半导体英文课件-PN-and-Metal-Semiconductor-Junctions

ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-1Chapter4PNandMetal-SemiconductorJunctionsPNjunctionispresentinperhapseverysemiconductordevice.

diodesymbol

N

PVI

–+4.1

BuildingBlocksofthePNJunctionTheoryVIReversebiasForwardbias

Donorions

N-typeP-typeModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-24.1.1

EnergyBandDiagramofaPNJunctionAdepletionlayerexistsatthePNjunctionwheren

0andp

0.EfisconstantatequilibriumEcandEvaresmooth,theexactshapetobedetermined.EcandEvareknownrelativetoEf

N-regionP-region(a)Ef(c)EcEvEf(b)

EcEfEvEvEc(d)

Depletionlayer

Neutral

P-region

NeutralN-regionEcEvEfModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-34.1.2Built-inPotentialCanthebuilt-inpotentialbemeasuredwithavoltmeter?

(b)

(c)(a)

N-typeNdP-typeNaNdNa

Ef

Ec

Ev

qfbi

xNxPx

0

VfbiModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-44.1.2Built-inPotential

N-regionP-regionModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-54.1.3Poisson’sEquationGauss’sLaw:

s:permittivity(~12

oforSi)

:chargedensity(C/cm3)Poisson’sequationDxrE(x)

E(x

+Dx)

xarea

AModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-64.2.1FieldandPotentialintheDepletionLayer

OntheP-sideofthedepletionlayer,

=–qNa

Onthe

N-side,=qNd4.2Depletion-LayerModelsaqNdxde-=E)()(1xxqNCxqNxPsasa-=+-=eeE)()(NsdxxqNx-=eENNNPPPModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-74.2.1FieldandPotentialintheDepletionLayerTheelectricfieldiscontinuousatx=0.Na|xP|=Nd|xP|

Whichsideofthejunctionisdepletedmore?Aone-sidedjunctioniscalleda

N+Pjunction

or

P+NjunctionNPModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-84.2.1FieldandPotentialintheDepletionLayerOntheP-side,Arbitrarilychoosethevoltageatx=xP

asV=0.OntheN-side,NNPPModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-94.2.2Depletion-LayerWidthViscontinuousatx=

0IfNa>>Nd,asinaP+N

junction,WhataboutaN+Pjunction?where

0@=adNPNNxx||||PNModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-10EXAMPLE:AP+NjunctionhasNa=1020cm-3andNd

=1017cm-3.Whatisa)itsbuiltinpotential,b)Wdep,c)xN

,andd)xP?Solution:a)

b)c)d)ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-114.3Reverse-BiasedPNJunction

Doesthedepletionlayerwidenorshrinkwithincreasingreversebias?+–V

NP

(b)reverse-biased

qVEcEcEfnEvq

bi+qVEfpEv

(a)V=0

EcEfEvEfEvq

biEcModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-124.4Capacitance-VoltageCharacteristics

Is

Cdep

agoodthing?

Howtominimizejunctioncapacitance?ReversebiasedPNjunctionisacapacitor.ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-134.4Capacitance-VoltageCharacteristics

FromthisC-VdatacanNa

and

Nd

bedetermined?

ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-14EXAMPLE:Iftheslopeofthelineinthepreviousslideis2x1023F-2V-1,theinterceptis0.84V,andAis1mm2,findthelighterandheavierdopingconcentrationsNlandNh

.

Solution:

IsthisanaccuratewaytodetermineNl

?Nh

?ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-154.5JunctionBreakdownA

Zenerdiode

isdesignedtooperateinthebreakdownmode.

VIVB,breakdownPN

ARForwardCurrentSmallleakageCurrent

voltage

3.7V

R

ICABCDZenerdiodeModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-164.5.1PeakElectricField2/1|)|(2)0(úûùêëé+==rbispVqNfeEEbicritsBqNVfe-=22EN+PNa

NeutralRegion

0

xp

(a)increasing

reversebiasx

E

xp

(b)increasingreversebiasEpModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-174.5.2TunnelingBreakdown

Dominantifbothsidesofajunctionareveryheavilydoped.

