17-May-15Actual problems of microworld physics. Gomel 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

17-May-15Actual problems of microworld physics. Gomel 2007 Very Forward Region of the ILC Detector Interaction point The purpose of the instrumentation of the very forward region is: –Hermeticity: increase the coverage to polar angles > 5mrad –Fast beam diagnostics EM calorimeter with sandwich structure: 30 layers of 1 X 0 3.5mm W and 0.3mm sensor Angular coverage from 5 mrad to 28 mrad Moliére radius R M ≈ 1cm Segmentation between 0.5 and 0.8 x R M BeamCal

17-May-15Actual problems of microworld physics. Gomel 2007 The Challenges for BeamCal e+e - pairs from beamstrahlung are deflected into the BeamCal e + e - per BX => E dep  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 e-e- e+e+ Creation of beamstrahlung at the ILC ≈ 1 MGy/y ≈ 5 MGy/y For 1 layer, per cell Bethe-Heitler process

17-May-15Actual problems of microworld physics. Gomel 2007 Irradiation facility Energy spectrum of shower particles in BeamCal V.Drugakov 2X 0 Superconducting DArmstadt LINear ACcelerator Technical University of Darmstadt Irradiation up to several MGy using the injector line of the S-DALINAC: 10 ± MeV and beam currents from 2 to 100 nA corresponding to doses about 10 to 600 kGy/h

17-May-15Actual problems of microworld physics. Gomel 2007 Irradiation facility

17-May-15Actual problems of microworld physics. Gomel Investigated materials  Gallium arsenide (GaAs),  Polycristalline CVD Diamond (pCVD)  Silicon (radiaton-hard and common detector-grade for comparison) GaAs SiDiamond Density5.32 g/cm  Pair creation E4.3 eV/pair  Band gap1.42 eV  Electron mobility8500 cm 2 /Vs Hole mobility400 cm 2 /Vs  Dielectric const  Radiation length2.3 cm Ave. E dep /100  m (by 10 MeV e - ) 69.7 keV Ave. pairs/100  m Structurep-n or insul. p-n insul.

17-May-15Actual problems of microworld physics. Gomel 2007 Methodology. Irradiation exit window of beam line collimator (I Coll ) sensor box (I Dia, T Dia, HV) Faraday cup (I FC, T FC ) Irradiation under bias voltage Monitoring of beam and sample currents, sample temperature

17-May-15Actual problems of microworld physics. Gomel 2007 Methodology. CCD Setup typical spectrum of an E6 sensor Sr90 source Preamplifier Sensor box Trigger box & Gate PA discr delay ADC Sr 90 sample Scint. PM1 PM2

17-May-15Actual problems of microworld physics. Gomel 2007 pCVD Diamond Detector pCVD diamonds are an interesting material: –radiation hardness –advantageous properties like: high mobility, low ε R = 5.7, thermal conductivity –availability on wafer scale –Solid-state ionisation chamber (no p- n junction) Samples from two manufacturers were investigated: –Element Six TM (ex-DeBeers) –Fraunhofer Institute for Applied Solid-State Physics – IAF 1 x 1 cm μm thick (typical thickness 300μm) Ti(/Pt)/Au metallization ( courtesy of IAF)

17-May-15Actual problems of microworld physics. Gomel 2007 >5470E6_4p (E6) >5470FAP 5 (IAF) >1300DESY 8 (IAF) >1500E6_B2 (E6) Dose, MGy Thickness, µm Sample 100 nA (E6_4p) 100 nA (FAP5) After absorbing 7MGy: CVD diamonds still operational. CVD Diamond. Irradiation E6_4p

17-May-15Actual problems of microworld physics. Gomel 2007 ~ -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 CVD Diamond. Irradiation results

17-May-15Actual problems of microworld physics. Gomel 2007 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’

17-May-15Actual problems of microworld physics. Gomel 2007 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)

17-May-15Actual problems of microworld physics. Gomel 2007 R pad  500 MOhm 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  100V

17-May-15Actual problems of microworld physics. Gomel 2007 GaAs. Signal Clear separation of peaks from Sr 90 source S8 pad4 ring 4 S8 pad4 ring 6 Quite homogeneous response over different pads Saturation of about 200V bias Collection efficiency  60%

17-May-15Actual problems of microworld physics. Gomel 2007 GaAs. Irradiation Samples 7&8, pad4, 200V Preliminary Sample 7 Sample 8

17-May-15Actual problems of microworld physics. Gomel 2007 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  200V)

17-May-15Actual problems of microworld physics. Gomel 2007 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

17-May-15Actual problems of microworld physics. Gomel 2007 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