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Celso Figueiredo 26/10/2015
Characterization and optimization of silicon sensors for intense radiation fields
Traineeship project within the PH-DT-DD sectionIntegrated within the SSD (Solid State Detectors) team
Supervisor: Christian Gallrapp on behalf of Michael MollMichael Moll is deputy of the PH-DT group and co-spokesperson of the RD50 collaboration
Characterization and optimization of silicon sensors for intense radiation fields
Project Description:
Motivation
Defect Characterization
Performed Tasks:
Initial theoretical training
Initial practical training:
CV/IV
TCT
TCAD Simulations
Main project:
Aim
Performed Simulations
I-DLTS setup
Outlook on future work
Acknowledgements
Outline
2
Characterization and optimization of silicon sensors for intense radiation fields
Project Description - Motivation
3
As the luminosity of the LHC keeps being upgraded, silicon detectors used for particle tracking need to become radiation harder
The signal performance of the silicon detectors degrades with radiation damage, due to the generation of electrically active defects in the silicon bulk
(Michael Moll, 04/2010, “Recent advances in the development of radiation tolerant silicon detectors for the super-LHC”)
Characterization and optimization of silicon sensors for intense radiation fields
Project Description - Motivation
4
1013 5 1014 5 1015 5 1016
eq [cm-2]
5000
10000
15000
20000
25000
signa
l [el
ectro
ns]
n-in-n (FZ), 285m, 600V, 23 GeV p p-in-n (FZ), 300m, 500V, 23GeV pp-in-n (FZ), 300m, 500V, neutrons
p-in-n-FZ (500V)n-in-n FZ (600V)
M.Moll - 08/2008
References:
[1] p/n-FZ, 300m, (-30oC, 25ns), strip [Casse 2008][2] n/n-FZ, 285m, (-10oC, 40ns), pixel [Rohe et al. 2005]
FZ Silicon Strip and Pixel Sensors
strip sensorspixel sensors
Note: Measured partly under different conditions!
Lines to guide the eye (no modeling)!
Strip sensors: max. cumulated fluence for LHC and LHC upgrade
Pixel sensors: max. cumulated fluence for LHC and LHC upgrade
The LHC upgrade will require more radiation tolerant tracking detector concepts!
Also, it will be useful to study and clarify the underlying solid state mechanisms related to radiation damage and tolerance, which are not yet well understood!
Characterization and optimization of silicon sensors for intense radiation fields
Project Description – Defect Characterization
5
Leakage Current Generation
Most effective closer to the middle of the bandgap
Charge Trapping
Impacts Charge Collection Efficiency of electrons and holes
Create Space Charge
Impacts Doping Concentration and Depletion Voltage
According to Shockley-Read-Hall statistics, the impact of defects on detector properties can be calculated if the following parameters are known:
σe,h – capture cross sections for electrons and holesΔE – ionization energyNt – defect concentration
A large number of defects levels have already been characterized (CiOi, VV, VO, …)
Characterization and optimization of silicon sensors for intense radiation fields
Initial theoretical training:
- Solid State and particle physics
- Semiconductor detector technology
- Phenomena of performance degradation in semiconductor detectors in
high radiation environments
Performed Tasks – Theory
6
n+ layer
p+ layer
p-doped bulk
Transversing Particle
+
-
++++
+
- -- -
-Electron Drift
Hole Drift
VRB > Vdep
Characterization and optimization of silicon sensors for intense radiation fields
Initial practical training:
- Operation of silicon sensor characterization setups in the laboratories:
- IV: leakage current vs. applied reverse bias voltage analysis
- CV: capacitance vs. applied reverse bias voltage analysis
- TCT: Laser pulse induced transient current technique
- CV, IV and TCT measurements were performed on n-bulk silicon pad
detectors
- Introduction to Technology Computer Aided Design (TCAD) of silicon
detector structures, using the Sentaurus Synopsys TCAD software suite
Performed Tasks – Practice
7
Characterization and optimization of silicon sensors for intense radiation fields
CV/IV Setup
Performed Tasks – CV/IV Setup
8
Capacitancevs.
Reverse Bias Voltage Analysis
Leakage Currentvs.
