17-May-15Actual problems of microworld physics. Gomel 2007. Investigation of radiation hard sensors for the ILC forward calorimeter K. Afanaciev, Ch. Grah,

Apr 18, 2023 Actual problems of microworld physics. Gomel 2007

. Investigation of radiation hard sensors for the ILC forward calorimeter

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

International school-seminar Actual problems of microworld Physics

Gomel 2007


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


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 the signature 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


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


Irradiation facility


.

Investigated materials

Gallium arsenide (GaAs), Polycristalline CVD Diamond (pCVD) Silicon (radiaton-hard and common detector-grade for comparison)

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.


Methodology. Irradiation

exit windowof beam line

collimator (IColl)

sensor box (IDia, TDia, HV) Faraday cup (IFC, TFC)

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


Methodology. CCD Setup

typical spectrum of an E6 sensor

Sr90 source

Preamplifier

Sensor box

Trigger box

& Gate

PA

discr

discr

delay

ADC

Sr90

sample

Scint.

PM1

PM2


pCVD Diamond Detector

• pCVD diamonds are an interesting material:– radiation hardness– advantageous properties like: high

mobility, low εR = 5.7, thermal conductivity

– availability on wafer scale– Solid-state ionisation chamber (no p-

n junction)

• Samples from two manufacturers were investigated: – Element SixTM (ex-DeBeers)– Fraunhofer Institute for Applied

Solid-State Physics – IAF • 1 x 1 cm2 • 200-500 μm thick

(typical thickness 300μm)• Ti(/Pt)/Au metallization

(courtesy of IAF)

(courtesy of IAF)


>5470E6_4p (E6)

>5470FAP 5 (IAF)

>1300DESY 8 (IAF)

>1500E6_B2 (E6)

Dose, MGy

Thickness, µm

Sample

100 nA (E6_4p)

100 nA (FAP5)

After absorbing 7MGy: CVD diamonds still operational.

CVD Diamond. Irradiation

E6_4p


~ -80%

Signal decreased by 80 % after absorbed dose of about 7 GyBut signal is still visible.Slight increase in current, but still in pA range

CVD Diamond. Irradiation results


CVD Diamond. Irradiation results

Signal from sample decreases with time after irradiationfurther decrease after ‘purging’ trapping levels with UV light

Signal increases back after irradiation with small dose - ‘pumping’


GaAs Detector

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 EL2+ 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)


Rpad 500 MOhm

I-V and C-V

-500 -400 -300 -200 -100 0 100 200 300 400 500

-0.0000016

-0.0000014

-0.0000012

-0.0000010

-0.0000008

-0.0000006

-0.0000004

-0.0000002

0.0000000

0.0000002

0.0000004

0.0000006

0.0000008

0.0000010

0.0000012

Guardring nicht angeschlossen

current-voltage-curve: Ring 6

curr

en

t [A

]

Voltage [V]

Pad-Nummer 1 3 5 7

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

Currents in the order of 0.2 A @ 100V


GaAs. 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%


GaAs. Irradiation

Samples 7&8, pad4, ring6 @ 200V

Preliminary

Sample 7 Sample 8


GaAs. Irradiation results

Sample 8 pad4 ring6

Results: CCE dropped to about 6% from 60% (by ~ 90%)but signal is visible for absorbed dose of about 1 MGy

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


Silicon. Comparison

For comparison purposes two silicon detectors were irradiated(detector grade by Micron)

Degradation of signal starts at doses 40 kGyAt higher doses dark current and noise levelincreases dramatically (from 10 nA to A).No clear signal visible

Tested this year Radiation hard silicon - no final results yetbut general behavior similar => high currents after about 70 kGy


Conclusion

New results - two more diamond samples from E6 irradiated this yearSingle crystal CVD diamond sample irradiated Radiation-hard silicon sample irradiated

Analysis in progress

Further work is planned for CVD diamond and GaAsPossible new material - SiC

At the moment CVD diamond and GaAs prove to be sufficientlyradiation hard for application in BeamCal

Inconsistent results from different diamond samples could be a problemPumping behavior could be a problem for calorimetry

Documents

17-May-15Actual problems of microworld physics. Gomel 2007. Investigation of radiation hard sensors for the ILC forward calorimeter K. Afanaciev, Ch. Grah,