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首页 ZnO CVD 笔记_肖锋伟

ZnO CVD 笔记_肖锋伟.PPT

ZnO CVD 笔记_肖锋伟

xiao_20141220
2012-08-26 0人阅读 举报 0 0 暂无简介

简介:本文档为《ZnO CVD 笔记_肖锋伟ppt》,可适用于工程科技领域

ZnO笔记摘抄肖锋伟看了两本书和大家共享欢迎您的完善!InfluenceofSubstrateTemperatureDEZ流量对ZnO薄膜的影响HO流量对ZnO薄膜的影响薄膜厚度对ZnO薄膜的影响气压对ZnO薄膜的影响B掺杂对ZnO薄膜的影响LPCVDZnO:BfilmBAl共掺杂对ZnO薄膜的影响退火对ZnO薄膜的影响两步法生长ZnO薄膜ZnO背电极ZnOIntermediatereflectorZnO薄膜的表面处理柔性衬底上的ZnO薄膜ZnO薄膜常见缺陷能级谱ZnODegradationDegradationEffectsDegradationeffectswithtimeoftheZnO:BfilmsItisthesamesamplethatwasmeasuredforsheetresistanceafterdifferenttime(~days)Source:XLChenetalThinSolidFilms()–BoronatomsubstitutestheZnatomduringthemigrationgrowthofZnO:Bfilm,whichdecreasethenumberofthedanglingbonds(fromZnandassociatedoxygenvacancies)andstrainedbondsatthegrainboundariesBoronobstructsthediffusionofoxygenintothegrainboundariesandtherebyZnO:BthinfilmsshownodegradationeffectsafterlongtermexposuretoairFrontContactDepositionSolutionoftheTCOPInterfaceContactinaSi:HSolarCellsSystematically,highervaluesofphotogeneratedcurrentintheaSi:HsolarcellhavebeenobtainedforCVDZnOfrontTCOHowever,lowervaluesofFFandVocweremeasuredinthosecases,thisbeingattributedtothedegradationoftheCVDZnOplayerinterfaceDesorptionofHOfromLPCVDZnO:BdepositedatlowtemperatureduringthesubsequentgrowthoftheamorphoussiliconlayercoulddamagetheZnOplayerinterfaceFrontContactDepositionAnnealingProcesspriortoplayerdepositionPostplasmatreatmentGermaniumlayertoblockimpurityincorporationstepgrowthtechniqueHighlyntypedopedμcSi:HbufferlayerbetweenTCOplayerInterfaceKeytosuccessKKKKKKnmnmnm衬底温度对ZnO薄膜的影响衬底温度对ZnO薄膜的影响表面自由能:()()()()()晶面:Jm()晶面:Jm()晶面:Jm衬底温度与ZnO薄膜的生长速率的关系随着衬底温度的增加DEZ的有效裂解增多与HO的反应速率加快加之沉积表面原子的迁移能增加表面扩散加剧。衬底温度对ZnO薄膜的影响衬底温度对ZnO薄膜的影响电学特性在整个温度区间当衬底温度为K时载流子浓度和迁移率达到最大值分别为×cm和cmVs温度较低(K)时大的晶粒有效减少晶界散射在较高温度(K)时电阻开始变大可能原因是相对不够致密的薄膜结构引起。光学特性衬底温度对ZnO薄膜的影响K衬底温度生长的ZnO薄膜特性较好温度改变对薄膜结构特性起主要作用厚度影响次之。InfluenceofSubstrateTemperatureIntheCVDprocess,thesubstratetemperatureisakeyparameter:GrowthRateAPCVDZnO:diffusionlimitedprocessesthetimeforthetransportofthereactantstothegrowingsurfaceisthemainlimitingfactorthegrowthrateshouldbealmostindependentofsubstratetemperaturebelow◦C,butnotforhighertemperaturesThegeometricalconfigurationofthedepositionsystemThetemperatureofthegrowingsurfaceTwodeterminants:growthrates:∼–˚As−–˚As−arapidincreaseofthegrowthratewhentheyreducedDintheirverticalreactorButreducingthedistancebetweenthegasinletandthesubstratewillhaveanadverseeffectontheuniformityHorizontalreactorvsVerticalreactorLPCVDZnO:kineticslimitedprocessesthegrowthrateofthefilmdependsmainlyontherateofreactionsatthegrowingsurfaceAsthespeedofthereactionsatthegrowingsurfaceisincreasedwhenthetemperatureisraisedafunctionofthesubstratetemperaturefortheLPCVDprocessdevelopedatmbarandusesDEZandwatervaporsasgrowthprecursorsfromlessthan˚As−at◦Ctomorethan˚As−at◦CVariationofStructuralPropertieswithSubstrateTemperatureAPCVDZnOfilmsgrownatdifferentsubstratetemperatures(a)◦C,(b)◦C,(c)◦C,(d)◦CAPCVDZnOfilmsgrownatdifferentsubstratetemperaturesLPCVDZnO,similarvariationsinthestructuralpropertiesofZnOfilmsoccurwithanincreaseofsubstratetemperature,butthistakesplaceatalowertemperature,ie,around◦C,andwithdifferentcrystallographicorientationsundopedLPCVDZnOfilmsLPCVDZnOfilmsgrownatdifferentsubstratetemperaturesVariationofElectricalPropertieswithSubstrateTemperatureAPCVDZnO:(a)eitheranincreaseoftheconductivitywhenthetemperatureisincreasedupto∼◦C,or(b),anincreasefollowedbyadecrease,leadingtoamaximumvalueofconductivityThelatterisoftenobservedaround−◦CPhenomenonthereasonstoexplainThesetwotrendsareinducedbyacorrespondingvariationofthecarrierdensityNNiscontinuouslyaugmentedwhenoneincreasesthetemperatureThiscanbeexplainedbyamoreefficientdopantincorporationathighersubstratetemperaturesHowever,insomecasesNhasalsobeenfoundtodecreasewhenthetemperaturewasincreased(eg,growthofAPCVDZnO:FusingDEZandethanolasreactants)Variationoftheelectronmobilityinfunctionofthegrainsizewhenthesizeofthegrainsisincreased,theelectronscatteringeffectbygrainboundariesisreduced,resultinggenerallyinhigherelectronmobilityµInsomecases,however,asaturationorevenadecreaseofµisobservedforhighertemperaturesInfact,ifNisaugmentedwithincreasingsubstratetemperature,thescatteringeffectbyionizedimpuritiesisalsoenhancedandthereforemayreduceµagainAPCVDZnOfilmsLPCVDZnO:theusuallyobservedincreaseofNwithincreasingsubstratetemperaturesuggestsalsoamoreefficientdopantincorporationathighertemperatureswhenthesubstratetemperatureisincreasedthetrendofµvstemperatureisstronglyrelatedtotheabruptmorphologicalchangesobservedaround◦CZnOfilmsarenolongerorientedalongasinglepreferentialdirection,theresistivitybecomesveryhighduetoasharpdropinµVariationsof(a)resistivityρ,(b)Hallmobilityµ,andgrainsizeδasafunctionofsubstratetemperaturefor∼µmthickundopedLPCVDZnOfilmsVariationofOpticalPropertieswithSubstrateTemperatureAPCVDZnO:Diffusetransmittance(DT)ofAPCVDZnO:FfilmsdepositedatvarioussubstratetemperaturesthelightscatteringcapabilityofAPCVDZnOfilmsisincreasedwithtemperatureThiscanbecorrelatedwiththeincreaseofthegrainsizewithtemperatureLPCVDZnO:TTdoesnotvarystronglywithsubstratetemperaturethevaluesofcarrierdensityNaretoolowtoproduceanobservablefreecarrierabsorptioneffectTotalanddiffusetransmittance(TTandDT)of∼μmthickundopedLPCVDZnOfilmsdepositedatvarioussubstratetemperatures温度对TT影响不大对DT影响很大DT在℃时最大。