Polarization effects in the radiation damaged sc CVD

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Polarization effects in the radiation damaged sc. CVD Diamond detectors Sergej Schuwalow, DESY Zeuthen

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

Diamond properties l l l l l Density 3. 52 g cm-3 Dielectric constant

Diamond properties l l l l l Density 3. 52 g cm-3 Dielectric constant 5. 7 Breakdown field 107 V cm-1 Resistivity >1011 Ω cm Band gap 5. 5 e. V 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 e. V Average signal created 36 e μm-1 *High purity single crystal CVD diamond 22 October 2009 FCAL workshop, Geneve 2

MIP Response of sc. CVD Diamond 90 Sr Source PA delay PM 1 ADC

MIP Response of sc. CVD Diamond 90 Sr Source PA delay PM 1 ADC Scint. discr & Sensor box & Preamplifier PM 2 discr Trigger box 22 October 2009 FCAL workshop, Geneve ADC spectrum 3

‘Ideal’ crystal charge collection CCE = Qcollected/Qproduced l CCD = CCE*d Charge collection efficiency

‘Ideal’ crystal charge collection CCE = Qcollected/Qproduced l CCD = CCE*d Charge collection efficiency depends on E HV=0 d Recombination + Full charge collection HV≠ 0 22 October 2009 Charge collection FCAL workshop, Geneve 4

Radiation damaged crystal l l Radiation causes local damages of the lattice structure These

Radiation damaged crystal l l 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 22 October 2009 FCAL workshop, Geneve 5

Irradiation of sc. CVD Diamond DALINAC, TU-Darmstadt June 2007 l l l l l

Irradiation of sc. CVD Diamond DALINAC, TU-Darmstadt June 2007 l l l l l After 5 MGy dose diamond detector is operational CCD is decreasing with the absorbed dose Generation of trapping centers due to irradiation Traps release? CCDcurrent < CCDMIP? Too high ‘missing charge’ ~Natoms in the sample Pure trapping mechanism is contradictory Recombination is important Polarization? 22 October 2009 FCAL workshop, Geneve CCD from 90 Sr setup ‘missing charge’ CCD from Isens 6

Irradiation of sc. CVD Diamond Continued in December 2008 l l No annealing! 1.

Irradiation of sc. CVD Diamond Continued in December 2008 l l No annealing! 1. 5 years, a lot of tests with 90 Sr Source, UVlight, several TSC measurements After 10 MGy absorbed dose MIP signal is still detectable Leakage current is very small ~p. A 22 October 2009 Jun 2007 Data FCAL workshop, Geneve Dec 2008 Data 7

Polarization origin l l l l Uniform generation of e-h pairs Asymmetry is introduced

Polarization origin l l l l 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 22 October 2009 FCAL workshop, Geneve + Eext - 8

Polarization origin l l l l Uniform generation of e-h pairs Asymmetry is introduced

Polarization origin l l l l 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 22 October 2009 FCAL workshop, Geneve + Eext - 9

Polarization origin l l l l Uniform generation of e-h pairs Asymmetry is introduced

Polarization origin l l l l 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 22 October 2009 FCAL workshop, Geneve + Eext - 10

Polarization origin l l l l Uniform generation of e-h pairs Asymmetry is introduced

Polarization origin l l l l 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 22 October 2009 FCAL workshop, Geneve + Eext - 11

Polarization origin l l l l Uniform generation of e-h pairs Asymmetry is introduced

Polarization origin l l l l 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 Eext + - Epol E 22 October 2009 FCAL workshop, Geneve 0 E 0 depth 12

Model: 340 μm sc. CVD diamond after 5 MGy CCD time dependence Space charge

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

Model: 340 μm sc. CVD diamond after 5 MGy CCD time dependence Space charge

Model: 340 μm sc. CVD diamond after 5 MGy CCD time dependence Space charge Neg Charge collection distance Pos Electric field Expected Signal shape E time Zero field 22 October 2009 FCAL workshop, Geneve 14

Model: 340 μm sc. CVD diamond after 5 MGy CCD time dependence Space charge

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

Long-term signal evolution l l l Try to minimize an influence of the measurement

Long-term signal evolution l l l 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! 22 October 2009 t 0 = 35 days FCAL workshop, Geneve 16

Damaged Sensor under 90 Sr Source: CCD vs time Illuminate by UV-light to free

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

Damaged Sensor under 90 Sr Source: CCD vs time Illuminate by UV-light to free

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

Damaged Sensor under 90 Sr Source: CCD vs time Illuminate by UV-light to free

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

Short living traps Damaged Sensor under 90 Sr Source: CCD vs time Illuminate by

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

Beam Pumping Test Trigger Box Linear Drive Collimator 90 Sr Beam Source Faraday Cup

Beam Pumping Test Trigger Box Linear Drive Collimator 90 Sr Beam Source Faraday Cup Collimator Detector+Preamp Box 22 October 2009 FCAL workshop, Geneve 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 21

Beam Pumping Test Dose rate ~ 100 x highest dose rate @ ILC detector

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

TSC measurements At least 3 levels are visible: trap 1 trap 2 trap 3

TSC measurements At least 3 levels are visible: trap 1 trap 2 trap 3 [e. V] 1. 144 +0. 002 0. 851 +0. 002 0. 746 +0. 006 n. T 0 5. 7 1. 5 0. 2 Ec-ET After 5 MGy [1014 cm-3] Trap concentration ~ 1015 cm-3 (still 8 orders of magnitude less than normal atom density) 22 October 2009 FCAL workshop, Geneve 23

Summary l l l The performance of sc. CVD Diamond sensor was studied as

Summary l l l The performance of sc. CVD Diamond sensor was studied as a function of absorbed dose up to 10 MGy Strong polarization effects are observed in the radiation damaged sc. CVD 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 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 22 October 2009 FCAL workshop, Geneve 24

Thank you 22 October 2009 FCAL workshop, Geneve 25

Thank you 22 October 2009 FCAL workshop, Geneve 25