半导体器件物理英文课件

2024/8/311§1-1Introduction2024/8/3122024/8/3132024/8/3142024/8/3152024/8/3162024/8/3172024/8/3182024/8/3192024/8/31102024/8/31112024/8/31122024/8/31132024/8/31142024/8/31152024/8/31162024/8/31172024/8/31182024/8/31192024/8/31202024/8/31212024/8/31222024/8/31232024/8/3124§1-2CrystalStructure2024/8/3125Solidstatematerialsincludes:insulator,semiconductorsandconductors.Semiconductormaterials2024/8/3126CompoundsSemiconductorsAbinarycompoundsemiconductorsisacombinationoftwo

elementsfromtheperiodictable.Ex:GaAs,GaP……etc.

Ternaryandquaternarycompounds.Ex:GaxIn1-xAsyP1-y

Element&CompoundSemiconductorsElementSemiconductors2024/8/3127SolidsAsatomsarebroughttogethertoformsolid,theinteractionofthevalanceelectronsholdthecrystaltogetheranddetermineitselectricalbehavior.CovalentBond:

sharingofapairofelectrons,SicrystalIonicBond:

transferofelectron,NaClMetallicBond:

Attractionbetweentheioncoreandtheseaofelectrons,AI(FCC)2024/8/3128Solids

Solidscanbeclassifiedascrystal,polycrystallineandamorphousCrystal–threedimensionallongrangeorderofatoms.Polycrystalline–mediumrangeorder,manysmallregionscalledgrains,eachhavingcrystallinestructure,joinedat“grainboundaries”whicharefullofdefects.Amorphous–nowelldefinedorder.2024/8/3129CrystalStructure2024/8/3130

Crystal

Lattice:Theperiodicarrangementofpointsinacrystal.

Basis:Theconstituentatomsattachedtoeachlattice

point.Everybasisisidenticalincomposition,

arrangement,andorientation.

Crystal=Lattice+BasisR=ma+nb+pca:latticeconstant2024/8/3131CrystalThelatticesisdefinedbythreefundamentaltranslationvectors2024/8/3132Unitcell:LatticecanbeconstructedbyrepeatedlyarrangingunitcellUnitCell2024/8/3133PrimitiveCell:AunitcelliscalledasprimitiveunitcellifthereisnocellofsmallervolumethatcanserveasabuildingblockforcrystalstructurePrimitiveCell2024/8/3134CrystalStructure2024/8/3135CrystalStructure2024/8/3136CrystalStructure2024/8/3137SystemBravaislatticeUnitcellSymmetryTriclinicSimpleNoneMonoclinicSimpleBase-centeredOne2-foldrotationaxisOrthorhombicSimpleBase-centerBody-centeredFace-centeredThreemutualityorthogonal2-foldTetragonalSimpleBody-centeredOne4-foldrotationaxisCubicSimpleBody-centeredFour-3-foldrotationaxis(alongcubediagonal)TrigonalSimpleOne3-foldrotationaxisHexagonalSimpleOne3-foldrotationaxis2024/8/3138MillerIndicesTheMillerindicesareobtainedusingthefollowingstepsFindtheinterceptsoftheplaneonthethreeCartesiancoordinateintermsofthelatticeconstant.Takethereciprocalsofthesenumbersandreducethemtothesmallestthreeintegershavingthesameradio.Enclosetheresultinparentheses(hkl)astheMillerindicesforasingleplane.2024/8/3139MillerIndices12=4x+3yMillerindices[43]2024/8/3140MillerIndices

2024/8/3141MillerIndices(hkl):Foraplanethatinterceptsthex-axisonthenegativesideoftheorigin.(100){hkl}:Forplanesofequivalentsymmetry.

(100)(010)(001)(100)(010)(001)<hkl>:Forafullsetofequivalentdirections.

