Table Of ContentOptical and
Infrared Detectors
Edited by R. .J Keyes
With Contributions by
R.J. Keyes P.W. Kruse D.Long A.F.Milton
E.H.Putley M.C.Teich H. .R Zwicker
Second Corrected and Updated Edition
With 511 Figures
Springer-Verlag Berlin Heidelberg New York 1980
Robert J. Keyes
nlocniL ,yrotarobaL sttesuhcassaM etutitsnI of ,ygolonhceT
l,exington, AM 02173, ASU
ISBN 3-540-10176-4 .2 Auflage Springer-Verlag Berlin Heidelberg New York
ISBN 0-387-10176-4 2rid Edition Springer-Verlag New York Heidelberg Berlin
ISBN 3-540-08209-3 I. Auflage Springer-Verlag Berlin Heidelberg New York
ISBN 0-387-08209-3 1st Edition Springer-Verlag Berlin Heidelberg New York
Library of Congress Cataloging in Publication Data Keyes, Robert J. 1927- Optical and infrared detectors. (Topics in applied
physics; v. 191 Includes bibliographies and index. .1 Infra-red detectors. I. Title. TAI570.K48 1980 681'.41 80-17985
ISBN 0-387-10176-4 (U+S.)
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Preface to the Second Edition
This edition, as was the first, is written for those who desire a comprehensive
analysis of the latest developments in infrared detector technology and a basic
insight into the fundamental processes which are important to evolving detection
techniques. Each of the most salient infrared detector types is treated in detail by
authors who are recognized as leading authorities in the specific areas addressed.
In order to concentrate on pertinent aspects of the present state of the detector art
and the unique point of view of each author, extensive tutorials of a background
nature are avoided in the text but are readily available to the reader through the
many references given. The editor highly recommends R. H. Kingston : Detection
of Optical and Infrared Radiation (Springer, Berlin, Heidelberg, New York 1978)
for those who desire a more tutorial presentation of the photon radiation and
detection processes.
The volume opens with a broad-brush introduction to the various types
of infrared detectors that have evolved since Sir William Herschel's discovery
of infrared radiation 175 years ago. The second chapter presents an overall
perspective of the infrared detector art and serves as the cohesive cement
for the more in-depth presentation of subsequent chapters. Those detector
types which, for one reason or other have not attained wide use today,
are also discussed in Chapter 2.
The more notable and widely used infrared detectors can be divided
into three basic classes which are indicative of the primary effect produced
by the photon-detector interaction, i.e., thermal, photoconductive, photo-
voltaic, and photoemissive. Chapters ,3 4, and 5 offer a detailed treatment
of each of these important processes.
The objectives of an infrared detector are to find a signal, measure it,
and extract some vital information for subsequent use. Charge-coupled
devices (CCD) and nonlinear photon interactions are new techniques for
extracting more information from weak infrared signals. These devices, when
directly or indirectly coupled to basic detector types, place a tremendous
amount of low noise, compact, inexpensive logic at the disposal of infrared
sensor designers. The marriage of CCD concepts to detector technology is
young, moving fast, and portends great strides in the ability to retrieve
small signal information from complex radiation environments. Chapter 5
presents some of the latest developments and concepts in this unique area.
Methods of measuring the phase and frequency of coherent infrared signals
have become important in order to extract the maximum information from
lV ecaferP
laser signals. The efficient nonlinear mixing of coherent infrared radiation in
standard detector materials has achieved sensitivities approaching the
theoretical limit (a few photons per measurement interval) and has stimulated
new applications for lasers in the communication, radar, and spectroscopy
fields. A volume concerned with infrared detectors would be incomplete
without addressing some of the salient aspects of heterodyne or nonlinear
detection--hence Chapter .7 Chapter 8 presents those recent developments in
the field of optical and infrared detectors which have evolved since the
publication of the first edition. It specifically embraces those advances which
the authors have deemed necessary in order to provide the reader an up-to-date
perspective of detector technology.
