1. Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/
Semiconductor Device Modeling and Characterization – EE5342 Lecture 21 – Spring 2011
Professor Ronald L. Carter

2. Linking current E-M circuit model
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3. Non-ideal effects in BJTs
Recombination/Generation effects
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
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4. npn Base-width mod. (Early Effect)
Fig 9.15*
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5. Base-width modulation (Early Effect, cont.)
Fig 9.16*
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6. Emitter current crowding in base
Fig 9.21*
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7. Interdigitated base fixes emitter crowding
Fig 9.23*
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8. Base region high- level injection (npn)
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9. Effect of HLI in npn base region
Fig 9.17*
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10. Effect of HLI in npn base region (cont)
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11. Effect of HLI in npn base region (cont)
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12. Emitter region high- level injection (npn)
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13. Effect of HLI in npn emitter region
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14. Effect of HLI in npn base region
Figs 9.18 and 9.19*
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15. Bandgap narrowing effects
Fig 9.20*
Replaces ni2
throughout
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16. 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.
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17. The npn Gummel-Poon Static ModelRC
ICC - IEC =
IS(exp(vBE/NFVt
- exp(vBC/NRVt)/QB B
RBB
ILC
IBR B’
ILE
IBF RE E
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18. Gummel Poon npn Model Equations
IBF = ISexpf(vBE/NFVt)/BF
ILE = ISEexpf(vBE/NEVt)
IBR = ISexpf(vBC/NRVt)/BR
ILC = ISCexpf(vBC/NCVt)
QB = (1 + vBC/VAF + vBE/VAR ) 
{½ + [¼ + (BFIBF/IKF + BRIBR/IKR)]1/2 }
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19. Making a diode from the GP BJT modelC RC
ICC - IEC =
IS(exp(vBE/NFVt
- exp(vBC/NRVt)/QB B
RBB
ILC
IBR B’
ILE
IBF RE E
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20. Making a complete diode with G-P BJT
RB = RC = 0
Set RE to the desired RS value
Set ILE and NE to ISR and NR so this is the rec. current
Set BR=BF>>1, ~1e8 so IBR, IBF are neglibigle
Set ISC = 0 so ILC is = 0
Set IS to IS for diode so ICC-IEC is the injection curr.
Set VAR = VAF = 0
IKF gives the desired high level injection, set IKR = 0
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21. Charge components in the BJT
**From Getreau, Modeling the
Bipolar Transistor, Tektronix, Inc.
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22. References
1 OrCAD PSpice A/D Manual, Version 9.1, November, 1999, OrCAD, Inc.
2 Semiconductor Device Modeling with SPICE, 2nd ed., by Massobrio and Antognetti, McGraw Hill, NY, 1993.
* Semiconductor Physics & Devices, by Donald A. Neamen, Irwin, Chicago, 1997.
** Modeling the Bipolar Transistor, by Ian Getreau, Tektronix, Inc., (out of print).
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