Silicon–germanium (SiGe) nanostructures
Production, properties and applications in electronics
Edited by Yasuhiro Shiraki and Noritaka Usami
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3 Understanding crystal growth mechanisms in silicon–germanium (SiGe) nanostructures 45 M. suEMitsu, Tohoku University, Japan and s. N. FiliMoNov, Tomsk State University, Russia
3.1
3.2
3.3
3.4
3.5
3.6
4 Types of silicon–germanium (SiGe) bulk crystal
N. usaMi, Tohoku University, Japan
4.1
4.3 Application of silicon–germanium (SiGe)
4.4
5 Silicon–germanium (SiGe) crystal
beam epitaxy 83 a. saKai, Osaka University, Japan
5.1
5.2
5.3
6 Silicon–germanium (SiGe) crystal growth using chemical vapor deposition 117 B. tillacK, IHP and Technische Universität Berlin, Germany and J. Murota, Tohoku University, Japan
6.1 Introduction 117
6.2 Epitaxial growth techniques – chemical vapor deposition (CVD) (ultra high vacuum CVD (UHVCVD), low pressure CVD (LPCVD), atmospheric pressure CVD (APCVD), plasma enhanced CVD (PECVD)) 119
6.3 Silicon–germanium (SiGe) heteroepitaxy by chemical vapor deposition (CVD)
6.4 Doping of silicon–germanium (SiGe)
6.5 Conclusion and future trends
6.6 References
7 Strain engineering of silicon–germanium (SiGe) virtual substrates 147 K. sawaNo, Tokyo City University, Japan
7.1 Introduction
7.2 Compositionally
7.3
7.4
7.5
7.6
8 Formation of silicon–germanium on insulator (SGOI) substrates 171
N. sugiyaMa and t tEzuKa, Toshiba Corporation, Japan
8.1 Introduction: demand for virtual substrate and (Si)Ge on insulator (SGOI) 171
8.2 Formation of (Si)Ge on insulator (SGOI) by the Ge condensation method
8.3 Extension toward Ge on insulator
8.4
8.5
8.6
9 Miscellaneous methods and materials for silicon–germanium (SiGe) based heterostructures
M. Miyao, Kyushu University, Japan
9.1 Introduction 190
9.2 Oriented growth of silicon–germanium (SiGe) on insulating films for thin film transistors and 3-D stacked devices 191
9.3 Heteroepitaxial growth of ferromagnetic Heusler alloys for silicon–germanium (SiGe)-based spintronic devices 201
9.4 Conclusion
9.5
10 Modeling the evolution of germanium islands on silicon(001) thin films 211 l. Miglio and F. MoNtalENti, University of Milano-Bicocca, Italy
10.1 A few considerations on epitaxial growth modeling 211
10.2 Introduction to Stranski–Krastanow (SK) heteroepitaxy 213
10.3 Onset of Stranski–Krastanow (SK) heteroepitaxy 219
10.4 Beyond the Stranski–Krastanow (SK) onset: Si–Ge intermixing 232
10.5 Beyond the Stranski–Krastanow (SK) onset: vertical and horizontal ordering for applications 235
10.6 Future trends: ordering Ge islands on pit-patterned Si(001) 241
10.7 References 243
11 Strain engineering of silicon–germanium (SiGe) micro- and nanostructures 247 F. pEzzoli, c. DENEKE and o. g. scHMiDt, IFW Dresden, Germany
11.1 Introduction
11.2
11.3
Part III Material properties of SiGe nanostructures
12 Self-diffusion and dopant diffusion in germanium (Ge) and silicon–germanium (SiGe) alloys 299 M. uEMatsu, Keio University, Japan
12.1 Introduction
12.2
12.3
in germanium (Ge)
12.4 Self-diffusion in silicon–germanium (SiGe) alloys
12.5 Silicon–germanium (Si–Ge) interdiffusion
12.6 Dopant diffusion in germanium (Ge)
12.7 Dopant diffusion in silicon–germanium (SiGe) alloys
12.8 Dopant segregation
12.9 Conclusion and future trends
12.10 Sources
13 Dislocations and other strain-induced defects in silicon–germanium (SiGe) nanostructures
M. l lEE, Yale University, USA
13.1 Introduction and background
13.2 Historical overview
13.3 Application of the Thompson tetrahedron to extended defects in silicon–germanium (SiGe)
13.4
13.5
14 Transport properties of silicon/silicon–germanium (Si/SiGe) nanostructures at low temperatures
14.1
a. golD, Université Paul Sabatier, France
15 Transport properties of silicon–germanium (SiGe) nanostructures and applications in devices
F. scHäFFlEr, Johannes Kepler Universität, Austria
15.2 Basic transport properties of strained silicon–germanium (SiGe) heterostructures
15.5 Carrier transport in silicon/silicon–germanium (Si/SiGe)
15.6
15.7
16 Microcavities and quantum cascade laser structures based on silicon–germanium (SiGe) nanostructures 433
J. Xia and y. sHiraKi, Tokyo City University, Japan, and J. yu, Chinese Academy of Sciences, P. R. China
16.1 Introduction 433
16.2 Germanium (Ge) dots microcavity photonic devices 434
16.3 Silicon–germanium (SiGe) quantum cascade laser (QCL) structures 445
16.4 Conclusions 451
16.5 References
17 Silicide and germanide technology for interconnections in ultra-large-scale integrated (ULSI) applications 456
s. zaiMa and o. NaKatsuKa, Nagoya University, Japan
17.1 Introduction 456
17.2 Formation of silicide and germanosilicide thin films 457
17.3 Crystalline properties of silicides 459
17.4 Electrical properties 462
17.5 References 466
Part IV Devices using silicon, germanium and silicon–germanium (Si, Ge and SiGe) alloys
18 Silicon–germanium (SiGe) heterojunction bipolar transistor (HBT) and bipolar complementary metal oxide semiconductor (BiCMOS) technologies 473
K. wasHio, Hitachi Ltd, Japan
18.1 Introduction 473
18.2 Epitaxial growth 474
18.3 Silicon–germanium (SiGe) heterojunction bipolar transistor (HBT) 479
18.4 Silicon–germanium (SiGe) bipolar complementary metal oxide semiconductors (BiCMOS) 486
18.5 Applications in integrated circuit (IC) and large-scale integration (LSI) 490
18.6 Conclusion 493
18.7 References 494
19 Silicon–germanium (SiGe)-based field effect transistors (FET) and complementary metal oxide semiconductor (CMOS) technologies 499 s taKagi, The University of Tokyo, Japan
19.1 Introduction 499
19.2
Silicon–germanium (SiGe) channel metal oxide semiconductor field effect transistors (MOSFETs) 506
19.3 Conclusion 524
19.4 References 524
20 High electron mobility germanium (Ge) metal oxide semiconductor field effect transistors (MOSFETs) 528 a toriuMi, The University of Tokyo, Japan
20.1 Introduction 528
20.2 Gate stack formation 529
20.3 Metal oxide semiconductor field effect transistor (MOSFET) fabrication and electron inversion layer mobility 536
20.4 Germanium (Ge)/metal Schottky interface and metal source/drain metal oxide semiconductor field effect transistors (MOSFETs) 544
20.5 Conclusion and future trends 548
20.6 Acknowledgments 549
20.7 References 549
21 Silicon (Si) and germanium (Ge) in optical devices 551 K. oHasHi, NEC Corporation, Japan
21.1 Background 551
21.2 Optical waveguides 552
21.3 Modulators 556
21.4 Photodetectors and photovoltaics 559
21.5 Light sources 565
21.6 Future trends 566
21.7 Sources of further information and advice 567