[100][010][001][100][010][001][100][hkl]:Foracrystaldirection.2024/8/3142CrystalStructureTwointerveningFCCcellsoffsetby¼ofthecubicdiagonalfromdiamondstructureandzincblendestructure:2024/8/3143DirectLattice:BravaisCellReciprocalLattice:Wigner-SeitzCell2024/8/3144ImperfectionsinSolid

LatticeThermalVibrationPointDefects

-Vacancy

-interstitial

-Vacancy+interstitial=FrenkelDefectLineDefects-Dislocation:disruptingnotonlygeometricperiodicitybutalsoideaatomicbonds2024/8/3145ImperfectionsinSolid2024/8/3146ImpuritiesinSolidIntentionallyaddingimpuritiesintocrystalcanaltertheelectricalproperty

-Diffusion

-IonImplantation2024/8/3147FromSandtoWaferQuartziteCoalMGSCarbonmonoxidepurificationMGShrydrochlorideTCShydrogenTCShydrogenhrydrochlorideEGS2024/8/3148GrowthTechniquesReductionofquartzitetometallurgicalgradesilicon(MGS)withapurityof~98%.ConversionofMGStotrichlorosilane(SiHCl3).PurificationofSiHCl3bydistillation.Chemicalvapordeposition(CVD)ofSifromthepurifiedSiHCl3,asEGS.2024/8/3149SiCrystalIncrystalstructure,atomsharesitsvalenceelectronswiththeneighbors.Thesesharingofelectronsiscovalentbonding.2024/8/3150Electron&HoleAthighertemperature,thermalvibrationmaybreakthecovalentbonds;thefreeelectronscanparticipateincurrentconduction.Whenelectronsleavethecovalentbond,thevacancieswereconsideredasaparticlesimilartoanelectron.Thisfictitiousparticleiscalledahole.2024/8/3151§1-3EnergyBands2024/8/3152Wave-ParticleDualityWave-particledualityappliesprimarytosmallparticles,suchaselectron,neutron,photonWavesbehavesasiftheyareparticlesandsometimesparticlesbehavesasiftheyarewavesDeBroglierelationship2024/8/3153One-electronApproximation2024/8/3154

HydrogenAtomicModelBohr’sModel2024/8/3155HydrogenAtomicModelForanatom,eachelectronmusthaveaseparatedistinctenergystatedefinedby4quantumnumbers:Principequantumnumber,n=1,2,3Angularmomentumquantumnumber,I=0,1,2,…,n-1Magneticquantumnumber,m=0,±1,…,±IElectronspin,s=±1/2Onlyhydrogenatomcanbesolvedduetoelectron-electroninteraction2024/8/3156BandFormationTheinteractionresultsinthediscretequantizedenergylevelsplittingintotwodiscreteenergylevelsProbabilitydensityfunctionofaisolatedhydrogenatom2024/8/3157EnergyBandDegenerateWhenNisolatedatomsarebroughttogethertoformasolid,theorbitsoftheouterelectronsofdifferentatomsoverlapandinteractwitheachother.2024/8/3158EnergyBandSchematicshowingthesplittingofthreeenergystatesintoallowedbandsofenergies2024/8/3159BandFormationSiAtomInteractionporbital:sixallowedstatessorbital:twoallowedstates2024/8/3160EnergyBandSchematicdiagramoftheformationofasiliconcrystalfromNisolatedsiliconatoms2024/8/3161EnergyBand2024/8/3162EnergyMomentumDiagramForafreeelectron,

energyEcanbegivenbym0:effectivemass

P:momentum2024/8/3163BolchElectronWavefunctionInperiodicpotential,anelectronwillbehaveinthismanner,i.e.,Blochelectronisalsoperiodic2024/8/3164Energy(E)vs.Wavevector(k)FreeElectron:Incrystal,free-electronE-kisnolongervalid,discontinuityatk=nπ/aemerges.