I would like to thank the contributors to this volume, P. Kruse, E.Putley,
D.Long, H.Zwicker, F.Milton, and M.Teich, for giving of their time,
energy, and expertise in preparation of their chapters; I also thank my wife,
Gladys, for her assistance.
Lexington, Mass. Robert J. Keyes
May, 1980
Contents
1. Introduction. By R.J. Keyes . . . . . . . . . . . . . . . . . . 1
2. The Photon Detection Process. By P.W. Kruse (With 22 Figures). 5
2.1 Classification and Phenomenological Descriptions of Selected
Photon Detection Mechanisms . . . . . . . . . . . . . . . 7
2.1.1 Photon Effects . . . . . . . . . . . . . . . . . . . . 8
2.1.2 Thermal Effects . . . . . . . . . . . . . . . . . . . 26
2.1.3 Wave Interaction Effects . . . . . . . . . . . . . . . 33
2.2 Noise in Radiation Detectors . . . . . . . . . . . . . . . . 36
2.2.1 Noise in Semiconductor Detectors . . . . . . . . . . . 37
2.2.2 Noise in Photoemissive Devices . . . . . . . . . . . . 41
2.3 Figures of Merit . . . . . . . . . . . . . . . . . . . . . 42
2.3.1 Spectral Response . . . . . . . . . . . . . . . . . . 42
2.3.2 Responsivity . . . . . . . . . . . . . . . . . . . . 43
2.3.3 D* . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.3.4 D** . . . . . . . . . . . . . . . . . . . . . . . . 45