21.8 References 567
22 Spintronics of nanostructured manganese germanium (MnGe) dilute magnetic semiconductor 575 K. l waNg and F. Xiu, University of California, Los Angeles, USA and a p. JacoB, Intel Corporation, USA
22.1 Introduction 575
22.2 Theories of ferromagnetism in group IV dilute magnetic semiconductor (DMS) 578
22.3 Growth and characterizations of group IV dilute magnetic semiconductor (DMS) and nanostructures 581
22.4 Electric field-controlled ferromagnetism 596
22.5 Conclusion and future trends 601
22.6 References 602
(* = main contact)
Editors
Y. Shiraki
Research Center for Si Nanoscience
Advanced Research Laboratories
Tokyo City University
8-15-1 Todoroki, Setagaya-ku
Tokyo 158-0082
Japan
E-mail: yshiraki@tcu.ac.jp
N. Usami
Institute for Materials Research
Tohoku University
2-1-1 Katahira, Aoba-ku
Sendai 980-8577
Japan
E-mail: usa@imr.tohoku.ac.jp
Chapter 1
E. Kasper
University of Stuttgart Institute for Semiconductor Engineering Pfaffenwaldring 47 70569 Stuttgart
Germany
E-mail: kasper@iht.uni-stuttgart.de
Contributor contact details
Chapter 2
N. Mori
Division of Electrical, Electronic and Information Engineering
Graduate School of Engineering
Osaka University
Suita City Osaka 565-0871
Japan
E-mail: nobuya.mori@eei.eng.osaka-u. ac.jp
Chapter 3
M. Suemitsu* Research Institute of Electrical Communication Tohoku University
2-1-1 Katahira, Aoba-ku
Sendai 980-8577
Japan
E-mail: suemitsu@riec.tohoku.ac.jp
S.N. Filimonov Department of Physics Tomsk State University 36 Lenina Avenue Tomsk 634050
Russia
E-mail: filimon@phys.tsu.ru
Chapter 4
N. Usami
Institute for Materials Research
Tohoku University
2-1-1 Katahira, Aoba-ku
Sendai 980-8577
Japan
E-mail: usa@imr.tohoku.ac.jp
Chapter 5
A. Sakai
Graduate School of Engineering Science
Osaka University
1-3 Machikaneyama-cho
Toyonaka Osaka 560-8531
Japan
E-mail: sakai@ee.es.osaka-u.ac.jp
Chapter 6
B. Tillack*
IHP
Im Technologiepark 25 15236 Frankfurt (Oder)
Germany
E-mail: tillack@ihp-microelectronics.com
Technische Universität Berlin
HFT4
Einsteinufer 25 10587 Berlin
Germany
J. Murota
Research Institute of Electrical Communication
Tohoku University
2-1-1 Katahira, Aoba-ku
Sendai 980-8577
Japan
Chapter 7
K. Sawano Tokyo City University
8-15-1 Todoroki, Setagaya-ku
Tokyo Japan
E-mail: sawano@tcu.ac.jp
Chapter 8
N. Sugiyama* and T. Tezuka
Corporate R&D Center
Toshiba Corporation
Komukai Toshiba-cho 1
Saiwai-ku, Kawasaki
Japan
E-mail: naoharu.sugiyama@toshiba.co.jp
Chapter 9
M. Miyao
Department of Electronics
Kyushu University
744-Motooka, Nishi-ku Fukuoka 819-0395
Japan
E-mail: miyao@ed.kyushu-u.ac.jp
Chapter 10
L. Miglio and F. Montalenti*
L-NESS and Materials Science Department
University of Milano-Bicocca Via Cozzi 53 20125 Milan Italy
E-mail: leo.miglio@mater.unimib.it francesco.montalenti@unimib.it
Chapter 11
F. Pezzoli*
L-NESS and Materials Science Department
University of Milano-Bicocca Via Cozzi 53 20125 Milan Italy
E-mail: fabio.pezzoli@unimib.it
Institute for Integrative Nanosciences
IFW Dresden
Helmholtzstraße 20 01069 Dresden Germany
C. Deneke and O. G. Schmidt
Institute for Integrative Nanosciences
IFW Dresden Helmholtzstraße 20 01069 Dresden Germany
E-mail: c.deneke@ifw-dresden.de o.schmidt@ifw-dresden.de
Chapter 12
M. Uematsu
School of Fundamental Science and Technology Keio University 3-14-1 Hiyoshi Yokohama 223-8522
Japan
E-mail: uematsu@a3.keio.jp
Chapter 13
M. L. Lee
Department of Electrical Engineering
Yale University PO Box 208284
New Haven, CT 06520-8284 USA
E-mail: minjoo.lee@yale.edu
Chapter 14
A. Gold UFR-PCA
Université Paul Sabatier 118 Route de Narbonne 31062 Toulouse France
Centre d’Elaboration de Materiaux et d’Etudes Structurales 29 Rue Jeanne Marvig 31055 Toulouse France
E-mail: gold@cemes.fr
Chapter
15
F. Schäffler
Institut für Halbleiter- und Festkörperphysik
Johannes Kepler Universität
Linz
Austria
E-mail: friedrich.schaffler@jku.at
Chapter 16
J. Xia* and Y. Shiraki
Research Center for Si Nanoscience
Advanced Research Laboratories
Tokyo City University
8-15-1 Todoroki, Setagaya-ku
Tokyo 158-0082
Japan
E-mail: jinsongxia@gmail.com
J. Yu
Institute of Semiconductors
Chinese Academy of Sciences
P. O. Box 912
Beijing 100083
P. R. China
E-mail: jzyu@red.semi.ac.cn
Chapter
17
S. Zaima and O. Nakatsuka* Department of Crystalline Materials Science
Graduate School of Engineering
Nagoya University Furo-cho, Chikusa-ku
Nagoya 464-8603
Japan
E-mail: zaima@alice.xtal.nagoya-u.ac.jp nakatuka@alice.xtal.nagoya-u. ac.jp
Chapter
K. Washio
18
Central Research Laboratory Hitachi Ltd 1-280 Higashi-Koigakubo
Kokubunji
Tokyo 185-8601
Japan
E-mail: katsuyoshi.washio.sq@hitachi. com
Chapter 19
S. Takagi Department of Electrical Engineering and Information Systems
School of Engineering
The University of Tokyo 7-3-1 Hongo, Bunkyo-ku
Tokyo 113-8656
Japan
E-mail: takagi@ee.t.u-tokyo.ac.jp
Chapter 20
A. Toriumi Department of Materials Engineering
Graduate School of Engineering
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku
Tokyo 113-8656
Japan
E-mail: toriumi@material.t.u-tokyo.ac.jp
Chapter 21
K. Ohashi
Green Innovation Research Laboratories
NEC Corporation
34 Miyukigaoka
Tsukuba
Ibaraki 305-8501
Japan
E-mail: k-ohashi@cb.jp.nec.com
Chapter 22
F. Xiu and K. L. Wang* Device Research Laboratory Department of Electrical Engineering
University of California, Los Angeles, CA 90095
USA
E-mail: wang@ee.ucla.edu
A. P. Jacob Intel Corporation
Santa Clara, CA 95054 USA
In 1975, epitaxial growth of SiGe/Si heterostructures was demonstrated by Erich Kasper and his co-workers using vapour deposition under ultrahigh vacuum which is now well known as molecular beam epitaxy (MBE). Although there were quite a few people who were interested in this work at that time, some research groups including the editor’s (Y. S.) started the research on silicon MBE in Europe, the United States and Japan. Thanks to the development of crystal growth techniques, particularly MBE, the research field of SiGe heterostructures has expanded substantially not only from the viewpoint of device applications but also from the point of materials science since then. This is because SiGe heterostructures have a high potential to improve the state-of-art Si devices particularly very large scale integrated circuits (VLSIs) and add new functions such as optics. Actually, strained Si structures are now implemented in the sophisticated VLSIs already. They also provide a new scientific field of materials properties and crystal growth relating to the lattice mismatch between Si and Ge which causes strain to modify band structures and growth modes.
