東南大學(xué)電子器件金半接觸.ppt

acceptor受主donor施主recombination復(fù)合majority多子minority少子transitionregion過渡區(qū)depletionregion耗盡區(qū)contactbarrier接觸勢壘p-njunctionpn結(jié)heterojunction/異質(zhì)結(jié)EHP電子空穴對homojunction/同質(zhì)結(jié),Schottkybarrier/肖特基勢壘barrierheight/勢壘高度ideal/理想的workfunction/功函數(shù)practical/實(shí)際的electronaffinity/電子親和能Fermilevel/費(fèi)米能級rectifier/整流器electrostaticpotential/靜電勢breakdown/擊穿rectifyingcontacts/整流接觸Ohmiccontacts/歐姆接觸surfacestate/表面態(tài)lattice-matched/晶格匹配的tunnelingeffect/隧道效應(yīng),半導(dǎo)體器件工作的基本方程,泊松方程,電流密度方程,電流連續(xù)性方程,Manyoftheusefulpropertiesofap-njunctioncanbeachievedbysimplyforminganappropriatemetal-semiconductor(MS)contact.,5.7Metal-Semiconductorjunctionsorcontacts(金屬-半導(dǎo)體結(jié)、金-半接觸）,5.7.1SchottkyBarriers,http:/en.wikipedia.org/wiki/Walter_H._Schottky,Possibly,inretrospect,Schottkysmostimportantscientificachievementwastodevelop(in1914)thewell-knownclassicalformula,nowwritten-q2/40 x,fortheinteractionenergybetweenapointchargeqandaflatmetalsurface,whenthechargeisatadistancexfromthesurface.Owingtothemethodofitsderivation,thisinteractioniscalledthe"imagepotentialenergy"(imagePE).Schottkybasedhisworkonearlierworkby(Lord)KelvinrelatingtotheimagePEforasphere.SchottkysimagePEhasbecomeastandardcomponentinsimplemodelsofthebarriertomotion,M(x),experiencedbyanelectrononapproachingametalsurfaceorametal-semiconductorinterfacefromtheinside.,1.Schottkyeffect,(TheimagePEisusuallycombinedwithtermsrelatingtoanappliedelectricfieldFandtotheheighth(intheabsenceofanyfield)ofthebarrier.Thisleadstothefollowingexpressionforthedependenceofthebarrierenergyondistancex,measuredfromthe"electricalsurface"ofthemetal,intothevacuumorintothesemiconductor:Here,eistheelementarypositivecharge,0istheelectricconstantandristherelativepermittivityofthesecondmedium(=1forvacuum).Inthecaseofametal-semiconductorjunction,thisiscalledaSchottkybarrier;inthecaseofthemetal-vacuuminterface,thisissometimescalledaSchottky-Nordheimbarrier.Inmanycontexts,hhastobetakenequaltothelocalworkfunction.ThisSchottky-Nordheimbarrier(SNbarrier)hasplayedinimportantroleinthetheoriesofthermionicemissionandoffieldelectronemission.Applyingthefieldcausesloweringofthebarrier,andthusenhancestheemissioncurrentinthermionicemission.Thisiscalledthe"Schottkyeffect",andtheresultingemissionregimeiscalled"Schottkyemission".,Theworkfunction(功函數(shù)):TheenergywiththeworkfunctionisrequiredtoremoveanelectronattheFermileveltothevacuumoutsidethemetal.(Al=4.3eV)theelectronaffinity(電子親和能):Theenergywiththeelectronaffinityisrequiredtoremoveanelectronatthebottomoftheconductionbandtothevacuumoutsidethesemiconductors.