theoptimumconditionsforlightscatteringareobtainedatthesametemperature,forwhichtheoptimaforthemobilityμandfortheresistivityρareobtained,ie,atasubstratetemperaturejustabovethetemperatureneededforthemorphologicaltransitionSummary:OptimizedSubstrateTemperatureforAPCVDandLPCVDZnOFilmsForbothAPCVDandLPCVDprocesses,thehighestsubstratetemperaturewillleadtothehighestgrowthrateSometimes,inthecaseofAPCVDsystems,saturationwilloccuratahighertemperature,butthisdependsstronglyonthereactorconfigurationAPCVDLPCVDthebestelectricalpropertiesisbetweenand◦CcarrierdensityNandmobilityμarestillincreasedafter◦C,asaturationorevendecreaseofthesetwoparametersforT>◦Ctheoptimumtemperaturethatleadstothebestelectricalpropertiesislocatedjustafterthemorphologicaltransition,ie,around◦CInfact,belowandabovethistemperature,μisreducedduetoastrongerscatteringatgrainboundaries:thiseffectisinducedbygrainsizeandorbytheabsenceofpreferentialcrystallographicorientationwithinthefilmsInconclusion,forbothAPCVDandLPCVDprocesses,onlyanarrowrangeoftemperaturescanbeidentifiedforoptimumperformance(arangethatistypically◦Cwide)WithinthisnarrowtemperaturerangehighlyorientedfilmsareobtainedthathaveelectricalandopticalpropertiessuitabletoactastransparentconductorsinsolarcellsThetypicalsubstratetemperatureisaround◦CfortheAPCVDprocess,whereasitisaround◦CfortheLPCVDprocessThetwoprocessesyieldfilmorientationsthatareperpendiculartoeachotherDEZ流量对ZnO薄膜的影响sccmsccmsccmsccmsccmsccm通过减少DEZ流量可适当降低生长速率调制出()取向增强的微观结构随着DEZ流量的减少()峰的相对强度增大在DEZ流量为sccm时获得最大DEZ流量较大时(sccm、sccm)薄膜中夹杂有少量细小球状晶DEZ流量对ZnO薄膜的影响DEZ流量对ZnO薄膜的影响光学和电学特性不同DEZ流量下薄膜的透过率曲线DEZ流量对ZnO薄膜的影响光学和电学特性HO流量对ZnO薄膜的影响sccm光学和电学特性过多的水流量降低了ZnO薄膜中的氧空位从而导致电阻率的增大较少的水流量也会影响薄膜的微结构。HO流量对ZnO薄膜的影响光学和电学特性InfluenceofPrecursorFluxStoichiometryActually,thesituationthatprevailsinaCVDreactorismorecomplexintermediatereactionsstronglydependonthedepositionconditionsandalsoonthereactorconfigurationeg:atlowHODEZratiosisloweredbelow,theformationofotherspecieslikezinc–ethylgroupsorelementalzincoccurs,apoorertransparencyofthedepositedZnOfilmsOZnratioisbetweenand,InfluenceoftheHODEZRatiotheHODEZratiowasvariedfromto,ToobtainTCOlayerswithsufficientopticaltransparency,theHODEZratiohastobekepthigherthanGrowthrateindependenceofmetalorganicprecursorflow(DMZ)forAPCVDZnO:Ffilmsdepositedatasubstratetemperatureof◦CThesefilmsaredepositedfromDMZ,oxygen,andfluorocarbondopinggasGrowthrateinfunctionofmetal–organicprecursorflow(DEZ)forLPCVDZnO:Bfilmsdepositedat◦CandmbarStructuralPropertiesintheHODEZratioWhentheHODEZratioisvariedfromtoHowever,thesizeofthepyramidsisdecreasedThisisdocumentedbyacorrespondingdecreaseintheparameterδNdoesnotvarywhentheHODEZratioisincreasedTheobserveddecreaseinμwouldthereforebeinducedheresolelybyanincreaseingrainboundaryscatteringwhenthegrainsbecomesmallertokeeptheHODEZratiocloseto,inordertoobtainZnOfilmswiththehighestconductivityandwiththebestlightscatteringcapabilityHowever,ithasbeenalsoexperimentallyverifiedthatasmallexcessofDEZinthechemicalreactionimmediatelyleadstoadropinthetotaltransmissionoftheZnOlayersTobesurenottofallintothisregime,theHODEZratioshouldbesetslightlylargerthantheHODEZratiothemeanwidthofthecrystallitestheelectronmobilitythelightscatteringcapabilityVariationsof(a)resistivityρ,(b)Hallmobilityμ,andcarrierdensityNasafunctionoftheHODEZratio,forμmthickLPCVDZnO:Bfilmsdepositedat◦C,mbar,andBHDEZ=ElectricalPropertiesintheHODEZratioTheresistivityρincreasesbyaboutwithanincreaseintheHODEZratiofromtoThisincreaseismainlyduetothedecreaseofμ,whereasNremainsconstantatavaluearound×cm−Variationof(a)thetotalanddiffusetransmittancecurves(TTandDT),(b)thehazefactormeasuredatλ=nm(DTTTatnm),asafunctionoftheHODEZratio,forμmthickLPCVDZnO:Bfilmsdepositedat◦C,mbarandwithBHDEZ=OpticalPropertiesintheHODEZratioThereductionofTTintheNIRareaissimilarforallthecurvesThisindicatesthatfreecarrierabsorption,whichdependsonthefreecarrierdensityoftheZnOfilms,isnotchangedbyavariationoftheHODEZratioThisisinaccordancewiththebehaviorofthecarrierdensityNDopingofCVDZnOFilmsTheChoiceoftheDopingGasFromafundamentalortheoreticalpointofview,fluorinehasbeenidentifiedasanidealdopant,Because:※inhigherelectronmobilitiesthangroupIIImetals(B,Al,Ga,In),whicharecommonlyusedasdopantsforZnOfilms,thereislesselectronscatteringifthedopantatomssubstitutewithintheZnOlatticeforoxygenatomsratherthanforzincatomsThereasonsforthisareasfollows:ZnOisarelativelyionicsemiconductor,andtheconductionbandisderivedmainlyfromthezincorbitalsThus,perturbingthearrangementofzincatomswillalsocauseastronglocalperturbationtotheconductionbandThiswilllead,inturn,toastrongerelectronscatteringthatwillprovokeareductionofelectronmobilityAnotheradvantageofusingfluorineatoms:※Fluorineatomsarethosehalogenatomswhosesizeshowsthebestfittothesizeoftheoxygenatoms,※ThedeterioratingthequalityofthethinfilmsiliconlayersbyoutdiffusionofthedopantatomsfromtheZnOlayerintothesiliconlayerFromanexperimentalpointofviewIntheAPCVDprocess,highermobilityvaluesforZnO:Ffilms(∼cm(Vs)−)thanforZnO:Alfilms(∼cm(Vs)−),However,depositiontemperaturesbelow◦C,thefluorineinthefilmisnotactivated,leadingtomoreresistiveZnOfilmsThisreducesthepossibilitytoobtainahighdopingefficiencywithfluorineatomswhenusingtheLPCVDprocess,forwhichtypicaldepositiontemperaturesarearound◦CIndeed,themostpromisingresultsforthedopingofLPCVDZnOfilmsatrelativelylowtemperatureshavesofarbeenobtainedwithboronatoms,derivedfromthedecompositionofdiborane(Notethatdiboranedecomposesalreadyat∼◦C)Furthermore,ithastoberemarkedthat,whenboronatomsareusedasdopant,mobilityvaluesofuptocm(Vs)−havealsobeenobtainedThesevaluesarejustashighasthemobilityvaluesobtainedwithfluorinedopantsinthecaseofAPCVD薄膜厚度对ZnO薄膜的影响minminminminminminmin薄膜厚度对ZnO薄膜的影响掠角(θ=°)广角InfluenceofThicknessthegrainsizeincreaseswithfilmthicknessVariationintheStructuralPropertieswithFilmThicknessaμmthickLPCVDZnO:BfilmcoveredbyaμcSi:Hsolarcelldepositedat◦CandmbarLPCVDZnO:BfilmTherelationofthepyramid’structureInfluenceofThicknessLPCVDZnO:Bfilm薄膜厚度对ZnO薄膜的影响光学和电学特性Hall测试TTdecreasesandtheDTincreaseswiththicknessincrease薄膜厚度对ZnO薄膜的影响ThetotalscatteredlightintensitydependsontheroughnessofthefilmThelightscatteringanglesdependonthelateralsizeofthesurfacetexture薄膜厚度对ZnO薄膜的影响InfluenceofDepositionPressureAhighpressureregime,APCVD(atmosphericpressurechemicalvapordeposition)thepressure:×~PaThegrowthrateoftheZnOfilmincreaseswhenthepressureisreducedAlowpressureregime,LPCVDthepressurerangefromlessthanTorrtoaboutTorrThisprocessismorekineticslimitedthandiffusionlimitedTheAPCVDprocessismorediffusionlimitedthankineticslimitedanincreaseofthegrowthratewithchamberpressure(atleastwithinthepressurerangeof–Torr)TheupperpressurelimitoftheLowPressureregimeisestimatedaround–Torr,气压对ZnO薄膜的影响APCVDLPCVDTorrTorrTorrTorr以下TorrTheupperpressurelimitAPCVDandLPCVD气压对ZnO薄膜的影响thegrowthrateincreaseswithpressureuptoTorr,anddecreasesthereafterforhigherpressuresHowever,atlowerdepositiontemperature,thegrowthratestaysconstantforpressurehigherthanTorrThisisprobablybecause,inthisspecificcase,thesurfacereactionsarestillthelimitingfactor,evenathigherpressuresVariationofgrowthrateasafunctionofchamberpressureforZnO:BfilmsdepositedbyCVDusingDEZandHOasprecursorsandBHasdopinggasVariationofgrowthrateasafunctionofchamberpressure气压对ZnO薄膜的影响B掺杂对ZnO薄膜的影响K衬底温度下不同掺杂浓度的ZnO薄膜sccmsccmsccmsccmsccmK衬底温度下不同掺杂浓度的ZnO薄膜B掺杂对ZnO薄膜的影响sccmsccmsccmsccmsccmsccmsccmK衬底温度下不同掺杂浓度的ZnO薄膜B掺杂对ZnO薄膜的影响K衬底温度下不同掺杂浓度的ZnO薄膜sccmsccmsccmsccmsccmB掺杂对ZnO薄膜的影响B掺杂对ZnO薄膜的影响不同衬底温度不同掺杂浓度下的XRDB掺杂对ZnO薄膜的影响不同衬底温度不同掺杂浓度下的电学特性公式:ρ=nqµ载流子浓度随着B掺杂浓度的的增加而增加薄膜电阻随着B掺杂浓度的的增加而降低迁移率随着B掺杂浓度的的增加缓慢变化B掺杂对ZnO薄膜的影响B掺杂对ZnO薄膜的影响cm×cm面积的玻璃衬底沉积的ZnO:B(sccm)薄膜均匀性B掺杂对ZnO薄膜的影响未掺杂和B掺杂(sccm)ZnO薄膜的稳定性B掺杂的ZnO薄膜的方块电阻变化不大基本维持在~Ω而未掺杂的ZnO薄膜空气中放置天后方块电阻从~Ω增加到Ω然后趋于稳定B掺杂对ZnO薄膜的影响光学特性PL谱带边发光峰(nm)的增强说明B掺杂提高了ZnO薄膜的晶体质量。与O空位相关的缺陷发光峰(~nm)减弱说明B掺杂有效消除了部分O缺陷和悬挂键。B掺杂对ZnO薄膜的影响光学特性透射谱此处的下降根据Drude理论近红外区的吸收与载流子浓度有关因此在提高薄膜电导的同时尽可能减少TCO材料的近红外波段(NIRregion)的光学吸收这就需要追求高迁移率的TCO薄膜。