Differences of interface and bulk transport properties

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1、OrganicElectronics7(2006)276–286www.elsevier.com/locate/orgelDifferencesofinterfaceandbulktransportpropertiesinpolymerfield-effectdevicesS.Grecu,M.Roggenbuck,A.Opitz,W.Bru¨tting*ExperimentalphysikIV,Universita¨tAugsburg,86135Augsburg,GermanyReceived8July2005;receivedi

2、nrevisedform23February2006;accepted15March2006Availableonline18April2006AbstractTheinfluenceofsubstratetreatmentwithself-assembledmonolayersandthermalannealingwasanalysedbyelectricalandstructuralmeasurementsonfield-effecttransistors(FETs)andmetal–insulator–semiconduct

3、or(MIS)diodesusingpoly(3-hexylthiophene)(P3HT)asasemiconductingpolymerandSi/SiO2wafersasasubstrate.Itisfoundthatsurfacetreatmentusingsilanisingagentslikehexamethyldisilazane(HMDS)andoctadecyltrichlorosi-lane(OTS)canincreasethefield-effectmobilitybyuptoafactorof50,rea

4、chingvaluesinsaturationofmorethan224·10cm/Vsatroomtemperature.Whilethereisaclearcorrelationbetweentheobtainedfield-effectmobilityandthecontactangleofwateronthetreatedsubstrates,X-raydiffractionandcapacitancemeasurementsonMISdiodesshowthatstructuralandelectricalproper

5、tiesinthebulkoftheP3HTfilmsarenotinfluencedbythesurfacetreatment.Ontheotherhand,thermalannealingisfoundtocauseanincreaseofgrainsize,bulkrelaxationfrequencyandtherebyofthemobilityperpendiculartotheSiO2/P3HTinterface,buthasverylittleinfluenceonthefield-effectmobility.Temp

6、eraturedependentinvestigationsonMISdiodesandFETsshowthatthetransportperpendiculartothesubstrateplaneisther-mallyactivatedandcanbedescribedbyhoppinginaGaussiandensityofstates,whereasthefield-effectmobilityinthesubstrateplaneisalmosttemperatureindependentoverawiderange

7、.Thus,ourinvestigationsrevealsignificantdifferencesbetweeninterfaceandbulktransportpropertiesinpolymerfield-effectdevices.Ó2006ElsevierB.V.Allrightsreserved.PACS:61.41.+e;61.10.Eq;72.80.Le;73.61.Ph;82.35.GhKeywords:Organictransistor;MISdiode;Self-assembledmonolayer;Pol

8、ythiophene;P3HT1.Introductionincombinationwithlow-costsolutionprocessingmakethemattractivecandidatesforthefabricationInrecentyearsconjugatedpolym