Metal-Semiconductor Schottky Barrier Junctions and Their Applications

379 Pages·1984·16.397 MB·English

by  M. S. Tyagi (auth.), B. L. Sharma (eds.)

Metal-Semiconductor
Schottky Barrier Junctions
and Their Applications
Metal-Setniconductor
Schottlcy Barrier Junctions
and Their Applications
Edited by
B. L.Sharma
Solid State Physics Laboratory
Delhi, India
Plenum Press .. New York and London
Library of Congress Cataloging in Publication Data
Main entry under title:
Metal-semiconductor Schottky barrier junctions and their applications.
Bibliography: p.
Includes index.
1. Diodes, Schottky-barrier-Addresses, essays, lectures. I. Sharma, B. L.
TK7871.89.S35M48 1984 621.3815'2 84-1723
ISBN-13: 978-1-4684-4657-9 e-ISBN-13: 978-1-4684-4655-5
001: \0. \007/978-1-4684-4655-5
©1984 Plenum Press. New York
Softcover reprint of the hardcover 1s t edition 1984
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N.Y. 10013
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
Contributors
Y. Anand MIA-COM Gallium Arsenide Products, Inc., Burlington, Massachusetts
R. Z. Bachrach Xerox Palo Alto Research Center, Palo Alto, California
Stephen J. Fonash Engineering Science Program, The Pennsylvania State
University, University Park, Pennsylvania
S. C. Gupta Solid State Physics Laboratory, Delhi, India
R.J. Nemanich Xerox Palo Alto Research Center, Palo Alto, California
H. Preier Fraunhofer-Institut fUr Physikalische Messtechnik, Freiburg, Federal
Republic of Germany
Dieter K. Schroder Department of Electrical and Computer Engineering,
Arizona State University, Tempe, Arizona
B.L. Sharma Solid State Physics Laboratory, Delhi, India
M.J. Thompson Xerox Palo Alto Research Center, Palo Alto, California
James A. Turner Plessey Research (Caswell) Ltd., Allen Clark Research Centre,
Caswell, Towcester, Northants, England
M.S. Tyagi Department of Electrical Engineering, Indian Institute of Technology,
Kanpur, India
v
Preface
The present-day semiconductor technology would be inconceivable without
extensive use of Schottky barrier junctions. In spite of an excellent book by
Professor E.H. Rhoderick (1978) dealing with the basic principles of metal
semiconductor contacts and a few recent review articles, the need for a
monograph on "Metal-Semiconductor Schottky Barrier Junctions and Their
Applications" has long been felt by students, researchers, and technologists. It
was in this context that the idea of publishing such a monograph by Mr. Ellis H.
Rosenberg, Senior Editor, Plenum Publishing Corporation, was considered
very timely. Due to the numerous and varied applications of Schottky barrier
junctions, the task of bringing it out, however, looked difficult in the beginning.
After discussions at various levels, it was deemed appropriate to include only
those typical applications which were extremely rich in R&D and still posed
many challenges so that it could be brought out in the stipulated time frame.
Keeping in view the larger interest, it was also considered necessary to have the
different topics of Schottky barrier junctions written by experts.
This monograph is divided into eight chapters. The first chapterreviews the
physics of Schottky barrier junctions, while the second deals with the interface
chemistry and structure of Schottky barrier formation. Chapter 3 emphasizes
the design considerations, fabrication processes, and characterization aspects
of metal-silicon and metal-gallium arsenide junctions in a general way. Chap
ters 4-8 are concerned with specific applications. Amongst these, Chapter 4
encompasses a number of optoelectronic structures which employ not only
Schottky barrier junctions but also Schottky barrier-type junctions. Chapters 5,
6, 7, and 8 deal with various theoretical and practical aspects of Schottky
photodiodes, microwave Schottky diodes, MESFETs, and Schottky barrier
gate CCDs, respectively. Considering the timely importance of metal
amorphous silicon junctions, a chapter on such junctions and their applications
is also included at the end. In a monograph of this type it is difficult to
maintain the interwoven nature of the text and ensure a uniformity of
presentation and notations, especially when the contributors are from
different parts of the world. For this, I regret any inconvenience to those
readers who prefer a textbook-type approach.
vii
viii PREFACE
Finally, I am indebted to the contributors for their self-contained
contributions and to Mr. Ellis H. Rosenberg and his staff, without whose
cooperation it would have been difficult to bring out this monograph in the
stipulated time.
B.L. SHARMA
Contents
1. PHYSICS OF SCHOTTKY BARRIER JUNCTIONS
M.S. Tyagi
1. Introduction . . . . . . . . . . . . . . . . . . . .
2. Origins of Barrier Height . . . . . . . . . . . . . . . 2
2.1. Schottky-Mott Theory of Ideal Metal-Semiconductor Contact 2
