simulation of current filaments in photoconductive semiconductor switches k. kambour, h. p....
TRANSCRIPT
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Simulation of Current Filaments in Photoconductive Semiconductor
Switches
K. Kambour, H. P. Hjalmarson, F. J. Zutavern and A. Mar Sandia National Laboratories*
Charles W. Myles**Texas Tech University
15th International IEEE Pulsed Power ConferenceJune 16, 2005
* Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the United States Department of Energy under contract DE-AC04-94AL85000.** Supported in part by an AFOSR MURI Contract
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Outline
Photoconductive Semiconductor Switches (PCSS's)
Lock-on
Collective Impact Ionization Theory
Monte Carlo Calculations
Continuum Calculations
Conclusions
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A PCSS
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Lock-on
Characterized by a persistent or 'locked-on' electric field (~5 kV/cm) after laser turn off.
High conductivity state
Always accompanied by the formation of current filaments.
The lock-on field is much lower than the bulk breakdown field for GaAs.
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Current Filaments
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Bistable Switch
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Carrier Distribution Function
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Collective Impact Ionization Theory
Inside (high carrier density): the carrier-carrier scattering increases the efficiency of impact ionization for the hot carriers.
Outside (low carrier density): the electric field is too low to create carriers by impact ionization.
Explains highly conductive filaments sustained by a lock-on field lower than the breakdown field.
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Monte Carlo Calculations
Determining the distribution function
Ensemble Monte Carlo
Maxwellian
Calculating the rate of change of particle number
kdrrrfdt
dndefectsAugeriiik
31 )(
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Evolution to a Steady State Solution(no carrier-carrier scattering)
nnFRdt
dn),(0
Auger
defectsii
defectsAugerii
C
CFCFn
CnCFCnFR
)()(
)(),( 20
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Steady State Solution(no carrier-carrier scattering)
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Evolution to Steady State Solutions(carrier-carrier scattering included)
nnFRdt
dn),(
defectsAugeriiii
defectsAugerii
CnCnFCFC
CnCnFCnFR
2
10
20
)()(
),(),(
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Steady State Solutions(carrier-carrier scattering)
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GaAs
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drtrJtrL
tI
tIRtV
RVtV
np
pDqp
nDqn
qnpnApnnpnBgtp
qnpnApnnpnBgtn
trtrptrn
p
pp
nn
nii
nii
)),(),((J1
)(
:currentcarrier Total
)()(V=tV(t)/
: resistance and tagesupply volpower a of in terms )( tageswitch vol for theequation line Load
)(q
-=
:field electric for theequation sPoisson'
)(
)(
:currents hole andelectron for equationsCurrent
/1)())((/
/1)())((/
:densitiescarrier ),(n intrinsic and ),,( holes ),,( electronsfor equations Continuity
n
00
00
p
n
22
22
i
E
EvJ
EvJ
J
J
Continuum Calculations
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Continuum Results
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V0
(KV)
(sec)
VLO
(KV)
50 0 30
50 1x10-9 40
50 1x10-10 no lock-on
50 1x10-11 no lock-on
200 0 40
200 1x10-11 60
Continuum Results
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Conclusions
Collective Impact ionization Theory (CIIT) predicts that lock-on will occur in GaAs at a field much less than the intrinsic breakdown field in GaAs, in qualitative agreement with experiment.
CIIT also predicts that the lock-on field will be independent of rise time and that the lock-on current will flow in stable current filaments in agreement with experiment.