Analysis and Simulation of Charge Collection Efficiency in Si Thin Detectors
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Analysis and Simulation of Charge Collection Efficiency
in Si Thin Detectors
M. Petasecca1,3, F.Moscatelli1,2,3, G.U. Pignatel1,3
1 DIEI - Università di Perugia, via G.Duranti,93 - Italy 2IMM-CNR sez.di Bologna, via Gobetti 101 – Italy
3INFN sez. Perugia – via Pascoli, 10 - Italy
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Outline
• Introduction
• Radiation damage modelling
• Simulation of Silicon Thin structures:– Depletion Voltage as a function of Fluence
– Charge Collection Efficiency as a function of thickness and Fluence
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Introduction
• Simulation of thin diodes:
– Activity included in the framework of CERN RD50 - Radiation hard semiconductor devices for very high luminosity colliders - collaboration
– Study of new structures which improve detector radiation hardness
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Simulation Tool
• Simulation tool:
–ISE-TCAD – discrete time and spatial solutions to equations
• Damage modelling:
- Deep levels: Et, n and p
- SRH statistics- Donor removal mechanism- Other effects: high density defect concentration (clusters) produces an increase of the leakage current
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Three-level model
1010-16-16 cm cm221010-15-15 cm cm228 8 1010-15-15cmcm22pp
1 cm1 cm-1-10.1 cm0.1 cm-1-126 cm26 cm-1-1 1010-15-15 cm cm221010-16-16 cm cm221010-16 -16 cmcm22nn
EEvv+0.36eV+0.36eVEEc c -0.50eV-0.50eVEEc c -0.42eV-0.42eVEEDonorAcceptor Acceptor
• Level characteristics*:
Comparison between simulated and experimental data shows that results have been well reproduced
*Passeri, D.; et al. Nuclear Science, IEEE Transactions on , vol. 48 (2001).
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Thin detectors
• Thin detectors have been proposed to investigate the possibility
to get a low depletion voltage and to limit the leakage current
of heavily irradiated silicon devices
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Simulation setup
Guard Ring Diode Guard Ring
6µm40µm15µm9µm
DBack
Simulated device structure and parameters:
–Doping profiles:
•n-doped substrate (71011 cm-3) 6kΩcm.
•Charge concentration at the silicon-oxide interface of :
–4 1011 cm-3 pre-irradiation
–1 1012 cm-3 post-irradiation
–Optimized variable mesh definition
– Temperature at 300 K
– Different thickness devices: D = 20-50-100-200-300 µm
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Simulation results
Simulated Depletion Voltage as function of the fluence
0.0 1.0x1014 2.0x1014
0
100
200
300
400
Vd
ep [
V]
Fluence [(1MeV) n/cm 2]
300 m
0.0 1.0x1014 2.0x1014
0
4
8
12
16
Vd
ep [
V]
Fluence [(1MeV) n/cm 2]
58 m
- Vdep in thin structures is one order of magnitude lower than in thick one
- Vdep of thin diode at a fluence of 11015 n/cm2 is about 120 V while in thick diode is more than 3000 V !
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
CCE Simulation results
MIP: 80 e-h pairs/ µmCylinder diameter= 2µm
dttIQ )(
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
CCE Simulation results
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
CCE Simulation results
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
CCE Simulation results
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
CCE Simulation results
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
CCE Simulation results
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
CCE Simulation results
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
CCE Simulation results
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Simulated Collected Charge as a function of the applied Bias at 21014 n/cm2 and Experimental data
[1] M.Bruzzi et al./ Nucl.Phys.61B(98)
Simulated data at fluence of 1014 reproduce experimental results [1]
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Simulated Collected Charge as a function of the applied Bias at 1015 and 1016 n/cm2 Fluence
[2] L.Beattie et al./ NIM 412A (98)
1. Simulated data at fluence of 1015 well reproduce experimental data [1,2]2. The simulation of thinner structures (50-100μm) at higher fluence shows a
saturation of the number of e-h pairs collected at the diode’s electrode.
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Simulated CCE as a function of the applied Bias at Fluence of 1015 and 1016 n/cm2
Simulated Charge Collection Efficiency
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Marco Petasecca – DIEI – University of Perugia Glasgow – July 28 - 2004
Conclusions
• Irradiated thin and thick diodes have been analyzed considering a three levels simulation model up to Φ=1e16 n/cm2
• Thin features:
– Vdep in thin structures is one order of magnitude lower
– The results suggest that an optimum thickness exists (50-100 um) which can maximize detector radiation hardness and signal-to-noise ratio.
• Next steps are:
– compare thin structures simulation data at higher fluences (1e16 n/cm2) with irradiated diode measuring results (Bruzzi-Florence and Casse-Liverpool).