9 Nov 2011 1

Rad-HardPhotomultiplier Chips™

Eric S. Harmon, Ph.D. Brad Cox, Ph.D.Vice President of Research Professor, Experimental High Energy Physicsharmon@lightspintech.com+1 508-809-9052 Chris Neu. Ph.D.

Asst. Prof. , Experimental High Energy PhysicsJim Hyland, Ph.DDavid B. Salzman, Ph.D Bob Hirosky, Ph.D.

Assoc. Prof., Experimental High Energy PhysicsBrian Francis

Mike Arenton, Ph.D. Sasha Ledovskoy, Ph.D.

9 Nov 2011 22

Outline

• GaAs Photomultiplier ChipTM

• Radiation damage in semiconductors

– Bulk damage

– Surface damage

– Dark-count rate

• Experimental Setup for GaAs PMC radiation testing

• Next Steps

• Summary

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LightSpin’s GaAs Photomultiplier ChipTM

• Array of single-photon avalanche devices (SPADs):– PMC™ uses GaAs (or GaInP) for direct absorption photonehp– SiPM and MPPCTM use Si for indirect photon+momentumehp

• PMC™ 1 mm 1 mm prototypes in hand• Straightforward scaling

– cm2 active area at high yield– Comparable production cost to SiPM

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Cost?• High Volume silicon CMOS: $700 per 8” wafer = 2.5 ¢/mm2

(http://www.gsaglobal.org/email/2010/general/0222w.htm)

• High Volume GaAs cost: $1,700 per 6” wafer = 10 ¢/mm2

• High Volume silicon = 100s of wafers per week!

• High Volume GaAs = 10s of wafers per week!

• Volume production wins

• Ultimate cost of 1 cm2 detector (in high volume):

– Silicon: $2.5 + packaging + testing

– GaAs: $10 + packaging + testing

• Current costs of SiPMs: $150/cm2 (http://sensl.com/estore/)

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LightSpin Photomultiplier Chip™

• Designed, grew, fabbed, and tested 1 mm2 devices– 400 SPADs per mm2

– Extremely low dark current (10 pA/mm2)

• High fill factor and high detection efficiency:– Single-photon detection efficiency > 20%

9 Nov 2011 66

LightSpin Photomultiplier Chip™

• Designed, grew, fabbed, and tested 1 mm2 devices– 400 SPADs per mm2

– Extremely low dark current (10 pA/mm2)

• High fill factor and high detection efficiency:– Single-photon detection efficiency > 20%

9 Nov 2011 77

LightSpin GaAs PMC™

• Initial evaluation of radiation hardness mixed:– Devices not designed to be rad hard– Surface vs. bulk radiation damage– Packaging & test issues

• Working on next generation:– 1st generation of Rad Hard GaAs PMC™

• Fab completion due this month– 2nd generation packaging

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Radiation Damage NIEL

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Radiation Damage NIEL

Not directly useful fo

r

comparing materials

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Relative lifetime damageGaAs vs. silicon

• Generation Rate: G = ni V / • Radiation Damage: rad = 1/K• G() ≈ ni V K

variation in neutron damage arises from silicon NIEL curves

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Relative lifetime damageGaInP vs. silicon

• Generation Rate: G = ni V / • ni(GaInP) ni(GaAs)/1E4

variation in neutron damage arises from silicon NIEL curves

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No irradiation

LightSpin preliminary investigation of 1 mm non rad

hard GaAs PMC

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Radiation Damage Analysis

• For low bias, observe reduction in dark current:

– Radiation induced annealing?

– Similar results reported by Sandia

– Indicative of low “bulk” damage

• For high bias, observe dramatic increase in dark current:

– Surface damage (hopping conduction)

– 1st generation Rad Hard GaAs PMC should not suffer this limitation

9 Nov 2011 1414

LightSpin – UVA collaboration

• Test LightSpin GaAs PMC chips for Radiation Hardness:

– Build new test box for GaAs PMC chips

– Develop printed circuit board to allow testing of multiple devices while under irradiation

– Test multiple devices:

• Individual SPAD elements

• PMC arrays (1.0 mm × 1.0 mm):– Approximately 100, 400, 1600 SPADs/mm2

9 Nov 2011 1515

Test SetupNew test fixtureunder construction

20 BNCbias cables

DC bias supply(LED driver)

Keithley 7001switch box

Keithley 237SMU

Programmablebias supply

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1st generation PC Board

Front of Board Back of Board

GaAs PMC

SMA

BNC

BiasCopper ground plane

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2nd generation PC BoardDIP Switch –Isolate individualdevices

Optional 50termination

10 LIMO Connectors(100 Gohmsto ground)

Bias connector

Filtered biasto DUT

Die attacharea

RC biasfilter

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DC Current-Voltage non Rad Hard GaAs PMC Characteristics

Board mounted device

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Board mounted device Probed mounted device

• Packaging + readout board introduced significant leakage current

DC Current-Voltage non Rad Hard GaAs PMC Characteristics

9 Nov 2011 2020

Next Steps

• 1st generation rad hard GaAs PMC: Nov. 2011

• 2nd generation PCB (improve dark current)

• Improved Test Fixture

• Radiation testing at PS at CERN

– Made contact and discussed irradiations with facility managers.

