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1、EE143F05Lecture3ElectricalResistanceVI_+WtMaterialwithresistivityρLVLResistanceR≡=ρ(Unit:ohms)IWtwhereρistheelectricalresistivityProfessorNCheung,U.C.Berkeley1EE143F05Lecture3ResistivityRangeofMaterialsAddingparts/billiontoparts/thousandof“dopants”topureSi
2、canchangeresistivityby8ordersofSiwithdopantsmagnitude!SiO2,Si3N4ProfessorNCheung,U.C.Berkeley1Ω-m=100Ω-cm2EE143F05Lecture3TheSiAtomTheSiCrystal“diamond”structureHigh-performancesemiconductordevicesrequiredefect-freecrystalsProfessorNCheung,U.C.Berkeley3EE1
3、43F05Lecture3CarrierConcentrationsofIntrinsic(undoped)SiBottomofelectron-conductionbandEnergygap=1.12eVhole+Topofvalencebandn(electronconc)=p(holeconc)=niProfessorNCheung,U.C.Berkeley4EE143F05Lecture3PurityofDevicePurityofDevice--GradeGradeSiSiwaferwafer99
4、.999999999%(so99.999999999%(so--called“elevennines”)!!called“elevennines”)!!MaximumimpurityallowedisequivalenttoMaximumimpurityallowedisequivalentto1mgofsugardissolvedinanOlympic-sizeswimmingpool1mgofsugardissolvedinanOlympic-sizeswimmingpool..ProfessorNCh
5、eung,U.C.Berkeley5EE143F05Lecture3DopantsinSiBysubstitutingaSiatomwithaspecialimpurityatom(ColumnVorColumnIIIelement),aconductionelectronorholeiscreated.Donors:P,As,SbAcceptors:B,Al,Ga,InProfessorNCheung,U.C.Berkeley6EE143F05Lecture3EnergyBandDescriptionof
6、ElectronsandHolesContributedbyDonorsandAcceptorsE=bottomofconductionbandCAtroomtemperature,E=topofvalencebandVthedopantsofinterestE=DonorenergylevelDareessentiallyfullyionizedE=AcceptorenergylevelADonorsAcceptorsProfessorNCheung,U.C.Berkeley7EE143F05Lectur
7、e3Semiconductorwithbothacceptorsanddonorshas4kindsofchargecarriersHoleMobile;theycontributetocurrentflowElectronwithelectricfieldisapplied.Immobile;theyDONOTIonizedDonorcontributetocurrentflowwithelectricfieldisapplied.However,theyaffecttheIonizedlocalelec
8、tricfieldAcceptorProfessorNCheung,U.C.Berkeley8EE143F05Lecture3ValidforhomogeneouslydopedChargeNeutralityConditionsemiconductoratthermalequilibriumEvenNAisnotequaltoND,microscopicvolumesurroundinganypositionx