2.3.5 Noise Equivalent Power . . . . . . . . . . . . . . . 45
2.3.6 Detectivity . . . . . . . . . . . . . . . . . . . . . 46
2.3.7 Frequency Response, Response Time, Time Constant, f* . 46
2.3.8 Noise Spectrum . . . . . . . . . . . . . . . . . . . 47
2.4 The Signal Fluctuation and Background Fluctuation Limits . 47
2.4.1 Signal Fluctuation Limit . . . . . . . . . . . . . . . 48
2.4.2 Background Fluctuation Limit . . . . . . . . . . . . . 50
2.4.3 Composite Signal Fluctuation and Background Fluctuation
Limits . . . . . . . . . . . . . . . . . . . . . . . 56
2.5 State-of-the-Art of Infrared and Optical Detectors . . . . . . . 59
References . . . . . . . . . . . . . . . . . . . . . . . . . 65
3. Thermal Detectors. By E.H.Putley (With 14 Figures) . . . . . . . 71
3.1 Basic Principles . . . . . . . . . . . . . . . . . . . . . . 72
3.2 The Thermopile . . . . . . . . . . . . . . . . . . . . . 79
3.3 The Bolometer . . . . . . . . . . . . . . . . . . . . . . 82
3.4 The Golay Cell and Related Detectors . . . . . . . . . . . . . 89
3.5 Pyroelectric Detector . . . . . . . . . . . . . . . . . . . 90
VIII Contents
3.6 Other Types of Thermal Detectors . . . . . . . . . . . . . 95
3.7 The Use of Thermal Detectors in Infrared Imaging Systems. 96
References . . . . . . . . . . . . . . . . . . . . . . . . . 98
4. Photovoltaic dna Photoconductive Infrared Detectors
By D. Long (With 15 Figures) . . . . . . . . . . . . . . . . 101
4.1 Basic Theory . . . . . . . . . . . . . . . . . . . . . . . 102
4.1.1 Direct Photon Detection . . . . . . . . . . . . . . . 102
4.1.2 Photocurrent, Gain, and Responsivity . . . . . . . . . . 103
4.1.3 Noise Mechanisms . . . . . . . . . . . . . . . . . . 104
4.1.4 Detectivity . . . . . . . . . . . . . . . . . . . . . 106
4.1.5 Other Detector Parameters . . . . . . . . . . . . . . 107
4.2 Photovoltaic Detectors . . . . . . . . . . . . . . . . . . 109
4.2.1 Theory . . . . . . . . . . . . . . . . . . . . . . . 109
4.2.2 Materials . . . . . . . . . . . . . . . . . . . . . . 114
4.3 Intrinsic Photoconductive Detectors . . . . . . . . . . . . . 120
4.3.1 Theory . . . . . . . . . . . . . . . . . . . . . . . 120
4.3.2 Materials . . . . . . . . . . . . . . . . . . . . . . 124
4.4 Extrinsic Photoconductive Detectors . . . . . . . . . . . . 129
4.4.1 Theory . . . . . . . . . . . . . . . . . . . . . . . 129
4.4.2 Materials . . . . . . . . . . . . . . . . . . . . . . 132
4.5 Summary and Conclusions . . . . . . . . . . . . . . . . . 133
References . . . . . . . . . . . . . . . . . . . . . . . . . 145
5. Photoemissive Detectors. By H.R.Zwicker (With 22 Figures) .... 149
1.5 Introduction . . . . . . . . . . . . . . . . . . . . . . . 149
5.1.1 Applications and Advantages . . . . . . . . - . . . . . 149
5.1.2 ,imitations . . . . . . . . . . . . . . . . . . . . . 150
5.1.3 Types of Photoemissive Surfaces: Classical and NEA . 150
5.1.4 RM and TM Modes . . . . . . . . . . . . . . . . . 151
5.1.5 Outline of Chapter . . . . . . . . . . . . . . . . . . 152
5.2 The Photoemission Process . . . . . . . . . . . . . . . . 152
5.2.1 Fundamentals of Electron Escape Energy . . . . . . . . 152
5.2.2 Escape-Energy Parameters for Metals and Semiconductors. 154
5.2.3 Thresholds of Various Materials and Choice of Photo-
emissive Substances . . . . . . . . . . . . . . . . . 155
5.3 Classical Photoemissive Surfaces . . . . . . . . . . . . . . 159
5.3.1 The (CsSb) Photoemitter . . . . . . . . . . . . . . . 159
5.3.2 The S-1 (AgCsO) Photocathode . . . . . . . . . . . . 161
5.4 Negative Electron Affinity (NEA) Devices . . . . . . . . . . 163
5.4.1 Introduction and Advantages . . . . . . . . . . . . . 164
5.4.2 Basic Physics of NEA Operation . . . . . . . . . . . . 165
5.4.3 NEA GaAs . . . . . . . . . . . . . . . . . . . . . 167
Contents IX
5.4.4 Modeling the NEA Surface . . . . . . . . . . . . . . 169
5.4.5 Fabrication and Optimization of RM and TM NEA GaAs. 172
5.4.6 Other NEA IR Photocathodes . . . . . . . . . . . . . 177
5.4.7 NEA Silicon . . . . . . . . . . . . . . . . . . . . 181
5.5 Photoemissive Devices: The Photomultiplier . . . . . . . . . 182