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Summary• Silicon APDs (including MAPD, SiPM and MPPC) will be unable to withstand the anticipated

high-radiation environment of the endcap electromagnetic detector.  Silicon devices also may not be able to be used in portions of the hadronic sections of the endcaps.

• GaAs Photomultiplier Chips™– Predicted to provide more than 100 times more radiation tolerance for neutrons– Predicted to provide 40 – 60 X times more radiation tolerance for protons/electrons

• GaInP Photomultiplier Chips™– Predicted to provide 1E6 times more radiation tolerance for neutrons– Predicted to provide 1E5 times more radiation tolerance for protons/electrons

• LightSpin/UVA collaboration– Completing development of 2nd generation PMC Test Fixture:

• Up to 10 devices can be tested during irradiation• DC and pulsed characterization• Ultra-low leakage design

• 1st generation rad hard GaAs PMC & boards to UVA by end of year• Irradiation regime

– EM– Hadronic– Hadronic + EM– control

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Backup Slides

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Materials Limitations100

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Irradiation materials limitations• Dark count rate & dark current modeled

– Radiation damage factor K

– Thermal generation rate G = ni V / • ni is the intrinsic carrier concentration• V = active volume = lifetime (this is a function of the radiation damage, described by K)

• Surface damage effects• Ultimate limits not included in calculation

– Transmutation doping of active region– Tunneling– Extended defect generation (defect coalescence)

• References:– Radiation Effects in Advanced Semiconductor Materials and Devices by C. Claeys and E. Simoen, Springer Series

in Materials Science, 57, pp. 28 – 36, 132 – 138 (2002).– M. D. Osborne, P. R. Hobson, and S. J. Watts, “Numerical Simulation of Neutron Radiation Effects in Avalanche

Photodiodes,” IEEE Trans. Electron. Dev. 47(3), pp. 529 – 536 (2000).– N. Dharmarasu et al., “High-radiation-resistant InGaP, InGaAs, and InGaAs solar cells for multijunction solar cells,

“ Appl. Phys. Lett. 79(15), pp. 2399 – 2401.

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Radiation Damage

• Bulk defects: intrinsic materials property, accurate measurements

• Surface defects: depends on surface treatment:

– Si: SiO2 vs. Si3N4

– GaAs:

• Imperfect dielectric surface passivationvs. perfect single-crystal passivation

X

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Why is GaAs (GaInP) rad hard?

• Generation Rate: G = ni V /

• Radiation Damage: rad = 1/K

• G() ≈ ni V K

V = 1 mm 1 mm 1 µm

ni K G ()cps/mm2

Cell density

Silicon 1E10/cm3 0.10E-6 cm2/s 1.0E-3

GaAs 2E6/cm3 1.25E-6 cm2/s 2.5E-6

GaInP 300/cm3 1.25E-6 cm2/s 3.8E-10

9 Nov 2011 2727

Why is GaAs (GaInP) rad hard?

• Result for = 1E14/cm2 (SLHC Barrel max dose)

• Cell density assumes saturation rate per cell occurs for count rates > 1E6 cps

V = 1 mm 1 mm 1 µm

ni K G (1E14)cps/mm2

Silicon 1E10/cm3 0.10E-6 cm2/s 1.0E11

GaAs 2E6/cm3 1.25E-6 cm2/s 2.5E8

GaInP 300/cm3 1.25E-6 cm2/s 3.8E4

9 Nov 2011 2828

Why is GaAs (GaInP) rad hard?

• Result for = 1E14/cm2 (SLHC Barrel max dose)

V = 1 mm 1 mm 1 µm

ni K G (1E14)cps/mm2

Cell density

Silicon 1E10/cm3 0.10E-6 cm2/s 1.0E11 100K/mm2

GaAs 2E6/cm3 1.25E-6 cm2/s 2.5E8 250/mm2

GaInP 300/cm3 1.25E-6 cm2/s 3.8E4 < 1/mm2

9 Nov 2011 2929

Why is GaAs (GaInP) rad hard?

• Result for = 7E15/cm2 (SLHC Barrel max dose)

• Cell density assumes saturation rate per cell occurs for count rates > 1E6 cps

V = 1 mm 1 mm 1 µm* 7.0e12 cps/mm2 = 1 µA/mm2 gain

ni K G (7E15)cps/mm2

Cell density

Silicon 1E10/cm3 0.10E-6 cm2/s 7.0E12* 7M/mm2

GaAs 2E6/cm3 1.25E-6 cm2/s 1.8E10 18K/mm2

GaInP 300/cm3 1.25E-6 cm2/s 2.6E6 3/mm2