→Creatingenergygap2024/8/3165BrillouinZone

ReducedBrillouinZone2024/8/3166Energy(E)vs.Wavevector(k)2024/8/3167EffectiveMassConceptElectronsinconductionbandandholesinvalencebandaresimilartofreeelectronssincetheycanmoverelativelyfreelyWecantreatelectronsandholesasclassicalparticlesmn:effectivemass

p:crystalmomentumofelectron2024/8/3168EffectiveMassConcept2024/8/3169EnergyBandDiagramofSiliconEg=1.12eVkT/q=0.0259eV@300k2024/8/3170EnergyBand:TemperatureEffect

BandGapvs.TemperatureSiGaAs2024/8/3171EnergyBandConductor,Semiconductor&insulator2024/8/3172BandStructureDirectSemiconductorThetopofthehighest

(occupied)valenceband

andthebottomofthe

lowest(unoccupied)

conductionbandareatthe

samevalueink-space.Examples:

GaAs,InP,GaN,ZnO.2024/8/3173BandStructureIndirectSemiconductor:Theextremeatthetop

ofthevalenceband

andatthebottomof

theconductionband

areatdifferentk-values.

Examples:Ge,Si.2024/8/3174Donor&AcceptorDeepimpurityLevel&ShallowImpurityLevel2024/8/3175§1-4CarrierConcentrationatThermalEquilibrium2024/8/3176DistributionFunctionsandDensitiesofStatesLetusconsiderthesituationwhenthenumberofstatesismuchgreaterthanthenumberofparticlesandtheprobabilityoffindingaparticleinagivenstatesismuchsmallerthanunity.Inthiscase,thePauliexclusionprincipleisnotimportant(sinceitisveryunlikelythattwoparticleswilloccupythesameenergylevel),andtheprobabilityoffindingaparticleinthestatewithenergyE,isgivenbywhereNiisthetotalnumberofparticlesinthisstate.Theaverageparticleenergycanbefoundas2024/8/3177Fermi-DiracDistributionFunctionForelectrons,thePauliexclusionprinciplestatesthatnomorethantwoelectrons(withoppositespins)canoccupyagivenenergylevel.Electronstendtooccupystateswithlowenergiesfirst.Hence,allthestateswithlowenergiesarefilledinexactlythesameway–oneelectronineachenergystate(countingthetwostateswiththesameenergyavailableforelectronswithoppositespinsastwoseparatestates).Atsuchlowenergies,theelectronprobabilityfunction,f,mustbeequaltounitysinceallthesestatesareoccupied.Howeverathighvaluesofenergy,whentheprobabilityofoccupyinganenergystateismuchsmallerthanunity,thePauliprinciplepresentsnolimitation,andthedistributionfunctionshouldreducetotheBoltzmanndistributionfunction.AmoredetailedanalysisshowsthattheelectrondistributionfunctionisgivenbytheFermi-Diracdistributionfunction2024/8/3178

BoltzmannDistributionFunctionInequilibrium,theprobabilitiesofhavingparticlesintwoenergystates,EkandEi,arerelatedviatheBoltzmannfactors:Thisequationmeansthattheprobabilityoffindingaparticlesinagivesenergystates,Ei,decreasesexponentiallywithEi.Foracontinuousenergyspectrum,theprobabilityoffindingaparticlewiththeenergybetweenEandE+dEisgivenbyThefunctionfiscalledtheBoltzmanndistributionfunction.2024/8/3179IntrinsicCarrierConcentrationIntrinsicSemiconductorisonethatcontainsrelativelysmallamountofimpuritiescomparedwiththethermallygeneratedelectronsandholesFermi-DiracDistributionFunction2024/8/3180Fermi-DiracDistributionprobabilitythataquantumstateattheenergyEwillbeoccupiedbyanelectron2024/8/3181f(T)2024/8/3182

FermiLevelatT=0oKTheFermiprobabilityfunctionversusforenergyforT=0oKDiscreteenergystatesandquantumstatesforaparticularsystematT=0oK2024/8/3183ThermalExcitation(T>0°K)DiscreteenergystatesandquantumstatesfortheparticularsystematT>0oK2024/8/3184

IntrinsicCarrierConcentration2024/8/3185

DensityofStatevs.Energy2024/8/3186

IntrinsicCarrierConcentrationIntrinsicsemiconductor(a)schematicbanddiagram(b)densityofstates(c)Fermidistributionfunction(d)carrierconcentration2024/8/3187

