Phonon-Mediated Distributed Transition- Edge-Sensor X-ray Detectors Steven W. Leman Department of...

Phonon-Mediated Distributed Transition-

Edge-Sensor X-ray Detectors

Steven W. LemanDepartment of Nuclear Engineering and Management, The University of Tokyo

LTD-12August 2007

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Important People• Paul Brink• Blas Cabrera• Astrid Tomada• Betty Young

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• Goals, applications and detector basics

• Energy systems, charge traps and neutralization

• 2-d Si• 2-d Ge• 2-d Si with deep trenches• Energy Resolution

Overview

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Scientific Motivation

Galaxy cluster surveys

Warm-hot intergalactic medium

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Performance Goals• 2 dimension resolving• 1-10 keV band• Position resolution x/x and y/y ~ 100• Energy resolution E/E ~ 1000• Large area ~1-10 cm2

– Via 30 x 30 multiplexed arrays– Equivalent to a 10 megapixel device

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Phonon Mediated DetectorL.E.D.

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3 Detector Comparisons

500350

220

500550

275

500350

320

Ge… ½ Si Debye freqTES reduced by ½

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Detector with Source

1cm

2cm

that little spot is the4 transition edge sensors

refrigeratorcold stage

x-ray source

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Position Determination

Resolution ~20m.

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Spectra

SiliconGermanium

Silicon deep trench

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Energy AbsorptionSilicon Germaniu

mSilicon deep trench

Silicon complete trench

Thickness [m]

350 550 350 350

Trench depth [m]

220 (63%)

275 (50%)

320 (91%)

350 (100%)

Energy absorbed [keV]

2.9 (49%)

~0.5 4.1 (70%)

4.5 (76%)

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Energy Losses• Energy resolution is degraded due to

energy going into nondetectable channels.– Electron—hole pairs lost in charge traps.– Electron—hole pairs diffuse through

bridge and lost to the environment.– Phonons escape through bridge and lost

to the environment.

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Electron-holenumber variation

0,/

EF

numberhe

• X-rays absorbed electron—hole pairs produced.

• F = 0.116, Fano factor.• E = 5.9 keV, X-ray energy.

• = 3.8 eV, electron-hole production energy.

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Phononenergy variation

0,/

EFE

gapenergyhe

• The electron—hole pairs shed energy until they reach the velocity of sound.

• Egap = 1.2 eV, electron-hole gap energy.

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Full-Width at Half-Maximum

• det ~ 0.5, detection efficiency.• 2.355 to convert to FWHM.

eV 77

355210

det

,

/εEFE.ε

ΔEγgapenergyFWHM

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Combined with baseline noise

• Baseline noise = 37 eV.• 68% of energy initially goes into

phonons. 76% could be absorbed in completely trenched TESs.

• Could this suggest the electron—hole pairs are not releasing their energy in the detector?

863777 22

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Trap Concentrations• Penn / Dougherty

– 8,000 cm– 1013 traps / cm3

• Us– 10 cm– 1016 traps / cm3