diodes二极管讲义-英文

Chapter3DiodesOutlineofChapter33.1Introduction3.2BasicSemiconductorConcepts3.3ThepnJunction3.4Analysisofdiodecircuits3.5Applicationsofdiodecircuits3.1Introduction•Thediodeisthesimplestandmostfundamentalnonlinearcircuitelement.•Justlikeresistor,ithastwoterminals.•Unlikeresistor,ithasanonlinearcurrent-voltagecharacteristics.•Itsuseinrectifiersisthemostcommonapplication.PhysicalStructureThemostimportantregion,whichiscalledpnjunction,istheboundarybetweenn-typeandp-typesemiconductor.pnjunctionSymbolandCharacteristicfortheIdealDiode(a)diodecircuitsymbol+v-iAnodeCathode(b)i–vcharacteristic---Reversebias------Forwardbias---i0v(c)equivalentcircuitinthereversedirectionv0i=0i+v-i(d)equivalentcircuitintheforwarddirectioni0v=0+v-Characteristics•ConductinginonedirectionandnotintheotheristheI-Vcharacteristicofthediode.•Thearrowlikecircuitsymbolshowsthedirectionofconductingcurrent.•Forwardbiasingvoltagemakesitturnon.•Reversebiasingvoltagemakesitturnoff.Howdoesithappen?•Toanswerthequestion,weneedtoknow:–Material,structureandtherelatedfeatures(crystalandsemiconductorinparticular)–Newparticlestocarrychargeinadditiontoelectrons–Newmechanism(s)ofconductioninadditiontowhatwehaveknown–Techniquestomanufacturethedevices(notincludedinthiscourse)3.2BasicSemiconductorConcepts•IntrinsicSemiconductor(本征半导体)•DopedSemiconductor(掺杂半导体)•Carriers(载流子)•Diffusion(扩散运动),Drift(漂移运动)Elementsandmaterial•PeriodictableElementsandmaterial•MaterialsSilicon---today’sICtechnologyisbasedentirelyonsiliconGermanium---earlyusedGalliumarsenide---usedformicrowavecircuitsMaterialandstructure•Structureisanotherimportantfactortodeterminethephysicalandchemicalcharacteristicsofthematerial！•Materialstructure:crystalAcrystalofpureandregularlatticestructureiscalledintrinsicsemiconductor.SiliconandGermaniumAtomicstructureofsiliconTetrahedron(四面体)•IVelement•EachatomisboundwithfourneighborsviaCovalentBond•Itsatomicstructureistetrahedron(四面体，与金刚石相同)Two-dimensionalrepresentationofthesiliconcrystal+4+4+4+4+4+4+4+4ValenceelectronsSiliconatomsCovalentbondIntrinsicSemiconductorPuresemiconductorAt0K,allbondsareintactandnofreeelectronsareavailableforcurrentconductionThermalionizationAtroomtemperature,someofthecovalentbondsarebrokenbythermalionization.Eachbrokenbondgivesrisetoafreeelectronandahole,bothofwhichbecomeavailableforcurrentconduction.Thermalionization•ThermalionizationValenceelectron---eachsiliconatomhasfourvalenceelectronsCovalentbond---twovalenceelectronsfromdifferenttwosiliconatomsformthecovalentbondBeintactatsufficientlylowtemperatureBebrokenatroomtemperatureFreeelectron---producedbythermalionization,movefreelyinthelatticestructure.Hole---emptypositioninbrokencovalentbond,canbefilledbyfreeelectron,positivechargeCarriers（载流子）•Freeelectron---producedbythermalionization.Itcanmovefreelyinthelatticestructuresoastoformcurrent.•Hole---emptypositioninbrokencovalentbond.Itcanbefilledbyfreeelectron(recombination)andcanalso“move”freelytoformcurrent.Carriers（载流子）•Afreeelectronisnegativechargeandaholeispositivecharge.•Bothofthemcanmoveinthecrystalstructure.•Theycanconductelectriccircuit.Recombination&Thermalequilibrium•RecombinationSomefreeelectronsfillingtheholesresultsinthedisappearanceoffreeelectronsandholes.•Thermalequilibrium–Atacertaintemperature,therecombinationrateisequaltotheionizationrate.thermalequilibrium–Theconcentrationofthecarriersatthermalequilibriumdoesnotchangeandcanbecalculated.Carrierconcentration•Carrierconcentrationinthermalequilibriumwhere(k:Boltzmannconstant)•Atroomtemperature(T=300K)carriers/cm3inpnkTEiGeBTn3210105.1inImportantnotes•stronglydependsontemperature.Thehighthetemperatureis,thedramaticallygreatthecarrierconcentrationis.•Atroomtemperatureonlyoneofeverybillionatomsisionized.•Silicon’sconductivityisbetweenthatofconductorsandinsulators.Actuallythecharacteristicofintrinsicsiliconapproachestoinsulators.inDopedSemiconductor•Conductivityofthesemiconductorcanbesignificantlychangedbydoping.Conductivityofdopedsemiconductorismuchgreaterthantheoneofintrinsicsemiconductor.•Therearetwotypesofdopedsemiconductors:ntypeandptype.•Theyareusedtoformpnjunction.DopedSemiconductor——ntypeSiSiSiSiSiSiSiSiSiP＋DonorFreeEBoundchargeAsiliconcrystaldopedbyapentavalentelement.Eachdopantatomdonatesafreeelectronandisthuscalledadonor.Thedopedsemiconductorbecomesntype.DopedSemiconductor——ntypeDopedSemiconductor——ntype•ConceptDopedsiliconinwhichthemajorityofchargecarriersarethenegativelychargedelectronsiscalledntypesemiconductor.•TerminologyDonor---pentavalentimpurityprovidesfreeelectrons,usuallyentirelyionizedatroomtemperature).Positiveboundcharge---impurityatomdonatingelectrongivesrisetopositiveboundchargecarriers•Majoritycarriers---freeelectrons(mostlygeneratedbyionizeddonorandaverytinyportionbythermalionization).•Minoritycarriers---holes(onlygeneratedbythermalionization).Carrierconcentrationforntype•Thermalequilibriumequation•ElectricneutralequationwhereNDisthedonorconcentration200innnpnDnnNpn00Carrierconcentrationforntype•InantypeSi,thefollowi