Strain-induced band modification brings increase of mobility of both electrons and holes, and the advantages of SiGe have been proved by the commercial spread of hetero-bipolar-transistors (HBTs) as well as the superior performance of strained Si CMOS. Quantum wells based on SiGe/ Si heterostructures or quantum dots grown by the Stranski-Krastanov mode make it possible to confine carriers, leading to efficient light emission even with indirect band-gap materials. Optical devices based on highly efficient light emission will provide a new possibility to enhance the performances and functions of Si VLSIs by realizing optical interconnection and optoelectronic integrated circuits (OEICs). Furthermore, SiGe spintronics have attracted enormous attention due to unique magneto-electro-optical properties. As illustrated by these examples, SiGe opens up the prospects of novel and enhanced device performances especially when structural control in nanometre scale is achieved.
This book is intended to provide a comprehensive overview on current understanding on materials science, technology and applications of SiGe
nanostructures. The target of this book is the research community in both industry and academia.
The introductory Part I covers the structural properties of SiGe nanostructures, with a further chapter discussing the electronic band structures of SiGe alloys. Part II concentrates on the formation of SiGe nanostructures, with chapters on different methods of crystal growth such as molecular beam epitaxy and chemical vapour deposition. This part also includes chapters covering strain engineering and modelling. Part III covers the material properties of SiGe nanostructures, including chapters on such topics as strain-induced defects, transport properties and microcavities, and quantum cascade laser structures. In Part IV, devices utilizing SiGe alloys are discussed. Chapters cover ultra large scale integrated applications, MOSFETs and the use of SiGe in different types of transistors and optical devices, and spintronics of nanostructured dilute magnetic materials and silicide/silicon heterostructures.
In the process of editing this book, we have received generous assistance from our colleagues. Especially, we are indebted to Erich Kasper for his advice on the organization of the chapters. We extend our sincere thanks to Nell Holden, Benjamin Hilliam, Adam Hooper, Cliff Elwell at Woodhead Publishing Limited for their patience and continuous support.
Yasuhiro Shiraki
Noritaka Usami
Tokyo and Sendai
Structural properties of silicon–germanium (SiGe) nanostructures
E. Kasp E r and H.-J. H E rzog, University of stuttgart, germany
Abstract: The heterostructure sige/si has contributed to a large extent to an understanding of lattice mismatched heterostructures and this understanding has led to rapidly increasing exploitation of sige in modern microelectronics. In this chapter crystallographic data of silicon–germanium alloys such as crystal structure and lattice parameters and the phase diagram are reviewed. The basic concepts of equilibrium strain and strain relaxation by misfit dislocations are described in the section on critical thickness. The lattice mismatch either causes strain or results in generation of misfit dislocations at the interface. X-ray diffraction is unrivalled as a tool to analyze heteroepitaxial layers.
Key words: heterostructure, silicon–germanium alloy, lattice structure, phase diagram, lattice mismatch, strain, misfit dislocations, critical thickness, X-ray diffraction.
1.1 Introduction
a reliable set of structural data is essential for many investigations of both epilayers, and bulk material. Even the structural assessment and analysis of sige epilayers, which are presently of enormous interest for novel and high-performance device applications, require the knowledge of sufficiently precise material data. In this chapter some crystallographic data of silicon–germanium alloys, such as crystal structure and lattice parameters and the phase diagram, are reviewed. For a more complete collection of data the reader is referred to standard volumes on physical properties of semiconductors, e.g. the Landolt-Börnstein Series [1, 2], or specific data reviews, e.g. the EMIs Datareview series [3, 4].
The technically important structure sige/si serves also as a model system for lattice mismatched heterostructures because chemical effects are less pronounced than in systems with elements from different columns of the periodic table. The basic concepts of equilibrium strain and strain relaxation by misfit dislocations are described in the section on critical thickness. The conceptual structure of this section follows that given in a lecture on ‘semiconductor Technology’ by one of the authors (Erich Kasper).
1.2 Crystal structure
silicon and germanium, which both crystallize in the diamond lattice, are completely miscible, forming si 1–xgex solid solutions with x ranging from 0 to 1. The space lattice of diamond consists of two face-centred-cubic (fcc) lattices which are displaced a quarter of the space diagonal. a perspective drawing of the unit cell is depicted in Fig. 1.1. The space group of the diamond structure is 0h–Fd3m. The cubic unit cell contains eight atoms that occupy the following positions:
The fractions denote the height above the base in units of the cube edge. In this structure each atom is bonded to four nearest neighbours with a distance of 3 /4 ¥ a arranged at the corners of a regular tetrahedron and to 12 nextnearest neighbours. Four tetrahedra form the non-primitive unit cell. The diamond structure is the result of the covalent bonding between the atoms represented by the rods in Fig. 1.1. The diamond lattice is not very compact. Only 34% of the available space is filled with hard spheres.
1.3 Lattice parameters
To date, the most precise and comprehensive determination of bulk lattice parameters (and densities) across the whole si 1–xgex system has been carried
1.1 Diamond crystal structure. Each atom is tetrahedrally bonded to its four nearest neighbours as displayed by the rods.
out by Dismukes et al. [5], including measurement of the variation of lattice parameters with temperature up to 800°C for some alloys. In Table 1.1 the lattice parameters of si1–xgex alloys at 25°C are listed for composition intervals of 5 at% ge. The data reveal a small deviation from Vegard’s law, which means that the sige alloy parameters are determined by a linear interpolation of the parameters of the end-point elements si and ge.
