Traineeship project within the PH-DT-DD section

1. 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. Project Description:MotivationDefect CharacterizationPerformed Tasks:Initial theoretical trainingInitial practical training:CV/IV TCT TCAD SimulationsMain project:Aim Performed Simulations I-DLTS setupOutlook on future workAcknowledgements Outline 2

3. Project Description - Motivation 3 (Michael Moll, 04/2010, “Recent advances in the development of radiation tolerant silicon detectors for the super-LHC”) 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

4. Pixel sensors: max. cumulated fluence for LHC andLHC upgrade Project Description - Motivation 4 Note: Measured partly under different conditions! Lines to guide the eye (no modeling)! Strip sensors: max. cumulated fluence for LHC andLHC 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. Project Description – Defect Characterization 5 Create Space Charge Impacts Doping Concentration and Depletion Voltage Charge Trapping Impacts Charge Collection Efficiency of electrons and holes Leakage Current Generation Most effective closer to the middle of the bandgap 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 holes ΔE – ionization energy Nt – defect concentration A large number of defects levels have already been characterized (CiOi, VV, VO, …)

6. 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 VRB > Vdep n+layer - - - - - ElectronDrift p-dopedbulk + - HoleDrift + + + + + p+layer TransversingParticle

7. 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. CV/IV Setup Performed Tasks – CV/IV Setup 8 Capacitance vs. Reverse Bias Voltage Analysis Leakage Current vs. Reverse Bias Voltage Analysis

9. TCT Setup Performed Tasks – TCT Setup 9 Induced current vs. time analysis Illumination by picosecond laser pulse

10. 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. 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 TCAD input Measured Defects

12. Simulations with the Sentaurus Synopsys software suite Performed Tasks – TCAD Simulations 12 Laser Induced current vs. time analysis Capacitance vs. Reverse Bias Voltage Analysis Leakage Current vs. Reverse Bias Voltage Analysis Red Laser

13. 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 µs pulsed red and IRlaser Bias Tee 2.5 GHz Oscilloscope DC Power Supply Detector

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 holes ΔE – ionization energy Nt – defect concentration Performed simulations Main Project 14 It is possible to calculate trap occupation in any point in the silicon bulk

15. I-DLTS SetupNew 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 2.5 GHz Oscilloscope µs pulsed red and IRlaser Bias Tee DC Power Supply Detector

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 structuresDevelopment:- 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++) 16 Outlook on Future Work

17. 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. Thank you for your attention Questions? 18 End