xe

ral R

Avalanche photodiode

GPD

rs (

d f

erfo

eld

g m

me

n a

era

time constants of 15 and 82ns. The cross-talk probability is a factor of 3 smaller than the after-

puling probability. Simulating the MPPC response, we nd that after-pulsing and cross-talk do not

t

desigARC acdetec

tromagdetecto

detection efciency, and being insensitive to magnetic eld. While

characterized in depth. The aim of this paper is to investigate

ableon as [4].

peaking time. Both electronics are expected to achieve the

ARTICLE IN PRESS

Contents lists availab

.e

te

Nuclear Instruments and Methods in Physics Research A 596 (2008) 396401do not affect the energy resolution and the timing resolution,quantitatively two possible drawbacks: after-pulsing and cross-talk, in order to determine to which extent they affect the detectorperformance.

required timing resolution of 3 ns or better. The energy resolutionrequirement is modest. The energy information will be usedmostly to identify muons from protons. The requirement for thePPD is that effects such as dark noise, cross-talk or after-pulsing

which should both be driven by the statistics of the number ofphoto-electrons.

Corresponding author. Tel.: +1604 2227572; fax: +1604 2221074.

E-mail address: fretiere@triumf.ca (F. Retie`re).0168-90

doi:10.1PPDs appear to be a perfect solution for experiments such as T2KND280, being newly developed devices, they have not been

In order to achieve the required timing resolution, the PPD pulsesare stretched by a RC-CR2 preamplier shaper with a 120nsIndeed, they provide a much larger gain than standard avalanchephotodiodes, while matching or surpassing the photo-tube photo-

signal that is subsequently time stamped by a eld programmgate array. The ne grain detector electronics is basedwaveform digitization scheme sampling at 50MHz for 10mwavelength shifting (WLS) ber threaded through a plasticscintillator bar and readout on one or both ends by a photosensor.Most of the photosensors are enclosed within a 0.2 T magnet,which rules out using simple photo-tubes. The recently developedpixelated Geiger-mode avalanche photon detectors (PPD) havebeen chosen in place of photo-tubes or avalanche photodiodes.

50ns. In practice, the integration time will follow the beamspill structure to be about 500ns depending on the acceleratoroperation mode. Most ND280 elements will use such electronicsbased on the TRIP-t ASIC that also provides a discriminatoroutput per channel [3]. The discriminator triggers when theintegrated charge exceeds a programmable threshold, providing a1. Introduction

1.1. The T2K near detector experimen

The T2K near detector (ND280) isof the neutrinos produced by the J-PThe building block of most ND280detector, ne grain detector, elecdetector, and side muon range02/$ - see front matter Crown Copyright & 20

016/j.nima.2008.08.130near detector.

Crown Copyright & 2008 Published by Elsevier B.V. All rights reserved.

ned to detect a fractioncelerator complex [1,2].tor elements (on axisnetic calorimeter, pi0r) is a Kuraray Y11

The most important detector performance that must beachieved is a detection efciency of 100% for minimum ionizingparticles (MIPs). Accounting for channel-to-channel variation andthe low-energy tail of the energy loss, this translates to requiringthe average number of photo-electrons produced by a MIP to be atleast 15. The light coming out of the WLS ber is not emittedinstantaneously but is fully collected in about 50ns, mostly due tothe WLS ber decay time constant of 9 ns. The T2K ND280electronics hence has to integrate the PPD current for at leastMPPC degrade the detector performance signicantly within the expected operating conditions of the T2KAfter-pulsing and cross-talk in multi-pi

Y. Du a, F. Retie`re b,

a Department of Physics and Astronomy, University of British Columbia, 6224 Agricultub TRIUMF, Science, 4004 Wesbrook Mall, Vancouver, BC, Canada V6T 2A3

a r t i c l e i n f o

Article history:

Received 17 January 2008

Received in revised form

18 July 2008

Accepted 12 August 2008Available online 28 August 2008

Keywords:

Photo-detector

Scintillator

a b s t r a c t

Multi-pixel photon counte

photonics. They will be use

T2K experiment. Their p

insensitivity to magnetic

cross-talk and after-pulsin

after-pulsing are precisely

At an over-voltage of 2V, a

pulsing, whereas it gen

journal homepage: www

Nuclear InstrumenPhysics R08 Published by Elsevier B.V. Alll photon counters

oad, Vancouver, BC, Canada V6T 1Z1

MPPC) are pixelated Geiger-mode photon manufactured by Hamamatsu

or reading out all the scintillator elements within the near detector of the

rmances photo-detection efciency, dark noise and gain, and their

fulll the ND280 requirements. On the other hand, two known issues,

ay adversely impact the detector response. In this paper, cross-talk and

asured by recording waveforms and identifying all the avalanche pulses.

valanche generates on an average 0.5 additional avalanches due to after-

tes 0.13 at 1V over-voltage. After-pulses follow two independent

le at ScienceDirect

lsevier.com/locate/nima

s and Methods insearch Arights reserved.

and VBD. The total charge per avalanche is governed by the diode

ARTICLE IN PRESS

thodcapacitance (C): Q CDV. The output current of the PPD is thesum of all the diode currents. The number of photons hitting thedevice is measured by counting the number of pixel avalanches.The photon detection efciency is the probability that a photontriggers an avalanche when hitting a PPD. The response is linear if(i) the number of pixel avalanches detected is small (o15%)compared to the total number of pixels, and (ii) the light isuniformly distributed across the surface.