The departure D from Vegard’s law, defined by D = a(si1–xgex) – {a(si) + [a(ge) – a(si)]x} 1.1 with x = atomic fraction of ge, is also listed in Table 1.1. D is negative throughout the system with a broad maximum in the middle of the system. This slight deviation from Vegard’s law has been confirmed in a recent study on sige epitaxial layers on si(100) substrates analysed by X-ray diffraction and Rutherford backscattering [6]. The experimentally determined deviation from Vegard has also been found theoretically by means of Monte Carlo simulations on si1–xgex alloys [7, 8].
By using the values given in [5] for x = 0%, x = 25% and x = 100%, a parabolic relation for the si1–xgex lattice parameter as a function of the ge fraction x,
Table 1.1 Lattice parameter a of Si1–xGex alloys for x from 0 to 100 at% in 5% steps after [5]. The right column gives the deviation from Vegard’s law D
Ge)
0.54825 0.54928 0.55038 0.55149 0.55261 0.55373 0.55492 0.55609 0.55727 0.55842 0.55960 0.56085 0.56206 0.56325 0.56575
– 0.00004
– 0.00014
– 0.00026
– 0.00041
– 0.00051
– 0.00062
– 0.00065
– 0.00067
– 0.00068
– 0.00069
– 0.00063
– 0.00060
– 0.00055
– 0.00053
– 0.00048
– 0.00027
– 0.00023
– 0.00019
a(si1–xgex) = 0.002733 x 2 (nm) + 0.01992 x (nm) + 0.5431 (nm) 1.2 can be derived which approaches the experimental data with a maximum deviation of about 0.0001 nm.
An even better fit is possible by a cubic approach as, for example, by the relation
a(si1–xgex) = a(si)x + a(ge)(1 – x) – 0.00436 x3 + 0.03265 x 2 – 0.02829 x 1.3
which is implemented in the philips simulation software for high-resolution X-ray diffraction [9]. The lattice parameter of si of a(si) = 0.5431 nm is confirmed by high-precision measurements on pure single crystal Si [10]. The published room-temperature data on the lattice parameter of undoped ge single crystal range from a(Ge) = 0.56573 nm [11] to 0.56579 nm [12].
In this context, it is to be noted that although SiGe is a well-known alloy system crystallizing in the rather simple diamond lattice, and although si/ SiGe heteroepitaxy structures presently find increasing application due to their promising potential for high-performance devices, the local atomic arrangement such as bond lengths and bond angles is still an object of controversial discussion. There are two extreme concepts for the correlation between bond configuration and alloy composition, termed Bragg/Pauling’s and Vegard’s limit. according to Bragg [13] and then to pauling and Huggins [14] the bond lengths in alloys are the sum of the atomic radii of their constituents and remain unchanged as composition varies. Consequently, the bond angles must change to accommodate the presence of different atoms. Vegard’s limit [15], on the other hand, means that the bond angles are fixed at the tetrahedral angle and the bond lengths change linearly with the composition. In most experimental studies done by X-ray diffraction (X rD) and in particular by (extended) X-ray absorption fine-structure ((E)XAFS) analysis it has been found that sige alloys are mostly, but not completely, pauling-type in nature, which is in disagreement with nearly all published theoretical results. a comprehensive overview on this topic is given in a recent paper by aubry et al. [16].
Concerning the composition dependency of further structural parameters such as elastic moduli covering the whole composition range, the number of publications in the literature is rather limited. The elastic constants, for example, are required if the lattice parameters of heteroepitaxial si1–xgex films have to be corrected for elastic strain. Mendik et al. [17] investigated si1–xgex alloys and found experimental values of the elastic constants Cij which are larger than those calculated from a linear combination of the Cij values of the pure constituents (Table 1.2). From raman measurements on si/si0.52ge0.48 strained layer superlattices on si, zhang et al. [18] obtained for the si layer a smaller sound velocity and density compared with the Si bulk values, and for the SiGe alloy layers a higher sound velocity and
Table 1.2 Elastic stiffness constants Cij of Si and Ge. For SiGe a linear interpolation is recommended
1.2 Liquidus–solidus curve of the Si1–xGex system after [21]. The circles and the crosses are taken from [18] and [19], respectively.
higher density than the values deduced by linear interpolation. However, these changes may possibly be due to strain introduced during formation of the superlattice.
1.4 Phase diagram
The phase diagram in Fig. 1.2 was established by elaborate thermal and X-ray analysis [19]. It is still the basis of the solidification curve of the SiGe system and only a few points have been later added to the ge-rich side of the phase diagram [20]. No phase changes or decomposition were detected by X-ray analysis after annealing homogeneous solid solution crystals for several months at temperatures in the range from 177°C to 925°C. The sige system is a typical representative for a system with strong segregation, i.e. for solid solutions in which the solid and liquid phases are separated by a large regime of coexistence. From this it is evident that, for example,
the preparation of a homogeneous solid solution from si and ge requires considerable effort because during solidification from the molten phase the si component strongly segregates and thus quasi-decomposition occurs. Under the assumption that si and ge form ideal liquid and solid solutions, Thurmond [21] calculated the liquidus and solidus curves and found the latter to coincide with that in Fig. 1.2. The liquidus lies only slightly below the experimental curve. some structural and thermodynamic data on the sige system are presented in [22] and an early review on the bulk growth of SiGe solid solutions is presented in [23]. Recent advances in the bulk growth of SiGe are summarized in Chapter 4 of this book.
1.5 Critical thickness
Heterostructure device concepts promise strong advantages in micro- and optoelectronics due to gainful effects of band line-up and strain on carrier transport. From the material point of view, the main obstacle to be overcome is the large lattice mismatch of silicon-based heterostructures. one of the best of them, silicon germanium (sige), is lattice mismatched to silicon by up to 4% depending on its ge content. Basic investigations on strained layer growth, interface properties, and deviation from equilibrium are done with sige/si heterostructures.
Within the historical development of microelectronics the community had to learn that serious technical obstacles had to be overcome in order to benefit from the heterostructure advantages. The most serious of these obstacles were chemical differences and lattice-mismatch. a model system for latticematched heterosystems was found in the III–V material realm with gaas/ GaAlAs nearly perfectly fitting together. But joining III–V semiconductors with silicon (Si) turned out to be difficult because of the chemistry defining each of the materials as dopants for the other group. The main attention was therefore focused on the group IV elements and compounds. In Table 1.3 the cubic (diamond or zincblende lattice cell) group IV compounds are summarized.
The differences in lattice constants are very large with the exception of the completely miscible alloy sige. In equilibrium only small amounts of carbon in si and of tin in ge are soluble. With the advent of low-temperature growth techniques like molecular beam epitaxy (MBE) or advanced chemical vapour deposition (CVD) methods, the formation of non-equilibrium compounds such as sige:C and sige:sn seemed possible. recently the incorporation of Sn in the Ge lattice has been attracting considerable attention [24–26] because already with 10% sn a direct (group IV) semiconductor material is predicted and, on top of ge:sn tensile strained ge, is expected to exhibit spectacular carrier transport properties.