InfluenceofThicknessthegrainsizeincreaseswithfilmthicknessVariationintheStructuralPropertieswithFilmThicknessaμmthickLPCVDZnO:BfilmcoveredbyaμcSi:Hsolarcelldepositedat◦CandmbarLPCVDZnO:BfilmTherelationofthepyramid’structureLPCVDZnO:BfilmInfluenceofThicknessVariationintheElectricalPropertieswithFilmThicknessLPCVDZnO:BfilmInfluenceofThicknessVariationintheOpticalPropertieswithFilmThicknesstheaveragevisibleabsorptionofZnOfilmsforsolarcellapplicationsaswhereΨ(λ)isthesolarirradiancespectrumforAM,andA(λ)isthewavelengthdependentabsorbanceoftheZnOfilmsobtainedfromreflectanceandtransmittancespectraanincreaseofAwithfilmthicknessforborondopedZnOInfluenceofThicknessLPCVDZnO:BfilmVariationoftheaveragevisibleabsorptionofAPCVDZnO:BfilmsasafunctionoffilmthicknessThefilmsweredepositedwithdifferenttimesat◦C,usingDEZandtertbutanolasprecursorsandBHasdopinggasVariationoftheaveragevisibleabsorptionofAPCVDZnO:BfilmsasafunctionoffilmthicknessLPCVDZnO:BfilmInfluenceofThicknessTotalanddiffusetransmittance(TTandDT)ofLPCVDZnO:Bfilmsgrownat◦Candmbar,infunctionoftheirthicknessdTotalanddiffusetransmittance(TTandDT)ofLPCVDLPCVDZnO:BfilmInfluenceofThicknessBAl共掺杂对ZnO薄膜的影响LPCVDBAl共掺杂对ZnO薄膜的影响BAl共掺杂对ZnO薄膜的影响LPCVDBAl共掺杂对ZnO薄膜的影响BAl共掺杂对ZnO薄膜的影响BAl共掺杂对ZnO薄膜的影响BAl共掺杂对ZnO薄膜的影响光学特性透射谱BAl共掺杂对ZnO薄膜的影响退火对ZnO薄膜的影响两步法生长ZnO薄膜ZnO背电极ZnOAg、ZnOAl、Ag、Al四种背反射电极比较对aSi在波长nm区域好的反射是重要的ZnOAg具有最好的效果Ag、ZnOAl具有相似的背反射效果。对µcSi在波长nm区域好的反射是重要的Ag比ZnOAl具有更高的QE和Jsc。Al在nm处发生带内吸收【Mullera】。ZnO背电极ZnOAg、ZnOAl、Ag、Al四种背反射电极比较ZnO背电极ZnOAg、ZnOAl、Ag、Al四种背反射电极比较ZnOIntermediatereflectorZnO薄膜的表面处理等离子体表面处理ZnO薄膜的表面处理MOCVDCHCOOH溶液表面处理HCl溶液腐蚀MOCVDZnO薄膜过于剧烈速度较快不易控制,容易损害薄膜特性。优化条件::sσrms=nm刻蚀对薄膜的电学和光学特性影响不大。柔性衬底上的ZnO薄膜KKKKMOCVD在PI衬底上沉积的未掺杂ZnO薄膜(t=min)MOCVDZnO薄膜在玻璃衬底上的沉积参数完全可以用于柔性衬底上。柔性衬底上的ZnO薄膜MOCVD在PI衬底上沉积的B掺杂ZnO薄膜沉积条件:衬底温度K沉积时间min厚度~nm薄膜特性:方块电阻~Ω□ZnO的各种成膜方法及优缺点比较:Sputter:湿法刻蚀技术(的HCl):Depositionprocesses:♦Sputtering♦Chemicalvapordeposition(CVD)highqualityTCOwitharesistivitydownto~ΩcmandavisibletransmittanceTT>DCRFmagnetronorreactivesputterAtmosphericpressure(APCVD)lowpressure(LPCVD)plasmaenhanced(PECVD)amoderatetemperatureprocess(℃℃largescaleproductioncapabilityhighgrowthrates♦Pulsedlaserdeposition(PLD)Alargevarietyofmaterials♦Spraypyrolysis♦Wettechnique(solutiondeposition)♦thermalevaporation♦molecularbeamepitaxyOthermethodsacompilationofmobilityandresistivitydataofdopedandundopedZnOfilmspreparedinthelastyearsasafunctionofthecarrierconcentrationbymagnetronsputtering(filledsquare,opensquare,opentriangledown),MOCVD(opendiamond)orpulsedlaserdeposition(opencircle)Thedashedlines(B)areatheoreticalestimationofthem

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