Charged Semiconductor Defects: Structure, Thermodynamics and Diffusion

303 Pages·2009·8.55 MB·English

by  Edmund G. Seebauer, Meredith C. Kratzer (auth.)

Engineering Materials and Processes
Series Editor
Professor Brian Derby, Professor of Materials Science
Manchester Materials Science Centre, Grosvenor Street, Manchester, M1 7HS, UK

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Edmund G. Seebauer • Meredith C. Kratzer
Charged Semiconductor
Defects
Structure, Thermodynamics and Diffusion
123
Edmund G. Seebauer, BS, PhD
Meredith C. Kratzer, BS, MS
University of Illinois at Urbana-Champaign
Department of Chemical and Biomolecular Engineering
600 S. Mathews Avenue
Urbana, Illinois 61801-3792
USA

ISBN 978-1-84882-058-6 e-ISBN 978-1-84882-059-3
DOI 10.1007/978-1-84882-059-3
Engineering Materials and Processes ISSN 1619-0181
A catalogue record for this book is available from the British Library
Library of Congress Control Number: 2008936490
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Preface
Defect charging can affect numerous aspects of defect properties, including physi-
cal structure, rate of diffusion, chemical reactivity, and interactions with the elec-
trons that give the semiconductor its overall characteristics. This book represents
the first comprehensive account of the behavior of electrically charged defects in
semiconductors. A comprehensive understanding of such behavior enables “defect
engineering,” whereby material performance can be improved by controlling bulk
and surface defect behavior. Applications are important and diverse, including
fabrication of microelectronic devices, energy production from solar power, ca-
talysis for producing chemical products, photocatalysis for environmental reme-
diation, and solid-state sensors. The scope of this book is quite large, which helps
to identify classes of behavior that are not as readily evident from an examination
of defect charging in a narrower material- or application-specific context. The text
summarizes current knowledge based on experiments and computations regarding
defect structure, thermodynamics, and diffusion for both bulk and surfaces in an
integrated way.
Indeed, defect charging effects continue to be a fertile area of scientific re-
search, with new phenomena coming to light during the past decade. Such effects
include ion-induced defect formation, photostimulated surface and bulk diffusion,
and electrostatically-mediated surface interactions with bulk defects. The present
work outlines key aspects of these new findings.
The most sophisticated forms of practical defect engineering have developed
within the context of microelectronic device fabrication, particularly in silicon.
Yet such engineering will almost certainly spread more broadly into other domains
such as semiconductor-based sensors and solar energy devices. The present work
does not attempt to review these advances in detail, but does point to more exten-
sive reviews where they exist.
v
vi Preface
In general, though, we hope that the scope and integration found in this book
will stimulate new scientific findings and offer a new basis for new forms of de-
fect engineering.
Urbana, Illinois, USA, July 2008 Edmund G. Seebauer
Meredith C. Kratzer
Acknowledgments
The authors would like to thank the following individuals:
• Richard Braatz for his advice and insight pertaining to maximum likelihood
approximation.
• Susan Sinnott for sharing her unpublished findings regarding TiO defect
2
ionization levels.
• Alumni and alumnae of the Seebauer research group including Charlotte Kwok,
Rama Vaidyanathan, Andrew Dalton, Kapil Dev, Mike Jung, and Ho Yeung
Chan, for their intellectual contributions over the years to our knowledge of
defect charging.
• Patrick McSorley for his literature research and administrative assistance.

