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www.nanohub.org

NCN

Lecture26:SchottkyDiode(II)

MuhammadAshrafulAlamalam@purdue.edu

Alam ECE606S09 1

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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

Alam ECE606S09 3

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

=

Alam ECE606S09 4

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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 = +

Alam ECE606S09 10

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JunctionCapacitance(MajorityCarriers)

Junction

Capacitance

0s A J

W

0

02

( )

sJ

sbi A

C

V V =

Alam ECE606S09 11

D

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NoDiffusionCapacitanceinSchottkyDiode

pnDiode Schottkydiode

n

x

VA

Alam ECE606S09 12

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

Alam ECE606S09 16Ref.Sze/Ng.,p.143

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

Alam ECE606S09 17

A B

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Conclusion

1) Schottkydiodeshavewiderangeofapplicationsinpracticaldevices.

2) ThekeydistinguishingfeatureofSchottkydiodeisthat

it is a ma orit carrier device.

3) Weuseadifferenttechniquetocalculatethecurrentin

.emission.

Alam ECE606S09 18