Tunablebandgapinfew-layergraphenebysurfaceadsorption

SUBJECTAREAS:

ELECTRONICDEVICES

ELECTRONICPROPERTIESAND

MATERIALSTWO-DIMENSIONALMATERIALSELECTRONICPROPERTIESAND

DEVICES

RugeQuhe1,2*,JianhuaMa3*,ZeshengZeng1,KechaoTang1,JiaxinZheng1,2,YangyangWang1,ZeyuanNi1,LuWang4,ZhengxiangGao1,JunjieShi1&JingLu1

1

StateKeyLaboratoryofMesoscopicPhysicsandDepartmentofPhysics,PekingUniversity,Beijing100871,P.R.China,2AcademyforAdvancedInterdisciplinaryStudies,PekingUniversity,Beijing100871,P.R.China,3SchoolofPhysicsandNuclearEnergyEngineering,BeihangUniversity,Beijing100191,P.R.China,4DepartmentofPhysics,UniversityofNebraskaatOmaha,Omaha,Nebraska68182-0266.

Received7March2013Accepted17April2013Published7May2013

ThereisatunablebandgapinABC-stackedfew-layergraphene(FLG)viaapplyingaverticalelectricfield,buttheoperationofFLG-basedfieldeffecttransistor(FET)requirestwogatestocreateabandgapandtunechannel’sconductanceindividually.Usingfirstprinciplecalculations,weproposeanalternativeschemetoopenabandgapinABC-stackedFLGnamelyviasingle-sideadsorption.Thebandgapisgenerally

proportionaltothechargetransferdensity.Thecapabilitytoopenabandgapofmetaladsorptiondecreasesinthisorder:K/Al.Cu/Ag/Au.Pt.Moreover,wefindthateventhebandgapofABA-stackedFLGcanbeopenedifthebondsymmetryisbroken.Finally,asingle-gatedFETbasedonCu-adsorbedABC-stackedtrilayergrapheneissimulated.Acleartransmissiongapisobserved,whichiscomparablewiththebandgap.Thisrendersmetal-adsorbedFLGapromisingchannelinasingle-gatedFETdevice.

CorrespondenceandrequestsformaterialsshouldbeaddressedtoJ.L.(jinglu@pku.edu.

cn)

O

*Theseauthorscontributedequallyto

thiswork.

peningatunablebandgapingraphenewithoutdegradingitshighcarriermobilityiscrucialforitsutilizationinnanoelectronics1.Sofar,therearetwofeasibleschemesthatcanreachthisgoalforbilayergraphene.Oneistheapplicationofanexternalelectricfieldtodestroytheinversionsymmetryofbilayer

graphene2–10.Boththeoretical6,7,9,10andexperimental2researchdemonstratedthatavariablebandgapupto0.25eVcanbeengineeredinbilayergraphene(BLG)byapplyingaperpendicularelectricfieldtobreaktheinversionsymmetryofBLG.ThisbandgapenablesthefabricationofaneffectivebilayergrapheneFETwiththecurrenton/offratioof100and2000atroomtemperatureand20K,respectively11.Themaindrawbackofthisschemeistherequirementoftwoindividualgatestocontrolthebandgapsandvarythechargecarrierconcen-trationsimultaneously.Fromatechnicalpointofview,itisdesirabletocontrolatransistor’sconductancebyonlyonegate.Analternativeschemeisusingsingle-sideadsorptiontobreaktheinversionsymmetryofBLG.Single-sideadsorptionwithmetalatomssuchaspotassium12,13andaluminum14ormoleculessuchaswater15,oxgen16,benzylviologen16,tetracyanoquinodimethane(TCNQ)17,18,tetrafluoro-tetracyanoquinodimethan(F4-TCNQ)19,decamethylcobaltocene20,and3,6-difluoro-2,5,7,7,8,8-hexacyano-quinodimethane(F2-HCNQ)20isfoundtoopenabandgapofBLG,andthisbandgapistunablebychangingtheadsorbatecoverage.Basedonthesurfaceadsorptionscheme,single-gatedBLG-basedFETshavebeenfabricated13,15,16,19,withanimprovedcurrenton/offratioupto45atroomtemperature14.

WiththeprogressinBLG,moreandmoreattentionisturnedtofew-layergraphene(FLG).TheoreticalstudyshowedthataverticalelectricfieldcanalsoopenatunablebandgapcomparabletobilayergrapheneinABC-stackedFLG21–23butfailinABA-stackedFLG21,23.Suchanelectricallytunablebandgaphasbeenrecentlyobserved24–30.ThenaturalnextstepshouldbeexplorationofthepossibilitywhetheradsorbatedopingisabletoopenabandgapinFLGandfabricationofasingle-gatedFLG-basedFETifitcan.Inthisarticle,wepresentthefirstsystematictheoreticalinvestigationoftheeffectsofsingle-sideadsorptionofmetalatoms(includingK,Al,Cu,Au,Ag,andPt)ontheelectronicstructureofABC-stackedFLG.AbandgapisopenedinthemostcasesasaresultofthebreakofinversionsymmetryinABC-stackedFLG,anditssizeistunablebychangingthedopantconcentrationandspecies.Surprisingly,eventhebandgapofABA-stackedFLGcanbeopenedifthebondsymmetryisbrokenbysurfaceadsorption.Finally,wesimulateasingle-gatedCu-adsorbedABC-stackedtrilayerFETbyusingabinitioquantumtransportcalculationandverifytheexistenceofatransportgapinthisdevice.Therefore,FLGwithsurfaceadsorptioncanserveasthechannelofasingle-gatedFET.