vii
Contents
1 Introduction............................................................................................. 1
References................................................................................................. 3
2 Fundamentals of Defect Ionization and Transport.............................. 5
2.1 Introduction................................................................................... 5
2.2 Thermodynamics of Defect Charging........................................... 5
2.2.1 Free Energies, Ionization Levels,
and Charged Defect Concentrations................................. 7
2.2.2 Ionization Entropy............................................................ 13
2.2.3 Energetics of Defect Clustering....................................... 15
2.2.4 Effects of Gas Pressure on Defect Concentration............ 17
2.3 Thermal Diffusion......................................................................... 19
2.4 Drift in Electric Fields................................................................... 24
2.5 Defect Kinetics.............................................................................. 25
2.5.1 Reactions.......................................................................... 25
2.5.2 Charging........................................................................... 29
2.6 Direct Surface-Bulk Coupling....................................................... 31
2.7 Non-Thermally Stimulated Defect Charging and Formation........ 32
2.7.1 Photostimulation.............................................................. 32
2.7.2 Ion-Defect Interactions.................................................... 33
References................................................................................................. 34
3 Experimental and Computational Characterization........................... 39
3.1 Experimental Characterization...................................................... 39
3.1.1 Direct Detection of Bulk Defects..................................... 39
3.1.2 Indirect Detection of Bulk Defects.................................. 43
3.1.3 Diffusion in the Bulk........................................................ 44
3.1.4 Direct Detection of Surface Defects................................. 45
3.1.5 Diffusion on the Surface.................................................. 46
ix
x Contents
3.2 Computational Prediction.............................................................. 47
3.2.1 Density Functional Theory............................................... 47
3.2.2 Other Atomistic Methods................................................. 50
3.2.3 Maximum Likelihood Estimation.................................... 51
3.2.4 Surfaces and Interfaces.................................................... 56
References................................................................................................. 56
4 Trends in Charged Defect Behavior...................................................... 63
4.1 Defect Formation........................................................................... 63
4.1.1 Effects of Crystal Structure and Atomic Properties......... 63
4.1.2 Effects of Stoichiometry.................................................. 66
4.2 Defect Geometry........................................................................... 68
4.3 Defect Charging............................................................................. 69
4.3.1 Bulk vs. Surface............................................................... 70
4.3.2 Point Defects vs. Defect Aggregates................................ 71
4.4 Defect Diffusion............................................................................ 71
References................................................................................................. 72
5 Intrinsic Defects: Structure.................................................................... 73
5.1 Bulk Defects.................................................................................. 73
5.1.1 Silicon.............................................................................. 76
5.1.2 Germanium...................................................................... 84
5.1.3 Gallium Arsenide............................................................. 86
5.1.4 Other III–V Semiconductors............................................ 92
5.1.5 Titanium Dioxide............................................................. 95
5.1.6 Other Oxide Semiconductors........................................... 100
5.2 Surface Defects.............................................................................. 105
5.2.1 Silicon.............................................................................. 106
5.2.2 Germanium...................................................................... 111
5.2.3 Gallium Arsenide............................................................. 112
5.2.4 Other III–V Semiconductors............................................ 116
5.2.5 Titanium Dioxide............................................................. 120
5.2.6 Other Oxide Semiconductors........................................... 122
References................................................................................................. 123
6 Intrinsic Defects: Ionization Thermodynamics.................................... 131
6.1 Bulk Defects.................................................................................. 131
6.1.1 Silicon.............................................................................. 131
6.1.2 Germanium...................................................................... 144
6.1.3 Gallium Arsenide............................................................. 148
6.1.4 Other III–V Semiconductors............................................ 156
6.1.5 Titanium Dioxide............................................................. 160
6.1.6 Other Oxide Semiconductors........................................... 166
Contents xi
6.2 Surface Defects.............................................................................. 173
6.2.1 Silicon.............................................................................. 173
6.2.2 Germanium...................................................................... 176
6.2.3 Gallium Arsenide............................................................. 178
6.2.4 Other III–V Semiconductors............................................ 181
6.2.5 Titanium Dioxide............................................................. 183
6.2.6 Other Oxide Semiconductors........................................... 185
References................................................................................................. 187
7 Intrinsic Defects: Diffusion.................................................................... 195
7.1 Bulk Defects.................................................................................. 195
7.1.1 Point Defects.................................................................... 196
7.1.2 Associates and Clusters.................................................... 212
7.2 Surface Defects.............................................................................. 215
7.2.1 Point Defects.................................................................... 215
7.2.2 Associates and Clusters.................................................... 222
7.3 Photostimulated Diffusion............................................................. 222
7.3.1 Photostimulated Diffusion in the Bulk............................. 223
7.3.2 Photostimulated Diffusion on the Surface....................... 225
References................................................................................................. 226
8 Extrinsic Defects..................................................................................... 233
8.1 Bulk Defects.................................................................................. 233
8.1.1 Silicon.............................................................................. 234
8.1.2 Germanium...................................................................... 249
8.1.3 Gallium Arsenide............................................................. 255
8.1.4 Other III–V Semiconductors............................................ 260
8.1.5 Titanium Dioxide............................................................. 265
8.1.6 Other Oxide Semiconductors........................................... 271
8.2 Surface Defects.............................................................................. 277
8.2.1 Silicon.............................................................................. 278
8.2.2 Gallium Arsenide............................................................. 280
8.2.3 Titanium Dioxide............................................................. 281
References................................................................................................. 281
Index................................................................................................................. 291