半导体界面的能带弯曲

BandBendinginSemiconductors:ChemicalandPhysicalConsequencesatSurfacesandInterfacesZhenZhangandJohnT.Yates,Jr.*DepartmentofChemistry,UniversityofVirginia,Charlottesville,Virginia22904,UnitedStatesCONTENTS1.Introduction55201.1.BandBending55211.1.1.Metal/SemiconductorContactInducedBandBending55211.1.2.Field-Effect-InducedBandBending55221.1.3.Surface-State-InducedBandBending55221.1.4.Adsorption-InducedBandBending55231.2.SpaceChargeRegion55231.2.1.InfiniteMetal/SemiconductorInterface55241.2.2.FiniteMetal/SemiconductorInterface55251.3.ApplicationsoftheBandBendingConcepts55251.3.1.IonDiffusioninMetalOxides55251.3.2.ChemicurrentMeasurements55262.MeasurementsofBandBendingatSemiconduc-torSurfaces55272.1.PhotoelectronSpectroscopy(PES)55272.2.Photoluminescence(PL)Spectroscopy55272.3.SurfacePhotovoltage(SPV)Measurements55292.4.ScanningProbeMicroscopy(SPM)andRelatedMethodsforBandBendingMeas-urements55312.4.1.STMandSTS55312.4.2.LocalBarrierHeight(LBH)Measurement55322.4.3.BallisticElectronEmissionMicroscopy(BEEM)55322.5.O2PhotostimulatedDesorption(PSD)andElectron-StimulatedDesorption(ESD)55332.6.OtherMeasurementMethods55343.EffectsofBandBendingonPhotochemistryProcesses55353.1.OverviewofBandBendingEffectsonPhotochemistry55353.1.1.BandBendingandMolecularAdsorp-tionorDesorption55353.1.2.BandBendingandPhotoexcitedChargeCarrierTransferandRecombination55363.2.ParticleSize-InducedBandBendingandPhotochemistry55373.3.ExternalElectricFieldInducedBandBend-ingandPhotochemistry55393.4.SurfaceStructure-InducedBandBendingandPhotochemistry55403.4.1.SurfaceReconstruction55403.4.2.CrystallographicSurfaceOrientation55403.5.Gas-Adsorption-InducedBandBendingandPhotochemistry55413.5.1.DualRolesofO2inCOOxidation55423.6.Metal/SemiconductorBandBendingandPhotochemistry55423.6.1.EnhancementofElectron−HoleSepara-tioninSemiconductors55423.6.2.EnhancementofElectron−HoleSepara-tioninMetals55453.7.Semiconductor/SemiconductorBandBend-ingandPhotochemistry55463.8.BandBendinginaRealPhotocatalyticSystem55474.Summary5547AuthorInformation5547CorrespondingAuthor5547Notes5547Biographies5548Acknowledgments5548References55481.INTRODUCTIONThisistheagewherethecaptureofsolarenergyforusefulpurposeshasgainedtheattentionofthescientificandengineeringworld.Theuseofsolarenergyforthegenerationofelectricity,coupledwithitspotentialtoproducefuelsfromCO2wasteandH2Obysolar-inducedphotochemistry,isagoalbeingpursuedworldwide.Theoptimizationofchargetransferprocessesatsemiconductorsurfacesbymanipulationoftheenergybandsisthereforeathemeofbroadgeneralityandcurrentapplicability.1Thefieldsofheterogeneousphotocatalysisandphoto-chemistryhavedevelopedextensivelyinthepast40yearsinresponsetochallengingenergyandenvironmentalissues.2−12Inphotocatalysisorphotochemistryonsurfaces,photonabsorptionisaccompaniedbyelectronicexcitationinthesubstrateorintheadsorbedmoleculesaccompaniedbyeitherchargeorenergytransfer;6,11inheterogeneouscatalysis,chargetransfercanoccurindependentlyofanyphotonexcitation.Inphotocatalysis,thephotogeneratedchargecarriertransferprocessbetweensurfaceandadsorbedmoleculesconstitutesaReceived:February15,2012Published:July11,2012Reviewpubs.acs.org/CR©2012AmericanChemicalSociety5520dx.doi.org/10.1021/cr3000626|Chem.Rev.2012,112,5520−5551complexandfundamentalstepinchemicalprocessesinducedbytheabsorptionoflight.Thereareover1000reviewpapersdealingwiththetopicof“photocatalysis”or“photochemistry”.Mostofthereviewpapersareconcentratedonsomespecificarea,suchasaspecificphotochemical/photocatalyticprocess(e.g.,photo-dissociationofH2O;photochemistryandenvironmentalremediation),photocatalystpreparationormodification,orfabricationofphotovoltaicdevices.Onlyrarelydoreviewpapersattempttoilluminatethegeneralmechanismsthatplayimportantrolesinheterogeneousphotocatalysisorphoto-chemicalprocessesatsurfaces.Inthisreview,wefocusontheprinciplesofbandbendinganditseffectonphotochemistryandphotocatalysis.Thismaybehelpfultochemistsandmaterialscientistsintheunder-standingofthephotoexcitationprocessandthedevelopmentofhighlyefficientphotoactivematerialsandprocesses.Thereviewisdividedintothreepartsdealingwith(1)thephysicalprinciplesofbandbendinginsemiconductors,(2)themeasurementofbandbending,and(3)theeffectsofbandbendingonphotochemistry.Thebandbendingconceptisofcoursewellestablishedinsemiconductorphysics13,14andhasbecomeoneofthecentralconceptsinelectrochemistry15−17andgassensors.18,19AsshowninFigure1,untilnow,therehavebeen∼10000paperswiththetopicwords“bandbending”or“Schottkybarrier”,butmostofthepapersareinthefieldofsolidstatephysics,andonly25papersarefoundwiththewords“bandbending”togetherwith“photochemistry”or“photo-catalysis”.1.1.BandBending1.1.1.Metal/SemiconductorContactInducedBandBending.ThebandbendingconceptwasfirstdevelopedbySchottkyandMotttoexplaintherectifyingeffectofmetal−semiconductorcontacts.20−23Figure2showstheidealenergybanddiagramsofmetalandn-typesemiconductorcontacts.Whenthemetalandsemiconductorareincontact,thefreeelectronswilltransferbetweenmetalandsemiconductorduetotheworkfunctiondifference.Ifthemetalworkfunction(ϕm