chapter 10 - CHAPTER 10 Jill {a} Common base. to) Common...

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Unformatted text preview: CHAPTER 10 Jill {a} Common base. to) Common emitter. (c) Saturation, active, inverted, and cutoff. (d) The buried layer serves as a low—resistance path between the active collector region of the BJT and the top-side collector contact. {6} Nae 3*} Nos 1* Nat: (f) W in both cases. {g} The width of the base is less than, typically much less than, the minority.r carrier diffusion length in the base. (h) The narrow nature of the base couples the current flow across the E—E and C—B junctions, a prefectuisite for transistor action. {i} The emitter efficiencyr specifies the fraction of the emitter can‘em that is associated with carrier injection from the emitter into the base. {1'} The base transport factor is the fraction of the minority carriers injected into the base that successfully diffuse across the quasineutral width of the base and enter the collector. lfl-l 31.3. (a) For the given doping Concentrations, one computes EF~— El = —{l_459eV. H.293eV, and "0.239e‘f reSpectively in the emitter, base, and collector. Also, with MAE 3.1:» N133. the EB depletion width will lie almost ettcltisi'trelg,r in the haae. Likewise. the r1tajorit1.-r of the (3—H depletion width will lie in the collector. The diagram produced by the HIT_Ehflflij prong is displayed below. P lb} ill—2 {c} fiVCE = (IMJHEi-Efiemiuer—(Ei—EFJmuccmr] = (kaqHIHWAEIHj) - MWACMH 01' dVCE= {mqnnwflymc} = {U.D259)1n(5><1n”21014) = 11.2211.r {{1} As noted in the tflxt (Eq. 1113}, W = WE — InEE: -Ince 1:2 44 . “3 IHEB = [EX—SEQ WEE] : = 994 x 1.3-5 cm 2ND]; (Lama—19mg”) Him fl_ M anB NAC+NDE INCH z 3]“ = (2m1.2;(225xm-14m214)(n.552)]m {l.fixlfl'19}{lfl15}{l.1Xlfl‘5) = 2.52 x 1&5 cm and therefdre w = 3 x124 — 9.94 x125 _ 2.52 x m-5 = 1.25 X1fl‘4 cm = 1.25 pm The cnfittcr-base and Collector—has: built—in voltagfis {VbiEE and Vhicfi} ware deduced From the EF— E5 VfllL’IfiS computed in part {a}. (e) 49 15 -5 161222-25 = mm = W = 1.52 x “2 Wm. ESE: (11.3){235xm-14} 49 15 -5 gmflmfi = inflating = W = 3.3.; x ma Wm Km (H.3)(3.35X1fl'”} 19—3 lili {3) For the given doping concentrations, one computes EF- E5 = [1.4TTeV, —fl.353eV, and H.298e‘v' respectiver in the emitter, base, and collector. Also, with NDE 3::- N35, the E—B depletion width will lie almost exclusivelyF in the base. Likewise, the majority of the {3-H depletion width will lie in the collector. The diagram produced by the BITJEbend program is displayed below. (b) 1e-4 (C) fivCE = {IMJHEP—Eikuliccmr— (BF—Ei)emiuflr] = {kaqulniNDdfli} - lfliNDEIHiH 'le fiVCE= (kaanWDdNDE) = (nflzsynnuufirmm) = 41.1%: v {d} Analngous m Eq.(10.3} in the mm, W = WE—IPEE—Iflfi 1a .14 “3 IPEB E lKggg WEE] = {2}(ll.8)(3.85><1fl Hams; = S‘Efixmficm Q'th (Lfixlfl-WJUUIIS] I 2 [2mm Nng‘fivhicflrfl Z (2)01.3)[3.35><lfl‘14}(1fl15)(fl.656} m “CB WAR NDC‘I'NAE (1Jana-19“1&15}(1_1><1{:~‘5) = 3.32 x lfl‘f" cm and marefun: w = 2 x m4 _ 3.3:) x 1D"5 — 3.32 x mvfi = 1.53 x134 cm = 1.53 pm Th3 strfltlcr—basc and callectnr—hasae built—in voltages {Vb-[EB and 1213.153} warn: dfldllfifid fmm 111+: E]: r- E} valuts mmputcd in part (a). (e) —19 16 -5 swam z MXPEB z = m x m4 we“. K580 {11.3}{3.35><m-14) —19 15 «‘5 IEImax{C'B) = QNAB IPCB = = 1.35 X [{I4 Vkm K533 [11.3){3.35x1{}"4) I'D—5 r .