V/cm

106»=critpEE

VIBreakdown

EmptyStatesFilledStates-EvEcModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-184.5.3AvalancheBreakdown

impactionization:anenergeticelectrongeneratingelectronandhole,whichcanalsocauseimpactionization.qNVcritsB22Ee=Impactionization+positivefeedback

avalanchebreakdownEcEfnEcEvEfporiginalelectronelectron-holepairgenerationModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-194.6ForwardBias–CarrierInjection

Minoritycarrierinjection

V=0I=0ForwardbiasedDriftanddiffusioncanceloutModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-204.6ForwardBias–Quasi-equilibriumBoundaryCondition

TheminoritycarrierdensitiesareraisedbyeqV/kTWhichsidegetsmorecarrierinjection?EcEfnEfpEvxEfnxNxPModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-214.6CarrierInjectionUnderForwardBias–Quasi-equilibriumBoundaryConditionkTVqaikTVqPeNnenn20)xP(==kTVqdikTVqNeNnepp20)(==xPModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-22EXAMPLE:CarrierInjectionAPNjunctionhasNa=1019cm-3andNd=1016cm-3.Theappliedvoltageis0.6V.Question:Whataretheminoritycarrierconcentrationsatthedepletion-regionedges?Solution:Question:Whataretheexcessminoritycarrierconcentrations?Solution: ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-234.7CurrentContinuityEquationModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-244.7CurrentContinuityEquationMinoritydriftcurrentisnegligible;

Jp=–qDpdp/dx

LpandLnarethediffusionlengthsModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-254.8ForwardBiasedJunction--ExcessCarriersModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-264.8ExcessCarrierDistributionsModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-27EXAMPLE:CarrierDistributioninForward-biasedPNDiode

Sketchn'(x)ontheP-side.xN-sideP-side1013cm-3

2´1012n’(=p’)p´(=n’)ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-28

HowdoesLncomparewithatypicaldevicesize?

Whatisp'(x)ontheP-side?EXAMPLE:CarrierDistributioninForward-biasedPNDiodeModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-294.9PNDiodeI-VCharacteristics

0

P-sideN-sideJtotalJpNJnPx

0

P-sideN-sideJtotal

JpNJnPJn=Jtotal

–JpJp=Jtotal

–JnModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-30ThePNJunctionasaTemperatureSensorWhatcausestheIVcurvestoshifttolowerVathigherT?ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-314.9.1

ContributionsfromtheDepletionRegionSpace-ChargeRegion(SCR)currentUnderforwardbias,SCRcurrentisanextracurrentwithaslope120mV/decadeModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-324.10ChargeStorageWhatistherelationshipbetween

s

(charge-storagetime)

and

(carrierlifetime)?ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-334.11Small-signalModeloftheDiodeWhatisGat300KandIDC

=1mA?DiffusionCapacitance:Whichislarger,diffusionordepletioncapacitance?CRVIqkTIeIkTqDCkTqV/)(/0==ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-344.12SolarCellsSolarCellsisalsoknownas

photovoltaiccells.Convertssunlighttoelectricitywith10-30%conversionefficiency.1m2solarcellgenerateabout150Wpeakor25Wcontinuouspower.Lowcostandhighefficiencyareneededforwidedeployment.PartII:ApplicationtoOptoelectronicDevicesModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-354.12.1SolarCellBasicsV0.7V

–IscMaximumpower-outputSolarCellIVIDarkIV0Eq.(4.9.4)Eq.(4.12.1)

NP-ShortCircuitlightIsc+(a)EcEvDirect-GapandIndirect-GapSemiconductors

ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-36Electronshavebothparticleandwaveproperties.AnelectronhasenergyEandwavevectork.indirect-gapsemiconductordirect-gapsemiconductor4.12.2