Reverse Bias Voltage Analysis
Characterization and optimization of silicon sensors for intense radiation fields
TCT Setup
Performed Tasks – TCT Setup
9
Induced current vs. time analysisIllumination by picosecond laser pulse
Characterization and optimization of silicon sensors for intense radiation fields
Simulations with the Sentaurus Synopsys software suite
- Powerful tool for simulation of 2D/3D semiconductor structures and devices:
- using finite element methods
- solver of coupled differential equations for semiconductors:
- Poisson’s equation, continuity equations for electrons and holes
- includes a wide range of models to calculate solid state physics mechanisms:
- Mobility, Shockley-Read-Hall, Carrier trapping, …
Performed Tasks – TCAD Simulations
10
Characterization and optimization of silicon sensors for intense radiation fields
Simulations with the Sentaurus Synopsys software suite
- The goal of the simulation work is to be able to reproduce the results obtained in IV, CV
and TCT measurements on unirradiated and irradiated detectors.
- Issues:
- There is a very large number of known defects and there is currently no computational power
to be able to include them all in a simulation;
- Need to build a simplified but functional radiation damage model based on a small number of
defects
Performed Tasks – TCAD Simulations
11
Measured Defects TCAD input
Characterization and optimization of silicon sensors for intense radiation fields
Simulations with the Sentaurus Synopsys software suite
Performed Tasks – TCAD Simulations
12
Capacitancevs.
Reverse Bias Voltage Analysis
Red Laser
Laser Induced current vs.
time analysis
Leakage Currentvs.
Reverse Bias Voltage Analysis
Characterization and optimization of silicon sensors for intense radiation fields
Goal:To study the trapping and de-trapping behaviour of proton and neutron irradiated silicon
sensors by means of experiments and simulations in order to identify the radiation induced
defects responsible for charge trapping in silicon detectors.
- Evaluate previous results from Current-Deep Level Transient Spectrocopy (I-DLTS):
- Temperature controlled TCT setup with long, microsecond pulses
- Used to study charge carrier detrapping phenomena
- Match simulation with measurement results and extract defect parameters and
detrapping time constants
Main Project
13
Detector
Bias Tee
DC Power Supply
2.5 GHz Oscilloscope
µs pulsed red and IRlaser
Characterization and optimization of silicon sensors for intense radiation fields
Performed simulations
Main Project
14
Up to now, the results of the simulations match the measurements
only qualitatively. Further work is needed to match the results
obtained in the I-DLTS setup, tuning the following parameters:- Laser Intensity and spot size diameter
- Number of acceptor and donor traps/defects
- For each trap/defect:σe,h – capture cross sections for electrons and holesΔE – ionization energyNt – defect concentration
It is possible to calculate trap occupation in
any point in the silicon bulk
Characterization and optimization of silicon sensors for intense radiation fields
I-DLTS Setup
New I-DLTS measurements:
- Need for a better understanding of the measurement conditions, concerning the laser:
- Characterization of laser power with commercial reference diode
- Tuning and characterization of laser beam width
- New irradiated detector samples are available for measurement and can also be included in
the aim of this project
Main Project
15
Detector
Bias Tee
DC Power Supply
2.5 GHz Oscilloscopeµs pulsed red and IRlaser
Characterization and optimization of silicon sensors for intense radiation fields
Outlook on Future Work
16
Measurements:- Maintenance and characterization of the I-DLTS setup
- Repeat a set of previously done I-DLTS measurements, with better understanding of the used
laser intensity (power and beam width)
- Measure recently available samples (unirradiated and irradiated)
Simulations:
- Use characterization information of the I-DLTS setup as input of TCAD simulations
- Tune simulated defect parameters, aiming to match measurements and simulations results,
and to obtain a predictive radiation model
- Cooperate with other people in the SSD team and the RD50 community in the simulation of
other detector structures
Development:
- Continue to develop scripts for the extraction and plotting of TCAD simulation results (Tcl)
- Development of scripts for data fitting and extraction of detrapping time constants (ROOT, C++)
Characterization and optimization of silicon sensors for intense radiation fields
Acknowlegdements
17
CERN Solid State Detectors Team
Laboratories: 28/2-019, 28/2-020, 28/2-026, 186/R-G25Contact: [email protected]
Characterization and optimization of silicon sensors for intense radiation fields
End
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Thank you for your attention
Questions?