1. Celso Figueiredo26/10/2015 Characterization and optimization of silicon sensors for intense radiation fields Traineeship project within the PH-DT-DD section Integrated within the SSD (Solid State Detectors) team Supervisor: Christian Gallrapp on behalf of Michael Moll Michael Moll is deputy of the PH-DT group and co-spokesperson of the RD50 collaboration

2. 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

3. 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”)

4. Characterization and optimization of silicon sensors for intense radiation fields Project Description - Motivation 4 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!

5. 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: σ e,h – capture cross sections for electrons and holes ΔE – ionization energy N t – defect concentration A large number of defects levels have already been characterized (C i O i, VV, VO, …)

6. 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 V RB > V dep

7. 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

8. Characterization and optimization of silicon sensors for intense radiation fields CV/IV Setup Performed Tasks – CV/IV Setup 8 Capacitance vs. Reverse Bias Voltage Analysis Leakage Current vs. Reverse Bias Voltage Analysis

9. Characterization and optimization of silicon sensors for intense radiation fields TCT Setup Performed Tasks – TCT Setup 9 Induced current vs. time analysis Illumination by picosecond laser pulse

10. 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

11. 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

12. Characterization and optimization of silicon sensors for intense radiation fields Simulations with the Sentaurus Synopsys software suite Performed Tasks – TCAD Simulations 12 Capacitance vs. Reverse Bias Voltage Analysis Red Laser Laser Induced current vs. time analysis Leakage Current vs. Reverse Bias Voltage Analysis

13. 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

14. 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: σ e,h – capture cross sections for electrons and holes ΔE – ionization energy N t – defect concentration It is possible to calculate trap occupation in any point in the silicon bulk

15. 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 Oscilloscope µs pulsed red and IRlaser

16. 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++)

17. 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-G25 Contact: celso.figueiredo@cern.ch

18. Characterization and optimization of silicon sensors for intense radiation fields End 18 Thank you for your attention Questions?