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Semiconductor Photon Detectors Ulrich Parzefall Universität Freiburg

Semiconductor Photon Detectors Ulrich Parzefall Universität Freiburg. Overview. Intro: Semiconductor Detectors Detector Materials Silicon CdTe Summary and Outlook. Basic Silicon Strip Detector. -. +. n + -type back side. - +. + -. + -. - +. + -. - +. + -. - +.

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Semiconductor Photon Detectors Ulrich Parzefall Universität Freiburg

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  1. Semiconductor Photon Detectors Ulrich Parzefall Universität Freiburg

  2. Overview • Intro: Semiconductor Detectors • Detector Materials • Silicon • CdTe • Summary and Outlook Ulrich Parzefall, Universität Freiburg

  3. Basic Silicon Strip Detector - + n+-type back side -+ +- +- -+ +- -+ +- -+ p-type surface implants • Take a diode (p-n-junction) • Segment it into strips and n+-dope back side • Apply bias voltage • Wait for photon to deposit charge • Conversion: e- h+ pairs are created • Separated by E-field • Drift towards electrodes • Create signal in p-strips n-type Si-Bulk Ulrich Parzefall, Universität Freiburg

  4. Operation of Si Detector - • MIP deposits 4fC in 300μm Si (23000 e-h+-pairs) • Free charge in 1 cm2 Si-detector is 104 that (T=300K) • Detector can only operate under reverse bias which removes free charges • Depletion zone starts at p-n-junction around strips and grows towards n+-back side + Ulrich Parzefall, Universität Freiburg

  5. Si-Strip Detector Example Ulrich Parzefall, Universität Freiburg

  6. Example: ATLAS SCT Module Ulrich Parzefall, Universität Freiburg

  7. Pixel Detector Overview HAPS design principle • Different pixel detector types • Hybrid Active Pixel Sensors (HAPS) • Detector and readout ASIC are sandwiched together (Nreadout = Npixel ) • Limitation from readout: Pixel size > 120 x 120 μm (2004) • Used widely in collider experiments • ATLAS: 100M Pixels (50x400μm2) • CMS: 23M Pixels (150x150μm2) • Monolithic Active Pixel Sensors (MAPS) • Preamplifier integrated into detector, ASIC nearby • Pixel size > 15 x 15 μm (2005) • Current research topic in many groups, (MIMOSA IReS Strasbourg) Ulrich Parzefall, Universität Freiburg

  8. Medipix Concept e h + HV - • Hybrid principle with sensor and readout ASIC sandwiched • Detector for X-rays • Aim: Replace traditional X-ray photography X-ray Ulrich Parzefall, Universität Freiburg

  9. Semiconductor Detector Material • Material needs to be adapted to photon energy • Absorption for X-rays crucial for detector material • Si only works for low energy X-rays up to ~60 keV • CdTe good up to ~300keV • Medipix-CdTe hot R&D topic Ulrich Parzefall, Universität Freiburg

  10. 3D Detectors n-columns p-columns wafer surface PLANAR 3D p+ p+ p+ n+ 50 mm - n-type substrate - 300 mm - - - - - - - - + + + + + + + + + + • “3D” Principle • narrow columns into detector • diameter 10mm, distance: 50 - 100mm • Effects • lower depletion voltage • smaller charge collection distance -> reduced trapping! 3D concept introduced by: S.I. Parker et al., NIMA 395 (1997) 328 Ulrich Parzefall, Universität Freiburg

  11. 3D Detectors • 3Ds generally complex to manufacture (price) • Different 3D designs exist • This talk restricted to Double-sided Double-Type-Column (DDTC) design • Simplification of full 3D • Made by CNM (Barcelona) and FBK (Trento) • Efficiency is big issue • Field has large variations across detector • Columns are hollow • Must study uniformity of efficiency Ulrich Parzefall, Universität Freiburg

  12. Efficiency in 3D DDTC • Make 2D efficiency map for unirradiated DDTC • Signal cut: SNR ≥ 5 (corresponds to ≈ 6500 e-, 1 fC) • Small efficiency dips in columns • OK – there is no silicon there • Overall efficiency: 99.8 % • 3D DDTC is fully functional as particle detector back column front column readout strips Ulrich Parzefall, Universität Freiburg

  13. Efficiency in 3D DDTC • Cut harder into the signal to look for structure (double cut) • Re-make 2D efficiency map for unirradiated DDTC • Signal cut: SNR ≥ 10 (corresponds to ≈ 13k e-, 2 fC) • Columns become clearly visible • Not a surprise as there is no silicon in columns • Signal comes from Si above/below column • Overall efficiency: 98.5 % • 3D DDTC is fully functional back column front column readout strips Ulrich Parzefall, Universität Freiburg

  14. 3D Detector Results • Compare 3D detectors before and after irradiation to 2·1015Neq in CERN MIP testbeam • Post-irradiation signal larger than expected from 150V onwards => Charge multiplication • Also observed in planar detectors but at much higher bias voltages (Ubias>1.5kV) • ATLAS Si strip upgrade has 500V bias limit • Can „gain“ be used in detector systems ? • Direct comparison: 3D vs planar with MIPs ATLAS planar Si stripHamamatsu detectors 3D DDTC detectorsfrom CNM Ulrich Parzefall, Universität Freiburg

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  16. Ulrich Parzefall, Universität Freiburg

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