1. 17-May-15FCAL collaboration meeting. Krakow.. Radiation hardness of GaAs Sensors K. Afanaciev, Ch. Grah, A. Ignatenko, W. Lange, W. Lohmann, M. Ohlerich

2. 17-May-15FCAL collaboration meeting. Krakow. 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

3. 17-May-15FCAL collaboration meeting. Krakow. The Challenges for BeamCal e+e - pairs from beamstrahlung are deflected into the BeamCal 15000 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 signatures 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

4. 17-May-15FCAL collaboration meeting. Krakow. 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 ± 0.015 MeV and beam currents from 2 to 100 nA corresponding to doses about 10 to 600 kGy/h

5. 17-May-15FCAL collaboration meeting. Krakow. Irradiation facility

6. 17-May-15FCAL collaboration meeting. Krakow.. The material Gallium arsenide (GaAs) Compound semiconductor, direct bandgap Two sublattices of face centered cubic lattice (zinc-blende type) GaAs SiDiamond Density5.32 g/cm 3 2.33 3.51  Pair creation E4.3 eV/pair 3.6 13  Band gap1.42 eV1.14 5.47  Electron mobility8500 cm 2 /Vs1350 1800 Hole mobility400 cm 2 /Vs 450 1200  Dielectric const.12.8511.9 5.7  Radiation length2.3 cm 9.4 18.8 Ave. E dep /100  m (by 10 MeV e - ) 69.7 keV 53.3 34.3 Ave. pairs/100  m 13000 9200 3600 Structurep-n or insul. p-n insul. Ga As

7. 17-May-15FCAL collaboration meeting. Krakow. The material 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 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) 2 samples

8. 17-May-15FCAL collaboration meeting. Krakow. Methodology. Irradiation exit window of beam line collimator (I Coll ) sensor box (I s, T s, HV) Faraday cup (I FC, T FC ) Irradiation under bias voltage Monitoring of beam and sample currents, sample temperature Beam

9. 17-May-15FCAL collaboration meeting. Krakow. Methodology. CCD Setup Typical spectrum of GaAs sensor Sr90 source Preamplifier Sensor box Trigger box & Gate PA discr delay ADC Sr 90 sample Scint. PM1 PM2

10. 17-May-15FCAL collaboration meeting. Krakow. R pad  500 MOhm Characterization: I-V and C-V Constant pad capacity no dependence on V => no structure Pad capacity about 12 pF Almost linear IV characteristics => resistor Pad parameters homegenious

11. 17-May-15FCAL collaboration meeting. Krakow. Characterization: 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 signal @ about 200V bias Collection efficiency  60%

12. 17-May-15FCAL collaboration meeting. Krakow. GaAs. Irradiation Samples 7&8 (GaAs1, GaAs2) pad4, ring6 @ 200V GaAs2 before irradiation GaAs2 after irradiation Absorbed doses 0.85 and 1.5 MGy

13. 17-May-15FCAL collaboration meeting. Krakow. GaAs. Irradiation results CCE dropped sharply after irradiation but signal is visible Signal increases with bias voltage CCD GaAs1 pad4 ring6, 0.85 MGy IV

14. 17-May-15FCAL collaboration meeting. Krakow. GaAs. Irradiation results CCD GaAs2 pad4 ring6, 1.5 MGy IV Results: CCE dropped to about 6% from 60% (by ~ 90%) but signal is still visible for absorbed dose of about 1.5 MGy Dark current increased  2 times (from 0.4 to 1  A @ 200V)

15. 17-May-15FCAL collaboration meeting. Krakow. GaAs. Neighbor pads GaAs2 pad5 ring6 Double peak - result of a partial exposure of neighbor pads pad size 5x5 mm vs. collimator size 10x10 mm Spectra measured a few weeks after the irradiation => no defect diffusion on this timescale at room temperature.

16. 17-May-15FCAL collaboration meeting. Krakow. Conclusion Signal still visible up to absorbed doses of 1.5 MGy Good homogeneity over the sensor area Predictable behavior under irradiation Signal could still be increased with increasing bias voltage New samples with higher radiation hardness are received by Zeuthen => new beamtest is needed. Irradiated samples are returned to manufacturer for the radiation damage investigation. At the moment GaAs proved to have radiation hardness close to the requirements of the BeamCal, but an improvement is still needed. Could be considered as one of the main candidates for the BeamCal prototype.

17. 17-May-15FCAL collaboration meeting. Krakow.