Maxwell-BoltzmanApproximationFermi-Diracdistribution:ForE-Ef>>kTMaxwell-Boltzmanapproximation2024/8/3188DensityofStatesandEffectiveDensityofStateswhereiscalledtheeffectivedensityofstatesfortheconductionband2024/8/3189DensityofStatesandEffectiveDensityofStatesIstheFermiintegralforconductionband,wherewhenηn>3,2024/8/3190whenηn<-3,ExampleExpressthevalueofenergycorrespondingtothepeakofdn/dEdistributionintermstemperature,T,assumingthatEc-EF>>kBT2024/8/3191

IntrinsicCarrierConcentration2024/8/3192IntrinsicCarrierConcentrationEffectivedensityofstatesinconductionbandEffectivedensityofstates

invalanceband2024/8/3193CarrierConcentrationinIntrinsicSilicon2024/8/3194FermiLevelinIntrinsicSiliconMassactionlawFermilevel:chargeneutralityn=p=niInintrinsicsiliconEcEvEiFermilevellocatesnearmiddle

bandgap2024/8/3195IntrinsicCarrierDensitiesIntrinsiccarrierdensitiesinSiandGaAsasafunctionofthereciprocaloftemperature2024/8/3196Donor&AcceptorExtrinsic:Asemiconductordopedwithoracceptorimpurities2024/8/3197Donor&AcceptorExcitedbythermalenergy

Mostofthedopantslocateatshallowenergylevel.Activationcanbemodeledbyhydrogenionizationwithreplacingdielectricconstant&effectivemass2024/8/3198CompensatedSemiconductor2024/8/3199NondegenerateSemiconductorElectronandholeconcentrationaremuchlowerthantheeffectivedensityofstatesInotherwords,EFisatleast3kTaboveEVor3kTbelowECForshallowdonorsoracceptors,thereusuallyisenergythermalenergytosupplytheenergyEDtoionizeallimpurities,i.e.,completeionizationTheconcentrationofelectron(hole)equalstothatofdonor(acceptor)ion2024/8/31100Donor&Acceptor

WhenCompleteIonization

ND:donorconcentration

NA:acceptorconcentration

2024/8/31101Inp-typesemiconductor

Donor&AcceptorWhendonorandacceptorexistinthesametimeInn-typesemiconductor2024/8/31102

CarrierConcentrationinn-DopedSilicon

2024/8/31103ChargeNeutrality2024/8/31104FermiLevelinExtrinsicSiliconThepositionofFermileveldeterminetheconcentrationofelectronsandholes2024/8/31105Donor&Acceptor2024/8/31106TemperatureEffect2024/8/31107Donor&Acceptor2024/8/31108DopantSolubilityinSilicon2024/8/31109DegenerateSemiconductorWhenthedopingconcentrationbecomesequalorlargerthattheeffectivedensityofstates,wecannolongerusetheapproximationofM-Bstatistics.Concentrationshouldbecalculatednumerically.EFwillbeaboveECorbelowEVBroadenshapeofimpurityenergydistributionresultinenergybandgapnarrowing2024/8/31110DegenerateSemiconductor2024/8/31111DegenerateSemiconductorLocalvariationofpotentialbyimpurity2024/8/31112§1-5CarrierTransport

Phenomena2024/8/31113TransportinDevicesThermalMotioninEquilibriumDrift:underinfluenceofelectricfieldDiffusion:concentrationgradientGenerationandRecombinationThermionicEmission

TunnelingImpactIonization2024/8/31114TopicsinTransportCurrentdensityequation:Drift&DiffusionContinuityequation:Generation-RecombinationOthertransportmechanisms:thermionicemission,tunneling,impactionizationIntroductionofresistivity,mobility……2024/8/31115ThermalMotionInthermalequilibrium,mobileelectronsintheconductionbandwillbeinrandomthermalmotion.Fromstatisticalfreedom.ThusKineticEnergyofanelectronwherek=Boltzmann’sconstantmn=Conductivityeffectivemassofelectron(nottoconfusedwiththedensityofstateeffectivemassVth=thermalvelocity~107cm/sec@300°K2024/8/31116ThermalMotionElectronsmovingrapidlyinalldirectionsThethermalmotionofanindividualelectroncanbevisualizedasasuccessiverandomscatteringwithlattervibration,impurity,andsoon.

