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Investigation of radiation hard sensor materials

Investigation of radiation hard sensor materials. K. Afanaciev on behalf of FCAL collaboration. The Xth International School-Seminar The Actual Problems of Microworld Physics Gomel, Belarus 2009. Very Forward Region of the ILC Detector. BeamCal. Interaction point.

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Investigation of radiation hard sensor materials

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  1. Investigation of radiation hard sensor materials . K. Afanaciev on behalf of FCAL collaboration The Xth International School-Seminar The Actual Problems of Microworld Physics Gomel, Belarus 2009 Actual problems of microworld physics. Gomel 2009

  2. Very Forward Region of the ILC Detector BeamCal Interaction point EM calorimeter with sandwich structure: 30 layers of 1 X0 • 3.5mm W and 0.3mm sensor Angular coverage from 5 mrad to 45 mrad Moliére radius RM ≈ 1cm Segmentation between 0.5 and 0.8 x RM • The purpose of the instrumentation of the very forward region is: • Hermeticity: increase the coverage to polar angles > 5mrad • Fast beam diagnostics Actual problems of microworld physics. Gomel 2009

  3. The Challenges for BeamCal Creation of beamstrahlung at the ILC e- e+ Interaction Bethe-Heitler process e+e- pairs from beamstrahlung are deflected into the BeamCal 15000 e+e- per BX => Edep 10 – 20 TeV ~ 5 MGy per year strongly dependent on the beam and magnetic field configuration => radiation hard sensors Detect the signature of single high energetic particles on top of the background. => high dynamic range/linearity ≈ 1 MGy/y ≈ 5 MGy/y For 1 layer, per cell Actual problems of microworld physics. Gomel 2009

  4. Irradiation facility Superconducting DArmstadt LINear ACcelerator Technical University of Darmstadt Irradiation up to several MGy using the injector line of the S-DALINAC: 8 and 10MeV electrons, beam currents from 2 to 100 nA corresponding to doserates about 10 to 600 kGy/h Actual problems of microworld physics. Gomel 2009

  5. Investigated materials • Gallium arsenide (GaAs), • Polycrystalline CVD (chemical vapour deposition) Diamond (pCVD) • Single crystall CVD Diamond (sCVD) • Silicon (common detector-grade Si for comparison) . GaAs Si Diamond Density 5.32 g/cm3 2.33 3.51  Pair creation E 4.3 eV/pair 3.6 13  Band gap 1.42 eV 1.14 5.47  Electron mobility 8500 cm2/Vs 1350 2200 Hole mobility 400 cm2/Vs 450 1600  Dielectric const. 12.85 11.9 5.7  Radiation length 2.3 cm 9.4 18.8 Ave. Edep/100 m (by 10 MeV e-) 69.7 keV 53.3 34.3 Ave. pairs/100 m 13000 9200 3600 Structure p-n or insul. p-n insul. Actual problems of microworld physics. Gomel 2009

  6. Methodology. Irradiation • Irradiation under bias voltage • Monitoring of beam and sample currents, sample temperature exit window of beam line Faraday cup (IFC, TFC) collimator (IColl) sensor box (IDia, TDia, HV) Actual problems of microworld physics. Gomel 2009

  7. Methodology. CCD Setup PA Sr90 sample ADC delay Sr90 source Scint. discr PM1 & Gate discr PM2 Preamplifier Sensor box Trigger box typical spectrum of an E6 sensor Actual problems of microworld physics. Gomel 2009

  8. pCVD Diamond Detector (courtesy of IAF) • pCVD diamonds are an interesting material: • radiation hardness • nice properties like: high mobility, low εR = 5.7, thermal conductivity • availability on wafer scale • Solid-state ionisation chamber (no p-n junction) • Samples from two manufacturers were investigated: • Element SixTM (ex-DeBeers) • Fraunhofer Institute for Applied Solid-State Physics – IAF • 1 x 1 cm2 • 200-500 μm thick (typical thickness 300μm) • Ti(/Pt)/Au metallization (courtesy of IAF) Actual problems of microworld physics. Gomel 2009

  9. pCVD Diamond. Irradiation A number of samples from two producers were irradiated Typical behaviour: Increase in CCD at low dose => pumping - i.e. filling of the traps Then gradual decrease of efficiency with dose After absorbing 7MGy: CVD diamonds still operational. %CCD of the pumped value vs dose Actual problems of microworld physics. Gomel 2009

  10. pCVD Diamond. Irradiation results E6_4 sample from Element 6, 500 μm ~ -80% Signal decreased by  80 % after absorbed dose of about 7 MGy But signal is still visible. Slight increase in current, but still in pA range Actual problems of microworld physics. Gomel 2009

