1. 22 October 2009FCAL workshop, Geneve1 Polarization effects in the radiation damaged scCVD Diamond detectors Sergej Schuwalow, DESY Zeuthen On behalf of FCAL collaboration

2. 22 October 2009FCAL workshop, Geneve2 Diamond properties Density 3.52 g cm -3 Dielectric constant 5.7 Breakdown field 10 7 V cm -1 Resistivity >10 11 Ω cm Band gap 5.5 eV Electron mobility 1800 (4500) cm 2 V -1 s -1 Hole mobility 1200 (3800) cm 2 V -1 s -1 Energy to create e-h pair 13.1 eV Average signal created 36 e μm -1 *High purity single crystal CVD diamond

3. 22 October 2009FCAL workshop, Geneve3 MIP Response of scCVD Diamond Diamond 90 Sr Scint. PM1 PM2 discr PAdelay & ADC 90 Sr Source Sensor box & Preamplifier Trigger box ADC spectrum

4. 22 October 2009FCAL workshop, Geneve4 ‘Ideal’ crystal charge collection Charge collection efficiency depends on E Full charge collection HV=0 Recombination HV≠0 Charge collection + - CCE = Q collected /Q produced CCD = CCE*d d

5. 22 October 2009FCAL workshop, Geneve5 Radiation damaged crystal Radiation causes local damages of the lattice structure These local damages (traps) are able to capture free charge carriers and release them after some time Assumptions we are using: Trap density is uniform (bulk radiation damage) Traps are created independently (linearity vs dose) electrons holes Ionization

6. 22 October 2009FCAL workshop, Geneve6 Irradiation of scCVD Diamond After 5 MGy dose diamond detector is operational CCD is decreasing with the absorbed dose Generation of trapping centers due to irradiation Traps release? CCD current < CCD MIP ? Too high ‘missing charge’ ~N atoms in the sample Pure trapping mechanism is contradictory Recombination is important Polarization? ‘missing charge’ DALINAC, TU-Darmstadt June 2007 CCD from 90 Sr setup CCD from I sens

7. 22 October 2009FCAL workshop, Geneve7 Irradiation of scCVD Diamond No annealing! 1.5 years, a lot of tests with 90 Sr Source, UV- light, several TSC measurements After 10 MGy absorbed dose MIP signal is still detectable Leakage current is very small ~pA Continued in December 2008 Jun 2007 Data Dec 2008 Data

8. 22 October 2009FCAL workshop, Geneve8 Polarization origin + - E ext

9. 22 October 2009FCAL workshop, Geneve9 Polarization origin + - E ext

10. 22 October 2009FCAL workshop, Geneve10 Polarization origin + - E ext

11. 22 October 2009FCAL workshop, Geneve11 Polarization origin + - E ext

12. 22 October 2009FCAL workshop, Geneve12 Uniform generation of e-h pairs Asymmetry is introduced by the applied electric field Specific free charge carrier density is largest near detector edges Asymmetric trap filling according to charge carrier density Space charge creation in the bulk of the detector Compensation of the external field by space charge Polarization E pol + - E ext Polarization origin E E0E0 0depth

13. 22 October 2009FCAL workshop, Geneve13 Model: 340 μm scCVD diamond after 5 MGy CCD time dependence time Space chargeCharge collection distance Electric field Expected Signal shape Neg Pos Initial field Low field, recombination Effective charge collection regions

14. 22 October 2009FCAL workshop, Geneve14 Model: 340 μm scCVD diamond after 5 MGy CCD time dependence time Space chargeCharge collection distance Electric field Expected Signal shape Neg Pos Zero field E

15. 22 October 2009FCAL workshop, Geneve15 Model: 340 μm scCVD diamond after 5 MGy CCD time dependence time Space chargeCharge collection distance Electric field Expected Signal shape Neg Pos To be confirmed!

16. 22 October 2009FCAL workshop, Geneve16 Long-term signal evolution Try to minimize an influence of the measurement onto the filled trap distribution Use the source only for short CCD evaluation runs Polarization is seen even after 1 month after the initial pumping – long living traps, possibility to fill all of them! t 0 = 35 days

17. 22 October 2009FCAL workshop, Geneve17 Damaged Sensor under 90 Sr Source: CCD vs time Illuminate by UV-light to free all traps Apply HV and source 90 Sr -HV

18. 22 October 2009FCAL workshop, Geneve18 Damaged Sensor under 90 Sr Source: CCD vs time 90 Sr ±HV Illuminate by UV-light to free all traps Apply HV and source

19. 22 October 2009FCAL workshop, Geneve19 Damaged Sensor under 90 Sr Source: CCD vs time 90 Sr ±HV Illuminate by UV-light to free all traps Apply HV and source

20. 22 October 2009FCAL workshop, Geneve20 Damaged Sensor under 90 Sr Source: CCD vs time 90 Sr ±HV Illuminate by UV-light to free all traps Apply HV and source Short living traps

21. 22 October 2009FCAL workshop, Geneve21 Beam Pumping Test Trigger BoxLinear Drive 90 Sr Source Collimator Faraday Cup Detector+Preamp Box Collimator Beam Use intensive beam to fill up short living traps Move (remotely) detector/preamp box to the low intensity 90 Sr line Measure signal evolution with time since beam-off

22. 22 October 2009FCAL workshop, Geneve22 Beam Pumping Test Clear indication to the presence of fast decaying traps. Additional polarization due to shallow defects filling 5 MGy 10 MGy Dose rate ~ 100 x highest dose rate @ ILC detector

23. 22 October 2009FCAL workshop, Geneve23 TSC measurements At least 3 levels are visible: trap1trap2trap3 Ec-E T [eV] 1.144 +0.002 0.851 +0.002 0.746 +0.006 n T 0 [10 14 cm - 3 ] 5.71.50.2 After 5 MGy Trap concentration ~ 10 15 cm -3 (still 8 orders of magnitude less than normal atom density)

24. 22 October 2009FCAL workshop, Geneve24 Summary The performance of scCVD Diamond sensor was studied as a function of absorbed dose up to 10 MGy Strong polarization effects are observed in the radiation damaged scCVD Diamond detector Polarizaton significantly decreases the detector charge collection efficiency in addition to pure trapping mechanism A simple model is developed in order to understand and describe observed phenomena Method of routinely switching bias HV polarity is proposed to suppress bulk polarization of long-living traps Beam pumping tests indicate that short-living traps are responsible for the residual detector inefficiency

25. 22 October 2009FCAL workshop, Geneve25 Thank you