Theaveragedistancebetweencollisionsisreferredtomeanfreepath(l).Typicalvalueof10-5cm.Thetimecalledmeanfreetime~1ps(τc=1/Vth)

2024/8/31117CarrierTransport:Drift(ElectricField)2024/8/31118CarrierTransport:MobilityInsteadystate,allmomentumgainedbetweencollisionswillbelosttolatticeinthecollision.Therefore,themomentumgainedbyaccelerationofelectricfieldduringfreemotioncanbeobtainedbyitmeansthatthereexistsarelationbetweendriftvelocityandappliedelectricfieldMobility:μn2024/8/31119ThermalVelocityTheaveragekineticenergyofthermalmotionperoneelectronis3kBT/2whereTisthetemperatureindegreesKelvinandkBistheBoltzmannconstant.Theelectronthermalvelocity,vthn,isfoundbyequatingtheelectronkineticenergyto3kBT/2:2024/8/31120DriftVelocityTheelectrondriftvelocity,vn,causedbyanappliedelectricfield,issuperimposedonthischaoticthermalmotion.Atroomtemperature,theelectronvelocityduetothethermalmotionisusuallygreaterthanoratleastcomparabletothedriftvelocity.Therefore,anexactdescriptionoftheelectronicmotioninasemiconductorhastorandomnessoftheelectronvelocity.2024/8/31121DriftVelocity(cont.)However,anapproximatedescriptionofthedriftvelocitycanbeobtainedfromNewton’ssecondlawofmotionforanelectronmovinginanelectricfieldF.Afreeelectroninspaceisacceleratedbyelectricfieldasfollows:2024/8/31122SecondLawofMotionEffectiveMassInasemiconductor,thefreeelectronmasshastobereplacedbytheeffectivemass,mn:2024/8/31123RelaxationTimeandMeanFreePathTheaveragedistancewhichanelectrontravelsbetweentwocollisionsiscalledthemeanfreepath.Inrelativelyweakelectricfieldswhentheelectrondriftvelocityismuchsmallerthanthenormalvelocity,themeanfreepathisgivenby:2024/8/31124MobilityAtlowfrequencies,ω<<1/τnp,mdv/dt<<qFiscalledtheelectronlowfieldmobilityorjustmobility.2024/8/31125ScatteringMechanismsLow-fieldmobilities:Mathiessens’srule:Inlowelectricfields

·ionizedimpurities

·acousticphononsInhighelectricfields

·opticalphonons

·intervalley

scatteringAthighconcentrations

·carrier-carrier

scattering2024/8/31126ExampleTheelectronmobilityinGaAsattemperaturesT=77KandT=300Kisequalto300,000cm2/Vsand9,000cm2/Vs,respectively.Theelectroneffectivemassisequalto0.067mewheremeisthefreeelectronmass.Findtheelectronmeanfreepathatthesetemperatures.2024/8/31127SolutionThemomentumrelaxationtimeisgivenbyHence,themeanfreepathSubstitutingtheparametervalues,wefind:

λn(77K)=2.67μm,λp(300K)=1570A2024/8/311281.Phononscattering-Latticeatomsvibratewithdiscreteallowablestates(quantummechanics).

2.Ionizadimpurityatomscattering(importantathighdopantconcentrations)

3.Neutalimpurityatomscattering(usuallynegligible)

4.Electron-electronandElectron-holescattering(importantathighcarrierconcentrations)

5.Crystaldefects(importantinpolycrystallinematerial)

6.Surfacescatteringeffects

(importantinMOSdevices)MobilityMobilityisdirectlyrelatedtothemeanfreetimebetweencollisions,whichisinturndeterminedbyscattering2024/8/31129ImpurityScattering2024/8/31130LatticeVibration2024/8/31131MobilityElectronmobilityinsiliconversustemperatureforvariousdonorconcentrations.Forlightlydopedsamples,thelatticescatteringdominates,andthemobilitydecreasesasthetemperatureincrease.Forheavilydopedsamples,theeffectofscatteringisthemostpronouncedatlowtemperature.Foragiventemperature,themobilitydecreaseswithincreasingimpurityconcentrationbecauseofenhancedimpurityscattering.2024/8/31132Mobility2024/8/31133MobilityAtlowfield