- m _ _ w _ _ w _ a. M The energyr band diagram for a typicallyr duped Si npn transistor under equilibrium conditidns was sketched in Fig. Ell}. 1(a). Under active [node biasing in the npn transistor VEE :5 fl and V3,: «r: t]. Appropriately modifying the Fig. Eli]. 1(a) diagram to account fer the applied biases, we Genelude Following the usual pmeedures in interpreting the energy,r band diagram t0 deduce the eleelmstatit: variables, we cenelude V Ifl—T 1!},2 i'ltf— I j + E c I I I C ............. "I ...-F—----------Ei In: ‘ fl n . _ _ _ _ _ _ __ I" (Annwsshuwthe direction flf CHINE! andfar current flow.) fc 10—3 \ ;+“ ' xx; $03355: I'D—9 (a) err = = —“I?§D’f = 0.98m} EP I {b} T _._EL_ = fi = 11,999] I ilép‘l-IEH lmA+flfllmA {C = Icp+fcn 2 {1.93m + Ulnar = {1.93m mA {3 = [5—123 = LGImAFflgflfllrmt-l = 29.9 MA {‘1} 0:41.; = WT = 0.93133 : as; = news :3“ *6“: l—Dtd‘; i—esms ' {e} As given by Eq. {10.12}, feee =an = fl-IHA Likewise, Eq. (113.1?) states I 9.1m ;,=Ji=”=s.sa A CD” new l—flHTflS ’1 (f) The fcp inerease while IEP remains fixed indieates that the base transport faeter has been improved. An increase in err in turn leads to an inerease in 0:3; = m and therefore to an increase in fidc. {g} An inerease in IE" while IEP remains fixed indicates that the emitter effieiene}r has been degraded. A decrease in at in turn leads to a decrease in 0:53 = m and therefore te a decrease in flat. “3— ll} a Fri—n _ Eli”: _ (a) err IE“ — 1m — {1.9901} (b) T: IE" fl,— = 4339,31 IE“ + IEP E 100% +1lw'3l. (fl) IE = fEn+pr = IUUM+1tLA == lfllpfit IQ = fcn+fcp = 99pA+UJpA = 99.111111 I3 = IE—L: = lfllttA—99.lttA = 1.9,ttA {d} (Inc = Tar = {1.93M 2*E1: =_Q&BflL= flit fled; t—tt.aso2 49'5 {e} Analogous to Eq. {143.12}, {C313 =ICI-I = [thttit Likewise, analogous to Eq. {1111?}, .2 least _ “Jim -5 ICE“ 1-4:th ‘ l--fl.93l}2 " “MFA {f} The ID. increase while IE" remains fixed indicates that the base transport factor has been improved. An increase in err in turn leads to an increase in 05.1.; = }ttT and therefore to an increase in fine. (g) An increase in IE1, while IE“ remains fixed indicates that the emitter efficiency has been degraded. A decrease in y in turn leads to a decrease in (rdE = 101‘ and therefore to a decrease in flat. lfl-ll 111 As pictured below, fliers will indeed be some minority carrier holes in the base that wander into the {3—H depletion region and thereby contribute to ICED. However. because the base is very narrow, the quasineutral region generation that sustains the hole current is expected to be small. and the hole cunent itself is therefore expected to be negligible compared to fen. Quantitatiyely. employing an analysis similar to that in Exercise 6.4, 2 2 fen = {HAL-C} [111111113] = an “i 3—0 13c Nae LC and r' e atAW}[—'———"2WDB) — art—L”; Eli-W CF TB q ND]; L3 L12] where the B and C subscripts refer to parameters in the base and colIector, respectively. Since Hug :> NAC and WILB cs: 1, and assuming D0114: ~ DBILE, we again conclude a..ij (1“: arc“. 111—12 ...
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chapter 10 - CHAPTER 10 Jill {a} Common base. to) Common...

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