Table Of Content

David S. Ginley Editor Hideo Hosono David C. Paine l Associate Editors Handbook of Transparent Conductors Editor Dr.DavidS.Ginley NREL Photovoltaics&ElectronicMaterials Center&BasicSciencesCtr. ColeBlvd.1617 80401-3393GoldenColorado USA [email protected] AssociateEditors Dr.HideoHosono Prof.DavidC.Paine TokyoInstituteofTechnology BrownUniversity Materials&StructuresLab. DivisionEngineering Nagatsuta4259 610Barus&Holley 226-8503Yokohama HopeStreet182 Midori-ku 02912ProvidenceRhodeIsland Japan USA [email protected] [email protected] ISBN978-1-4419-1637-2 e-ISBN978-1-4419-1638-9 DOI10.1007/978-1-4419-1638-9 SpringerNewYorkHeidelbergDordrechtLondon LibraryofCongressControlNumber:2010935196 #SpringerScienceþBusinessMedia,LLC2010 Allrightsreserved.Thisworkmaynotbetranslatedorcopiedinwholeorinpartwithoutthewritten permissionofthepublisher(SpringerScience+BusinessMedia,LLC,233SpringStreet,NewYork,NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software,orbysimilarordissimilarmethodologynowknownorhereafterdevelopedisforbidden. Theuseinthispublicationoftradenames,trademarks,servicemarks,andsimilarterms,eveniftheyare notidentifiedassuch,isnottobetakenasanexpressionofopinionastowhetherornottheyaresubject toproprietaryrights. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface TransparentConductingOxides(TCOs)areauniqueclassofmaterialsthatexhibit both transparency and electronic conductivity simultaneously. These materials havefoundwidespreaduseindisplays,photovoltaics,low-ewindows,andflexible electronics.Inmanyoftheseapplications,theTCO’s,areenablingintheirroleas transparent contacts. However,increasingly, the demands required extend beyond the combination of conductivity and transparency, where indeed higher performance is needed, but now include work function, morphology, processing and patterningrequirements, long term stability, lower cost and elemental abundance/ green materials. As these needs have begun to emerge over the last 5 years they havestimulatedadramaticresurgenceofresearchinthefieldleadingtomanynew materials and processes. Overall it is the purpose of this book to provide both a snapshotofthenewandenablingworkinthefieldandtoprovidesomeindications of what might be coming next. We note that now the field of Transparent Con- ductors (TC’s) includes not only conventional TCOs but also metal and carbon nano-composites, grapheme and polymer based TC materials. While the book primarilyfocusesontheTCOssomecomparisonsaremadetothenewermaterials. Todothiswehaveassembledagroupofauthorsrepresentingmostoftheleading groupsinthefield. Historically,TCOswerelimitedprimarilytotinoxidewithfluorinedoping,zinc oxide with aluminum doping and Indium tin oxide. Over the past 5–10 years the fieldhasexplodedtoincludeavastlyincreasednumberofn-typematerialsandto add in a class of new p-type materials. In addition, the historically held view that crystallinematerialshavesuperiorproperties,hasbeenchallengedbyanemergence of new amorphous TCOs that have properties as good as or better than their crystallinecounterparts.Thesematerialshaveledtothedevelopmentofamorphous oxidetransistorswhichoffertheadvantageoflowtemperatureprocessingandthe promise of flexible electronics on polymer substrates. In their role as a channel material in thin film transistor structures, TCO’s with controlled carrier densities areoftentermedtransparentoxidesemiconductors(TOS)sincetheirkeyproperties v vi Preface may lie in the limited to non-conductive regime. To capture this diversity of materials,processingandapplications,wehaveorganizedthebookasfollows. Chapter1introducesTCOsandcoversthehistoricmaterialsandtheirproperties and uses this background to put some of the newly emergent materials into a technologicalcontext.Chapter2presentsadetaileddiscussionofthebasicelectronic structures ofTCO materials emphasizing thekeyproperties whichgive them their uniqueproperties.Chapter3thenprovidesanoverviewofmethodsforthemeasure- ment andinterpretation of transport properties in TCOs based of the Drude model with a focus on the method of four coefficients for the determination of critical parameters such as carrier type, mobility and scattering mechanisms in multinary