Vd=μζ

Mathiessen’srule2024/8/31134CarrierMobilitiesinSilicon2024/8/31135MaterialPropertiesofImportantSemiconductors2024/8/31136SurfaceScatteringInaMOSFET,carriersareattractedtowardsurface,whichmakesthemsufferingfrommoreseverescattering2024/8/31137Poisson’sEquationPotential:Electricfield:Poisson’sEq.:Guass’slaw2024/8/31138DiffusioncurrentLetusconsiderann-typesamplewithnon-uniformcarrierconcentrationindirectionx(whichmayberelatedtoanon-uniformdoping)andnoelectriccurrent(i=jdrift+jdiff=0)sothat(*)2024/8/31139SinceweobtainandandfromEq.(*)EinsteinRelationship2024/8/31140ExampleTheelectronandholemobilitiesinSiatroomtemperature(T=300K)are1,000cm2/Vsand300cm2/Vs,respectively.Calculatetheelectronandholediffusioncoefficients.2024/8/31141SolutionSinceforT=300K,kBT/q=0.02584eV,

Dn=μn

kBT/q=0.02584×1000=25.8cm2/sand

Dp=μp

kBT/q=0.02584×300=7.75cm2/s2024/8/31142ResistivityofSilicon2024/8/31143SheetResistivity2024/8/31144HallEffectForp-typesemiconductorLorentzforceHallFieldHallvoltageHallcoefficientForn-typesemiconductor2024/8/31145HallEffectWecandomeasurementoftheHallvoltageforaknowncurrentandmagneticfieldyields.Thus,thecarrierconcentrationandcarriertypecanbeobtaineddirectly.2024/8/31146ElectronDriftCurrentDensityjFOhm’sLaw2024/8/31147EnergyBalanceandEnergyRelaxationTimeElectrontemperature2024/8/31148DriftVelocityinSemiconductors2024/8/31149MobilityandSaturationVelocityinSilicon2024/8/31150ElectionandHoleVelocityinSi2024/8/31151Generation&RecombinationInthermalequilibrium:Ifexcesscarriersareintroducedtoasemiconductor.Wehaveanon-equilibriumsituation.Theprocessofintroducingexcesscarriersiscalledinjection.Whentheequilibriumconditionisdisturbed,processexisttorestorethesystemtoequilibrium.Whenweinjectiontheminoritycarrierstothesemiconductor.Theinjectionminoritycarrierswillrecombinewithmajoritycarriers.Thereleasedenergythatresultsfromtherecombinationprocesscanbeemittedasaphoton(radiativerecombination)ordissipatedasheattolattice(nonradiativerecombination).2024/8/31152DirectRecombinationIndirect-bandgapsemiconductor,whenthethermalvibrationcausessomebondsbetweenneighboringatomstobebroken,anelectron-holepairisgenerated.Thethermalenergyenablesavalanceelectrontomakeanupwardtransitiontotheconductionband,leavingaholeinvalenceband.Thisprocessiscalledcarriergeneration.2024/8/31153DirectRecombinationWhenanelectronmakesatransitiondownwardfromtheconductionbandtovalanceband,anelectron-holepairisannihilated.Thisprocessiscalledrecombination.2024/8/31154AugerRecombinationAuger

recombinationoccursbythetransferoftheenergyandmomentumreleasedbytherecombinationofanelectron-holepairtoathirdparticlethatcanbeeitheranelectronorahole2024/8/31155Underthermalequilibrium,thegenerationratemustequaltorecombinationrate.Whenexcesscarriesareintroducedtoadirect-bandgapsemiconductorRecombinationrateThermalequilibriumThesubject0indicatesanequilibriumquantity△meansexcessconcentrationThenetrateofchangeofholeconcentrationisβisthepropotionalityconstant2024/8/31156Insteadystate,UistherecombinationrateByaboveequationsForlowlevelinjection△p,andpno<<nn0τpislifetimeThephysicalmeaningoflifetimecanbeillustratedbythetransientresponseofadeviceafterthesuddenremovalofthelightsource.2024/8/31157

