Semiconductor Devices

234 Pages·1994·8.587 MB·English

by  J. J. Sparkes (auth.)

Semiconductor Devices
TUTORIAL GUIDES IN ELECTRONIC ENGINEERING
Series editors
Professor G.G. Bloodworth, University of York
Professor A.P. Dorey, University of Lancaster
Professor J. K. Fidler, University of York
This series is aimed at first- and second-year undergraduate courses. Each text is
complete in itself, although linked with others in the series. Where possible, the
trend towards a 'systems' approach is acknowledged, but classical fundamental
areas of study have not been excluded. Worked examples feature prominently
and indicate, where appropriate, a number of approaches to the same problem.
A format providing marginal notes has been adopted to allow the authors to
include ideas and material to support the main text. These notes include refer
ences to standard mainstream texts and commentary on the applicability of
solution methods, aimed particularly at covering points normally found difficult.
Problems and exercises, with answers at the end of the book, are included in the
text.
1. Transistor Circuit Techniques: discrete and integrated (3rd edition)-
G .J. Ritchie
2. Feedback Circuits and Op Amps (2nd edition)-D.H. Horrocks
3. Pascal for Electronic Engineers (2nd edition)-J. Attikiouzel
4. Computers and Microprocessors: components and systems (3rd edition)
A.C. Downton
5. Telecommunication Principles (2nd edition)-J.J. O'Reilly
6. Digital Logic Techniques: principles and practice (2nd edition)
T.J. Stonham
7. Instrumentation: Transducers and Interfacing-B.R. Bannister and
D.G. Whitehead
8. Signals and Systems: models and behaviour (2nd edn)-M.L. Meade and
C.R. Dillon
9. Basic Electromagnetism and its Applications-A.J. Compton
10. Electromagnetism for Electronic Engineers (2nd edn)-R.G. Carter
11. Power Electronics-D.A. Bradley
12. Semiconductor Devices (2nd edition)-J .J. Sparkes
13. Electronic Components and Technology (2nd edition)-S.J. Sangwine
14. Optoelectronics-J. Watson
15. Control Engineering-C. Bissell
16. Basic Mathematics for Electronic Engineers: models and applications
J.E. Szymanski
17. Integrated Circuit Design and Technology-M.J. Morant
Semiconductor
Devices
Second edition
J.J. Sparkes
The Open University
Milton Keynes
UK
IU!11
Spring.,--Science+Busine" Media, B.V.
First edition 1987
Reprinted 1988, 1992
Second edition 1994
© J.J. Sparkes 1987,1994
Originally published by Chapman & Hall in 1994
ISBN 978-0-412-58770-2 ISBN 978-1-4899-7128-9 (eBook)
DOI 10.1007/978-1-4899-7128-9
Apart from any fair dealing for the purposes of research or private study,
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The publisher makes no representation, express or implied, with regard
to the accuracy of the information contained in this book and cannot
accept any legal responsibility or liability for any errors or omissions that
may be made.
A catalogue record for this book is available from the British Library
Library of Congress Catalog Card Number: 94-70269
@l
Printed on permanent acid-free text paper, manufactured in accordance
with ANSI/NISO Z39.48-1992 and ANSIINISO Z39.48-1984 (Permanence
of Paper).
Contents
Preface to second edition vii
Preface
Vlll
1 Semiconductors and applications of semiconductor devices 1
Semiconductor materials 2
Pure semiconductors 2
Doped semiconductors 5
The Fermi level 7
Recombination 10
Summary 13
Typical applications of semiconductor devices 15
Semiconductor diodes 16
Field effect transistors (FETs) 24
Bipolar junction transistors (BJTs) 30
Thyristors 37
Summary 42
2 p-n junction diodes 44
The silicon p-n junction 44
Current flow in semiconductors 51
The p-n junction in equilibrium 56
Current through a p-n junction 61
Further comments on the current through a p-n junction 64
Transition region width and capacitance 67
Breakdown diodes 73
Band-gap diodes 75
Recombination and generation in p-n junctions 78
Solar cells and photodiodes 82
Charge storage and diffusion capacitance 84
Small-signal equivalent circuit of a diode 89
Metal-silicon junctions and Schottky diodes 90
SPICE 98
Summary 100
3 Field effect transistors 101
The junction field effect transistor (JFET) 101
Theoretical characteristics of a JFET 106
Metal oxide silicon field effect transistors (MOSFETs) 109
Theoretical characteristics of a MOSFET 114
The formation of the channel and the threshold voltage 117
The small-signal equivalent circuit 124
Summary 127
v
4 Bipolar junction transistors 129
The principles of the operation of the bipolar transistor 132
The hybrid n small-signal equivalent circuit 142
Practical design considerations 149
The dependence of fT and p on the d.c. collector current 153
The bipolar transistor as a switch 154
Thyristors 164
Summary and SPICE parameters for bipolar transistors 168
5 Integrated circuits 173
Introduction 173
Silicon integrated circuits based on bipolar n-p-n transistors 173
The processing steps 176
p-n-p transistors 177
Diodes 179
Resistors 179
Capacitors 180
Schottky diodes 181
MOSFETs in silicon integrated circuits 181
Charge-coupled devices 185
Summary and conclusion 188
6 New technologies 189
Introduction 189
III-V compounds 189
The gallium arsenide MESFET 192
Ternary and quaternary compound semiconductors 193
Light-emitting diodes 196
Heterojunction LEDs 198
Semiconductor lasers 200
Heterojunction bipolar transistors 202
Summary 203
Appendix A The carrier distributions through a BJT in the active region of
operation 205
Appendix B List of symbols; physical constants and other data 207
Answers to exercises 209
References 220
Index 221
vi
Preface to second edition
Many of the features of the first edition are included in this enlarged second
edition, including a first chapter introducing some of the concepts needed in later
chapters and a final chapter on some of the more recent device designs. But the
