Numerical Modelling of Si Sensors for HEP Experiments and XFEL

1. Numerical Modelling of Si Sensors for HEP Experiments and XFEL A.Srivastava, D. Eckstein, E. Fretwurst, R. Klanner, G. Steinbrück Institute for Experimental Physics, University of Hamburg, Germany Work within RD-50, CEC (within CMS) and AGIPD (@XFEL) Collaboration 9th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detectors, Florence, Italy

2. Outline • Motivation to develop radiation harder detectors • Introduction – • Macroscopic radiation damage in Si detectors • Sensor simulation • :Sensor model/experiment • :Physical models and Synopsis-TCAD simulation procedure • :Simulation work done • Inclusion of radiation effects (surface, bulk) • Conclusion and next steps 2

3. 5 years 10 years 2500 fb-1 500 fb-1 Main Motivations for R & D on Radiation Tolerant Detectors • LHC, L=1034cm-2s-1(14 TeV pp collider, 25 ns bunch spacing • Φneq. (r=4cm) ~3·1015cm-2 • Super-LHC, L=1035cm-2s-1Φneq. (r=4cm) ~1.6·1016cm-2 • Detector for European Free-Electron-Laser XFEL at DESY, Hamburg (start in 2013) :Photon fluxes up to: 1016(12 keV  /cm2 ≙ 109 Gy [109 J/kg] • (200 ns distance between the pulses)  5 (Simulation by M. Huntinen for CMS) 3

4. Introduction Macroscopic Radiation Damage Effects in Silicon Detectors • Bulk (crystal) damage due to Non Ionizing Energy Loss (NIEL) • (displacement damage, point defects and cluster defects) • I. Change of effective doping concentration Neff (full depletion voltage VFD) • II. Increase of leakage current (increase of shot noise, thermal runaway) • III. Increase of charge carrier trapping (reduced charge collection efficiency (CCE)) • Surface damage due to Ionizing Energy Loss (IEL) I. Charge build-up in SiO2(shift of flatband voltage Vfb, breakdown at critical corners, change of interpixel capacitance/resistance) II. Traps at Si-SiO2 interface III. Surface generation current (increase shot noise) 4

5. Sensor Simulation including Radiation Effects • . Simulation of non-irradiated sensors • . Inclusion of radiation effects based on experimental results • Program used: TCAD from Synopsis Physical model used: • SRH (Shockley-Read-Hall) recombination statistics •  Recombination through deep level traps • Impact ionization ( determine breakdown voltage) • Trap model • Doping dependent mobility and high field saturation model • Trap to trap interaction model for charge exchange • Fixed oxide charges+ traps at Si/SiO2 interface  Compare results to analytical calculations for cross-check 5

6. Sensor Simulation: for Particle Physics • Simple p+ on n PAD diode (0.25 cm2) to verify simulations SimulatedPAD Si Sensor model Method:Obtain parameters from experimental data and put into simulation to check data are reproduced 6

7. Four Trap Level Model for n-type MCz Si Sensors • *Modified cross-sections for n-type MCz Si sensor @RT=300K βn=3.66x10-16 cm2/ns and βp=4.92x10-16 cm2/ns • **σp for E5,H152K to agree with data • ***Cluster effect taken into account by increasing the introduction rate of the cluster related defect center E5 by an one order of magnitude 7

8. Comparison with Experiments No charge exchange taken in E5(-/0) H152K(0/-) • Good agreement between simulation, experimental data and model (ii) for VFD and Leakage current • Theoretical calculations underestimate simulated and experimental current values 8

9. Effect of Generation Life Time on E-field for 1x1014 neq./cm2 E-Field expected from double junction g=4.5x10-7 sec g=4.5x10-9 sec Electric field (V/cm) versus device depth (μm) In base region-field –> 100 – 1000 V/cm depends on g • Double junction for fluence of 1x1014 neq./cm2 dueto occupation of traps • Generation life time (deep traps) affects the E-field 9

10. Sensor Simulation: In the Framework of CEC (CMS) Layout for Near-Far Strixel Baby Si strixel Sensor • First step in simulation: Compare 2-D AC-coupled strixel sensor with 3-D AC-coupled strixel sensor 10

