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FundamentalsofPowerSemiconductorDevicesB.JayantBaligaFundamentalsofPowerSemiconductorDevices13B.JayantBaligaPowerSemiconductorResearchCenterNorthCarolinaStateUniversityUSALibraryofCongressControlNumber:2008923040©2008SpringerScience+BusinessMedia,LLCAllrightsreserved.Thisworkmaynotbetranslatedorcopiedinwholeorinpartwithoutthewrittenpermissionofthepublisher(SpringerScience+BusinessMedia,LLC,233SpringStreet,NewYork,NY10013,USA),exceptforbriefexcerptsinconnectionwithreviewsorscholarlyanalysis.Useinconnectionwithanyformofinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodologynowknownorhereafterdevelopedisforbidden.Theuseinthispublicationoftradenames,trademarks,servicemarksandsimilarterms,eveniftheyarenotidentifiedassuch,isnottobetakenasanexpressionofopinionastowhetherornottheyaresubjecttoproprietaryrights.Printedonacid-freepaper.987654321springer.comISBN978-0-387-47313-0e-ISBN978-0-387-47314-71010MainCampusDriveRaleigh,NC27695-7924vDedicationTheauthorwouldliketodedicatethisbooktohiswife,Pratima,forherunwaveringsupportthroughouthiscareerdevotedtotheenhancementoftheperformanceandunderstandingofpowersemiconductordevices.PrefaceTodaythesemiconductorbusinessexceeds$200billionwithabout10%oftherevenuederivedfrompowersemiconductordevicesandsmartpowerintegratedcircuits.Powersemiconductordevicesarerecognizedasakeycomponentforallpowerelectronicsystems.Itisestimatedthatatleast50%oftheelectricityusedintheworldiscontrolledbypowerdevices.Withthewidespreaduseofelectronicsintheconsumer,industrial,medical,andtransportationsectors,powerdeviceshaveamajorimpactontheeconomybecausetheydeterminethecostandefficiencyofsystems.Aftertheinitialreplacementofvacuumtubesbysolid-statedevicesinthe1950s,semiconductorpowerdeviceshavetakenadominantrolewithsiliconservingasthebasematerial.ThesedevelopmentshavebeenreferredtoastheSecondElectronicRevolution.Bipolarpowerdevices,suchasbipolartransistorsandthyristors,werefirstdevelopedinthe1950s.Becauseofthemanyadvantagesofsemiconductordevicescomparedwithvacuumtubes,therewasaconstantdemandforincreasingthepowerratingsofthesedevices.Theirpowerratingandswitchingfrequencyincreasedwithadvancementsintheunderstandingoftheoperatingphysics,theavailabilityoflargerdiameter,highresistivitysiliconwafers,andtheintroductionofmoreadvancedlithographycapability.Duringthenext20years,thetechnologyforthebipolardevicesreachedahighdegreeofmaturity.Bythe1970s,bipolarpowertransistorswithcurrenthandlingcapabilityofhundredsofamperesandvoltageblockingcapabilityofover500Vbecameavailable.Moreremarkably,technologywasdevelopedcapableofmanufacturinganindividualpowerthyristorfromanentire4-inchdiametersiliconwaferwithvoltageratingover5,000V.Myinvolvementwithpowersemiconductordevicesbeganin1974whenIwashiredbytheGeneralElectricCompanyattheircorporateresearchanddevelopmentcentertostartanewgrouptoworkonthistechnology.Atthattime,IhadjustcompletedmyPh.D.degreeatRensselaerPolytechnicInstitutebyperformingresearchonanovelmethodforthegrowthofepitaxiallayersofmajorresearchlaboratoriesduetoalackofinterestinthisunprovengrowthtechnology.Ironically,theOMCVDepitaxialgrowthprocessthatIpioneeredwithProfessorGhandhihasnowbecomethemostcommonlyusedmethodforthegrowthofhighqualitycompoundsemiconductorlayersforapplicationssuchaslasers,LEDs,andmicrowavetransistors.MyfirstassignmentatGEwastodevelopimprovedprocessesforthefabricationofhighvoltagethyristorsusedintheirpowerdistributionbusiness.SincethethyristorswereusedforhighvoltageDCtransmissionandelectriclocomotivedrives,theemphasiswasonincreasingthevoltageratingandcurrenthandlingcapability.Theabilitytouseneutrontransmutationdopingtoproducehighresistivityn-typesiliconwithimproveduniformityacrosslargediameterwafersbecameofinterestatthistime.Iwasfortunateinmakingsomeofthecriticalcontributionstoannealingthedamagecausedtothesiliconlatticeduringneutronirradiationmakingthisprocesscommerciallyviable.5Thisenabledincreasingtheblockingvoltageofthyristorstoover5,000Vwhilebeingabletohandleover2,000Aofcurrentinasingledevice.Meanwhile,bipolarpowertransistorswerebeingdevelopedwiththegoalofincreasingtheswitchingfrequencyinmediumpowersystems.Unfortunately,thecurrentgainofbipolartransistorswasfoundtobelowwhenitwasdesignedforhighvoltageoperationathighcurrentdensity.Thepopularsolutiontothisproblem,usingtheDarlingtonconfiguration,hadthedisadvantageofincreasingtheon-statevoltagedropresultinginanincreaseinthepowerdissipation.Inadditiontothelargecontrolcurrentsrequiredforbipolartransistors,theysufferedfrompoorsafe-operating-areaduetosecondbreakdownfailuremodes.Theseissuesproducedacumbersomedesign,withsnubbernetworks,thatraisedthecostanddegradedtheefficiencyofthepowercontrolsystem.Inthe1970s,thepowerMOSFETproductwasfirstintroducedbyInternationalRectifierCorporation.Althoughinitiallyhailedasareplacementforallbipolarpowerdevicesduetoitshighinputimpedanceandfastswitchingspeed,thepowerMOSFEThassuccessfullycorneredthemarketforlowvoltage(100V)andhighswitchingspeed(100kHz)applicationsbutfailedtomak