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Lecture26:SchottkyDiode(II)
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EnergyResolvedThermionicFlux
occupation
min
~ DOS
34
F
s x xm y z J q dk edk dk
=
min
q(VbiVA)
A
ECEF
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x
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ThermionicFluxfromSemitoMetal..
E( )
min
34
F
s m x y z x
E E J q dk dk edk
=
ECEF
* 2 * 2 * 21 1 1( ) ( )
C x zC F C F FE E E E E E m m mE E + ++ = = +
( )min2 2 2
* ** x y zx z
m m mE E
d m d m d m + +3
4
c
xqe e
=
( ) ( )2 22
min
3 * ***
2 22
3 34
y xz
c F
m mm
E E
s m y z x x
q m J e e d e d d e
=
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ThermionicCurrent
( )min *2
bi A
qV V=
( ) ( )2 22
min
3 * ***
2 22
y xz
c F
m mm
E Eq m
=3 3
4s m y z x x
( )1 bi AV Vq
*
2
( )203
bF C i A AE E qV qV Vq
s m
qm J T e e A e
h
= =
( )0 1AqT s m m s V J J J A e = =
5Comparewithpnjunctionwhereisthebandgap,doping?
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Recombination/Generation/Impactionization
EFMEc
EFEFSEFM
EV
6SAMEtechnique
as
in
p
n
junction
except
integrate
to
xponly
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Outline
1) DCThermioniccurrent(detailedderivation)
2) ACsmallsignalandlargesignalresponse
3) Additionalinformation
4) Conclusions
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TopicMap
signal
SignalDiode
Schottky
BJT/HBT
MOS
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ACresponse
ConductanceJunction
Series
ResistanceDiffusion
Capacitance
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ForwardBiasConductance
gFB
( )
( )/
1A Sq V R I m
o I I e
=
ln ( ) / o A SI I
q V R I m+
= 0
m dV
0( )
S
FB
Rg q I I = + +( )
S
oq I I dI = +
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JunctionCapacitance(MajorityCarriers)
Junction
Capacitance
0s A J
W
0
02
( )
sJ
sbi A
C
V V =
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D
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NoDiffusionCapacitanceinSchottkyDiode
pnDiode Schottkydiode
n
x
VA
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therefore no diffusion capacitance ..
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Reducingdiffusioncapacitanceinpndiode
pnDiode Schottkydiode
n
x
VA
13
Short minority carrier lifetime in p-n junction diode
equivalent to rapid energy relaxation in SB diode.
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Outline
1) DCThermioniccurrent(detailedderivation)
2) ACsmallsignalandlargesignalresponse
3) Additionalinformation
4) Conclusions
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OhmicContactvs.Schottkycontacts..
OxideMetal
n+
nSi
LowDoping ModerateDoping HighDoping
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LoweringofSchottkyBarrier
E
q1qB q1qB
SemiMetal
Metal Semi
SurfaceElectronmageCharge
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x x
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FermilevelPinning
Densityof
StatesRegardless the workfunction, nomodulation in potential.
-
Full
Full
EfEv
. .
Metal MetalSemiconductor
Ec
Shiftinthe
Bandedge
FullFull
f
Ev
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A B
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Conclusion
1) Schottkydiodeshavewiderangeofapplicationsinpracticaldevices.
2) ThekeydistinguishingfeatureofSchottkydiodeisthat
it is a ma orit carrier device.
3) Weuseadifferenttechniquetocalculatethecurrentin
.emission.
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