In the following part of the chapter, the impact of lattice mismatch and
Table 1.3 Group IV elements and compounds diamond (C), silicon carbide (SiC), silicon (Si), germanium (Ge) and tin (Sn), showing their atomic number (Z), atomic weight (M), density (r), lattice constant a0 and band gap Eg (eV) at 0 k
1.3 A positive edge dislocation formed by inserting an extra halflayer of atoms between atomic planes above the slip plane. The Burgers vector of a dislocation is represented as a closure failure EA = b in the ideal lattice when a closed circle was drawn around the dislocation in a real lattice.
strain on nanometre layers and their electronic structure is evaluated. surface morphology and misfit dislocation networks play an important role in strain relief processes. The basics of dislocations were introduced in metallurgy where plastic deformation was explained as an atomic phenomenon by dislocation movement. For the reader not so familiar with dislocation concepts they are listed below.
In the diamond cubic lattice the dislocations propagate primarily by glide on {111} planes. The dislocation (Fig. 1.3) is a line defect which is characterized by its local line vector l and its characteristic Burgers vector b, the nature of which is indicated by an atom-by-atom circuit along the path around the dislocation. The dominant Burgers vector in the diamond lattice is along 1/2<110>, and the Burgers vector length b is a /2 (0.38 nm in si). a dislocation cannot end in the interior of a crystal; it either ends at a surface or is closed as a dislocation loop. Under undisturbed conditions the
dislocation follows preferentially the <110> directions. a simple construction due to Thompson [27] greatly assists in the understanding of interactions between dislocations (Fig. 1.4). The tetrahedron aBCD is made up of the four {111} planes. For convenience this tetrahedron is opened, the vertex D having originally been above the plane of the paper. In Fig. 1.3 the Burgers vector is perpendicular to the dislocation line, which is referred to as an edge dislocation. Dislocations with Burgers vector parallel to the dislocation line are known as screw dislocations (Fig. 1.5). Other angles between l and b exist; these are mixed dislocations, e.g. 60° dislocations of aB dislocation lines with aD Burgers vector in Thompson’s reference tetrahedron. Dislocations may easily glide along the {111} slip planes; the slip plane is defined by both vectors – the line direction l and Burgers vector b. Movement of the dislocation perpendicular to the glide plane is called climb, which needs generation or annihilation of point defects and is therefore much slower. However, there are four {111} planes and so a dislocation can change to another plane under certain circumstances; this is called cross-slip: see, e.g., in Thompson’s tetrahedron the dislocation with aD Burgers vector, which may move within the aCD plane and also within the aDB plane (Fig. 1.4).
Despite the severe local distortion around the dislocation, there is still matching of most lattice planes (except the one which causes the displacement b). The strain decreases with increasing distance from the dislocation such that displacement of atoms a few atomic spacings away from the dislocation
1.4 Thompson’s reference tetrahedron.
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27 (AUG. 17, SUN.)
The port is near, the bells I hear, the people all exulting.
—Whitman
Gov's guerrillas had spent the rest of Saturday and much of Sunday completing their examination of the android and making their plans for the rally At least I assumed they were planning some kind of foray; no one told me very much and I had no idea what my role was to be, or if I was to be included at all.
The fat Sunday Times, the middleweight Herald Tribune and the radio filled me in on what was happening—or what appeared to be happening—in the outside world.
The Monolithian pretenders seemed to be solving a number of world problems.
The alien disguised as the President of the United Arab Republic announced a tentative settlement with Israel on the issue of the Palestine refugees.
The one posing as India's Prime Minister reported that he and Pakistan's leader had had a "meeting of the minds" on the explosive Kashmir question.
There was a curious dispatch from Taipei, full of Oriental undertones, which appeared to indicate that peace of a sort had been made between Formosa and the Communists in Peking.
There had been a tremendous kaffee-klatsch on the border of East and West Berlin and, while nothing was explicitly agreed to, the feeling was that the long division of Germany was coming to an end,
in what a punning correspondent saw fit to refer to as "an arithmetical solution." The correspondent was vague on details but indubitably hopeful.
It was as if the fondest dreams of Moral Re-Armament were being realized. I looked for a happy communiqué from Mackinac Island on the subject, but there was nothing. I assumed the Buchmanites were sulking because the Monolithians had stolen their thunder.
I also looked in vain for a follow-up to "President Allison's" appeal to the nation to beware of imitations. The fact that there was no reference to it at all led me to think that the Monolithians had panicked only momentarily. It was obvious that they had known about the Allison underground. Their current silence on the matter gave me a small chill. It was as if the Monolithians were contemptuously tolerant of Gov's guerillas, seeing them as no threat whatever to the ultimate alien scheme.
I was mulling over this deflating thought when Timmie bustled in, saying, "Time to get ready, Mr. Kent."
He sat me down, wrapped a towel around my neck and proceeded to alter my appearance with grease pencil, nose putty and other backstage devices. It was the first inkling I had that I was to be a part of Operation Madison Square Garden.
Timmie backgrounded me and gave me my instructions as he worked deftly to make me look twice my age.
"That android, now. Doc didn't exactly take him apart, but he found out enough. He wasn't transmitting back to Monolithian headquarters, as we suspected, but he did have a kind of tape device inside his skull that recorded everything he saw and heard. In other words, he'd've had to get back to the aliens for his spying to've done them any good....
"We're all going to leave here at different times, so as not to be suspicious, and rendezvous at the Garden. You're to go in by the
Press entrance on 49th Street. We've got some fake JournalAmerican credentials for you...."
There were a lot of cops at the 49th Street entrance. They were needed, because the street was packed solid with humanity and immobilized cars from Broadway to Eighth Avenue.
I shouldered my way through and flashed my police-press shield at a police sergeant, who waved me inside.
The first person I saw was Joy Linx. She was holding a sort of impromptu press briefing for a bunch of yelling reporters.
"Keep quiet a minute and I'll tell you," she was saying. "The President is going to come right up that aisle. You'll be as close to him as anybody. Then he goes up to the platform and Spookie Masters introduces him."
She was wearing a skirt and blouse and there were little beads of perspiration on her upper lip.
Somebody asked where Sam Kent was.
"I don't know," Joy said. "He was here a minute ago. He'll be back soon, I'm sure."
She glanced around, her eyes flitting over me without recognition.
People were jammed together on camp chairs all over the floor of the Garden. The speakers' stand was at the north end. There was red-white-and-blue bunting everywhere and banners reading "U.S. + M = Peace," "Give Common Sense a Try," and "Two Worlds Are Better Than One."
A band on the platform was in a segue from God Bless America to The Battle Hymn of the Republic, without losing a note, but it could barely be heard over the din of the 20,000 people who packed the Garden to the rafters.
I heard a yell from the street behind me. "He's coming!" Other voices joined in: "It's Gov!" "Don't he look swell!" There was a chant: "We love Gov.... We love Gov...."
True to Joy's word, Gov—that is, the Monolithian masquerading as the President—passed within a dozen feet of us on his way to the platform. He was accompanied by a dozen or more men who could have been the Secret Service or some of his fellow Monolithians.
The fake Gov smiled and waved to the masses of people in the Garden who were shouting themselves into a frenzy as section after section of them realized he was coming among them.