LightAbsorption

α(1/cm):absorptioncoefficient1/α

:lightpenetrationdepthModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-37Athinnerlayerofdirect-gapsemiconductorcanabsorbmostofsolarradiationthanindirect-gapsemiconductor.ButSi…4.12.3Short-CircuitCurrentandOpen-CircuitVoltage

ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-38IflightshinesontheN-typesemiconductorandgeneratesholes(andelectrons)attherateofGs-1cm-3,Ifthesampleisuniform(noPNjunction),d2p’/dx2=0

p’=GLp2/Dp=GtpSolarCellShort-CircuitCurrent,IscModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-39AssumeverythinP+layerandcarriergenerationinNregiononly.xNP+Isc0xP'Lp0Gisreallynotuniform.Lpneedsbelargerthanthelightpenetrationdepthtocollectmostofthegeneratedcarriers.Open-CircuitVoltageModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-40TotalcurrentisISCplusthePVdiode(dark)current:Solvefortheopen-circuitvoltage(Voc)by

settingI=0HowtoraiseVoc?ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-414.12.4OutputPowerTheoretically,thehighestefficiency(~24%)canbeobtainedwith1.9eV>Eg>1.2eV.LargerEgleadtotoolowIsc(lowlightabsorption);smallerEgleadstotoolowVoc.Tandemsolarcellsgets35%efficiencyusinglargeandsmallEgmaterialstailoredtotheshortandlongwavelengthsolarlight.

AparticularoperatingpointonthesolarcellI-Vcurvemaximizestheoutputpower(IV).Sisolarcellwith15-20%efficiencydominatesthemarketnowModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-42Lightemittingdiodes(LEDs)LEDsaremadeofcompoundsemiconductorssuchasInPandGaN.Lightisemittedwhenelectronandholeundergo

radiativerecombination.EcEvRadiativerecombination

Non-radiativerecombinationthroughtraps

4.13LightEmittingDiodesandSolid-StateLightingDirectandIndirectBandGapDirectbandgapExample:GaAsDirectrecombinationisefficientaskconservationissatisfied.IndirectbandgapExample:SiDirectrecombinationisrareaskconservationisnotsatisfiedTrapModernSemiconductorDevicesforIntegratedCircuits(C.Hu)ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-444.13.1LEDMaterialsandStructureModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-454.13.1LEDMaterialsandStructure

redyellowblue

Wavelength(μm)ColorLatticeconstant(Å)InAs0.363.44

6.05InN0.651.91infrared

3.45InP1.360.92

violet5.87GaAs1.420.875.66GaP2.260.555.46AlP3.390.515.45GaN2.450.373.19AlN6.200.20UV3.11Light-emittingdiodematerials

compoundsemiconductors

binarysemiconductors:-Ex:GaAs,efficientemitterternarysemiconductor:-Ex:GaAs1-xPx,tunable

Eg

(tovarythecolor)quaternarysemiconductors:-Ex:AlInGaP,tunableEgandlatticeconstant(forgrowinghighqualityepitaxialfilmsoninexpensivesubstrates)Eg(eV)RedYellowGreenBlueModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-46CommonLEDsSpectralrangeMaterialSystemSubstrateExampleApplicationsInfraredInGaAsPInPOpticalcommunicationInfrared-RedGaAsPGaAsIndicatorlamps.RemotecontrolRed-YellowAlInGaPGaAorGaPOpticalcommunication.High-brightnesstrafficsignallightsGreen-BlueInGaNGaNorsapphireHighbrightnesssignallights.VideobillboardsBlue-UVAlInGaNGaNorsapphireSolid-statelightingRed-BlueOrganicsemicon-ductorsglassDisplaysAlInGaP

QuantunWellModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-474.13.2Solid-StateLightingIncandescentlampCompactfluorescentlampTubefluorescentlampWhiteLEDTheoreticallimitatpeakofeyesensitivity(λ=555nm)Theoreticallimit(whitelight)176050-10090-?683~340luminosity(lumen,lm):ameasureofvisiblelightenergy normalizedtothesensitivityofthehumaneyeatdifferentwavelengths

Luminousefficacyoflampsinlumen/watt

Terms:luminositymeasuredinlumens.luminousefficacy,OrganicLightEmittingDiodes(OLED):haslowerefficacythannitrideoraluminidebasedcompoundsemiconductorLEDs.

ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-484.14DiodeLasers(d)NetLightAbsorption(e)NetLightAmplificationStimulatedemission:emittedphotonhasidenticalfrequencyanddirectionalityasthestimulatingphoton;lightwaveisamplified.(b)SpontaneousEmission(c)StimulatedEmission(a)Absorption4.14.1LightAmplificationLightamplificationrequires

populationinversion:electronoccupationprobabilityislargerforhigherEstatesthanlowerEstates.ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-494.14.1LightAmplificationinPNDiodePopulationinversionisachievedwhen

Populationinversion,qV>EgEquilibrium,V=0ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-50R1,R2:reflectivitiesofthetwoendsG:lightamplificationfactor(gain)foraround-triptravelofthelightthroughthediodeLightintensitygrowsuntil,whenthelightintensityisjustlargeenoughtostimulatecarrierrecombinationsatthesameratethecarriersareinjectedbythediodecurrent.4.14.2OpticalFeedbackandLaserlightoutCleavedcrystalplaneP+N+Laserthresholdisreached(lightintensitygrowsbyfeedback)whenModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-514.14.2OpticalFeedbackandLaserDiode

DistributedBraggreflector(DBR)reflectslightwithmulti-layersofsemiconductors.Vertical-cavitysurface-emittinglaser(VCSEL)isshownontheleft.Quantum-welllaserhassmallerthresholdcurrentbecausefewercarriersareneededtoachievepopulationinversioninthesmallvolumeofthethinsmall-Egwell.ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-524.14.3LaserApplicationsReddiodelasers:CD,DVDreader/writerBluediodelasers:Blu-rayDVD(higherstoragedensity)1.55mminfrareddiodelasers:

Fiber-opticcommunication

Photodiodes:ReversebiasedPNdiode.Detectsphoto-generatedcurrent(similartoIscofsolarcell)foropticalcommunication,DVDreader,etc.

Avalanchephotodiodes:

Photodiodesoperatingnearavalanchebreakdownamplifiesphotocurrentbyimpactionization.4.15PhotodiodesModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-53Twokindsofmetal-semiconductorcontacts:RectifyingSchottkydiodes:

metalonlightlydopedsiliconLow-resistanceohmiccontacts:metalonheavilydopedsiliconPartIII:Metal-SemiconductorJunctionSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-54fBn

IncreaseswithIncreasingMetalWorkFunction

Theoretically,

fBn=

yM

–cSi

yMcSi:WorkFunctionofmetal:ElectronAffinityofSi

qfBnEcEvEfE0qyMcSi

=4.05eVVacuumlevel,ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-554.16SchottkyBarriersEnergyBandDiagramofSchottkyContact

Schottkybarrierheight,fB

,isafunctionofthemetalmaterial.

fBisthemostimportantparameter.ThesumofqfBnandqfBpisequaltoEg

.