opportunity has been taken not only to give a more detailed account of how the
concept of electron energy bands can be used in explanations of device charac
teritics, but also to explain more fully how mathematical models of device
behaviour can be used to predict and explain device performance in electronic
circuits.
The operation and properties of semiconductor devices depend strongly on the
behaviour of p-n junctions and metal-semiconductor contacts. To understand
the behaviour of these devices the reader therefore needs to become familiar with
two different physical models that represent the energy and motion of charge
carriers (electrons and holes) in solid materials. The first, which is known as the
band model, represents the distribution of the energies of the charge carriers. The
second, which may be called the bond model, gives a clearer mental picture of the
structure of a semiconductor and of the mechanisms by which charge carriers
move within a device. Neither of these models can give a wholly satisfactory
representation of all the different kinds of behaviour of p-n junctions and
metal-semiconductor contacts, so more space is devoted to explaining the band
model and its relationship with solid state theory, and to explaining where and
why it is essential to use the bond model instead.
In addition to fuller explanations of the operation of various semiconductor
devices (avoiding some of the common over-simplifications) the second edition
includes a number of further topics which are frequently included in under
graduate courses. These include 'band-gap' diodes, Schottky diodes and the
theory of junction field-effect transistors (JFETs) which complements the theory
of the metal oxide silicon field effect transistors (MOSFETs) already in the first
edition. More space is devoted to the modelling of the electrical characteristics of
diodes and transistors for different purposes and to how the various models can
be used to calculate the performance of amplifiers and switching circuits based on
these devices.
J.J.S. November 1993
VII
Preface
It is not too easy to decide where to begin and end a book on semiconductor
devices. On the one hand it is necessary to rely on the reader's prior knowledge of
semiconductor materials; on the other hand it is necessary to rely to some extent
on the reader knowing why certain device properties are important. However, the
depth of knowledge in either field need not be particularly great. The solid state
physicist's understanding of semiconductor properties usually goes much deeper
than is required; and the experienced circuit designer knows more than is needed
to put transistors and the like into a meaningful context. However, in each
field there is a minimum level of prior knowledge and understanding needed if
coherent explanations of device behaviour are to make sense. Accordingly, and in
order to avoid misunderstandings, I have begun this book with brief statements,
in both areas of knowledge, which set the context for the rest of the book.
Chapter 1 is in two parts: the first part explains the properties of semicon
ductors to the depth needed for the subsequent device explanations; the second
part introduces simple circuit applications of each of the devices to be dealt with
later, and explains which parameters are important for the successful operation of
each circuit. It is to be expected that one or other part might be familiar material
for some students of devices, so each part ends with a detailed summary, from
which it is possible to measure one's own prior knowledge and understanding
against the requirements of the rest of the book.
Chapters 2 to 5 then explain the main semiconductor devices in use today in
order of increasing complexity, beginning with p-n junctions in their various
forms for different applications, and ending with integrated circuits which incor
porate resistors and capacitors as well as transistors of various kinds. Particular
attention is paid to the explanations of the behaviour of p-n junctions and
metal-semiconductor contacts because they lie at the heart of the properties of
semiconductor devices. Both the 'band' model and the 'bond' model of semicon
ductors are explained since neither on its own is capable of giving wholly satis
factory accounts of all device behaviour.
The final chapter introduces a different kind of complexity, namely the use of
compound semiconductors instead of silicon as the basic material. It explains what
benefits they offer in return for the added complexity of the production methods
they involve. Production methods of devices are not, however, discussed in detail,
only to the extent that they illuminate the explanations of device properties.
The depth to which device explanations are taken is consistent with the fact that
the book is intended for the use of 1st and 2nd year undergraduate students. It
makes reference, where appropriate, to more advanced texts, to which it is to be
thought of as an introduction. The emphasis is very much on the fundamental
principles that underlie the operation of semiconductor devices and on how these
can be simply and effectively modelled mathematically. The depth of analysis
presented is such as to facilitate the intelligent use of the computer circuit
simulation program known as SPICE. The main parameters required by SPICE as
viii
regards p-n junction diodes and bipolar junction transistors are fully explained
and related to the physical structure of the devices. The corresponding SPICE
parameters for field effect transistors and thyristors are not included because
these devices are a good deal more difficult to represent by lumped elements than
junction diodes and transistors, to the same degree of accuracy. Suitable refer
ences for further study are, of course, given.
ix