chap5 - ' $ EE432 Bipolar Junction Transistors Chapter 5...

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Unformatted text preview: ' $ EE432 Bipolar Junction Transistors Chapter 5 & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 0 The Ohio State University % ' $ Lecture # 17 Introduction & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 1 The Ohio State University % ' $ BJT Symbols P E N P C N E P C Β B E N C Β E C Β C C Β Β E E B= Base, E = emitter, C= Collector & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 2 The Ohio State University % ' $ Ampli cation with a BJT iC =βiB iE iB E + E − B C E R V EC iB R iC E V BC Current ampli cation: iC = iB Operating point is established by the loadline: E = iC R + VBC ) VBC = E ; iC R = E ; iB R & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 3 The Ohio State University % ' & $ Transistor # 1 T.H.E OHIO Invented in 1948 by Bardeen, Brattain and Schockley at Bell Lab. S ATE T Patrick Roblin UNIVERSITY 4 The Ohio State University % ' & Patrick Roblin $ Little Giants T.H.E OHIO S ATE T UNIVERSITY 5 The Ohio State University % ' $ Transistor to Radio & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 6 The Ohio State University % ' $ Photo Diode + − P I N Ec E F Ev V h ω > Eg Optical Generation Rate E F & − + T.H.E The diode leakage is controled by the light. Patrick Roblin 7 OHIO S ATE T UNIVERSITY The Ohio State University % ' $ Diode Leakage Current + − P I N Ec E F Ev V h ω > Eg Optical Generation Rate E F − + I = Ith eqV=(kT ) ; 1 ; Iopt with 0 1 @ Lp p + Ln n A with I = qA th p n n p Derivation of di usion region: & 0 1 @ Lp pn + Ln npA Iopt = qA Patrick Roblin p Iopt = qAgopt(Lp + Ln + W ) n 8 with 8 > p =g < n opt p > : np = gopt n T.H.E OHIO S ATE T UNIVERSITY The Ohio State University % ' $ Band Diagram of PNP iE + V − EB P+ N P P+ + V − iC BC N P − + Ec Ec Ef & E E B Ev v C E In Equilibrium Patrick Roblin B C Forward Biased T.H.E OHIO S ATE T UNIVERSITY 9 The Ohio State University % ' $ Band Diagram Analysis Ln W Lp Space Charge P N W Space Charge P A Neutral Neutral Neutral 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 + 0− i + 1 0 1 0V − 1 B 1 0 1 0 BC 0 1 0 VEB 1 0 1 1 0 Drift 0 1 0 1 0 1 0 Excess electrons 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0i 1 i Bp 0 1 0 1 0 1 0 Bn 1 0 1 0 1 0 E cp 1 0 1 0 1 0 i Bn 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 Recombination 1 0 1 0 1 0 1 0 E Fn 1 0 1 0 −qV B = EFp 1 0 1 0 1 0 E 1 0 1 0 1 0 1 0 Recombination 1 0 1 0 1 0 1 0 1 0 1 0 1 0 E vp 1 0 1 0 1 0 1 0 i En 1 0 Drift iE & Patrick Roblin i Ep Excess holes Neutral iC E cp −qV = EFp CB E vp iC Drift T.H.E OHIO S ATE T UNIVERSITY 10 The Ohio State University % ' $ Transistor Optimization Ln W Space Charge P Lp N W Space Charge P A Neutral Neutral Neutral Neutral 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 +0 − i + − 1 0V 0 1 1 0 B 1 0 BC 0 1 0 1 0 VEB 1 0 1 0 1 0 Drift 0 1 1 0 1 0 Excess electrons 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0i