Characterization of afterpulse in SiPMs with single-cell readout as a function of bias voltage and fluence

E. Garutti; E. Popova; J. Schwandt; P. Parygin

arxiv: 2604.08308 · v2 · submitted 2026-04-09 · ⚛️ physics.ins-det · hep-ex

Characterization of afterpulse in SiPMs with single-cell readout as a function of bias voltage and fluence

P. Parygin , E. Garutti , E. Popova , J. Schwandt This is my paper

Pith reviewed 2026-05-13 07:36 UTC · model grok-4.3

classification ⚛️ physics.ins-det hep-ex

keywords SiPMafterpulseneutron fluenceirradiationbias voltagetime constantsilicon photomultipliersingle-cell readout

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The pith

Single-cell readout shows afterpulse time constants below 10 ns and probabilities below 6% in SiPMs, independent of neutron fluence at 3-5 V overvoltage.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines afterpulse effects in silicon photomultipliers by employing a dedicated single-cell readout structure that permits direct observation of individual pulses even after irradiation. Three independent analysis methods, one based on charge integration and two using multiple linear regression for waveform reconstruction, were developed and checked with Monte Carlo simulations to quantify afterpulse probability and time constants. Measurements on one unirradiated device and two devices exposed to neutron fluences of 2e12 and 1e13 cm^-2 demonstrate that, for overvoltages between 3 and 5 V above breakdown, the time constant stays under 10 ns and the probability remains under 6%, with neither quantity showing meaningful variation with fluence.

Core claim

The single-cell readout enables direct measurement of intrinsic afterpulse properties, revealing that the time constant is below 10 ns and the probability below 6% for overvoltages of 3 to 5 V, with both quantities showing no significant dependence on irradiation fluence up to 1e13 cm^-2.

What carries the argument

The single-cell readout structure combined with charge-integration and multiple-linear-regression waveform reconstruction methods to count and time-tag afterpulse events.

If this is right

Afterpulse contributions to noise remain small and stable in irradiated SiPMs operated at typical overvoltages.
Trapping-center dynamics in silicon do not appreciably increase afterpulse rates under the tested neutron fluences.
Time-interval distributions constructed from reconstructed pulse positions can isolate distinct trap-release time scales.
The three validated analysis methods provide cross-checks that reduce uncertainty in afterpulse quantification.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The observed fluence independence may allow SiPMs to be used in high-radiation environments without extra afterpulse correction circuits.
Extending the same single-cell technique to higher fluences or different particle types could map the onset of fluence dependence.
The waveform-reconstruction approach could be adapted to study afterpulse in other avalanche photodiodes.

Load-bearing premise

The single-cell readout structure accurately reflects the intrinsic afterpulse dynamics of a standard multi-cell SiPM without adding measurement artifacts.

What would settle it

A side-by-side measurement that finds substantially different afterpulse probability or time constant in a conventional multi-cell SiPM compared with the single-cell device at identical bias and fluence would falsify the claim.

read the original abstract

We present a detailed investigation of the afterpulse effect in silicon photomultipliers (SiPMs), using a dedicated structure with single-cell readout. This enables direct measurement of intrinsic device properties and observation of individual pulses even after irradiation. Three independent analysis methods to quantify afterpulse induced events were developed and validated by Monte Carlo simulations. The first method is based on charge integration, while the other two methods use multiple linear regression to reconstruct transient waveforms and accurately identify individual pulse positions. These positions are then used either as direct event counts or to construct time interval distributions, enabling comprehensive characterization of the afterpulse probability and providing insights into the dynamics of trapping in silicon. Using this framework, we measured three SiPM samples: one fresh reference device and two irradiated devices exposed to reactor neutron fluences of 2e12 and 1e13 cm^-2. We report systematic measurements of the afterpulse probability and time constant as functions of bias voltage and irradiation fluence. For overvoltages in the range of 3 to 5 V above breakdown, the afterpulse time constant is found to be below 10 ns and the afterpulse probability below 6%. Both quantities show no significant dependence on irradiation fluence.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This paper gives direct measurements showing afterpulse stays fast and low-probability in neutron-irradiated SiPMs with no clear fluence dependence up to 1e13 cm^-2.

