Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/ Semiconductor Device Modeling and Characterization EE5342, Lecture 13 -Sp 2002 Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/ L13 26Feb02

npn BJT currents (F A region, ©RLC) IC = JCAC IB=-(IE+IC ) JnE JnC IE = -JEAE JRB=JnE-JnC JpE JGC JRE JpC L13 26Feb02

npn BJT topology x x’ p-Base n-Collector N-Emitter z WB WB+WC -WE x”c Charge Neutral Region Depletion Region x x’ p-Base n-Collector N-Emitter z WB WB+WC -WE x”c x” xB x’E IE IC IB L13 26Feb02

E current equations in FA mode npn BJT L13 26Feb02

C current equations in FA mode npn BJT L13 26Feb02

FA npn figure of merit emitter eff L13 26Feb02

FA npn figure of merit base transp L13 26Feb02

FA npn figure of merit recomb fact L13 26Feb02

E current equations in npn BJT (w/o gen/rec) L13 26Feb02

C current equations in npn BJT (w/o gen/rec) L13 26Feb02

Common base current gain, a aT d L13 26Feb02

Common base current gain, a (cont.) L13 26Feb02

Common emitter current gain, b L13 26Feb02

Ebers-Moll Model (Neglecting G-R curr) (Fig. 9.30* Semiconductor Physics & Devices, by Neamen, Irwin, Chicago, 1997, * throughout) -JEAE=IE JCAC=IC L13 26Feb02

Ebers-Moll Model (No G-R curr) -JEAE = IE JCAC = IC E B C aRIR aFIF (Fig. 9.30 Semiconductor Physics & Devices, by Neamen, Irwin, Chicago, 1997, * throughout) L13 26Feb02

Source of Ebers- Moll Equations (E) L13 26Feb02

Source of Ebers- Moll Equations (C) L13 26Feb02

Recombination/Gen Currents (FA) L13 26Feb02

Non-ideal effects in BJTs Base-width modulation (FA: xB changes with changes in VBC) Current 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 L13 26Feb02

npn Base-width mod. (Early Effect) Fig 9.15* L13 26Feb02

Base-width modulation (Early Effect, cont.) Fig 9.16* L13 26Feb02

Emitter current crowding in base Fig 9.21* L13 26Feb02

Interdigitated base fixes emitter crowding Fig 9.23* L13 26Feb02

Non-ideal effects in BJTs Base-width modulation (FA: xB changes with changes in VBC) Current crowding in 2-dim base High-level injection (minority carriers g.t. dopant - especially in the base). Emitter Bandgap narrowing for NE --> density of states at cond. band. edge Junction breakdown at BC junction L13 26Feb02

Base region high- level injection (npn) L13 26Feb02

Effect of HLI in npn base region Fig 9.17* L13 26Feb02

Effect of HLI in npn base region (cont) L13 26Feb02

Effect of HLI in npn base region (cont) L13 26Feb02

Emitter region high- level injection (npn) L13 26Feb02

Effect of HLI in npn emitter region L13 26Feb02

Effect of HLI in npn base region Figs 9.18 and 9.19* L13 26Feb02

Bandgap narrowing effects Fig 9.20* Replaces ni2 throughout L13 26Feb02

Junction breakdown at BC junction Reach-through or punch-through when WCB and/or WEB become large enough to reduce xB to zero Avalanche breakdown when Emax at EB junction or CB junction reaches Ecrit. L13 26Feb02

References * Semiconductor Physics & Devices, by Donald A. Neamen, Irwin, Chicago, 1997. L13 26Feb02