(Si=4.1eV),Foursetsofcombination:(1)metal-ntypesemiconductor,qm>qs(2)metal-ntypesemiconductor,qmqs(4)metal-ptypesemiconductor,qmqsMetal/n-typesemiconductor,2.Schottkybarriers（肖特基勢壘）,chargetransferoccursuntiltheFermilevelsalignatequilibrium,theelectrostaticpotentialofthesemiconductormustberaisedV0theelectronenergymustbelowered.qV0thedepletionregionisformednearthejunction.Contactpotentialbarrier:qV0=qm-qspotentialbarrierheightqB=qm-q,BiscalledSchottkybarrier,（2）Metal/ptypesemiconductor,qm<qs,ElectronsflowfrommetaltosemiconductortilltheFermilevelsalignatequilibrium,theelectrostaticpotentialofthesemiconductormustbeloweredV0theelectronenergymustberaisedqV0thedepletionregionisformednearthejunction.Contactpotentialbarrier:qV0=qs-qm,V0retardsholediffusionfromthesemiconductortothemetal,5.7.2Rectifyingcontacts(diode),YoucantreattheSchottkybarrierforM/n-typeS(orM/p-typeS)astheP+N(orN+P)junctionexceptthatnoholeinjectionoccursfromthemetalintothesemiconductor.,(a)Forwardbias,ElectronsflowfromsemiconductortoMetalunderforwardbias.,Case1:Metal-ntypecontact,(b)Reversebias,OneimportantfeatureisthatthesaturationcurrentI0dependsuponBandisunaffectedbythebiasvoltage.I0Exp(-qB/kT),Howaboutp-njunction?,Forpnjunction:ForM-Sjunction,10-11A/cm2,Case2:metal-ptypeSchottkycontact?,(a)Forwardbias,(b)Reversebias,Holesflowfromsemiconductortometalunderforwardbias.,Areversevoltageincreasesthebarrierforholeflowandthecurrentbecomesnegligible.,5.7.3Ohmiccontacts(ideal,resistor),Inmanycaseswewishtohaveanohmicmetal-semiconductorcontact,havingalinearI-Vcharacteristicinbothbiasingdirections.Forexample,theinterconnectedlines(互連線)arerequiredinIC.So,itisimportantthatsuchcontactsbeohmic,withminimalresistanceandnotendencytorectifysignals.,R,Thebarriertoelectronflowbetweenthemetalandsemiconductorissmallandeasilyovercomebyasmallvoltage.,Case1M/ntype,qmqs,Unliketherectifyingcontacts,nodepletionregionoccursinthesemiconductorinthesetwocasessincetheelectrostaticpotentialdifferencerequiredtoaligntheFermilevelatequilibriumcallsforaccumulationofmajoritycarriersinthesemiconductor.,5.7.3Ohmiccontacts(practical),Inpractice,itisalwaysimpossibleforustoformtheohmiccontactsofmetal-semiconductorbychoosingtheappropriateworkfunctionofthemetal.Thereasonisthatthesemiconductorsurfacecontainssurfacestatesduetoincompletecovalentbonds.Themetal/semiconductorcontactsformalwaysabarrierwhatevermetalsareused.So,toobtaintheohmiccontactsformetal/semiconductor,apracticalmethodisbydopingthesemiconductorheavilyinthecontactregions.Therefore,ifabarrierexistsattheinterface,thedepletionwidthissmallenoughtoallowcarrierstotunnelthroughthebarrier.,Tunnelingprobabilitycanbereferredto(P236-238).,5.7.4TypicalSchottkyBarriers,Pinningeffect(釘扎效應(yīng)）:becauseofsurfacestatesandinterfaciallayer,P168ItiseasiertoobtainthewidthofthedepletionregionatM-SSchottkyjunction.,Forp-njunction,ForM-ntypeSchottkybarrier,ForM-ptypeSchottkybarrier,PROBLEM1,Whatisthedifferencebetweenp-ndiodeandSchottkybarrierdiode?,Problem2,ASchottkybarrierisformedbetweenametalhavingaworkfunctionof4.3evandptypeSi(electronaffinityis4ev).TheacceptordopingintheSiliconis1017cm-3.(a)CalculateqV0anddrawtheequilibriumbanddiagram.(b)Drawthebanddiagramwith0.3Vforwardbiasand2Vreversebias.,3.一塊Ge材料(),其中摻有51013cm-3的施主雜質(zhì)和2.51013cm-3的受主雜質(zhì)（均勻摻雜），Dn=100cm2/s，Dp=50cm2/s.試計(jì)算該樣品的電導(dǎo)率。設(shè)該樣品的電子親和勢為4.0ev，則它與功函數(shù)為4.5eV的金屬接觸時(shí)，功函數(shù)之差為多大？所形成的接觸是整流接觸還是歐姆接觸？,