The band played Hail to the Chief, then For He's a Jolly Good Fellow, and finally The Star-Spangled Banner. It was quite impressive and I was patriotically moved despite my knowledge that it was all a fraud. I could imagine how the thousands in the Garden and the millions watching television felt. To them it must have been the culmination of mankind's yearning for respite from the decades of insecurity and fear of another global war, coupled with worship of that greatest of heroes, the man who had negotiated an interplanetary peace.
It was hot as hell and I longed to scratch my itching putty nose.
The Monolithian who was pretending to be the President seated himself behind a long table on the platform and Spookie Masters took over the microphone.
Spookie made a few jokes. Everything he said was greeted with laughter, cheers and applause. In that atmosphere he could have read a shopping list and won an ovation. Finally he got down to business.
"Friends," he said, "—or maybe I should say fellow members of the interplanetary alliance—" (applause) "tonight we celebrate the passing of an old era and the birth of a new one. The change in which we participate tonight," he said solemnly, "and I choose my words carefully and with reverence and humility, is, I think, as historic as that which marked the division of the calendar from B.C. to A.D."
He paused, eyes cast down humbly, and a murmur went through the crowd. Somebody said "Amen," and I half expected a Hallelujah or two, but Spookie hurried on before any revival meeting atmosphere had a chance to develop.
As he went on talking about interplanetary amity and the benefits to all mankind of this glorious turn in the history of the world, I saw Gov's guerrillas filtering through the aisles toward the platform. Some carried cameras, others had police-press shields paperclipped to their lapels, and others merely wore ribbons printed with the word COMMITTEE. Nobody challenged any of them. They got as close to the platform as they could.
Those with cameras brazened themselves closest and aimed their equipment directly at the fake President from less than a dozen feet away.
I knew what the equipment was, and I pushed closer myself to see whether it would work. It was the conscience gas I'd stolen from Ultra.
Gov's plan was a simple one—when the fake Gov got up to talk, dozens of cameras would record the scene. At the same time the conscience gas would spurt out of the guerrillas' cameras and smite the alien impostor.
The fake President would then go through the same mental turmoil that had assailed the dictator of El Spaniola. He would, in effect, become one with the thousands in the Garden and the millions on television who were about to be subjected to whatever nefarious fate the Monolithians had planned for them. The dichotomy of being simultaneously the victor and the victim would be too much for him. Then he would either confess everything or—if the Monolithians
were actually a race with a common, interlocking intelligence, as some people suspected—he would make a decision in Earth's favor which would be binding on all the other aliens. Either way, it would be interesting to watch.
Spookie was finishing his introduction. "And now, my dear friends everywhere, I give you the man you all know and love—the man who has had the courage and foresight to switch Earth's destiny in midstream from its course of destruction to its new and exciting path —your President and mine—Gouverneur—good old 'Gov'—Allison!"
The place went wild. Everybody stood up and yelled or cheered. Balloons of all colors with the words GOV and PEACE on them were released by the scores and floated up toward the roof. Confetti and streamers showered and spiraled down from the balconies. The band was playing fit to bust—but only visibly, not audibly, in the din. The fake Gov stood there smiling, his arms out at his sides, waiting patiently to be heard.
I saw the quick bursts of flash bulbs, including ours, and watched the face of the alien masquerading as the President. There was no flicker of change in his expression of benevolence.
There was a scuffle somewhere on the floor. The center of the disturbance was where I had last seen the real Gov, disguised as a devoted follower of his impersonator. Four men had him by the arms and were moving him quickly and as inconspicuously as possible toward a curtained-off area near the platform. Then four men closed in on me. They took me by both arms, lifted me an inch off the floor and propelled me vertically in the same direction. "Hey," I began, but one of them said, "Come on, Kent. Don't make a commotion."
I didn't because I was well and truly outnumbered and, besides, each time I resisted they began to ruin my arms.
By the time I got to the curtained area the real Gov had been sat in a chair and stripped of his disguise by his Monolithian captors. All of our fellow conspirators were there, too, including the photographers whose cameras had been loaded with conscience gas instead of
super-pan. I was crowded up against one of them and asked him, "Didn't you have a chance to shoot?"
"Sure I did. All of us did. But it didn't make a damn bit of difference. He's still out there lapping it up. Look at him."
I could see out to the platform, as from the wings of a stage. The noise of the crowd had diminished, but only slightly. The Monolithian duplicate of Gov still stood there. His smile seemed as genuine as ever and his conscience apparently didn't bother him in the least.
28 (AUG. 18, MON.)
We must not gargle with euphoria.
—Charles de Gaulle
Gov—the real one—said to me, "It's as clear as that fake nose you were wearing last night that they sold you a pup, Sam."
I asked him what he meant.
"That so-called conscience gas we banked so much on. They must have engineered the whole thing, including your escape from Ultra."
Gov and I and the rest of his crew were at the penthouse office on Fifth Avenue.
The rally at Madison Square Garden had been a smashing success, as we'd been allowed to see, to our discomfiture, from the wings where we'd been herded after our capture.
We were now, on Monday morning, sitting or standing around in Addison Madison's office, wondering what was going to happen to us. The Monolithians had treated us gallantly so far, having put us up for the night at the Taft Hotel, guarded no more obtrusively than a bunch of suburban high-school seniors staying in town after the prom.
Now, at the Monolithian GHQ, though there was a constant flow of aliens in and out, none of them so far had had anything to say to us except busy good mornings. I didn't recognize any of them. Frij, alias Addison Madison, hadn't arrived yet, if he was due at all.
He had been very much in evidence at the Garden last night, public relationing in his most offensive manner, and I supposed he was still
resting from his exertions which, Lord knew, had been a Monolithian triumph. The usually unimpressionable New York Times replated six times for it and gave it a three-line, eight-column banner head.
I had been trying to explain to Gov how he could tell one late city edition of the Times from another by the decreasing number of dots between the volume and number up under the left ear on page one, but all Gov had on his mind was the conscience-gas fiasco.
"Maybe they used their defense shield against it," Gov said. "Or maybe they're just naturally immune. But the best explanation is that they palmed off a phony on you when you swiped the stuff from Ultra. It was all just too pat to be real."
Addison Madison came in and said, "Oh, yeah, Mr. former President? Is that so?" He sounded as if he'd heard everything we'd said and when I asked him he had no qualms about admitting it.
"Let me tell you wise guys something," Addison Madison-Frij went on. "The conscience gas is the genuine article. It worked on General Rafael Domingo Sanchez of El Spaniola when we kept him from Obombing your retrograde civilization and it also worked, believe it or not, on my colleague, the new President, at the Garden last night. So put that in your pipes and smoke it, Mr. Ex-President, and you, too, Mr. Ex-Hotshot Newspaperman."
"You're crazy," I said. "Let's assume for the sake of argument that it worked on Domingo Sanchez and that the Spaniola thing wasn't a hoax...."
"Your assumption would be correct," Frij said. "You don't know how irresponsible you Earthpeople are."
I let that go for the moment and said, "But your colleague, as you call him—the fake President Allison—was no more affected by the stuff in our phony cameras than the man in the moon."