  11. pCVD Diamond. Irradiation results FAP5 sample from IAF, 500 μm Signal from sample decreases with time after irradiation further decrease after ‘purging’ trapping levels with UV light Signal increases back after irradiation with small dose - ‘pumping’ Actual problems of microworld physics. Gomel 2009

  12. sCVD Diamond detector Single crystal CVD (chemical vapour deposition) diamond CVD growth on top diamond substrate +Low defect content, very good detector properties - Small area (up to 5x5mm), very high price Sample produced by Element Six 5x5 mm, 320μm thickness initial charge collection efficiency about 100% (CCD 320μm) Actual problems of microworld physics. Gomel 2009

  13. sCVD Diamond. Irradiation results Irradiation to 10 MGy CCE dropped to 10% of the initial value No visible annealing in 18 month No significant increase in the dark current after the irradiation (still in pA range) Actual problems of microworld physics. Gomel 2009

  14. sCVD Diamond. Switched HV Charge trapping leads to the decrease in the efficiency due to nonuniform charge distribution => switched HV supply => more uniform charge distribution CCD converge to about 1.5x higher and no time dependence Actual problems of microworld physics. Gomel 2009

  15. Diamond Detector. Linearity Testbeam at CERN Proton Synchrotron. 4 GeV hadrons Response to 10 ns spills of variable intensity linear response for particle fluxes from 2x104 MIP/cm2 up to 3x106 MIP/cm2 Actual problems of microworld physics. Gomel 2009

  16. GaAs Detector Supplied by FCAL group at JINR Produced by Siberian Institute of Technology, Tomsk Sample is semi-insulating GaAs doped by Sn (shallow donor) and compensated by Cr (deep acceptor). This is done to compensate electron trapping centers EL2+ and provide i-type conductivity. Sample works as a solid state ionisation chamber Structure provided by metallisation (similar to diamond) 500 m thick detector is divided into 87 5x5 mm pads and mounted on a 0.5mm PCB with fanout Metallisation is V (30 nm) + Au (1 m) Same material - simple 4 pad structure Actual problems of microworld physics. Gomel 2009

  17. GaAs. Signal S8 pad4 ring 4 Clear separation of peaks from Sr90 source S8 pad4 ring 6 Quite homogeneous response over different pads Saturation of signal @ about 200V bias Collection efficiency  60% Actual problems of microworld physics. Gomel 2009

  18. GaAs. Irradiation results  Sample 7  Sample 8 Preliminary Samples 7&8, pad4, ring6 @ 200V Results: CCE dropped to about 6% from 60% (by ~ 90%) after 1.5 MGy this corresponds to signal size of about 2000 e- Actual problems of microworld physics. Gomel 2009

  19. GaAs. Irradiation results Dark current increased  2 times (from 0.4 to 1 A @ 200V) Signal is still visible for an absorbed dose of about 1.5 MGy Actual problems of microworld physics. Gomel 2009

  20. GaAs. Second testbeam A set of GaAs samples with different doping concentrations was irradiated Batch # Shallow donor type Concentration, cm-3 1 Te (1-1.5)*1017 2 Te (5-6)*1016 3 Sn (1-3)*1016 Thicknesses 150 – 200 µm Metallization: V (30 nm) + Au (1 µm) from both sides Actual problems of microworld physics. Gomel 2009

  21. GaAs. Irradiation results A set of GaAs samples with different doping concentrations was irradiated Batch 3 - 90% drop in CCE @ 1.2 MGy Batch with lowest shallow donor concentration shows best radiation hardness Actual problems of microworld physics. Gomel 2009

  22. Silicon. Comparison For comparison purposes two silicon detectors were irradiated (detector grade by Micron) Degradation of signal starts at doses  40 kGy At higher doses dark current and noise level increases dramatically (from  10 nA to A range). No clear signal visible Actual problems of microworld physics. Gomel 2009

  23. Conclusion • For Electromagnetic irradiation: • pCVD Diamond operational up to 7 MGy • sCVD Diamond operational up to 10 MGy • Semiinsulating GaAs operational up to 1.5 MGy Diamond detector have linear response for particle fluxes from 2x104 MIP/cm2 up to 3x106 MIP/cm2 At the moment CVD diamond and GaAs prove to be sufficiently radiation hard for application in BeamCal Inconsistent results from different diamond samples could be a problem Pumping-depumping behavior could be a problem for calorimetry Actual problems of microworld physics. Gomel 2009

  24. Future work A new testbeam is planned for this year New GaAs samples are being produced by JINR FCAL group We are going to test samples with different donor and acceptor concentrations. More tests are needed to understand the possible application of switched HV to improve the diamond detector efficiency Possible new materials? Thank you for your attention Actual problems of microworld physics. Gomel 2009

  25. Backup slides Actual problems of microworld physics. Gomel 2009

  26. Irradiation facility Actual problems of microworld physics. Gomel 2009

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