11. 2-D and 3-D Strixel Sensor Simulation • Different Strixel design proposed under CEC like Si strixel (1 metal), double metal layer, near far strixel, pitch adapter integrated into Si strixel sensor 11

12. Sensor Simulation: Potential and E-field 12

13. Comparison of I/V Characterstics for 2-D and 3-D 2-Strixel Si Sensor 13

14. Comparison of C/V Characterstics for 2-D and 3-D Strixel Si Sensor Applied bias=100 V, frequency=1 MHz 3-D C/V 2-D C/V CAC CAC CIiM2, CIjM1, Nox=1e12 CIiIj (Cint), Nox=1e12 CIiM2, CIjM1, Nox=1e12 CIiIj (Cint), Nox=1e12 CIiIj , Nox=0.7e11 CIiIj (Cint), Nox=0.7e11 CIiM2, CIjM1, Nox=0.7e11 CIiM2, CIjM1, Nox=0.7e11 CIiM2, CIjM1, Nox=0 CIiIj (Cint), Nox=0 • Diff. of C/V curve due to different geometry of the 2-D and 3-D p+ electrodes • CAC in good agreement with theoretical calculation for both 2-D/3-D • Detector capacitances increases @VFD with surface charges • Up to 0.7x1011 cm-2 Nox, capacitance b/w the p+-strips (Cint) higher than Al-strips. But, for Nox=1x1012 cm-2, vice versa 14

15. Sensor Simulation: for X-FEL X-ray Sensor (AGIPD) CTR- current terminating ring, CR- Current ring, GR- Guard ring 15

16. Surface Damage due to 10 keV X-Rays Results from gated diode measurements for 5 MGy Nox=2 x1012 cm-2, Acceptor@Ec-E=0.35eV,σ=0.05 eV,Nit=4x1012 cm-2 Acceptor@Ec-E=0.6 eV,σ=0.05 eV,Nit=4x1013 cm-2 16

17. Simulation of Guard ring Structure for 5 MGy • VBD observed @995 V, Emax observed on curvature of junction • Compensation of electric field in presence of interface trap and thus low field and high VBD(VBD=299V for Nox=2x1012 cm-2) 17

18. Conclusion and Next Steps • Detailed sensors simulation for radiation damage effects • -Bulk damage induced by hadrons • Good description of leakage current + depletion voltage including “double junction” • Simulation of CEC strixel sensors started • (comparison of 2-D with 3-D simulation) • -Surface damage induced by X-Rays • Detailed simulation of measurements with gated diodes (not shown) • extraction of relevant parameters • Simulation of radiation damage for guard ring started • Next Steps • Mixed irradiation model for n-type MCz Si – In process of upgrade •  for CCE study of an irradiated sensors (for Avalanche Multiplication effect • Comparison of n+ in n and p+ in n pixel for I/V and C/V: AGIPD 18

19. Back-up slides Next Step 19

20. Advanced SFH modelsfor Avalanche Multiplication • The recipe: • Relax the assumption on the trap introduction rate (changes with fluence and particles) • Let the parameters (NA, ND – vary with fluences, sA/De, sA/Dh – fitting and calculated@300K • Keep the traps energy levels (EA, ED) to the exp. values • Normalized to Exp. Room tem. @ 293K • Constraints to the model: • Charge collection profiles (at different Vbias and Φeq) • Trapping rates • Generated leakage current βe/h @T calculated/experimental from G.K. thesis Feq known 20

21. Detector simulation Charge transport ROOT Analysis Trapping Synopsis ISE TCAD n-MCz four level deep traps models (DESSIS) 3-D Electric field mesh Trapping times from literature ROC+FED response Electronic response + data formatting Charge deposit PIXELAV 21

22. Numerical modelling of radiation damage of Si sensor based on emission-capture dynamics of deep trap The leakage current at full depletion (VFD) and effective doping concentration can be calculated by following expressions;    i.e. I(300K) =1.76 x I(293K) (i)  (ii)  22

23. Theoretical Calculation • For 2-D simulaton, half of strixel width (W/2)=12.5µm, Length of strixel(L)= 1 µm (default length) and for 3-D simulation, L=75 µm Coupling capacitance, • Ignoring surface effects, the leakage current @VFD(generation current of the • depletion region: IGEN) can be calculated for 2 strixel Si sensor and 23