Slide 1Test 2 – Tuesday 05Apr11npn BJT currents in the forward active region ©RLCSlide 4Slide 5Slide 6Slide 7Slide 8E-M model equationsEbers-Moll Model (Neglecting G-R curr)E-M linking current modelE-M linking current model (cont)E-M linking current model (cont)More non-ideal effects in BJTsSlide 15FA npn figure of merit – emitter efficiencyFA npn figure of merit – base transport factorFA npn figure of merit – recombination factorCommon base current gain, aFCommon base current gain, aF (continued)Common emitter current gain, bFCommon base current gain, aF (cont.)Common emitter current gain, bFReferencesEE 5340Semiconductor Device TheoryLecture 19 – Spring 2011Professor Ronald L. [email protected]://www.uta.edu/ronc©rlc L19-31Mar20112Test 2 – Tuesday 05Apr11•11 AM Room 129 ERB•Covering Lectures 11 to19•Open book - 1 legal text or ref., only.•You may write notes in your book.•Calculator allowed•A cover sheet will be included with full instructions. For examples see http://www.uta.edu/ronc/5340/tests/.npn BJT currents in the forward active region ©RLC©rlc L19-31Mar20113IC = JCACIB=-(IE+IC )JnEJnCIE = -JEAEJRB=JnE-JnCJpEJGCJREJpC©rlc L19-31Mar20114E current equations mode npn BJT (w/o gen/rec)         ditto. , L/xsinhV/VfexpL/xtanhV/VfexpLnqDJdir. x' in , 1VVexpL/xtanhLpqDJxxnqDJ- ,x''xp-qDJBBtBCBBtBEBB0BnEtBEEEEE0EpE0xBBnE0x'EEpE©rlc L19-31Mar20115C current equations in npn BJT (w/o gen/rec)         BBtBCBBtBEBB0BnCtBCCCCC0CpCxxBBnC0x"CCpCLxVVfLxVVfLnqDJ1VVLxLpqDJ-xxnqDJ- ,x"xpqDJ-B/tanh/exp/sinh/expexp/tanh"©rlc L19-31Mar20116Ebers-Moll Model(Neglecting G-R curr)(Fig. 9.30*)-JEAE=IEJCAC=IC©rlc L19-31Mar2011Source of Ebers-Moll Equations (E)           tBEFFBBBB0BtBCRREESBBBB0BEEEE0EESBBtBCBBtBEBB0BnEtBEEEEE0EpEEEnEpEEV/VfexpJ L/xsinhLnqDV/VfexpJAIL/xtanhLnqDL/xtanhLpqDJL/xsinhV/VfexpL/xtanhV/VfexpLnqDJ1VVexpL/xtanhLpqDJA/IJJJαα7©rlc L19-31Mar2011Source of Ebers-Moll Equations (C)          tBCRRBBBB0BtBEFFCCSBBBB0BCCCC0CCSBBtBEBBtBCBB0BnCtBCCCCC0CpCCCnCpCCV/VfexpJ L/xsinhLnqDV/VfexpJAIL/xtanhLnqDL/xtanhLpqDJL/xsinhV/VfexpL/xtanhV/VfexpLnqDJ1VVexpL/xtanhLpqDJ-A/IJJJαα8©rlc L19-31Mar2011E-M model equationsBBBC2iCSRSESFBBBE2iStBCCSRtBEESEtBEESFtBCCSCxNDAqnIIIxNDAqnI gives iprelationsh yreciprocit TheVVfIVVfIIVVfIVVfIIexpexpexpexp9©rlc L19-31Mar2011Fig. 9.30*-JEAE = IEJCAC = ICEBCaRIRaFIFEbers-Moll Model (Neglecting G-R curr)10©rlc L19-31Mar2011E-M linking current modelECCCCTECI-IIICBtBCRSRECIVVfexpIItBEFSFCCEBVVfexpIIIBEC11©rlc L19-31Mar2011tBCtBESECtBCStBEFSEtBEStBCRSCSVVexpVVexpIIbranch E-C the links"" that current TheVVfexpIVVfexpIIVVfexpIVVfexpIIbecome eqns. M-E the ,I of terms In12E-M linking current model (cont)©rlc L19-31Mar2011E-M linking current model (cont)EBECECBECCFFFtBEFSEBRRRtBCRSCBI-II andIII sdefinition with eqns M-E the for values same the give still 1 with VVfexpII& 1 with VVfexpII:Similarly13©rlc L19-31Mar201114More non-ideal effects in BJTsaBase-width modulation (FA: xB changes with changes in VBC)aCurrent crowding in 2-dim base•High-level injection (minority carriers g.t. dopant - especially in the base).•Emitter Bandgap narrowing (NE ~ density of states at cond. band. edge)•Junction breakdown at BC junction©rlc L19-31Mar201115Recombination/GenerationCurrents (FA) CBCBBCeff,1genBCeff,BCbiCBCgenBCiGC1recBEtBEreciBERENNNNN and rate, ionrecombinat the is and DR CB the is qNVV2W where ,2WqnJ.rate ionrecombinat the is and DR EB the is W where ,V2Vexp2nqWJ©rlc L19-31Mar201116FA npn figure of merit – emitter efficiency  1L/x and L/x if ,xDNxDN1L/xtanhLDnL/xtanhLDp1VV if ,J/J11JJJEEBB1EBEBEB1EEEB0BBBBE0EtBEnEPEPEnEnE©rlc L19-31Mar201117FA npn figure of merit – base transport factor     2BBBBtBEBBtBETBBtBCtBEnEnCTLx1Lx0Lx , Lx1LxVV1LxVVLx and VV , VV For . JJ factor, transport base Thecoshlim/cosh/cosh/exp/cosh/exp©rlc L19-31Mar201118FA npn figure of merit – recombination factorBB1tBE0BBOBBEinE10BEtBE0iBERRnEnEpERnEpEnELx for ,V2VexpDn2xxn1,J from rate, ionrecombinat the is and DR EB the is x where ,V2Vexp2nqxJJJJJJJJJ factor, Recomb©rlc L19-31Mar201119Common base current gain, aFTpEREnEpEnEnEnCpEnEnEEpCGCpEREnEnCECpEREnEpCGCnCEC0JJJJJJJJJJ asFactors .I of fctns not are J and J since , JJJJII :signal smallJJJJJJII gain, current DCgaTd©rlc L19-31Mar201120Common base current gain, aF (continued)     