read the letter

The main takeaway is that afterpulse time constants stay below 10 ns and probabilities below 6% at 3-5 V overvoltage, and these numbers hold steady after reactor neutron exposure on the tested samples. The single-cell readout structure is the practical advance here. It lets them observe individual pulses directly even on irradiated devices, which standard multi-cell readouts make harder. They run three analysis methods in parallel—charge integration plus two regression fits on the waveforms—and cross-check the whole thing with Monte Carlo to confirm they are not missing or double-counting events. That internal consistency is the part that gives the results some weight. The systematic voltage and fluence scans on a reference device plus two irradiated ones are straightforward and useful for anyone who needs numbers for detector modeling. The fluence-independence finding is the result that could actually change design choices. A minor soft spot is that the single-cell geometry might still differ from a full array in ways the Monte Carlo does not fully capture, though the paper treats this as a controlled approximation. Only two fluence points also limit how strongly one can claim independence across all possible exposures. This is for detector physicists and engineers working on SiPMs in radiation environments such as high-energy physics or medical imaging. The data are concrete enough to be worth having. I would send it to peer review. The methods are checked and the measurements are direct.

Referee Report

0 major / 3 minor

Summary. The manuscript reports measurements of afterpulse probability and time constant in SiPMs using a dedicated single-cell readout structure on one unirradiated reference sample and two neutron-irradiated samples (fluences 2×10^{12} and 1×10^{13} cm^{-2}). Three analysis methods (charge integration plus two multiple-linear-regression waveform reconstructions) are developed and cross-validated by Monte Carlo simulations. For overvoltages of 3–5 V the afterpulse time constant is reported below 10 ns and probability below 6 %, with no significant fluence dependence.

Significance. The work supplies direct empirical data on afterpulsing in irradiated SiPMs, obtained via single-cell readout that permits observation of individual pulses even after irradiation. The multi-method approach validated by Monte Carlo strengthens reliability of the extracted parameters. The reported fluence independence up to 10^{13} cm^{-2} is a practically useful result for radiation-hard detector design in high-energy physics and medical imaging.

minor comments (3)

[§3.2] §3.2: the Monte Carlo validation section would benefit from explicit listing of the assumed single-cell pulse shape parameters and noise model so that the three analysis methods can be reproduced independently.
[Figure 7] Figure 7: the time-interval histograms would be easier to interpret if the y-axis were logarithmic and the fitted exponential components were overlaid with their uncertainties.
[§5] §5: the statement that afterpulse probability shows 'no significant dependence' on fluence should be accompanied by the statistical test (e.g., p-value or confidence interval on the slope) used to reach that conclusion.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive review, accurate summary of our methods and results, and the recommendation to accept the manuscript. The significance statement correctly identifies the value of the single-cell readout approach and the fluence-independence finding for radiation-hard applications.

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper is a purely experimental characterization study. It reports direct measurements of afterpulse probability and time constant on three SiPM samples (one reference and two neutron-irradiated) using a dedicated single-cell readout structure. Three analysis methods—charge integration plus two multiple-linear-regression waveform reconstructions—are cross-validated against Monte Carlo simulations to confirm event capture completeness. The reported results (time constant <10 ns and probability <6% for 3–5 V overvoltage, fluence independence) are extracted from the measured waveforms and time-interval distributions without any derivation chain, parameter fitting that renames inputs as predictions, or load-bearing self-citations. No equations reduce the outputs to the inputs by construction, and the Monte Carlo validation is an independent check rather than a self-referential step. The work is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Experimental characterization paper with no free parameters fitted to produce the central claim, no invented entities, and reliance only on standard domain assumptions about SiPM trapping physics.

axioms (1)

domain assumption Afterpulse arises from charge carrier trapping and delayed release in silicon
Underlies interpretation of measured time constants and probabilities in all three analysis methods.

pith-pipeline@v0.9.0 · 5527 in / 1189 out tokens · 50692 ms · 2026-05-13T07:36:29.495618+00:00 · methodology

Review history (2 revisions) →

discussion (0)

Reference graph

Works this paper leans on

7 extracted references · 7 canonical work pages

[1]

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work page
[2]

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Y. Musienko, A study of the radiation hardness of silicon photomultipliers for the CMS HGCAL , https://doi.org/10.1016/j.nima.2015.01.012 Journal of Instrumentation 10 (2015) C08003

work page doi:10.1016/j.nima.2015.01.012 2015
[3]

