Chalcogenides: Metastability and Phase Change Phenomena

287 Pages·2012·10.437 MB·English

by  Alexander V. Kolobov, Junji Tominaga (auth.)

Springer Series in Materials Science
Volume 164
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The Springer Series in Materials Science covers the complete spectrum of
materialsphysics,includingfundamentalprinciples,physicalproperties,materials
theory and design. Recognizing the increasing importance of materials science in
future device technologies, the book titles in this series reflect the state-of-the-art
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classes of materials.
Alexander V. Kolobov Junji Tominaga
•
Chalcogenides
Metastability and Phase Change Phenomena
123
Alexander V.Kolobov Junji Tominaga
Nanoelectronics Research Center Nanoelectronics Research Center
National InstituteofAdvanced Industrial National InstituteofAdvanced Industrial
Science and Technology Science and Technology
Tsukuba Tsukuba
Ibaraki Ibaraki
Japan Japan
ISSN 0933-033X
ISBN 978-3-642-28704-6 ISBN 978-3-642-28705-3 (eBook)
DOI 10.1007/978-3-642-28705-3
SpringerHeidelbergNewYorkDordrechtLondon
LibraryofCongressControlNumber:2012936758
(cid:2)Springer-VerlagBerlinHeidelberg2012
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To our daughters, Ilaria and Morie
Foreword
Alexander Kolobov and Junji Tominaga have in this book made a remarkable,
indeed a monumental achievement. They cover the very large field of amorphous
andglassymaterialsandphasechangememoriesandtheirvariousmanifestations,
whichisquiteatask.Bothauthorsareveryimportantcontributorstoourfieldand
arehighlyregarded.Theirremarkableabilitytocoversuchimportantbasicscience
and technology and also understand that new concepts and mechanisms are con-
tinually expanding the field should be welcome to all who labor in this growing
area.Itisexemplarythatthisisthefirstbookinourliteraturerecognizingthatthe
fieldofthechalcogenidesisnowplayinganimportantpartintheexcitingfieldof
topological insulators.
Therearestillbroadanddeepareasthatourscientificeffortsareaddressing,and
Ibelievetherealwayswillbe.Thisbookcertainlyprovidesagreatandinformative
corewhichisabasisfornewwork.Theoutreachthattheauthorshavegivenusis
very impressive and comprehensive especially because the authors are strong
participators and offer original insights of their own.
Their understanding and their own considerable talents make this a book that
I believe will get the attention it deserves for amorphous materials generally and
uniquely for the chalcogenides whose physics is now impacting various other
applications where they are receiving great attention. I believe that the chalcog-
enides have entirely new physical, electronic, structural mechanisms effectively
presentedinthisbookthatwillbeasourceofknowledgeforthereaderswhowith
enhancedunderstandingcanmakepossiblemanynewapproachesandwillinterest
many in the field. There should be a single book that covers the field of many
investigations so that there is a commonality of knowledge for the reader. This is
such a book.
Ovonicphasechangeandthresholdswitchingdevicesarenowbeingstudiedfor
important new functionality, cognitive computing, and multi-function thin film
devices that open up a whole new group of potential applications including a
provocative possibility that includes dynamic superconductivity.
The authors are personally wonderful models of the type of creativity that
alwaysseeks,explores,andcontributes.Iamcertainlyfamiliarwiththeimportant
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viii Foreword
contributions of Junji Tominaga and I have long recognized the contributions,
creativity,andexcitementthatAlexKolobovprovidestoourfield.Wehonorthem
for their leading roles and pay homage to those who preceded them. Japan has a
leading role in development of phase change memory and Kolobov represents
Russia with great pride as a student of Boris Kolomiets and pays respect to the
Russian literature.
The authors have made a great contribution and the book lives up to its title.
Metastability, chalcogenide glasses, and phase change alloys certainly deserve to
beaddressedinascholarly,descriptive,andinformativemannerastheyareindeed
a rapidly expanding field with entirely new materials, physics, and electronic
mechanisms. I am sure the book will be read and studied, and it will become the
reference of choiceby those who are involved and interested inwhathas become
an area of not only such exciting research and development but a basis for
expanding existing and valuable new industries.
Thesubjectsofthebookareexpandingandimportantnewfieldsofinnovative
science and technology are already being considered and proposed and certainly
now one speaks of usages that will advance not our world’s knowledge but the
neededeconomicgrowthofourplanet.Thusweareenteringintoanewadvanced
era and it promises a great time for its participants and builders.
This outstanding book is a welcomed contribution with the ambition and
actualization to embrace the present field and lay the groundwork for future
understanding.Iheartilyrecommendthisbookbytheseveryimportantauthorsfor
its publication is a landmark event.
Bloomeld Hills, MI, January 2012 Stanford R. Ovshinsky
Preface
The discovery in the mid-1950s by N. A. Goryunova and B. T. Kolomiets
at A. F. Ioffe Physico-Technical Institute in Leningrad of the semiconducting
properties of amorphous chalcogenide alloys opened up a new field in solid state
physics, namely, amorphous semiconductors. The existence of semiconducting
properties, i.e. of the forbidden energy gap in the density of states of disordered
materials was very puzzling since the band structure of solids had been usually
derived from the long-range order, or the periodic nature of the crystalline phase.
Another important class of amorphous semiconductors includes hydrogenated
amorphoussiliconandrelatedtetrahedrallybondedmaterials.Whilechalcogenide
glasses typically possess p-type conductivity and cannot be doped, hydrogenated
amorphoussiliconcanbedopedwhichopenedupcompletelynewperspectivesof