MetalDepletion

layer

NeutralregionqfBnEcEcEfEfEvEvqfBpN-SiP-SiModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-56SchottkybarrierheightsforelectronsandholesfBn

increaseswithincreasingmetalworkfunctionfBn

+fBp

EgModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-57

Ahighdensityofenergystatesinthebandgapatthemetal-semiconductorinterfacepinsEftoanarrowrangeandfBn

istypically0.4to0.9V

Question:WhatisthetypicalrangeoffBp?FermiLevelPinning

qfBnEcEvEfE0

qyMcSi

=4.05eVVacuumlevel,+-ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-58SchottkyContactsofMetalSilicideonSiSilicide-Siinterfacesaremorestablethanmetal-siliconinterfaces.AftermetalisdepositedonSi,anannealingstepisappliedtoformasilicide-Sicontact.Thetermmetal-siliconcontactincludesandalmostalwaysmeanssilicide-Sicontacts.Silicide:Asiliconandmetalcompound.Itisconductivesimilartoametal.fBnfBpModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-59UsingC-VDatatoDeterminefBQuestion:HowshouldweplottheCVdatatoextractfbi?EvEfEcqfbiqfBn

EvEcEfqfBnq(fbi+V)qVModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-60Once

fbiisknown,fB

canbedeterminedusingUsingCVDatatoDeterminefBV1/C2

-fbiEvEfEcqfbiqfBnModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-614.17ThermionicEmissionTheoryEfn-q(fB-

V)

qfB

qVMetalN-typeSiliconVEfmEvEcxvthxModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-624.18SchottkyDiodesVI

ReversebiasForwardbiasV=0ForwardbiasedReversebiasedModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-634.18SchottkyDiodesModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-644.19ApplicationsofSchottlyDiodes

I0ofaSchottkydiodeis103to108timeslargerthanaPNjunctiondiode,dependingonfB

.

AlargerI0meansasmallerforwarddropV.ASchottkydiodeisthepreferredrectifierinlowvoltage,highcurrentapplications.I

VPNjunctionSchottky

fBI

VPNjunctionSchottkydiode

fBdiodeModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-65SwitchingPowerSupplyACDCACACDCutilitypower110V/220V

PNJunction

rectifier

Hi-voltage

MOSFET

inverter

100kHzHi-voltage

Transformer

Schottky

rectifierLo-voltage50A1VfeedbacktomodulatethepulsewidthtokeepVout

=1VModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-66ThereisnominoritycarrierinjectionattheSchottkyjunction.Therefore,SchottkydiodescanoperateathigherfrequenciesthanPNjunctiondiodes.4.19ApplicationsofSchottkydiodesQuestion:WhatsetsthelowerlimitinaSchottkydiode’sforwarddrop?SynchronousRectifier:Foranevenlowerforwarddrop,replacethediodewithawide-WMOSFETwhichisnotboundbythetradeoffbetweendiodeVandleakagecurrent.ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-674.20

QuantumMechanicalTunnelingTunnelingprobability:ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-684.21OhmicContactsModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-694.21OhmicContactsTunnelingprobability:--

xSilicideN+SiEvEc

,EffBn--

xVEfmEvEc

,EffBn

–VModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-704.21OhmicContactsModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-714.22ChapterSummaryThepotentialbarrierincreasesby1Vifa1VreversebiasisappliedjunctioncapacitancedepletionwidthPartI:PNJunctionModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-724.22ChapterSummary

Underforwardbias,minoritycarriersareinjectedacrossthejucntion.

Thequasi-equilibriumboundaryconditionofminoritycarrierdensitiesis:

Mostoftheminoritycarriersareinjectedintothemorelightlydopedside.ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-734.22ChapterSummary

Steady-statecontinuityequation:

Minoritycarriersdiffuseoutward

e–|x|/Lp

ande–|x|/Ln

Lp

and

Ln

arethediffusionlengthsModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-744.22ChapterSummaryChargestorage:

Diffusioncapacitance:Diodeconductance:ModernSemiconductorDevicesforIntegratedCircuits(C.Hu)Slide4-754.22ChapterSummaryPartII:OptoelectronicApplications~100umSior<1umdirect–gapsemiconductorcanabsorbmostofsolarphotonswithenergylargerthanEg.CarriersgeneratedwithindiffusionlengthfromthejunctioncanbecollectedandcontributetotheShortCircuitCurrentIsc.Theoretically,thehighestefficiency(~24%)can