"Ha ha," Frij said. "That shows how much you know. He was affected but it made no difference." He let that sink in for a while. "Do you want to know why?"
"Why?" Gov asked.
"Because," Frij said "—now grasp this concept if you can—because my colleague, the new President, was sincere. His conscience was already clear."
Gov and I looked from him to each other. Much as we detested Frij, it began to dawn on us that he might be telling the truth.
"You mean," Gov said, "that it's true that you Monolithians have no purpose other than saving us from ourselves?"
"Precisely," Frij said. "You could not have put it more aptly."
"Then my story—the big exposé Rod and I wrote on Ultra—was all wrong?"
"It couldn't have been more wrong," Frij said.
"And Domingo Sanchez wasn't your patsy?" I was slowly and reluctantly patching it together.
"You assumed that a minute ago," Frij said. "Now you believe it."
Gov, looking unutterably weary, said, "I'm afraid I believe it—and all that it implies. It means that Earth really had no choice whatever. The other Presidents and the Prime Ministers and I were forced to accept the Monolithians' terms to avert the Spaniolan threat—which I am now again convinced was no idle one. So we had to agree to the super-summit on Ultra, which, of course, set the stage for the substitution of Monolithian duplicates for Earth's leaders."
Gov smiled wanly and went on. "The fact that I sent a double of myself to Ultra only delayed matters slightly. You finally got me anyway."
Mox came in then. Like Frij before him, he obviously knew everything that had been said.
Mox, looking like a saint in his Monolithian robe, in contrast to Frij's flashy American clothes, said, "Frij, I think you've been out here too long. You've adopted not only the Earthman's protective coloration but some of his sadistic ways. Why haven't you told Mr. Allison why we wanted him?"
"I was coming to it," Frij said defensively.
"Go, Frij," Mox said. "I will tell him. Go back to Monolithia on the next lighter and re-enroll at the Foreign Service School for a refresher course in interplanetary relations. Consider your punishment the fact that I have reprimanded you in public. Leave us now."
"Yes, Mox," Frij said humbly. He went out, and that was the last Earth saw of Addison Madison or anyone like him.
Mox smiled. "My apologies, gentlemen." He looked like dignity incarnate and I wondered suddenly if this were the mysterious "Mr. M.," the head Monolithian who had taken part in the conference on Ultra that decided Earth's fate. I halfway hoped so; he seemed so much the just, kindly, elder-statesman, father-image type who inspired trust and confidence.
Gov said, "Mr. Mox, I'm a tired old man, especially after last night. I'd appreciate it if you'd tell me what the hell's going on and, particularly, where I go from here. If I'm going to be led out and shot I'd just as soon get it over with, frankly, if it's all the same to you."
Mox looked shocked. "My dear sir," he said. "Nothing is further from our plans. All we want is for you to resume your rightful place in the White House, at the head of your government."
Gov exhaled a long sigh of relief.
Therefore he had no choice except to breathe in again—by which time Mox had crushed a tiny capsule in his palm and held it under Gov's nose.
29 (AUG. 19, TUES.)
The score stands today: Strontium 90; Humanity 13. —James Thurber
Tuesday went by like a montage, or a series of fades and dissolves in a documentary movie.
Scene: The Fifth Avenue penthouse. Mox's (formerly Frij's) office.
Mox, benevolent, wanting to be understood; Sam Kent, groping, wanting to be convinced.
M : There were several ways it might have been done. One requisite was a common denominator— something everybody uses, such as water But water was not quick enough. Air is better.
S : You mean you contaminated the air?
M : Not contaminated, no. Diluted it, you might say. It started in El Spaniola, with Domingo Sanchez.
S : But you said—Frij said, up on Ultra—that it wasn't communicable.
M : Ah, but Frij lied to you. I don't know why; perhaps he had absorbed too many of Earth's ways. He was becoming dangerous. That's why I sent him home. Our conscience gas, as your press calls it, is transferable from person to person, and rapidly. Like your own oral polio vaccine, it is contagious on contact.
S (wordless): !!!
M : You need not look so horrified. Remember the greater good. Recall the game you've been playing with yourselves—a game where there is no winner. You had to be stopped because of the way the odds against survival were mounting. One of your more perceptive observers put it very well when he said the score stood Strontium 90, Humanity 13."
Gouverneur Allison, President of the United States, a good man basically and one who had long worried in his private soul, needed no more indoctrination than the whiff of conscience gas he'd been given by Mox to be convinced that the World's salvation lay not in the haphazard politics of Earthmen, but in the clear-seeing, galacticminded altruism of Monolithian logic. He went back to Washington by Pennsylvania Railroad day coach, contaminating a few hundred people along the way, and when he got to the White House he signed an executive order as Commander-in-Chief directing that all American nuclear weapons be deactivated, transported expeditiously to the Challenger Deep, and sunk.
Immediately the four other atomic powers—Britain, the Soviet Union, France and El Spaniola—followed suit.
You could almost hear the collective sigh of relief that went up around the world.
Scene: Joy Linx's hotel room in Manhattan. Joy Linx, beautiful, hostile, in housecoat. Sam Kent, anxious, somewhat wild-eyed, truth-seeking.
J : All right, I guess. Come on in.
S : Listen, Joy, it's important.
J : It better be.
S : It's about Spookie Masters. How well do you know him? I mean really?
J : What kind of question is that?
S : I know it sounds crazy, Joy, but it's the key to the whole thing. Has he—did he ever—oh, God damn it,
what I mean is, did he ever make love to you?
J (scornfully): I won't answer that stupid question. Did you think I would?
S : It isn't just me asking it, Joy. Honestly, you've got to realize how vital it is.
J : Look, Sam, my dear, sweet someone else's Sam: In a kind of crazy, hopeless way I once loved you. It was no good. You know why. Mae, that's why. That lucky girl. So go away before you kill me any further, will you?
S (emotionally torn): Joy, Joy—how can I say I wish it were otherwise, when I both do and don't? Damn Mae (I don't mean that) and damn you—but particularly —damn me.
J (touched, quietly): Tell me what you want me to do.
S (with a sigh, then getting it over with): All right. When Spookie comes to see you, lead him on. Let him think you're crazy about him—as maybe you are.
J (looking at the floor, hands on Sam's chest): Maybe I am, in a second-best sort of way.
S (on brink of tears): Listen, my second-best darling ... (a quick, antiseptic, apologetic kiss) what I have to know is—whether Spookie Masters is a Monolithian.
J (withdrawing): What!
S : That's the key to the whole thing. He could have come to Earth years ago as an advance agent for them —his early life has always been a mystery. His career took him all over the world. He knows everybody. Then he got himself to Ultra. Of course! He was the "Mr. M." who represented Monolithia at the super-summit.
J (coldly): Isn't that pretty far-fetched, Sam?
S : No. It fits perfectly Then he arranged to get himself "captured" and thrown in with us so he could learn what we were up to. And I'll bet he engineered our "escape," too, and saw to it somehow that I stole that conscience gas. They knew I would lead them to the only holdout in their scheme—the real Gov—and that the gas would be the bait that put him in their trap at the Garden—where, you must admit, Spookie was very much the big wheel.