i Bp 0 1 0 1 0 1 0 Bn 1 0 1 0 1 0 E cp 1 0 1 0 1 0 i Bn 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Recombination0 1 0 1 0 1 0 1 0 1 0 1 0 E Fn −qV B = EFp 1 0 1 0 1 0 E 1 0 1 0 1 0 1 0 1 0 1 0 Recombination 1 0 1 0 1 0 1 0 1 0 E vp 1 0 1 0 1 0 1 0 i En 1 0 Drift iE i Ep 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 iC E cp −qV = EFp CB E vp iC Drift Excess holes To increase # of holes collected: narrow base << di usion length large hole lifetime & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 11 The Ohio State University % ' $ Bean Counting iE + V − EB + iB VBC − iC 11 00 11 i Bn 00 000 11 00 111 11 1111111 0000000 1 0 i 00 11 1 Bp 00 i En 0 11 00 1 0 1111111111111111111111 0000000000000000000000i 11 00 1 0 iE 0000000000000000000000C 1111111111111111111111 1 0 1111111111111111111111 0000000000000000000000 1111111111111111111111 0000000000000000000000 i Ep 1111111111111111111111 0000000000000000000000 P N 8 > iEn = iBn > > < with > iEp = iBp + iC > > : iE = iB + iC EMITTER & 8 > i =i +i < E En Ep > i =i +i : B Bn Bp Patrick Roblin P BASE COLLECTOR T.H.E OHIO S ATE T UNIVERSITY 12 The Ohio State University % ' $ Emitter E ciency and Base Transport Emitter injection e ciency: iEp < 1 = iE (ideal is = 1) Base transport factor (Wb < Lp, B = iiC p (ideal is B = 1) Ep Current transfer ratio: iC = BiEp = B < 1 = iE large) (ideal is = 1) iE Ampli cation factor: & = iC = Patrick Roblin iB iE = iE ; iC 1 ; (ideal is >> 1) T.H.E OHIO S ATE T UNIVERSITY 13 The Ohio State University % ' $ Principle of Current Ampli cation The Base-Emitter forward bias reduces the potential barrier and an excess hole charge Qp is injected in the base. An electron charge arises in the base achieving charge neutrality Qn = Qp The electrons recombine with a fraction of the holes injected: Qn iB = n But most of the holes injected are collected by the collector: iC = Qp t with t the transit time across the base The ampli cation factor is then given by: & i = C= iB Patrick Roblin p t T.H.E OHIO S ATE T UNIVERSITY 14 The Ohio State University % ' $ Lecture # 18 Minority Carrier Distribution and Ebers Moll's Model & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 15 The Ohio State University % ' $ Minority Carrier Distribution Space Charge P N Space Charge P A Neutral Neutral E Neutral Neutral 1 0 1 0 1 0 1 0 1 0 1 0 1 B0 1 0 1 0 1 0 0 Wb C xn Our goal is to calculate p(x) in the base. In the absence of drift, p(x) is obtained from the di usion equation: d2 p(x) = p dx2 L2 p which admits a solution of the form: p(x) = C1ex=Lp + C2e;x=Lp & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 16 The Ohio State University % ' $ What are the Boundary Conditions? Space Charge P N Space Charge P A Neutral Neutral E Neutral Neutral 1 0 1 0 1 0 1 0 1 0 1 0 1 B0 1 0 1 0 1 0 Wb 0 C xn The boundary conditions are: p(0) = pE = pn eqV =(kT ) ; 1 p(Wb) = pC = pn eqV =(kT ) ; 1 ?? & Patrick Roblin ?? T.H.E OHIO S ATE T UNIVERSITY 17 The Ohio State University % ' $ Boundary Conditions Space Charge P N Space Charge P A Neutral Neutral Neutral Neutral 1 0 1 0 1 0 1 0 1 0 1 0 1 B0 1 0 1 0 1 0 0 Wb E C xn The boundary conditions are: p(0) = pE = pn eqVEB =(kT ) ; 1 p(Wb) = pC = pn eqVCB =(kT ) ; 1 & pE = p(0) = C1 + C2 pC = p(Wb) = C1eW =L + C2e;W =L Patrick Roblin b p b p T.H.E OHIO S ATE T UNIVERSITY 18 The Ohio State University % ' $ System Solution pE = p(0) = C1 + C2 pC = p(Wb) = C1eW =L + C2e;W =L Solve this linear system for C1 and C2: C1 = 1 pE + 1 pC C2 = 2 pE + 2 pC b p b p with = ; e;Wb=Lp 1 1= 1 = eWb=Lp 2 2 = ;1 with = eWb=Lp ; e;Wb=Lp & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 19 The Ohio State University % ' $ Base Charge in Normal Mode Space Charge P Space Charge N P A Neutral Neutral Neutral B E 0 Neutral 1 0 1 0 1 0 1 0 1 0 1 0 Wb C xn δ p(xn ) ∆ pE & ∆ pC 0 pE ' pneqV Patrick Roblin EB =(kT ) Wb pC ' ;pn and 20 xn T.H.E OHIO S ATE T UNIVERSITY The Ohio State University % ' $ How Are We to Calculate the Emitter and Collector Currents? δ p(xn ) ∆ pE ∆ pC & 0 Wb p(x) = C1ex=L + C2e;x=L Patrick Roblin p p xn T.H.E OHIO S ATE T UNIVERSITY 21 The Ohio State University % ' $ Emitter and Collector Current (Hole component) δ p(xn ) ∆ pE ∆ pC 0 & IEp ICp Patrick Roblin Wb xn d p(0) = ; AqDp C + AqDp C = ;AqDp dx Lp 1 Lp 2 d p(Wb) = ; AqDp eW =L C + AqDp e;W =L C = ;AqDp 1 2 OHIO dx Lp Lp S ATE T B p b pT .H.E UNIVERSITY 22 The Ohio State University % ' $ Emitter and Collector Current (Hole component) δ p(xn ) ∆ pE ∆ pC 0 Wb xn IEp = a pE ; b pC = ISp eqV =(kT ) ; 1 ; BISp eqV =(kT ) ; 1 ICp = b pE ; a pC = BISp eqV =(kT ) ; 1 ; ISp eqV =(kT ) ; 1 with (using B = b=a and ISp = apn and BISp = bpn) 01 01 a = qADp Dp ctnh @ Wb A and b = qADp Dp csch @ Wb A Lp Lp Lp Lp OHIO EB EB & Patrick Roblin CB CB T.H.E S ATE T UNIVERSITY 23 The Ohio State University % ' $ Base Current and Approximate Equation δ p(xn ) ∆ pE ∆ pC 0 Wb 01 Dp ( p + p )tanh @ Wb A IB ' IEp ; ICp = qA L E C 2Lp p xn In normal mode pC ' 0 & IB = Qp Patrick Roblin p with Q p = 1 p E Wb 2 24 T.H.E OHIO S ATE T UNIVERSITY The Ohio State University % ' $ Total Currents Adding the electron components from the regular diode model: qADn n eqV IE = IEp + L p n IC = ICp + qADn np eqV L EB |n } {z =(kT ) ; 1 CB =(kT ) ; 1 ISn Using IS = ISn + ISp and BISp = IS (( = B = BISp=IS ) gives: IE = IS eqVEB =(kT ) ; 1 ; IS eqVCB =(kT ) ; 1 IC = IS eqVEB =(kT ) ; 1 ; IS eqVCB =(kT ) ; 1 & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 25 The Ohio State University % ' $ Current Transfer Ratio Emitter e ciency (homework problem) 2 ISp = 41 + Lnnn p = p IS Base transport: 3;1 p n tanh Wb 5 Lnpp n Ln p p 2 b 41 + Wp nn ' p 3;1 n5 Lnpp n p IC = csch(Wb=Lp) = sech Wb B=I Ln Ep ctnh(Wb =Lp ) p Current transfer ratio: 2 3;1 nn p WLn = 4cosh nb + pp n n sinh5 & Example Patrick Roblin Lp Lnpp p p = cosh 0:1 + 2(0:1)(0:5) sinh 0:1];1 = 0:988 T.H.E OHIO S ATE T UNIVERSITY 26 The Ohio State University % ' $ Non Symmetrical Device Ebers Moll Model IE = IES eqV =(kT ) ; 1 ; I ICS eqV IC = N IES eqV =(kT ) ; 1 ; ICS eqV EB CB EB =(kT ) ; 1 CB =(kT ) ; 1 Reciprocity requires that: N IES = I ICS & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 27 The Ohio State University % ' $ Alternate Representation The Ebers-Moll model: IE = IES eqVEB =(kT ) ; 1 ; I ICS eqVCB =(kT ) ; 1 IC = N IES eqVEB =(kT ) ; 1 ; ICS eqVCB =(kT ) ; 1 can be alternately written: IE = IE0 eqV =(kT ) ; 1 + I IC IC = ;IC 0 eqV =(kT ) ; 1 + N IE with IC 0 = (1 ; N I )ICS and IE0 = (1 ; EB CB & Patrick Roblin N I )IES T.H.E OHIO S ATE T UNIVERSITY 28 The Ohio State University % ' Equivalent Circuit of Ebers-Moll Model I E0 E αN IE IE IC α I IC & $ IB B IC0 IE = IE0 eqV =(kT ) ; 1 + I IC IC = ;IC 0 eqV =(kT ) ; 1 + N IE Patrick Roblin C EB CB T.H.E OHIO S ATE T UNIVERSITY 29 The Ohio State University % ' $ Lecture # 19 & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 30 The Ohio State University % ' $ Transit Time csch Wpb 2L2 2Dp p p Wb2 L p= = t= Wb ' W 2 2 = t with Wb 2Dp tanh 2Lp b Identi cation of t as a transit time is obtained as follow: p IC = ip(xn) = qAp(xn) < v(xn) >' qADp W E b using the triangular approximation. The transit time is then: Z Wb qAp(xn) Z Wb dxn Wb2 =0 dxn = 2D t= 0 < v(xn) > IC p where we used the triangular approximation for the base charge p(xn). & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 31 The Ohio State University % ' $ Transistor Modes δ p(xn ) δ p(xn ) δ p(xn ) ∆ pE ∆ pE ∆ pE ∆ pC 0 Wb a) Normal mode ∆ pC xn 0 Wb b) Normal mode ∆ pC xn 0 Wb xn c) Inverted mode in saturation Mode Regime Emitter Base diode Collector Base diode Normal Active ON OFF Normal Saturation ON ON Inverted Active OFF ON Inverted Saturation ON ON OHIO Cuto OFF OFF S ATE T & Patrick Roblin T.H.E UNIVERSITY 32 The Ohio State University % ' $ Transistor Modes iC Saturation Active Region & Patrick Roblin iC =βiB iB Cutoff E −VCE T.H.E OHIO S ATE T UNIVERSITY 33 The Ohio State University % ' $ DC Charge Control Analysis δ p(xn ) δ p(xn ) ∆ pE δ p(xn ) ∆ pE ∆ pC ∆ pC Q QN N Q Q I ∆ pC 0 Wb xn 0 Wb For normal mode: QN ICN = IBN For inverted mode: IEI = ; QI IBI = QI tN Patrick Roblin ∆ pE 0 tI QN = IEN pN Wb QN + QN = tN pN ICI = ; QI ; QI pI tI pI T.H.E OHIO S ATE T UNIVERSITY 34 xn c) Inverted mode b) Saturation a) Normal mode & xn I The Ohio State University % ' $ Combined Normal and Inverted Model δ p(xn ) δ p(xn ) ∆ pE δ p(xn ) ∆ pE ∆ pC ∆ pC Q QN N Q Q I ∆ pC 0 xn Wb 0 @1 IE = QN tN & ; QN + QI IB = Patrick Roblin Wb b) Saturation a) Normal mode tN 0 1 1 A QI ; pN tI xn ∆ pE 0 Wb c) Inverted mode 0 QN ; Q @ 1 IC = I tN I tI ; 1 1A pI tI T.H.E OHIO S ATE T UNIVERSITY 35 xn The Ohio State University % ' $ Equivalence with Ebers Moll Model N= pN + 0 tN pN 1 @1 ; 1A IES = qN tN pN pE QN = qN p n I= pI tI + 0 pI 1 @1 ; 1A ICS = qI tI pI QI = qI p n pI For short symmetric devices qN = qI = 1 qWb Apn. The voltage 2 dependence is set by: pE = pn eqVEB =(kT ) ; 1 pC = pn eqVCB =(kT ) ; 1 & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 36 The Ohio State University % ' $ Switching and Saturation δ p(xn ) ∆ pE 00000000000000000000000000000000000 11111111111111111111111111111111111 11111111111111111111111111111111111 00000000000000000000000000000000000 11111111111111111111111111111111111 00000000000000000000000000000000000 11111111111111111111111111111111111 00000000000000000000000000000000000 Same slope => same I C 11111111111111111111111111111111111 00000000000000000000000000000000000 11111111111111111111111111111111111 00000000000000000000000000000000000 111 000 11111111111111111111111111111111111 00000000000000000000000000000000000 111 000 11111111111111111111111111111111111 00000000000000000000000000000000000 111 000 11111111111111111111111111111111111 00000000000000000000000000000000000 111 000 11111111111111111111111111111111111 111 ∆ pE 00000000000000000000000000000000000 Excess Carrier 000 11111111111111111111111111111111111 00000000000000000000000000000000000 111 000 11111111111111111111111111111111111 00000000000000000000000000000000000 1 0 Stored 11111111111111111111111111111111111 00000000000000000000000000000000000 1 0 11111111111111111111111111111111111 00000000000000000000000000000000000 1 0 11111111111111111111111111111111111 00000000000000000000000000000000000 ∆ p 1 0 11111111111111111111111111111111111 00000000000000000000000000000000000 C 1 0 11111111111111111111111111111111111 00000000000000000000000000000000000 1 0 11111111111111111111111111111111111 00000000000000000000000000000000000 1 0 11111111111111111111111111111111111 00000000000000000000000000000000000 1 0 11111111111111111111111111111111111 00000000000000000000000000000000000 11111111111111111111111111111111111 00000000000000000000000000000000000 11111111111111111111111111111111111 00000000000000000000000000000000000 p 11111111111111111111111111111111111 00000000000000000000000000000000000 ∆ 11111111111111111111111111111111111 00000000000000000000000000000000000 C 11111111111111111111111111111111111 00000000000000000000000000000000000 11111111111111111111111111111111111 000000000000000000000000000000000000b W & xn Excess stored charge slows down the transistor when switching Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 37 The Ohio State University % ' $ Cuto I ED E αN IED IE IC α I ICD C E (1− αI ) ICS IE (1− α N ) IES IB B ICD Patrick Roblin IC IB B pE = pC = ;pn ) IED = IES and iE = ;(1 ; N )IES iC = ;(1 ; I )ICS & C ICD = ICS iB = iE ; iC T.H.E OHIO S ATE T UNIVERSITY 38 The Ohio State University using % ' Early E ect 111111111111111111111111111111111111 000000000000000000000000000000000000 Active Region 111111111111111111111111111111111111 000000000000000000000000000000000000 i 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 Cutoff 111111111111111111111111111111111111 000000000000000000000000000000000000 111111111111111111111111111111111111 000000000000000000000000000000000000 E V $ Saturation iC C =βiB iB −VCE A Space Charge P N Space Charge P A Neutral Neutral