thecreationofamorphoussemiconductordevicesattractingfurtherinteresttothis
new field of research.
Possessing the typical properties of their crystalline counterparts, amorphous
semiconductors additionally have characteristics unique to the amorphous phase.
Intrinsically metastable, they can undergo transformations between different
structural states with concomitant property changes. Such changes are known for
both chalcogenide glasses and tetrahedrally bonded amorphous semiconductors.
A special class of materials, the so-called phase-change materials exhibit a
reversible transition between the crystalline and amorphous phases with an
unusually large optical and electrical property contrast between the two phases.
The proposal by S. R. Ovshinsky in the early 1960s to use these materials for
memory applications marked the beginning of a vast and extremely fruitful field.
The reader may have never thought about this, but when one takes a laptop
computerinone’shands,orwatchesahigh-resolutionTVonecomesintocontact
withamorphoussilicon:mostoftheflatpaneldisplayscontainthinfilmtransistors
that utilise amorphous silicon. Should one save data on a re-writable optical disc,
one uses phase-change materials, another class of amorphous chalcogenides
withoutwhichmodernmultimediasystemswouldhavebeenimpossible.Inrecent
yearsphase-changematerialshavebeenattractingincreasingattentionduetotheir
excellent scaling and cycling characteristics which made them the leading
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x Preface
candidate to replace the currently ubiquitous FLASH memory. Samsung and
Micron Technology Inc. have already started commercial production of phase-
changerandom-accessmemorychipsandSamsunghasalsostartedtousethelatter
intheirmobilephones.Notonlyareamorphoussemiconductorssuitableforthese
applications, they are unique materials which ensured that the present computers,
TVs, DVDs and quite a few other mobile devices became available to modern
society.
Thepresentmonographisdevotedtostructuralmetastabilityinbothclasses of
chalcogenide alloys, i.e. chalcogenide glasses and phase-change alloys. While
these two classes of materials are usually considered separately in the published
literature, they possess numerous similar features and the authors believe that the
inclusion of them under a single cover will close the gap and be enriching.
Thestructureofthisbookisasfollows.Chapter1dealswiththefundamentals
of amorphous semiconductors whose properties are described in Chap. 2. Since
material properties are determined by the structure, the latter is of significant
importance and methods to investigate it are described in Chap. 3. Chapters 4–7
are dedicated to photo-induced metastability in chalcogenide glasses. This
description starts with reversible photostructural changes (Chap. 4), followed by
phenomenainducedbypolarisedlight(Chap.5).Photo-inducedcrystallisationand
amorphisation are the subject of Chap. 6 and phenomena occurring in chalco-
genideglass–metalstructuresaredescribedinChap.7.Chapters8–11concentrate
on phase-change alloys. First, the structure of phase-change alloys in the crys-
talline(Chap.8)andamorphous(Chap.9)phasesisdescribed.Chapter10reviews
pressure-induced transformationsinphase-change alloysandthispartofthebook
is concluded by Chap. 11 where atomistic mechanisms of the phase-change pro-
cess are discussed. Finally, in Chap. 12 we discuss the present and future appli-
cations of these materials.
The authors are grateful to K. Shimakawa, K. Mitrofanov and especially
P.Fonsforcriticalreadingofthemanuscriptandnumeroususefulsuggestions.We
sincerelyhopethatthismonographwillbeausefulreferencenotonlyforscientists
and engineers working in the fields of solid-state physics, amorphous semicon-
ductors and memory devices but also for graduate and post-graduate students
specialising in solid-state physics and materials science.
Tsukuba, January 2012 Alexander V. Kolobov
Junji Tominaga
Contents
Part I Amorphous Semiconductors
1 Fundamentals of Amorphous Semiconductors . . . . . . . . . . . . . . . 3
1.1 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Glass Transition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 Phenomenology of Glass Transition . . . . . . . . . . . . . 4
1.2.2 Glass-Formation Criteria. . . . . . . . . . . . . . . . . . . . . 5
1.2.3 Reversible Amorphous-to-Crystal Transition . . . . . . . 7
1.3 Atomic Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.1 Long-Range Order . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.2 Short-Range Order . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.3.3 Medium-Range Order. . . . . . . . . . . . . . . . . . . . . . . 14
1.3.4 Melting of Semiconductors . . . . . . . . . . . . . . . . . . . 14
1.4 Structure of Prototypical Chalcogenides . . . . . . . . . . . . . . . . 15
1.4.1 Elemental Chalcogens. . . . . . . . . . . . . . . . . . . . . . . 15
1.4.2 Chalcogenide Glasses . . . . . . . . . . . . . . . . . . . . . . . 17
1.4.3 Phase-Change Materials . . . . . . . . . . . . . . . . . . . . . 18
1.5 Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.5.1 Ideal Glass and the ‘‘8–N’’ Rule. . . . . . . . . . . . . . . . 19
1.5.2 Topological Defects . . . . . . . . . . . . . . . . . . . . . . . . 20
1.5.3 Soft Configurations. . . . . . . . . . . . . . . . . . . . . . . . . 23
1.6 Electronic Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.6.1 Origin of the Bandgap. . . . . . . . . . . . . . . . . . . . . . . 24
1.6.2 Anderson Localisation. . . . . . . . . . . . . . . . . . . . . . . 25
1.6.3 Percolation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1.7 Fabrication of Amorphous Semiconductors . . . . . . . . . . . . . . 27
1.7.1 Melt Quenching. . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1.7.2 Vapour Deposition . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.7.3 Spin Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
1.7.4 Ion Implantation. . . . . . . . . . . . . . . . . . . . . . . . . . . 32
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
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