oxides.Chapter4coversthebasicphysicsof,andpracticaltoolsfor,thecharacteri- zationofimportantTCOparametersincludingatomicstructure,opticalproperties, electricaltransport,workfunctionandotherpropertiesthatmustbebetterunderstood asTCO’sbecomeusedinnovelapplicationssuchasthinfilmtransistors.Chapter5 presentsapictureofthecurrentInbasedTCOscoveringboththetraditionalInSnO x materialswhichhavebeenthegoldstandardofTCOsandtheemergingamorphous materials. Chapter 6 presents an overview of the tin oxide based TCO materials. While historically thesematerialshavebeen producedinexceptionallylargeareas newworkhasbeguntoimprovetheirproperties.Chapter7reviewsthestateoftheart forZnO.Thismaterial,duetoitsnaturalabundanceandtheeasewithwhichitcanbe depositedviabothphysicalandchemicalroutes,hasimportantapplicationsbothasa traditional transparent contact and great potential as an active optoelectronic material. To realize this potential, a great deal of work has been done to identify newapproachestobothnandp-typedoping.Chapter8looksattherapidlyexpand- ing class of multi-cation TCO materials. Recent work shows that much higher performance can be achieved in some TCO materials by the addition of elements thatservetomodifydefectandelectronicbandstructure.Thisabilitytocreatemulti- componentTCOmaterialswithoutsignificantlydegradingkeytransportparameters (e.g., carrier mobility) is a characteristic of the TCO class of materials. Chapter 9 looksatthetheoreticalframeworkusedtodescribethebandstructuresofbothn-and p-type oxide materials and includes a discussion of emerging non-oxide based transparent conductors. This fundamental backgroundprovides the basis for a discussion on considerations for the discovery of new high performance transparent conductingmaterials.Chapter10considersnewmaterialsthathaveemergedinthe transparentconductorfieldoverthelastfewyears.Historically,thesetofelements whose oxides provide useful TCO properties have been constrained to single or mixed oxides of In, Ga, Zn, Sn, and Cd. This chapter discusses how the pallet of useful elements for TCO applications has grown to open whole new classes ofmaterials. ThesecondhalfofthebookbeginstoaddresstheapplicationsofTCOsandhow new materials can significantly change the paradigm for a technology or be enabling for another. Chapter 11 discusses the application of TCO materials for solar energy and energy efficiency applications. In fact, though a key focus is the active devices like PV, the reality is that in terms of energy efficiency, the use of TCO’s in energy conservation applications are greater in the near term than Preface vii production. In any case it needs to be looked in an integrated way which is the themeofthechapter.Chapter12considerstheideathatTCOsneednotbeplanar films but that in many cases the films can be enabling or integrated into a more complexhybrid(organic/inorganicforexample)devicebyhavingananostructured morphology. Enabling this is a broad set of solution and PVD approaches to creating controlled nanostructures in TCO materials from texture to nano-rods etc. Chapter 13 explores the application of amorphous TCOs and their semicon- ducting/insulatingTOScounterpartstodevelop newflexibleandtransparentelec- tronics for displays and more. The demonstration of TOS materials as a channel materials in thin film transistor applications has dramatically altered the potential for amorphous oxides in an increasingly diverse set of technologies. Chapter 14 considers the potential for makingtrue oxide based p/njunctions torealizeactive devices that are entirely based on TCO/TOS materials. The ability to make such junctions expands the potential for oxide based electronics including transparent electronics,oxidebasedsolarcellsandLED/lasers.Finally,Chap.15discussesthe scalingofTCOmaterialstolargeareaindustrialprocessing.Thisisakeyissueasit addressessomeofthecriticalpropertiesdependenceonprocessparameters. We note that there is increasing interest in solution processed transparent conductors consisting of nanostructures of carbon (nanotubes), oxides (nanorods i.e., ZnO)andmetals(suchasAgnanorods).However,thusfaralthoughtheyarevery interesting, these materials still have conductivities approximately an order of magnitude below