1. 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
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2. npn BJT currents (F A region, ©RLC)
IC = JCAC
IB=-(IE+IC )
JnE
JnC
IE =
-JEAE
JRB=JnE-JnC
JpE
JGC
JRE
JpC
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3. 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
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4. E current equations in FA mode npn BJT
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5. C current equations in FA mode npn BJT
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6. FA npn figure of merit emitter eff
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7. FA npn figure of merit base transp
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8. FA npn figure of merit recomb fact
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9. E current equations in npn BJT (w/o gen/rec)
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10. C current equations in npn BJT (w/o gen/rec)
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11. Common base current gain, aaT d
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12. Common base current gain, a (cont.)
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13. Common emitter current gain, b
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14. Ebers-Moll Model (Neglecting G-R curr)
(Fig. 9.30* Semiconductor Physics & Devices, by Neamen, Irwin, Chicago, 1997, * throughout)
-JEAE=IE
JCAC=IC
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15. Ebers-Moll Model (No G-R curr)
-JEAE
= IE
JCAC
= IC E B C
aRIR
aFIF
(Fig Semiconductor Physics & Devices, by Neamen, Irwin, Chicago, 1997, * throughout)
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16. Source of Ebers- Moll Equations (E)
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17. Source of Ebers- Moll Equations (C)
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18. Recombination/Gen Currents (FA)
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19. 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
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20. npn Base-width mod. (Early Effect)
Fig 9.15*
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21. Base-width modulation (Early Effect, cont.)
Fig 9.16*
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22. Emitter current crowding in base
Fig 9.21*
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23. Interdigitated base fixes emitter crowding
Fig 9.23*
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24. 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
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25. Base region high- level injection (npn)
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26. Effect of HLI in npn base region
Fig 9.17*
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27. Effect of HLI in npn base region (cont)
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28. Effect of HLI in npn base region (cont)
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29. Emitter region high- level injection (npn)
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30. Effect of HLI in npn emitter region
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31. Effect of HLI in npn base region
Figs 9.18 and 9.19*
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32. Bandgap narrowing effects
Fig 9.20*
Replaces ni2
throughout
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33. 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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34. References
* Semiconductor Physics & Devices, by Donald A. Neamen, Irwin, Chicago, 1997.
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