J (thoughtfully): Well, maybe. Tell me what you want me to do.
I'd told her, unable to look her in the eye, that I had to know whether Spookie Masters was a whole man, and therefore terrestrial, or a sexless creature like the android, and thus a Monolithian. Joy had heard me out, saying nothing except with her contemptuous eyes, then showed me out.
Something puzzled me. I was feeling no pain. And yet I should have been, I reasoned, since I had been subjected to the C-gas at the same time Gov inhaled it and I was probing around in what must be considered an anti-Monolithian way.
I was also running around loose and doing a certain amount of independent thinking, which didn't seem to fit into the concept of a true Monolithian state whose subjects had been C-gassed into cooperating for the greater good.
True, I was on a loose rein. Mox had given me the day off, in effect, telling me to report to the White House in the morning. I supposed I'd find myself fired when I got there, since Gov's ex-guerrillas, including Josh Holcomb, his original press secretary, had all been C-gassed into conformity and my services would therefore be superfluous.
I decided to go back to the penthouse and have a heart-to-heart talk with Mox or one of his lieutenants.
Mox saw me himself. He must have had a million things to do, but he took the time to talk to me for more than an hour, answering every question I asked.
When I left his office I found Joy sitting at her desk, typing. She glanced at me and said, "Sit down, Sam. This is for you. I'll be through in a minute."
She rattled through another paragraph, then, after a look at me, typed one final line. With a pen she wrote two words. Joy sighed and said, "There—I've got that out of my system." She folded the single sheet of paper, sealed it in an envelope and handed it to me.
"Please go before you read it," she said.
Then she smiled, as if she were now at peace with me and the rest of the world.
"Joy——" I started to say.
"Just go—please," she said, and I went.
I read Joy's letter over a martini at a solitary table at the Brass Rail, then decided to have several more martinis and skip dinner altogether.
Joy's letter started: "Sam (not at all dear):" and went on to tell me quite explicitly that Spookie Masters—whom she called Robert, his real name—was male as male could be.
What she had said, actually, was: "He's as human as you are—if you are."
This was empirical knowledge, she said, not theory or hearsay. She had known this before today, she said, and hoped I was hurt by this fact as she had been hurt by me. She did not know whether Robert was an Earthman or a Monolithian, but this didn't matter to her. Her happiness was what mattered and it was obvious that I could only cause her pain.
"I've made my choice, Sam," she had written. "I had to choose between what I wanted and what I could get. There are times when the ideal is just too unattainable and when the second best becomes, in the long run, the best. Maybe this also has a universal application. I hope so."
The last line of her letter was: "One last thing, Sam—I hate you."
But she had edited this. One of her two handwritten words was her signature. The other, inserted in the last sentence above a caret, was "can't."
That had made her farewell read: "I can't hate you."
Over my third martini I thought I understood Joy's parting smile. Remembering it again, I could see the signs in her eyes. It wouldn't be long, I suspected, before I saw one of those headlines peculiar to the society pages of The New York Times, reading: TROTH PLIGHTED OF MRS. JOY LINX; MONOLITHIAN AIDE FIANCEE OF ENTERTAINMENT STAR.
I wished her joy and ordered a fourth martini.
Then I got up and telephoned Mae in Bethesda and told her I'd be home that night. Mox had told me, among other things, that my double wouldn't be there.
30 (AUG. 20, WED.)
And now we all have a new King. I wish him and you, his people, happiness and prosperity with all my heart.
—Duke of Windsor
It's done now. It's all over but the shouting, or maybe the weeping, depending on how you look at it.
Earth has been absorbed into the greater scheme of things. There'd been a telephone call from the White House at 7 A.M., from Gov personally. There was no need for me to come in, he said. My job was intact but different. I wasn't the Presidential Press Secretary any more, but my new assignment was just as important—maybe more so. Mox, who came on the line on an extension, said the same, so I knew it was official.
I tried to explain it to Mae over breakfast.
"I'm the historian," I said. "That's what it's all about."
"Eat your eggs," she said. "They'll get cold." She had sprinkled them with Pep.
"My job is to write it just as it happened. The way I see it. No propaganda, no censorship."
"That's nice. You want your coffee now or later?"
"I can work at home if I want to. And they'll send out a secretary if I want somebody to type up notes or take dictation. Now, please."
"That's sweet of them," Mae said. She poured the coffee. "Maybe they'll send that nice Joy Linx."
I carefully broke a yolk and stirred Pep into it with my fork, giving it all my attention. I think Mae was serious. "I don't believe I'll need anybody," I said carefully.
"You need me." Mae was standing at the stove with her back to me, frying an egg for herself. She was wearing a sort of maternity middy blouse and skirt and looked very good. "Don't you?"
I got up and put my arms around her gently and kissed the back of her neck.
"You can hug us gently," she said.
I did. I thought I felt my son or daughter give a kick, not of protest, but just to let me know someone was there.
"Say it," Mae whispered.
"I love you and I need you," I said.
"Good." She gave her egg a poke and sighed as if in relief. "And I love you and need you. What I don't need is that crazy robot that's been hanging around pretending to be you."
"What!"
"He didn't fool me any—except at first."
"He didn't?"
"Oh, he's a very good imitation—as far as he goes. But he worked too hard at keeping me from finding out that he lacked a few male— or even human—necessities."
"You mean he didn't—uh, sleep with you?" I had to get it said, any old way.
"He certainly did not. Actually it was his own idea to sleep in the guest room. I'd have seen that he did anyway. But that wasn't the only thing. He never went to the bathroom."
"Well," I said.
"Oh, he'd go in and take a bath, but he never—how do they say it in hospitals?—he never voided."
"Oh? How do you know?"
"I listened at the door. There was never a sound till he flushed."
"Oh, Mae!" I said, not knowing whether to laugh or cry. "And I thought you were completely fooled, and that I had to stay away because if you saw two of us the shock would be too much for you. Why didn't you say something?"
"I figured it was important to you and your job, and maybe even the world. You usually have a good reason when you do something peculiar. Want some toast?"
"Yes, please—wait a minute. The toaster's broken."
"He fixed it. That's how I really knew he wasn't you. He went right ahead without a murmur and repaired half a dozen things you've been putting off ever since we were married, practically. He fixed the stuck zippers and my sewing machine and that lamp with the short in it and the switch on the vacuum cleaner. That wasn't my fumblefingered old Sam."
All that was a long time ago. It's been only a little more than two years, but it seems like ancient history now.
A lot has happened since. It's all been fully recounted and interpreted in the press and magazines, so I'll just hit the highlights.
A year ago all the nuclear weapons in the world were deactivated and sunk in a remote corner of the Pacific. The scientists who were working on bigger and worse ones were transferred to peaceful research.
Six months ago the Moon was colonized by a six-man international expedition, whose names are Underwood, Chih-ho, Cohen, Raswaplindi, Buragin and Thorwald, and their wives.
Five months ago the cure for cancer was announced. They'd solved the riddle of muscular dystrophy, Parkinson's disease and arthritis
