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Cryogenic Si detectors for Ultra Radiation Hardness in SLHC Environment Zheng Li (BNL)

The Sixth International “Hiroshima” Symposium on the Development and Application of Semiconductor Tracking Detectors. Cryogenic Si detectors for Ultra Radiation Hardness in SLHC Environment Zheng Li (BNL) On behalf of CERN RD39 Collaboration.

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Cryogenic Si detectors for Ultra Radiation Hardness in SLHC Environment Zheng Li (BNL)

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  1. The Sixth International “Hiroshima” Symposium on the Development and Application of Semiconductor Tracking Detectors Cryogenic Si detectors for Ultra Radiation Hardness in SLHC Environment Zheng Li (BNL) On behalf of CERN RD39 Collaboration Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  2. CERN RD39 Collaboration: Cryogenic Tracking Detectors Outline Trapping effect on Charge Collection Efficiency (CCE) in SLHCLHe temperature TCT setupOperation of current-injected-detectors (CID)CCE measurements on CIDSummary Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  3. CERN RD39 Collaboration: Cryogenic Tracking Detectors Trapping effect on CCE in S-LHC Trapping term Depletion term CCEGF is a geometrical factor CCEt is related with trapping For fluence less than 1015 n/cm2, the trapping term CCEt is insignificant For fluence 1016 n/cm2, the trapping term CCEt is a limiting factor of detector operation ! Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  4. To get better CCE: Combined effect (RD39) Improve Neff Reduce trapping >1015 n/cm2 1/2 Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  5. CERN RD39 Collaboration: Cryogenic Tracking Detectors TRAPPING The thermal velocity vth107cm/s 1016cm-2 irradiation produces NT3-5*1016 cm-3 with 10-14cm2 On average (e and h) it gives a t 0.2 ns! Even in highest E-field (Saturation velocity, 107 cm/s), carrier drifts only 20-30 m before it gets trapped regardless whether the detector is fully depleted or not ! In S-LHC conditions, about 90% of the volume of d=300m detector is dead space ! Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  6. CERN RD39 Collaboration: Cryogenic Tracking Detectors • Trapping time: t • 1/ t=  n • e = 7.5010-7 cm2/s • h = 3.75 10-7 cm2/s • for 1016 neq/cm2: • te = 0.13 ns • th = 0.26 ns • t = 0.20 ns as average • Trapping distance (or effective charge collection distance) is: • deff≤ t Vs = 20 μm << d, the detector thickness or depletion depth • The main limiting factor is trapping for SLHC! H.W. Kraner et al., Nuclear Instruments and Methods in Physics Research A326 (1993) 350-356 Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  7. Effective CCE thickness d : thickness (200- 300 μm) w: depletion depth ( ≤ d) t: trapping distance (20-50 µm) Thickness d Q(t) = Q(w) t/w Q(w)= W/d  Q0 Q(t) = Q0 t/d Thickness t (fully depleted, t = w) Q(t) = Q(w) t/w = Q(w) Q(w) = w/d  Q0 = t/d  Q0 Q(t) = Q0 t/d The same! Effective thickness = t Al Al Al SiO2 n+ n+ n+ t substrate e p-type W d p+ Al Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  8. Possible Si detector solutions for SLHC’s most inner region Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  9. CERN RD39 Collaboration: Cryogenic Tracking Detectors DETRAPPING If a trap is filled (electrically non-active) the detrapping time-constant is crucial The detrapping time-constant depends exponentially on T For A-center (O-V at Ec-0.18 eV with  10-15 cm2 ) Fill Freeze T< 77K T> 77K EC EC filled Electron trap Electron trap Hole trap Hole trap filled EV EV Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  10. CERN RD39 Collaboration: Cryogenic Tracking Detectors LHe Temp TCT Setup • A fast TCT setup at CERN with sub-LN2 temp for CCEmeasuements • All components of the setup have been made • The electical part (TCT with ps laser) and the He cryostat are now operational • The final calibration and actual CCE measurements at sub-LN2 temperatures are now underway Sample chamber 160 K Signal recording 250 K 295 K He cryostat First TCT signal of a Si detector He cryostat, to 40 K in 2 hours Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  11. CERN RD39 Collaboration: Cryogenic Tracking Detectors E(x) Em Current injected detector (principle of operation) Jp = epμE divJ=0 divE=ptr E(x=0) = 0 (SCLC: Space Charge Limited Current mode) +Jp P+ P+ x The key advantage: The shape of E(x) is not affected by fluence Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006 V. Eremin, RD39, CERN, November 11, 2005

  12. E(x) Evolution of E(x) in CID with the injected current E(x) E(x) x x x Deep Level saturation p >> ptr E(x) = ax SCLC mode Ndl>ptr E(x) ~ SQR(x) J ~ V2 “Diode” mode p>ptr E(x) ~ E(0) + ax Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  13. log J DL saturation SCLC, J ~ V2 “Diode” Ohmic, J ~ V log V I-V characteristic of CID Proof of CID concept: – observation of SCLC and DL saturation behavior Problem: - optimal range of V for CID operation Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  14. CID I-V simulation software Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  15. CERN RD39 Collaboration: Cryogenic Tracking Detectors I-V characteristics of CID Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  16. CERN RD39 Collaboration: Cryogenic Tracking Detectors I-V characteristics of CID 220 K Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  17. SLHC fluencec -65 C Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  18. CERN RD39 Collaboration: Cryogenic Tracking Detectors Main advantages CID over standard PN detectors • The detectors are always fully depleted • The electric field profile does not change with fluence • Much lower bias voltage is needed • The higher the radiation fluence, the lower the operation current at given bias and temperature • The operation bias range increases with fluence • No breakdown problem due to self-adjusted electric field by space charge limited current feedback effect • Simple detector processing technology (single-sided planar technology) • Injection can also be used to deactivate trapping centers --- CCE Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  19. CCE to 90Sr source at various temperatures for CID CID Mode Forward bias (250 V) Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  20. Φn = 11015 cm-2, T = 180 K, MIPs (1050 nm laser) CID mode Standard mode Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  21. CID mode Measurements from He cryostat, at 60K P-type MCZ, red laser 1x1015/cm2 Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  22. Charge Injected Diode high p : continuous (DC) illumination of n+ side by red laser: changing Neff (DC) probing pulse (elec.) n+ p+ probing pulse (holes) Increase of leakage current due to illumination • Neff controlled by: • illumination intensity ( p ) • operation voltage ( p ) • temperature (trapping -detrapping process) drift time of holes through the detector Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  23. Charge Injected Diode hole current pulse electron current pulse Feq=5x1013 cm-3 (after ~10 days at 20oC) A significant reduction of VFD in case of continuous hole injection! Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  24. CERN RD39 Collaboration: Cryogenic Tracking Detectors CCE Measurements on CID DC injection with a red laser (electrons or holes)Or current injection (forward bias) SLHC fluencec 0.25 cm2 Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  25. CCE to 90Sr source at various temperatures for CID SLHC fluencec Close to 0 at RT! Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

  26. CERN RD39 Collaboration: Cryogenic Tracking Detectors Summary • To increase CCE for SLHC, cryogenic operation of Si detectors at cryogenic temps may be necessaryTrapping can be frozen at such low tempsCID can stablize the detector electric field and increase the detector CCECCE measurements on CID at crogenic temperatures with laser and forward current injection have shown significant increase in CCE Zheng Li on behalf of CERN RD39 Collaboration, September 14, 2006

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