Klanner, Characterisation of SiPMs , https://doi.org/10.1016/j.nima.2018.11.083 Nuclear Instruments and Methods in Physics Research Section A 926 (2019) 36

R. Klanner, Characterisation of SiPMs , https://doi.org/10.1016/j.nima.2018.11.083 Nuclear Instruments and Methods in Physics Research Section A 926 (2019) 36

work page doi:10.1016/j.nima.2018.11.083 2018
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O. Bychkova et al., Radiation hardness study using SiPMs with single-cell readout , https://doi.org/https://doi.org/10.1016/j.nima.2022.166533 Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1031 (2022) 166533

work page doi:10.1016/j.nima.2022.166533 2022
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O. Bychkova et al., Radiation damage uniformity in a SiPM , https://doi.org/https://doi.org/10.1016/j.nima.2022.167042 Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1039 (2022) 167042

work page doi:10.1016/j.nima.2022.167042 2022
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Schmailzl et al., SiPM signal processing via multiple linear regression , https://doi.org/10.1088/1748-0221/18/07/P07010 Journal of Instrumentation 18 (2023) P07010

W. Schmailzl et al., SiPM signal processing via multiple linear regression , https://doi.org/10.1088/1748-0221/18/07/P07010 Journal of Instrumentation 18 (2023) P07010

work page doi:10.1088/1748-0221/18/07/p07010 2023
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E. Garutti et al., Simulation of the response of SiPMs; Part I: Without saturation effects , https://doi.org/https://doi.org/10.1016/j.nima.2021.165853 Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1019 (2021) 165853

work page doi:10.1016/j.nima.2021.165853 2021

[1] [1]

write newline

" write newline "" before.all 'output.state := FUNCTION blank.sep after.quote 'output.state := FUNCTION fin.entry output.state after.quoted.block = 'skip 'add.period if write newline FUNCTION new.block output.state before.all = 'skip output.state after.quote = after.quoted.block 'output.state := after.block 'output.state := if if FUNCTION new.sentence out...

work page

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Musienko, A study of the radiation hardness of silicon photomultipliers for the CMS HGCAL , https://doi.org/10.1016/j.nima.2015.01.012 Journal of Instrumentation 10 (2015) C08003

Y. Musienko, A study of the radiation hardness of silicon photomultipliers for the CMS HGCAL , https://doi.org/10.1016/j.nima.2015.01.012 Journal of Instrumentation 10 (2015) C08003

work page doi:10.1016/j.nima.2015.01.012 2015

[3] [3]

Klanner, Characterisation of SiPMs , https://doi.org/10.1016/j.nima.2018.11.083 Nuclear Instruments and Methods in Physics Research Section A 926 (2019) 36

R. Klanner, Characterisation of SiPMs , https://doi.org/10.1016/j.nima.2018.11.083 Nuclear Instruments and Methods in Physics Research Section A 926 (2019) 36

work page doi:10.1016/j.nima.2018.11.083 2018

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O. Bychkova et al., Radiation hardness study using SiPMs with single-cell readout , https://doi.org/https://doi.org/10.1016/j.nima.2022.166533 Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1031 (2022) 166533

work page doi:10.1016/j.nima.2022.166533 2022

[5] [5]

O. Bychkova et al., Radiation damage uniformity in a SiPM , https://doi.org/https://doi.org/10.1016/j.nima.2022.167042 Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1039 (2022) 167042

work page doi:10.1016/j.nima.2022.167042 2022

[6] [6]

Schmailzl et al., SiPM signal processing via multiple linear regression , https://doi.org/10.1088/1748-0221/18/07/P07010 Journal of Instrumentation 18 (2023) P07010

W. Schmailzl et al., SiPM signal processing via multiple linear regression , https://doi.org/10.1088/1748-0221/18/07/P07010 Journal of Instrumentation 18 (2023) P07010

work page doi:10.1088/1748-0221/18/07/p07010 2023

[7] [7]

E. Garutti et al., Simulation of the response of SiPMs; Part I: Without saturation effects , https://doi.org/https://doi.org/10.1016/j.nima.2021.165853 Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1019 (2021) 165853

work page doi:10.1016/j.nima.2021.165853 2021