Radiation Damage Studies for Solid State Sensors Subject to Mrad Doses [T506 9-2016 Follow-on] Bruce Schumm UC Santa Cruz September 7, 2016

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

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

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 10-20 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

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

Daughter Board Assembly Pitch adapter, bonds Sensor 1 inch 6 6

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

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

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

Charge Collection Measurement For pad sensors use single-channel readout Daughter-board Low-noise amplifier circuit (~300 electrons) 10 10

Charge Collection Apparatus Readout: 300 ns 2.3 MeV e- through sensor into scintillator Sensor + FE ASIC DAQ FPGA with Ethernet 11 11

Pulse-height distribution for 150V bias Median pulse height vs. bias Measurement time Pulse-height distribution for 150V bias Mean Pulse Shape Single-channel readout example for, e.g., N-type float-zone sensor Readout noise: ~300 electrons (plus system noise we are still addressing) Median pulse height vs. bias 12 12

GaAs Charge Collection (21 Mrad Exposure)  Try even higher annealing temperatures  Higher exposure in next T506 run 21 Mrad Exposure Vbias = 600 V Slice at VB=600 vs. function annealing temp 13 13

PF Charge Collection after 270 Mrad @600 V, ~20% charge collection loss (60C annealing) 14 14

Some Trends So Far Also, PF pad sensor irradiated to ~300 MRad GaAs hasn’t done so well so far SiC (not shown above) down by ~50% after 80 Mrad; maintains low current Si Diode shows 20-60% charge loss after 300 Mrad P-type Si diode sensors perhaps better than N-type (expected?) Both N and P type develop substantial dark current, but probably very tolerable level (10W across entire instrument) Irradiated with 5.7 and 21.0 Mrad doses of electromagnetically-induced showers Also, PF pad sensor irradiated to ~300 MRad 15 15

But: Are electrons the entire picture? G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993) NIEL e- Energy 2x10-2 0.5 MeV 5x10-2 2 MeV 1x10-1 10 MeV 2x10-1 200 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? 16 16

GOALS FOR THIS RUN A bunch of 300 Mrad exposures Expose shard of N-type sensor already under development for use elsewhere in detector New type of sensor: industrial sapphire P-type sensor from 300 to 600 Mrad SiC sensor to 300 Mrad GaAs to higher exposure

BACKUP

Incorporate hadronic processes by placing sensor at maximum of tungsten-induced shower Up to 10W beam absorption; operate at about freezing to avoid annealing 19 19

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 20 20