The Influence of Surface Charge and Bevel Angle

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1、IEEETRANSACTIONSONELECTRONDEVICES,VOL.ED-31,NO.6,JUNE1984733TheInfluenceofSurfaceChargeandBevelAngleontheBlockingBehaviorofaHigh-Voltagep+-n-n+DeviceK.-P.BRIEGER,WILL1GERLACH,ANDJOACHIMPELKAAbstract-Thebreakdownvoltageofp+-n-n+devicesisinvestigated.Thetwo-dimensionalP

2、oissonequationissolvedusingthefinitedif-ferencemethod.Thequestionsofoptimalbevellingandtheinfluenceofsurfacechargesontheblockingcapabilityareextensivelystudied.Furthermore,itisinvestigatedtoreplaceasmallbevelangleatthen+-space-regionbyamesa-likestructure.dielectrlcI.I

3、NTRODUCTIONlcathodeIHEBLOCKINGbehaviorofhigh-voltagep-njunctionsde-IIAB-cTpendsstronglyonthetreatmentandthecontouringofFig.1.Thedifferentregionsofthecalculatedsection.thesurface.Surfacecharges,whichnormallyarefoundinanorderofsomelo1'cm-2positiveelementarycharges,defor

4、mthespace-chargelayernearthesurface.Thisincreasesthesur-A@=-E(1)faceelectricfieldandresultsinasurfacebreakdownatvolt-Eagesmuchlowerthanthebulkbreakdownvoltage.byneglectingthemobilecarriersinthespace-chargelayerNearlyallpapers,concerningtheproblemofsurfacebreak-(deplet

5、ionmodel).@representsthepotential,pthespacedown,dealwithsimplep+-njunctions.Thepointsofmainchargedensity,andethepermittivity.effortarebevelledp-njunctions[11-[9]andmesa-likestruc-IngeneralPoisson'sequationhastobeusedinthreedimen-tures[101-[141.Ontheotherhandasymmetric

6、althyristorssions.Becausemostpowerdeviceshaveacircularsymmetryneedp+-n-n+structures.Previousinvestigationsconcerning(1)canbewrittenasthesedevices[151-[191givenocompletepresentationoftheblockingcapabilities.Thereareinvestigationsonbevelledstructureswithdifferentdopingp

7、rofiles,butonlySundersinghandGhatol[19]considertheinfluenceofsurfacecharges.wherezistheaxisofsymmetryandrthedistancefromtheTheseauthorsuseanewconcentrationprofiletosuppressaz-axis.Becauseinpowerdevicesrisverylarge,thethirdsurfacebreakdown.Theydonotcalculatebreakdownvo

8、ltagestermontheleftsideof(2)canbeneglected.butonlydistributionsoftheelectricfields.Thenumericalproblemthenisreducedtothetwo-