Simulation of Current Filaments in Photoconductive Semiconductor Switches ambour, H. P. Hjalmarson, F. J. Zutavern and A. Sandia National Laboratories* Charles W. Myles** Texas Tech University 15 th International IEEE Pulsed Power Conference June 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
Transcript
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
Outline
Photoconductive Semiconductor Switches (PCSS's)
Lock-on
Collective Impact Ionization Theory
Monte Carlo Calculations
Continuum Calculations
Conclusions
A PCSS
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.
Current Filaments
Bistable Switch
Carrier Distribution Function
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.
Monte Carlo Calculations
Determining the distribution function
Ensemble Monte Carlo
Maxwellian
Calculating the rate of change of particle number
kdrrrfdt
dndefectsAugeriiik
31 )(
Evolution to a Steady State Solution(no carrier-carrier scattering)
nnFRdt
dn),(0
Auger
defectsii
defectsAugerii
C
CFCFn
CnCFCnFR
)()(
)(),( 20
Steady State Solution(no carrier-carrier scattering)
Evolution to Steady State Solutions(carrier-carrier scattering included)
nnFRdt
dn),(
defectsAugeriiii
defectsAugerii
CnCnFCFC
CnCnFCnFR
2
10
20
)()(
),(),(
Steady State Solutions(carrier-carrier scattering)
GaAs
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
Continuum Results
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
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.