IndirectionRecombinationThedominaterecombination

processinindirection

semiconductor

(EX:Si)isindirecttransitionvialocalized

energystatesin

theforbidden

energygap.2024/8/31158IndirectionRecombinationTheproportionalityconstantcanbevisualizedasthevolumesweptoutperunittimebyanelectron.Ifthecentrelieswithinthisvolume,theelectronwillbecapturedbyit.2024/8/31159Atequilibrium,Ra=RbIndirectionRecombination2024/8/31160IndirectionRecombinationatsteadystateatequilibrium,GL=0Ra=RbandRc=Rd

understeadystatenonequilibrium

GL=Ra-Rb=Rc-Rd≡U2024/8/31161IndirectionRecombination2024/8/31162TheMinority-carrierLifetime

(Single-levelRecombination)TheAsymptoticLifetime

(Multiple-levelRecombination)2024/8/31163Experiments:Solid-stateDiffusionEX.(Goldinsilicon)High-energyRadiationEX.(Electronirradiation,Neutronirradiation,Deuteronirradiation)2024/8/31164Theminority-carrierlifetimemeasurementPC:PhotoconductionEffectStevenson-KeyesMethodPEM:Photo-electromagneticEffect2024/8/31165SurfaceRecombinationTheabruptdiscontinuityofthelatticestructureatthesurface,alargenumberiflocalizedenergystatesorgenerationrecombinationcentresmaybeintroducedatthesurfaceregion.Theseenergystatescalledsurfacestates,maygreatlyenhancetherecombinationrateatthesurfaceregion.

Low-injectionsurface

recombinationvelocity2024/8/31166§1-6PhononSpectraandOptical,Thermal,andHigh-FieldPropertiesofSemiconductors2024/8/31167PHONONSPECTRALA—longitudinalacousticmodesLO—longitudinalopticalmodesTA—transverseacousticmodesTO—transverseopticalmodes2024/8/31168OpticalPropertyT----TransmissioncoefficientR----Reflectioncoefficienta----absorptioncoefficienta~(hν-Eg)γ2024/8/31169ThermalPropertyThermoelectricPowerTodeterminetheconductiontypeofasemiconductorP-type----------------positiveN-type----------------negative2024/8/31170ThermalPropertyThermalconductivityκ~T2024/8/31171High-FieldPropertyNonlinearmobility(μ)Effectivetemperature(Te)Saturationofdriftvelocity2024/8/31172Vd,sat≈107cm/sVelocitySaturationVelocityincreaseslinearlywithincreasingelectricfield,butsaturatesathighfield2024/8/31173DiffusionVelocityoftheGaAsForn-typeGaAs,thedriftvelocityreachesamaximum,thendecreasesasthefieldfurtherincreases.ThisisduetotheenergybandstructureofGaAsallowsthetransferofconductionelectronfromahigh-mobilityenergyminimumtolow-mobility,higherenergysatellitevalleys.2024/8/31174DriftVelocityoftheGaAs2024/8/31175IntervalleyTransfer2024/8/31176DriftVelocityoftheGaAsThesteady-stateconductivityofthen-typeGaAs2024/8/31177Velocity-FieldCurvesforGaAs2024/8/31178AnalyticalApproximationVelocityin105m/s

Mobility,μ，inm2/V-s2024/8/31179ImpactIonizationWhentheelectricfieldishighenough,electronintheconductionbandcangainkineticenergybeforeitcollideswiththelattice.Onimpactwiththelattice,theelectronimpartsmostofitskineticenergytobreakabond,thatis,toionizeavalenceelectronfromthevalencebandtotheconductionbandandtherebygenerateanelectron-holepair.Thenthegenerationpairwillrepeatthisprocessagain.Thisprocessiscalledtheimpactionizationprocess.2024/8/31180Considerafast-movingelectronhasakineticenergyandamomentum.Aftercollision,therearethreecarries:theoriginalelectronplusanelectron-holepair.ImpactIonizationItisobviousthatE0mustbelargerthanthebandgapfortheionizationprocesstooccur.2024/8/31181IonizationRateThenumberofelectronholepairsgeneratedbyanelect