1. EE 5340 Semiconductor Device Theory Lecture 18 – Spring 2011
Professor Ronald L. Carter

2. Test 2 – Tuesday 05Apr11 11 AM Room 129 ERB Covering Lectures 11 to19
Open book - 1 legal text or ref., only.
You may write notes in your book.
Calculator allowed
A cover sheet will be included with full instructions. For examples see
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5. Ideal diode equation for EgN = EgN
Js = Js,p + Js,n = hole curr + ele curr
Js,p = qni2Dp coth(Wn/Lp)/(NdLp), [cath.] = qni2Dp/(NdWn), Wn << Lp, “short” = qni2Dp/(NdLp), Wn >> Lp, “long”
Js,n = qni2Dn coth(Wp/Ln)/(NaLn), [anode] = qni2Dn/(NaWp), Wp << Ln, “short” = qni2Dn/(NaLn), Wp >> Ln, “long”
Js,n<<Js,p when Na>>Nd , Wn & Wp cnr wdth
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6. Ideal diode equation for heterojunction
Js = Js,p + Js,n = hole curr + ele curr
Js,p = qniN2Dp/[NdLptanh(WN/Lp)], [cath.] = qniN2Dp/[NdWN], WN << Lp, “short” = qniN2Dp/(NdLp), WN >> Lp, “long”
Js,n = qniP2Dn/[NaLntanh(WP/Ln)], [anode] = qniP2Dn/(NaWp), Wp << Ln, “short” = qniP2Dn/(NaLn), Wp >> Ln, “long”
Js,p/Js,n ~ niN2/niP2 ~ exp[[EgP-EgN]/kT]
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7. Bipolar junction transistor (BJT)E B C
VEB
VCB
Charge neutral Region
Depletion Region
The BJT is a “Si sandwich” Pnp (P=p+,p=p-) or Npn (N=n+, n=n-)
BJT action: npn Forward Active when VBE > 0 and VBC < 0
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8. 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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9. BJT boundary and injection cond (npn)
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10. BJT boundary and injection cond (npn)
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11. IC npn BJT (*Fig 9.2a)
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12. npn BJT bands in FA region
q(VbiE-VBE )
q(VbiC-VBC )
qVBE
qVBC
injection
high field
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13. Coordinate system - prototype npn BJT (Fig 9.8*)
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14. Notation for npn & pnp BJTs
NE, NB, NC E, B, and C doping (maj)
xE, xB, xC E, B, and C CNR widths
DE, DB, DC Dminority for E, B, and C
LE, LB, LC Lminority for E, B, and C (L2min = Dmin tmin)
tE0, tB0, tC0 minority carrier life- times for E, B, and C regions
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15. Notation for npn BJTs only
pEO, nBO, pCO: E, B, and C thermal equilibrium minority carrier conc
pE(x’), nB(x), pC(x’’): positional mathe- matical function for the E, B, and C total minority carrier concentrations
dpE(x’), dnB(x), dpC(x’’): positional ma- thematical function for the excess minority carriers in the E, B, and C
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16. Notation for pnp BJTs only
nEO, pBO, nCO: E, B, and C thermal equilibrium minority carrier conc
nE(x’), pB(x), nC (x’’): positional mathe- matical function for the E, B, and C total minority carrier concentrations
dnE(x’), dpB(x), dnC(x’’): positional ma- thematical function for the excess minority carriers in the E, B, and C
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17. npn BJT boundary conditions
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18. Emitter solution in npn BJT
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19. Base solution in npn BJT
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20. Collector solution in npn BJT
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21. Hyperbolic tangent function
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22. npn BJT regions of operation
VBC
Reverse Active
Saturation
VBE
Forward Active
Cutoff
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23. npn FA BJT minority carrier distribution (Fig 9.4*)
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24. npn RA BJT minority carrier distribution (Fig 9.11a*)
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25. npn cutoff BJT min carrier distribution (Fig 9.10a*)
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26. npn sat BJT minority carrier distribution (Fig 9.10b*)
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27. npn BJT currents in the forward active region ©RLC
IC = JCAC
IB=-(IE+IC )
JnE
JnC
IE =
-JEAE
JRB=JnE-JnC
JpE
JGC
JRE
JpC
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28. References
* Semiconductor Physics and Devices, 2nd ed., by Neamen, Irwin, Boston, 1997.
**Device Electronics for Integrated Circuits, 2nd ed., by Muller and Kamins, John Wiley, New York, 1986.
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