5.5.1 Introduction . . . . . . . . . . . . . . . . . . . . 182
5.5.2 Photocathode Dark Current . . . . . . . . . . . . . . 182
5.5.3 The Electron Multiplier . . . . . . . . . . . . . . . . 184
5.5.4 Spectral Response Data . . . . . . . . . . . . . . . . 188
5.5.5 Specialized NEA Analysis Tools . . . . . . . . . . . . 191
References . . . . . . . . . . . . . . . . . . . . . . . . . 192
.6 Charge Transfer Devices for Infrared Imaging. By A. F. Milton
(With 18 Figures) . . . . . . . . . . . . . . . . . . . . . . . 197
6.1 Historical . . . . . . . . . . . . . . . . . . . . . . . . 197
6.2 Charge Coupled Devices . . . . . . . . . . . . . . . . . . 200
6.2.1 Basic Operating Principles . . . . . . . . . . . . . . 200
6.2.2 Limitations . . . . . . . . . . . . . . . . . . . . . 203
6.3 Time Delay and Integration (TDI) and IR Sensitive CCD . . 213
6.4 Direct Injection: Hybrid and Extrinsic Silicon . . . . . . . 216
6.5 Accumulation Mode: Extrinsic Silicon . . . . . . . . . . . . 219
6.6 IR CID . . . . . . . . . . . . . . . . . . . . . . . . . 220
6.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . 227
References . . . . . . . . . . . . . . . . . . . . . . . . . 228
7. Nonlinear Heterodyne Detection. By M.C.Teich (With 24 Figures). 229
7.1 Two-Frequency Single-Photon Heterodyne Detection . . . . . 231
7.2 Two-Frequency Multiphoton Heterodyne Detection . . . . . . 232
7.2.1 Multiple-Quantum Direct Detection . . . . . . . . . . 232
7.2.2 Theory of Multiphoton Photomixing . . . . . . . . . . 234
7.2.3 Signal-to-Noise Ratio and Minimum Detectable Number
of Photons . . . . . . . . . . . . . . . . . . . . . 237
7.2.4 Experiment . . . . . . . . . . . . . . . . . . . . 239
7.2.5 Discussion . . . . . . . . . . . . . . . . . . . . . 242
7.3 Three-Frequency Single-Photon Heterodyne Detection Using a
Nonlinear Device . . . . . . . . . . . . . . . . . . 243
7.3.1 System Configuration . . . . . . . . . . . . . . . . 244
7.3.2 Application to cw Radar with Sinewave Input Signals. . 249
7.3.3 Application to cw Radar with Gaussian Input Signals
(Gaussian Spectra) . . . . . . . . . . . . . . . . . 257
7.3.4 Application to cw Radar with Gaussian Input Signals
(Lorentzian Spectra) . . . . . . . . . . . . . . . . 263
7.3.5 Application to an Analog Communications System. . 266
x Contents
7.3.6 Operation at Low Frequencies and in Various Con-
figurations . . . . . . . . . . . . . . . . . . . . . 267
7.3.7 Numerical Example: A CO 2 Laser Radar . . . . . . . 269
7.3.8 Application to Binary Communications and Pulsed Raaar
(Vacuum Channel) . . . . . . . . . . . . . . . . . 270
7.3.9 Application to Binary Communications and Pulsed Radar
(Lognormal Atmospheric Channel) . . . ~. . . . . . . 282
7.3.10 Discussion . . . . . . . . . . . . . . . . . . . . . 287
7.4 Multifrequency Single-Photon Selective Heterodyne Radio-
metry for Detection of Remote Species . . . . . . . . . . . . 288
7.4.1 Configuration for Two Received Frequencies . . . . . . 289
7.4.2 n Received Frequencies and the Factor k' . . . . . . . . 291
7.4.3 SNR and MDP for Two Gaussian Signals . . . . . . . 293
7.4.4 Numerical Example: Astronomical Radiation from CN 294
7.4.5 Discussion . . . . . . . . . . . . . . . . . . . . . 295
References . . . . . . . . . . . . . . . . . . . . . . . . . 297
8. Recent Advances in Optical and Infrared Detector Technology.
By R. J. Keyes . . . . . . . . . . . . . . . . . . . . . . . . 301
8.1 Thermal Detectors . . . . . . . . . . . . . . . . . . . . 301
8.1.1 The Thermopile . . . . . . . . . . . . . . . . . . 302
8.1.2 The Bolometer . . . . . . . . . . . . . . . . . . 302
8.1.3 The Golay Cell and Related Detectors . . . . . . . . 303
8.1.4 Pyroelectric Detector . . . . . . . . . . . . . . . . 304
8.1.5 Other Types of Thermal Detectors . . . . . . . . . . 305
8.1.6 The Use of Thermal Detectors in Infrared Imaging Systems306
8.2 Photovoltaic, Photoconductive, and Avalanche Diode Detectors 306
8.2.1 Intrinsic Photovoltaic Detectors . . . . . . . . . . . 307
8.2.2 Intrinsic Photoconductive Detectors . . . . . . . . . 307