E & Neutral Neutral 1 0 1 0 1 0 1 0 1 0 1 0 1 B0 1 0 1 0 1 0 0 Wb C xn As the collector base voltage increases the depletion increases, OHIO increasing in turn S ATE T Patrick Roblin T.H.E UNIVERSITY 39 The Ohio State University % ' $ Avalanche E ects Avalanche iC =βiB Active Region Saturation iC iB Cutoff & E 1 IC (avalanche) ' IC 0 1 ; M Patrick Roblin −VCE T.H.E N OHIO S ATE T UNIVERSITY 40 The Ohio State University % ' $ AC Model δ p(xn ) δ p(xn ) ∆ pE δ p(xn ) ∆ pE ∆ pC ∆ pC Q QN N Q Q I ∆ pC 0 Wb xn 0 Wb b) Saturation a) Normal mode 1 1 A QI dQN ; ; + dt tN pN tI 0 1 IC = QN ; QI @ 1 ; 1 A ; dQI dt 0 @1 IE = QN tN & tI Patrick Roblin ∆ pE 0 Wb xn c) Inverted mode pI IB = QN + QI + dQI + dQN dt dt tN xn I tI T.H.E OHIO S ATE T UNIVERSITY 41 The Ohio State University % ' $ Equivalent Circuits Cbc rb rc b c + vbe G se e qI Gse = kT B & Patrick Roblin gm veb Cbe − 2G Cbe = Cje + 3 se e p qI gm = kT C T.H.E OHIO S ATE T UNIVERSITY 42 The Ohio State University % ' $ Principle of HBT Wider bandgap emitter. Abrupt and graded heterojunction -qVBE -qVBE -qVCB & Patrick Roblin N Emitter P Base -qVCB N Collector N Emitter P Base N Collector b) a) T.H.E OHIO S ATE T UNIVERSITY 43 The Ohio State University % ' $ Current Flow in HBT Ln W Space Charge P Lp N W Space Charge P A Neutral iE E cp −qV B = EFp E & Patrick Roblin E vp Neutral Neutral 1 0 1 0 11 00 1 0 11 00 1 0 1 0 1 0 11 00 1 0 1 0 1 0 1 0 1 0 11 00 1 0 11 00 1 0 1 0 1 0 11 00 1 1 0 1 0 11 0 0 −0 1 0 1 0 + +1 11 00 1 0 iB 1 0 V 0− 1 0 10 0 VEB 0 1 1 1 0 BC 1 0 1 0 Drift 0 1 1 0 11 00 Excess electrons 11 00 1 0 1 0 1 0 11 00 1 0 1 0 1 0 1 0 1 0 1 0 11 00 1 0 1 0 1 0 11 00 11 00 1 0 1 0 1 0 1 1 0 1 0 11 00 i0 i Bp 1 0 1 0 11 0 0 Bn 1 0 i Bn 11 00 1 0 1 0 1 0 1 0 1 0 11 00 1 0 1 0 1 0 11 00 1 0 11 00 1 0 1 0 1 0 1 0 1 0 11 00 1 0 1 0 1 0 11 00 1 0 11 00 1 0 1 0 1 0 1 1 0 11 0 0 E0 1 0 Recombination0 1 0 1 0 10 01 1 0 Fn 1 01 1 0 1 0 1 0 11 00 1 0 1 0 1 0 Recombination 11 00 1 0 1 0 1 0 11 00 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 i En Drift Neutral iC E cp −qV = EFp CB E vp iC Drift T.H.E i Ep Excess holes OHIO S ATE T UNIVERSITY 44 The Ohio State University % ' $ Improved Current Gain in HBT InE = Dn B Lp E nB = Dn B Lp E ND E n2 B i IpE Dp E Ln B pE Dp E Ln B NA B n2 E i Dn B Lp E ND E Nc E Nv E exp Eg E ; Eg B ! = Dp E Ln B NA B Nc B Nv B kB T IC = IC InE = B = IE InE InE + IpE & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 45 The Ohio State University % ' $ Advantages of HBTs Large (as large 1600) can be obtained Base resistance RB can be reduced by increasing doping without degrading the emitter injection e ciency Lower emitter doping can be used to reduce the emitter capacitance CEB . A small capacitance leads to improve linearity from mobile RF power ampli er application. The lower RB CEB products leads to higher frequency of operation & Patrick Roblin T.H.E OHIO S ATE T UNIVERSITY 46 The Ohio State University % ...
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