1. Radiation Damage Studies for Solid State Sensors Subject to MRaD Doses
[T Follow-on]
Bruce Schumm
UC Santa Cruz
December

2. The Issue: ILC BeamCal Radiation Exposure
Covers between 5 and 40 miliradians
Radiation doses up to 100 MRad per year
Radiation initiated by electromagnetic particles (most extant studies for hadron –induced)
EM particles do little damage; might damage be come from small hadronic component of shower? 2 2

3. Radiation Damage in Electromagnetic Showers
Folk wisdom: Radiation damage proportional to non-ionizing component of energy loss in material (“NIEL” model)
BeamCal sensors will be embedded in tungsten radiator
Energy loss dominated by electromagnetic component but non-ionizing contribution may be dominated by hadronic processes

4. Hadronic Processes in EM Showers
There seem to be three main processes for generating hadrons in EM showers (all induced by photons):
Nuclear (“giant dipole”) resonances
Resonance at MeV (~Ecritical)
Photoproduction
Threshold seems to be about 200 MeV
Nuclear Compton scattering
Threshold at about 10 MeV;  resonance at 340 MeV
 These are largely isotropic; must have most of hadronic component develop near sample 4 4

5. Daughter Board Assembly
Pitch adapter, bonds
Sensor
1 inch 5 5

6. Actual Setup In ESA Beamline
2 X0 pre-radiator; introduces a little divergence in shower
Sensor sample
Not shown: 4 X0 and 8 X0 radiators just before and after sensor

7. Proposed split radiator configuration
5mm Tungsten “pre”
13mm Tungsten “post”
Separated by 1m
Fluence (particles per cm2)
1.0
2.0
3.0 7
Radius (cm) 7

8. Rastering
Need uniform illumination over 0.25x0.75 cm region (active area of SCIPP’s charge collection measurement apparatus).
Raster in 0.05cm steps over 1x1 cm, assuming fluence profile on prior slide (see next slide for result)
Exposure rate:
100 MRad at 0.75 nA and 15 GeV  ~ 6 Hours

9. Charge Collection Apparatus
Sensors
DAQ FPGA
with Ethernet
Sensor +
FE ASIC
Recently upgraded for multiple samples
P-type and N-type sensors
Float-zone and Magnetic Czochralski bulk
Will maintain 0-5o C during irradiation
Continue studies begin in 2013 9 9

10. Summer 2013: Initial Si Diode Sensor Doses
“P” = p-type “N” = n-type
“F” = float zone “C” = Czochralski 10 10

11. Other Notable Exposures
GaAs pad sensors via Georgy Shelkov, JINR Dubna
Irradiated with 5.7 and 21.0 Mrad doses of electromagnetically-induced showers
Also, PF pad sensor irradiated to ~300 MRad 11 11

12. NC charge collection after 200 Mrad ~15% charge loss at 300 ns shaping
Dose of 220 Mrad
Incidental annealing
~15% charge loss at 300 ns shaping 12 12

13. PF Current after 300 Mrad Exposure
At 600 V, about 75 A (0.05 W) per cm2 (sensor area ~ cm2) 13 13

14. PF Charge Collection after 300 Mrad
At 600 V, about 30% charge collection loss 14 14

15. GaAs Charge Collection: 5.7 Mrad Exposure
15-20% charge loss at 300 ns shaping
Seems to worsen with annealing
Sensor detached at 30o annealing step
GaAs
Dose of 5.7 Mrad 15 15

16. GaAs Dark Current (-100 C) O(100 nA/cm2) after 6 MRad irradiation
Not observed to improve with annealing 16 16

17. GaAs I-V after 21 Mrad Exposure (-10 C)
At 600 V, about 0.7 A ( W) per cm2
GaAs IV
GaAs
Dose of 21 Mrad
Post-anneal
Pre-anneal 17 17

18. Including 1 HR room-temperature annealing
GaAs Charge Collection after 21 Mrad Exposure and Room Temperature Annealing
GaAs
Dose of 21 Mrad
Including 1 HR room-temperature annealing
Pre-irradiation
Post-irradiation, pre-anneal
Post-irradiation, RT anneal 18 18

19. GOALS FOR THIS RUN Continue exploration of promising Si Diode sensors
300 Mrad exposures for NF, PC, NC type sensors
Put PF back in for another 300 Mrad

20. But: Are electrons the entire picture?
G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993)
NIEL e- Energy
2x MeV
5x MeV
1x MeV
2x MeV
Damage coefficients less for p-type for Ee- < ~1GeV (two groups); note critical energy in W is ~10 MeV
But: Are electrons the entire picture? 20 20

21. BACKUP

22. Incorporate hadronic processes by placing
sensor at maximum of tungsten-induced shower
Up to 10W beam absorption; operate at about freezing to avoid annealing 22 22

23. Summer 2015: SiC and Further Si Exposure
SiC sensor array provided by Bohumir Zatko, Slovak Institute of Science
Irradiated to ~100 Mrad dose
Also, PF pad sensor irradiated to ~300 MRad 23 23