8.2.3 Extrinsic Photoconductive Detectors . . . . . . . . . 308
8.2.4 Avalanche Photodiodes (APD) . . . . . . . . . . . . 308
8.3 Photoemissive Detectors . . . . . . . . . . . . . . . . . 309
8.4 Charge Transfer Imaging Devices . . . . . . . . . . . . . 310
8.4.1 Near Infrared and Visible CCD hnagers . . . . . . . 310
8.4.2 Thermal Scene CCD Imagers . . . . . . . . . . . . 311
8.5 Heterodyne Detectors . . . . . . . . . . . . . . . . . . 313
8.6 Desirable Optical and Infrared Detector Technology Advances . 314
References . . . . . . . . . . . . . . . . . . . . . . . . . 315
Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . 321
Contributors
Keyes, Robert J.
Lincoln Laboratory, Massachusetts Institute of Technology,
Lexington, MA 02173, USA
Kruse, Paul W.
Honeywell Corporate Technology Center, Bloomington, MN 55420, USA
Long, Donald
Honeywell Corporate Technology Center, Bloomington, MN 55420, USA
Milton, Albert F.
Naval Research Laboratory, Washington, D.C., USA
Putley, Ernest H.
Royal Signals and Radar Establishment, Malvern, Worcs.,
WR 41 3 PS, U.K.
Teich, Malvin C.
Department of Electrical Engineering, Columbia University,
New York, NY 10027, USA
Zwicker, Harry R.
Lincoln Laboratory, Massachusetts Institute of Technology,
Lexington, MA 02173, USA
I. Introduction
R. J. Keyes
Optical or visible photons emitted by our sun provide the most important source
of radiation on our planet. It has been sensed, felt, and used (although not fully
understood) by living things since the onset of evolution. The process of natural
evolution of the eye retina has produced an array of optical detectors capable of
sensing a few photons. In the past century technology has approached this
sensitivity through the development and perfection of photographic emulsions,
video intensifier tubes, and charge coupled devices.
Infrared is the second most intense radiation source in our environment; yet
it was not until the turn of the nineteenth century (1800) that Sir William lehcsreH
(1738-1822) discovered it and gave it a name. Infrared detector development
proceeded at a leisurely pace for the next 150 years. In 1947 William Shockley,
John Bardeen, and Walter Brattain, through the discovery of the transistor,
sparked large-scale research and development into the band structure and
transport processes of semiconductors. This spark, fanned by huge injections of
government and industrial funds, affected nearly every aspect of infrared
detection technology for the next 30 years (impurity and intrinsic photocon-
ductivity in binary, ternary, and group IV compounds; photoemission of
cesiated semiconductors; thermistors; silicon target vidicons; charge-coupled
devices; and heterodyne detection, to name a few). The present emphasis of
infrared detector research and development is shifting from the perfection of
new classes of materials to techniques for information retrieval through charge-
coupled device logic and heterodyne signal processing. The shift in emphasis is
due in part to the fact that detector materials are asymptotically approaching the
theoretical limit of sensitivity (leaving little room for spectacular improvements)
while sophisticated signal processing promises unlimited opportunities to
extract vital information about objects in complex scenes through their emitted
and reflected infrared radiations. Although these methods of signal processing
are relatively new, they utilize as the first step in the processing chain many of the
basic materials and concepts presented here in Chapters 4 and .5
There is no unique set of characteristics which can be used to describe the
"ideal" infrared detector. The ideal detector has nearly as many definitions as
there are applications. For "hot box" detection on railroad-caraxles, reliability
and simple maintenance are measures of perfection. For satellite operations
compactness, light weight, low power and high sensitivity may be the important
yardsticks. In the discussion which follows, an ideal detector is defined as one
whose minimum detectible power is determined by the statistical fluctuation in