2.2. Modifications to Schottky Theory. . . . . . 8
2.3. Classifications of Metal-Semiconductor Interfaces . . . . . 11
2.4. Contacts on Reactive Interfaces. . . . . . . . . . . . 12
2.5. Contacts with Surface States and an Insulating Interfacial Layer 13
2.6. Contacts on Vacuum Cleaved Surfaces 17
3. Measurement of Barrier Height . . . 19
3.1. Capacitance-Voltage Measurement 19
3.2. Current-Voltage Measurement. . 20
3.3. Photoelectric Measurement . . . 21
4. Results of Barrier Height Measurements 21
4.1. Chemically Prepared Surfaces 21
4.2. Vacuum Cleaved Surfaces. . . 23
4.3. Concluding Remarks . . . . 24
5. Capacitance-Voltage Characteristics. 27
5.1. Electric Field and Potential Distribution in the Depletion Region. 27
5.2. Depletion Region Capacitance . 29
5.2.1. Ideal Schottky Barrier. . 29
5.2.2. Effect of Minority Carriers 32
5.2.3. Effect of Interfacial Layer. 33
5.2.4. Effect of Deep Traps 34
6. Current-Voltage Characteristics . . 35
6.1. Transport Mechanisms. . . . 35
6.1.1. Diffusion and Thermionic Emission over the Barrier 36
6.1.2. Tunneling through the Barrier. . . . . . . . 41
6.1.3. Carrier Generation and Recombination in the Junction
Depletion Region 44
6.1.4. Minority Carrier Injection 45
6.2. Forward Characteristics 46
6.3. Reverse Characteristics. 51
7. Transient Behavior 53
ix
x CONTENTS
8. Low-Resistance Schottky Barrier Contacts 54
References . . . . . . . . . . . . . 56
2. INTERFACE CHEMISTRY AND STRUCTURE OF SCHOTTKY
BARRIER FORMATION
R.z. Bachrach
1. Introduction. . 61
2. Perspectives on Schottky Barrier Formation. 63
2.1. Introduction . . . . . . . . . . 63
2.2. Brief Review of Phenomenological Schottky Barrier Data 65
3. The Chemistry and Structure of the Interfacial Layer. . . . 70
3.1. Synopsis of the Layer-by-Layer Evolution. . . . . . 72
3.2. Some Techniques for Studying the Stages of Interface Formation. 72
4. Evolution of the Interfacial Layer. . . . . . 73
4.1. Stage 0: The Clean Semiconductor Surface. 74
4.1.1. Silicon (100) and (111) Surfaces. . . 76
4.1.2. GaAs (110) and GaAs (100) Surfaces. 77
4.2. Stage 1: The Dilute Limit « 1/2 Monolayer). 78
4.3. Stage 2: Monolayer Formation-Metal Film Nucleation. 81
4.4. Stage 3: Additional Monolayers and Interdiffusion. . 82
4.5. Some Specific Characteristics of the Interfacial Layers. . 84
5. Formation of Interface States. . . . . . . . . . . . 85
5.1. Intrinsic Interface States Derived from the Metal and Semiconductor 86
5.2. Localized Defect and Impurity Related States. . . . . . 87
5.3. Interface States and the Stages of Interface Formation. . . 90
6. Case Studies of the Chemistry and Structure of Schottky Barrier
Formation. . . . . . . . . . . . . . 93
6.1. Case Studies of Silicon Schottky Barriers . 93
6.1.1. AI, Ag, Cu, and Au Schottky Barriers 93
6.1.2. Silicide-Silicon Interfaces. . . . . 96
6.2. Case Studies of III-V and II-VI Compound Semiconductor
Schottky Barriers. . . . . . . . . . . . . . . . 99
6.2.1. The Ga-AI-As System. . . . . . . . . . . . 99
6.2.2. The GaAIAs Ternary System with Au Schottky Barriers. 104
6.2.3. InP . . . . . . . 106
6.2.4. Some II-VI Examples. 107
7. Summary 108
References. . . . . . . . . . 108
3. FABRICATION AND CHARACTERIZATION OF METAL
SEMICONDUCTOR SCHOTTKY BARRIER JUNCTIONS
B.L.Sharma
1. Introduction. . . . . . . . . 113
2. Selection of Semiconductor Materials 115
CONTENTS xi
3. Metal-Semiconductor Systems. 120
3.1. Metal-Silicon Systems. . 120
3.2. Metal-GaAs Systems . . 127
3.3. Multilayer Metallization Systems 130
4. Design Considerations 131
5. Fabrication Technology. . . 135
5.1. Surface Processing . . . 136
5.2. Dielectric Film Deposition 137
5.3. Ohmic Contact Formation 137
5.4. Metal Deposition. 139
5.5. Other Steps. 141
6. Characterization. 142
References. . . . 148
4. SCHOTTKY-BARRIER-TYPE OPTOELECTRONIC
STRUCTURES
Stephen J. Fonash
1. Introduction. . . 161
2. Barrier Formation in Schottky-Barrier-Type Junctions 163
3. Transport in Schottky-Barrier-Type Structures 168
3.1. MS and MIS Structures . . . . . . . 168
3.2. SIS Structures. . . . . . . . . . . 173
4. Schottky-Barrier-Type Optoelectronic Structures 174
4.1. Schottky-Barrier-Type Light-Emitting Structures. 174
4.2. Schottky-Barrier-Type Photodiodes . . . 181
4.3. Schottky-Barrier-Type Photovoltaic Devices 185
4.3.1. MS and MIS Photovoltaic Devices 185
4.3.2. SIS Photo voltaic Devices 187
3. Summary 187
R~ferences. . . . . . . . . . . 188
5. SCHOTTKY BARRIER PHOTODIODES
s.c.
Gupta and H. Preier
1. Introduction. . . . . . 191
2. General Parameters of Photodiodes . 193
2.1. Signal-to-Noise Ratio (SIN). . 193
2.2. Noise Equivalent Power (NEP) . 193
2.3. Detectivity (D). . . . . . . 194
2.4. Normalized Detectivity (D*). . 194
2.5. Detectivity Normalized Also with Respect to the Field of
View (D**). . . . . 196
2.6. Resistance Area Product 196
2.7. Response Time. . 200
3. Selection of Materials. . . 203