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Investigation of radiation hard sensors for the ILC forward calorimeter

Investigation of radiation hard sensors for the ILC forward calorimeter. K. Afanaciev, Ch. Grah, A. Ignatenko, W. Lange, W. Lohmann, M. Ohlerich. International school-seminar Actual problems of microworld Physics Gomel 2007. Very Forward Region of the ILC Detector. BeamCal.

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Investigation of radiation hard sensors for the ILC forward calorimeter

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  1. Investigation of radiation hard sensors for the ILC forward calorimeter . K. Afanaciev, Ch. Grah, A. Ignatenko, W. Lange, W. Lohmann, M. Ohlerich International school-seminar Actual problems of microworld Physics Gomel 2007 Actual problems of microworld physics. Gomel 2007

  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 28 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 2007

  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 2007

  4. Irradiation facility Superconducting DArmstadt LINear ACcelerator Technical University of Darmstadt V.Drugakov 2X0 Energy spectrum of shower particles in BeamCal Irradiation up to several MGy using the injector line of the S-DALINAC: 10 ± 0.015 MeV and beam currents from 2 to 100 nA corresponding to doses about 10 to 600 kGy/h Actual problems of microworld physics. Gomel 2007

  5. Irradiation facility Actual problems of microworld physics. Gomel 2007

  6. Investigated materials • Gallium arsenide (GaAs), • Polycristalline CVD Diamond (pCVD) • Silicon (radiaton-hard and common detector-grade 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 1800 Hole mobility 400 cm2/Vs 450 1200  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 2007

  7. Methodology. Irradiation • Irradiation under bias voltage • Monitoring of beam and sample currents, sample temperature exit window of beam line collimator (IColl) Faraday cup (IFC, TFC) sensor box (IDia, TDia, HV) Actual problems of microworld physics. Gomel 2007

  8. 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 2007

  9. pCVD Diamond Detector (courtesy of IAF) • pCVD diamonds are an interesting material: • radiation hardness • advantageous 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 2007

  10. Sample Thickness, µm Dose, MGy E6_B2 (E6) 500 >1 DESY 8 (IAF) 300 >1 FAP 5 (IAF) 470 >5 E6_4p (E6) 470 >5 100 nA (E6_4p) 100 nA (FAP5) CVD Diamond. Irradiation E6_4p After absorbing 7MGy: CVD diamonds still operational. Actual problems of microworld physics. Gomel 2007

  11. CVD Diamond. Irradiation results ~ -80% Signal decreased by  80 % after absorbed dose of about 7 Gy But signal is still visible. Slight increase in current, but still in pA range Actual problems of microworld physics. Gomel 2007

  12. CVD Diamond. Irradiation results 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 2007

  13. 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) Actual problems of microworld physics. Gomel 2007

  14. I-V and C-V Constant pad capacity no dependence on V => no structure Pad capacity about 12 pF Almost linear IV characteristics => resistor Currents in the order of 0.2 A @ 100V Rpad 500 MOhm Actual problems of microworld physics. Gomel 2007

  15. 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 2007

  16. GaAs. Irradiation  Sample 7  Sample 8 Preliminary Samples 7&8, pad4, ring6 @ 200V Actual problems of microworld physics. Gomel 2007

  17. GaAs. Irradiation results Sample 8 pad4 ring6 Results: CCE dropped to about 6% from 60% (by ~ 90%) but signal is visible for absorbed dose of about 1 MGy Dark current increased  2 times (from 0.4 to 1 A @ 200V) Actual problems of microworld physics. Gomel 2007

  18. 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). No clear signal visible Tested this year Radiation hard silicon - no final results yet but general behavior similar => high currents after about 70 kGy Actual problems of microworld physics. Gomel 2007

  19. Conclusion New results - two more diamond samples from E6 irradiated this year Single crystal CVD diamond sample irradiated Radiation-hard silicon sample irradiated  Analysis in progress Further work is planned for CVD diamond and GaAs Possible new material - SiC 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 behavior could be a problem for calorimetry Actual problems of microworld physics. Gomel 2007

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