those for high performance TCOs. Over the next few years we expectthesematerialswillbecomeincreasinglyimportantperhapsincombination withTCOmaterials.Theirinclusioninthisvolumeatpresentis,however,beyond theintendedscopeofthispublication. Thisbookpresentsapictureofanimportantclassofmaterialsthathas,inrecent years, drawn increasinginterestforapplicationsinactivedevices andasacritical component in any structure that requires both electrical connectivity and optical transparency.Despitetheirtechnologicalimportanceandrelativelylonghistoryof use,ourunderstandingoftheexistingsetofTCOmaterialsareonlynowreceiving the kind of combined fundamental/experimental materials research attention that willinevitablyleadtonewmaterialsdiscoveriesandnovelapplications.Overall,it isclearthattransparentconductiveoxidesandtransparentconductorsareavibrant fieldthatisadvancingrapidlyacrossaneverbroadeningspectrumofapplications. Wehopethisbookwillprovideavaluablereference forthoseinterestedinthe topic and stimulate additional development of new TCO materials and their applications. DavidGinley(Editor) HideoHosonoandDavidPaine (AssociateEditors) . Contents 1 TransparentConductors ................................................. 1 DavidS.GinleyandJohnD.Perkins 2 ElectronicStructureofTransparentConductingOxides ............ 27 J.RobertsonandB.Falabretti 3 Modeling,Characterization,andPropertiesofTransparent ConductingOxides ....................................................... 51 TimothyJ.Coutts,DavidL.Young,andTimothyA.Gessert 4 CharacterizationofTCOMaterials ................................... 111 DavidC.Paine,BuragYaglioglu,andJosephBerry 5 InBasedTCOs .......................................................... 149 YuzoShigesato 6 TransparentConductingOxidesBasedonTinOxide ............... 171 RobertKykyneshi,JinZeng,andDavidP.Cann 7 TransparentConductiveZincOxideandItsDerivatives ............ 193 KlausEllmer 8 TernaryandMultinaryMaterials:Crystal/Defect Structure–PropertyRelationships ..................................... 265 ThomasO.Mason,StevenP.Harvey,andKennethR.Poeppelmeier 9 ChemistryofBandStructureEngineering ........................... 295 ArtSleight ix x Contents 10 Non-conventionalMaterials ............................................ 313 HideoHosono 11 ApplicationsofTransparentConductorstoSolarEnergy andEnergyEfficiency .................................................. 353 ClaesG.Granqvist 12 NanostructuredTCOs(ZnO,TiO ,andBeyond) .................... 425 2 DanaC.OlsonandDavidS.Ginley 13 TransparentAmorphousOxideSemiconductorsforFlexible Electronics ............................................................... 459 HideoHosono 14 Junctions ................................................................. 489 HiromichiOhta 15 ProcessTechnologyandIndustrialProcesses ........................ 507 MamoruMizuhashi Index .......................................................................... 527 Contributors Joseph Berry National Renewable Energy Laboratory, Mail-stop 3211, 1617 ColeBlvd,Golden,CO80401,USA David P. Cann Associate Professor of Materials Science, Department of MechanicalEngineering,303DDearbornHall,OregonStateUniversity,Corvallis, OR97331,USA,[email protected] Dr. Timoth J. Coutts Research Fellow Emertus, National Renewable Energy Laboratory,1617ColeBlvd.Golden,CO80401,USA Dr. Klaus Ellmer Dept. solar fuels, Helmholtz-Zentrum fu¨r Materialien und Energie Berlin GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, Germany, ellmer@ helmholtz-berlin.de BarbaraFalabretti DepartmentofEngineering,UniversityofCambridge,Trum- pingtonStreet,Cambridge,CB21PZ,UK,[email protected] Dr.TimothA.GessertGroupManager ThinFilmPhotovoltaics,NRELNational Center For Photovoltaics, 1617 Cole Blvd, Golden, CO 80401, USA, Tim. [email protected] David S. Ginley Research Fellow Group Manager Process Technology and AdvancedConcepts,NRELSERFW102,15313DenverWestPkwy,Golden,CO 80401,USA,[email protected] Claes G. Granqvist Professor Solid State Physics, Department of Engineering Sciences, The Angstrom Laboratory Uppsala University, Uppsala, SE-75121, Sweden,[email protected] Steven P. Harvey Institute of Physical Chemistry, RWTH Aachen University, Landoltweg2,AachenD-52056,Germany xi