Apr 21, 2023 FCAL collaboration meeting. Krakow.

.Radiation hardness of GaAs Sensors

K. Afanaciev, Ch. Grah, A. Ignatenko, W. Lange, W. Lohmann, M. Ohlerich

Apr 21, 2023 FCAL collaboration meeting. Krakow.

Very Forward Region of the ILC Detector

Interaction point

• The purpose of the instrumentation of the very forward region is:

– Hermeticity: increase the coverage to polar angles > 5mrad

– Fast beam diagnostics

EM calorimeter with sandwich structure:

30 layers of 1 X0

3.5mm W and 0.3mm sensor Angular coverage from 5 mrad to 28 mrad Moliére radius RM ≈ 1cm Segmentation between 0.5 and 0.8 x RM

BeamCal

Apr 21, 2023 FCAL collaboration meeting. Krakow.

The Challenges for BeamCal

e+e- pairs from beamstrahlung are deflected into the BeamCal

15000 e+e- per BX => Edep 10 – 20 TeV

~ 5 MGy per year strongly dependent on the beam and magnetic field configuration

=> radiation hard sensors

Detect signatures of single high energetic particles on top of the background.

=> high dynamic range/linearity

e- e+

Creation of beamstrahlung at the ILC

≈ 1 MGy/y

≈ 5 MGy/y

For 1 layer, per cell

Bethe-Heitler process

Apr 21, 2023 FCAL collaboration meeting. Krakow.

Irradiation facility

Energy spectrum ofshower particles in BeamCal

V.Drugakov

2X0

Superconducting DArmstadt LINear ACceleratorTechnical University of Darmstadt

Irradiation up to several MGy using the injector line of the S-DALINAC:10 ± 0.015 MeV and beam currents from 2 to 100 nA corresponding to doses about 10 to 600 kGy/h

Apr 21, 2023 FCAL collaboration meeting. Krakow.

Irradiation facility

Apr 21, 2023 FCAL collaboration meeting. Krakow.

.

The material

Gallium arsenide (GaAs)Compound semiconductor, direct bandgapTwo sublattices of face centered cubic lattice(zinc-blende type)

GaAs Si DiamondDensity 5.32 g/cm3 2.33 3.51

Pair creation E 4.3 eV/pair 3.6 13 Band gap 1.42 eV 1.14 5.47 Electron mobility 8500 cm2/Vs 1350 1800

Hole mobility 400 cm2/Vs 450 1200 Dielectric const. 12.85 11.9 5.7 Radiation length 2.3 cm 9.4 18.8

Ave. Edep/100 m(by 10 MeV e-) 69.7 keV 53.3 34.3 Ave. pairs/100 m 13000 9200 3600Structure p-n or insul. p-n insul.

Ga

As

Apr 21, 2023 FCAL collaboration meeting. Krakow.

The material

Supplied by FCAL group at JINRProduced by Siberian Institute of Technology, Tomsk

Sample is semi-insulating GaAs doped by Sn(shallow donor) and compensated by Cr (deep acceptor). This is done to compensate electron trapping centers and provide i-type conductivity.

Sample works as a solid state ionisation chamberStructure provided by metallisation (similar to diamond)

500 m thick detector is divided into 87 5x5 mm padsand mounted on a 0.5mm PCB with fanout

Metallisation is V (30 nm) + Au (1 m)

2 samples

Apr 21, 2023 FCAL collaboration meeting. Krakow.

Methodology. Irradiation

exit windowof beam line

collimator (IColl)

sensor box (Is, Ts, HV) Faraday cup (IFC, TFC)

•Irradiation under bias voltage•Monitoring of beam and sample currents, sample temperature

Beam

Apr 21, 2023 FCAL collaboration meeting. Krakow.

Methodology. CCD Setup

Typical spectrum of GaAs sensor

Sr90 source

Preamplifier

Sensor box

Trigger box

& Gate

PA

discr

discr

delay

ADC

Sr90

sample

Scint.

PM1

PM2

Apr 21, 2023 FCAL collaboration meeting. Krakow.

Rpad 500 MOhm

Characterization: I-V and C-V

0 20 40 60 80 100

1.20E-011

1.30E-011

cap

aci

tan

ce [F

]

Stepnummer [Dealy = 2000ms]

r8p5 r6p4 r3p3 r11p6

Zeitkonstante Spannung

Constant pad capacityno dependence on V =>no structure

Pad capacity about 12 pF

Almost linear IV characteristics => resistor

Pad parameters homegenious

Apr 21, 2023 FCAL collaboration meeting. Krakow.

Characterization: signal

Clear separation of peaks from Sr90 source

S8 pad4ring 4

S8 pad4ring 6

Quite homogeneous response over different pads

Saturation of signal @ about 200V bias

Collection efficiency 60%

Apr 21, 2023 FCAL collaboration meeting. Krakow.

GaAs. Irradiation

Samples 7&8 (GaAs1, GaAs2) pad4, ring6 @ 200V

GaAs2 before irradiation

GaAs2 after irradiation

Absorbed doses 0.85 and 1.5 MGy

Apr 21, 2023 FCAL collaboration meeting. Krakow.

GaAs. Irradiation results

CCE dropped sharply after irradiation but signal is visibleSignal increases with bias voltage

CCD GaAs1 pad4 ring6, 0.85 MGy IV

Apr 21, 2023 FCAL collaboration meeting. Krakow.

GaAs. Irradiation results

CCD GaAs2 pad4 ring6, 1.5 MGy IV

Results: CCE dropped to about 6% from 60% (by ~ 90%)but signal is still visible for absorbed dose of about 1.5 MGy

Dark current increased 2 times (from 0.4 to 1 A @ 200V)

Apr 21, 2023 FCAL collaboration meeting. Krakow.

GaAs. Neighbor pads

GaAs2 pad5 ring6

Double peak - result of a partial exposure of neighbor padspad size 5x5 mm vs. collimator size 10x10 mmSpectra measured a few weeks after the irradiation =>no defect diffusion on this timescale at room temperature.

Apr 21, 2023 FCAL collaboration meeting. Krakow.

Conclusion

• Signal still visible up to absorbed doses of 1.5 MGy• Good homogeneity over the sensor area• Predictable behavior under irradiation• Signal could still be increased with increasing bias voltage

• New samples with higher radiation hardness are received by Zeuthen => new beamtest is needed.• Irradiated samples are returned to manufacturer for the radiation damage investigation.

• At the moment GaAs proved to have radiation hardness close to the requirements of the BeamCal, but an improvement is still needed.• Could be considered as one of the main candidates for the BeamCal prototype.

Apr 21, 2023 FCAL collaboration meeting. Krakow.