-Signal Current Gain 83 3.3.2. Transconductance... 83 3.3.3. Output Conductance. 84 3.3.4. Junction Capacitances. 85 3.3.5. Cutoff Frequency... 85 3.3.6. Maximum Oscillation Frequency. 86 3.3.7. S-Parameters... 87 3.4. Transient Operation and Simulation. 88 3.4.1. Turn-on Transients 89 3.4.2. Tum-off Transients 91 References........ 96 CHAPTER 4. Junction Field-Effect Transistors 4.1. Concept and Theory............ 4.2. MEDICI Simulation............ 4.2.1. DC Characteristics of Long- and Short-Channel JFETs 4.2.2. Transient Characteristics of JFETs.. 4.2.3. Small-Signal Characteristics of JFETs References.................. CHAPTER 5. Metal-Oxide Semiconductor Field-Effect Transistors 5.1. Current -Voltage Characteristics. 5.1.1. Strong Inversion. 5.1.2. Weak Inversion.. 5.2. MEDICI Simulation... 5.2.1. DC Characteristics. 99 103 103 117 117 124 128 130 135 138 138

CONTENTS xi 5.2.2. Transient and AC Characteristics 5.3. Hot Electron Effect References......... 140 157 161 CHAPTER 6. BiCMOS Devices 6.1. Comparisons of BiCMOS, CMOS, and BIT. 163 6.2. Principles of BiCMOS Operation.. 164 6.3. BiCMOS Switching Delay.......... 166 6.4. BiCMOS Device Simulation......... 169 6.5. BiCMOS Transient Analysis Including High-Current Effects. 172 6.5.1. Analytical Approach........ 172 6.5.2. Numerical Approach.......... 175 6.5.3. Normalized Base Pushout Factor... 181 6.6. Radiation Effect on BiCMOS Performance. 185 6.6.1. Radiation Effects on the BJT in a BiCMOS Device.. 186 6.6.2. Radiation Effects on the MOSFET in a BiCMOS Device.. 187 6.6.3. Leakage Paths in BiCMOS.................. 188 6.6.4. MEDICI Simulation Including Radiation Effects...... 189 6.6.5. The Model Including Effects of Base Pushout and Radiation.. 190 6.7. Scaling............ 197 6.7.1. Temperature Scaling... 197 6.7.2. Geometrical Scaling... 199 6.7.3. Supply Voltage Scaling. 200 6.8. Hot Electron Reliability of BiCMOS Devices. 202 References.................... 206 CHAPTER 7. Metal-Semiconductor Field-Effect Transistors 7.1. Schottky Diode......... 210 7.1.1. Basic Concept.... 210 7.1.2. Effect ofinterface States......... 213 7.1.3. Bias Dependence ofthe Barrier Height. 215 7.1.4. Current-Voltage Characteristics..... 216 7.1.5. Effect of Interfacial Layer on Current Transport. 219 7.2. Simple MESFET Model.... 219 7.3. MEDICI Simulation....... 221 7.3.1. Steady-State Simulation. 222 7.3.2. Transient Response.... 224 7.3.3. Small-Signal Analysis.. 229 7.3.4. Advanced MESFET Structure. 234 7.4. Heterojunction FETs. 239 References............... 250 CHAPTER 8. Heterojunction Bipolar Transistors 8.1. Heterojunction Physics... 256

xii CONTENTS 8.2. DC Characteristics.... 8.2.1. Collector and Base Currents.... 8.2.2. Offset Voltage.... 8.2.3. Velocity Overshoot and Ballistic Transport.... 8.2.4. Self-heating Effect........... 8.3. RF Behavior............................ 8.3.1. Junction Capacitance.... 8.3.2. Transconductance.... 8.3.3. Output Conductance........ 8.3.4. Cutoff Frequency.... 8.3.5. Flicker Noise................. 8.4. Transient Characteristics...................... 8.4.1. Emitter-Coupled Logic Using HBTs.... 8.4.2. HBT Turn-off Transient.... 8.5. InP HBTs.................................. 8.6. SiGe HBTs................................. 8.7. Reliability ofhbts.... 8.7.1. Multiemitter Fingers.... 8.7.2. Emitter Collapse Phenomenon.... 8.7.3. Emitter Ballasting Resistors.... References............................ 258 258 258 259 260 265 265 266 266 268 269 270 270 271 272 273 279 281 286 290 293 CHAPTER 9. Photoconductive Diodes 9.1. Horizontal PCE.... 9.1.1. Analytical Model.... 9.2. MEDICI Simulation.......... 9.2.1. DC Characteristics.... 9.2.2. Transient Characteristics.... 9.3. Vertical PCE.... 9.3.1. DC Characteristics.... 9.3.2. Transient Characteristics.... 9.4. Self-heating Effects on PCE Performance........... References................................. INDEX.... 297 297 301 301 307 313 313 314 325 331 333