An avalanche in 1 pixel at a given time can trigger additionalavalanches either in neighboring pixels or in the same pixel at alater time. The former phenomenon is called cross-talk whereasthe latter is called after-pulsing. Cross-talk is believed to becaused by photons produced in an avalanche, which knock offelectrons in a neighbor pixel and trigger an additional avalanche[9]. It has been recently shown that the trajectories of the cross-talk inducing photons may not be straight lines but instead gothrough reections within the substrate [10]. Either way, thephoton propagation time is very short, hence the original andneighbor avalanches occur essentially at the same time.

On the other hand, an after-pulsing avalanche occurs after theoriginal avalanche. It is believed to be triggered by the release of acharge carrier that has been produced in the original avalancheand trapped on an impurity [11,12]. It is also possible that thephotons produced in the original avalanche generate after-pulsesif instead of knocking of an electron in the depletion region of aneighbor pixel, they do so within the silicon substrate. One of thecharge carriers hence produced may eventually nd its way backto the pixel and trigger a second avalanche. This phenomenonwasobserved in Ref. [13] but the carriers were found to diffuse backinto the depletion region in o1ns, which would be invisible toPPDs. However, the PPD doping prole may allow for much longercarrier diffusion time within the substrate.

1.3. Multi-pixel photon counters (MPPCs)

MPPCs are PPDs designed and manufactured by Hamamatsuphotonics [14,15]. They have been extensively tested in thecontext of the ND280 detector within the T2K experiment[4,5,16], together with similar devices [17]. A total number ofabout 50,000 MPPCs will be used in the T2K experiment. Theirperformances fulll the detector requirements. A large gain(4500,000), and large (415%) photo-detection efciency can beachieved while maintaining the dark noise rate below 1MHz.

The MPPCs that were tested in this paper have 400 pixels(5050mm2) covering a total area of 1 by 1mm2. A 100kOresistor is used for quenching the avalanche. The total capacitanceof the device is 35pF, which translates into 87.5 fF per pixel1.2. Pixelated Geiger-mode avalanche photon detectors

PPD, also called silicon photo-mutipliers (SiPM) are becoming amature technology, both for particle physics and medical imaging[57]. A PPD is an array of 100 to several 1000 s photodiodesarranged into square pixels operating in Geiger-mode with acurrent limiting resistor. Free charge carriers drifting through thedepleted region are able to free additional carriers when thereverse bias voltage across the junction goes above a criticalbreakdown voltage (VBD). An avalanche develops as described inRef. [8] until the current owing through the resistor (R) in serieswith the diode brings the voltage across the junction to VBD. Themaximum current owing through the diode is Imax DV/R, DVbeing the over-voltage, i.e. the difference between the reverse bias

Y. Du, F. Retie`re / Nuclear Instruments and Meignoring parasitic capacitances. With a 1V over-voltage, the gain,i.e. the number of electrons produced by 1 photo-electron in 1pixel is about 550,000.2. Measuring cross-talk and after-pulsing

2.1. Test setup

The MPPC was housed in a light tight tube. The data weretaken at a temperature of 25 1C. A Keithley 6485 picoammeter wasused to bias the MPPC between 69.4 and 70.6V through a 100kOresistor. The MPPC pulse was readout by decoupling the bias linewith a 1nF capacitor. A custom amplier was used to achieve again of 10 before feeding the signal into a CAEN V1729 waveformdigitizer sampling for 2.5ms at 1GHz. The trigger was generatedby further amplifying the signal using a CAEN N978 amplier anda discriminator, with the threshold set to 0.10.2 avalancheequivalent signal, depending on the MPPC bias voltage.

2.2. Waveform analysis: pulse nding

Two events with multiple pulses are shown in Fig. 1 toillustrate the pulse nders ability. Most events have only onepulse at 270ns, which is where the trigger happens to be. A pulsender analysis was performed on the waveforms in order tomeasure the time and amplitude of the avalanches occurringwithin the acquisition window. The pulses were found in twosteps. First, all the pulses with a signal-to-noise ratio over 5 wereidentied unless they were too close to an earlier pulse, becausethe rst pass algorithm required the signal to return to thebaseline before accepting a subsequent pulse. The waveformswere then tted by a superposition of single avalanche responsefunctions (SARF). The SARFs were extracted directly from the databy calculating the average waveforms for events that have only 1avalanche within a 150ns wide integration window around thetrigger pulse. An analytical function tting the SARFs perfectlycould not be found and standard spline interpolation techniqueswould smooth out the SARF too much. A linear interpolation ofthe SARFs was used instead, which yield to about 1ns resolutionin the reconstruction of the pulse arrival time.

The correlation between the pulse amplitude and trigger timeintroduced by the leading edge discriminator was corrected forbefore calculating the average waveform. A w2 was computed toassess the quality of the t. The number of degrees of freedom(dof), i.e. the t range, was set to 50 unless two or more pulsespartially overlapped, in which case the t range was extended toencompass all the pulses. If the w2 per dof (w2/dof) was found to bemore than 5, an additional pulse was added and the t was re-run.Pulses were added until the w2/dof fell below 2 or until 5additional pulses were added. This method was reliable to ndpulses close to each other, even when they almost fully overlapbecause the shape of the waveform provides a strong constraint.

2.3. Extracting cross-talk

The time and amplitude of the pulses found in a 500nswindow following the trigger are shown in Fig. 2. The timeis dened with respect to the trigger pulse time. The amplitude isthe scale applied to the SARFs to reproduce the data, so it isautomatically proportional to the signal given by the avalanche atnominal gain. The trigger pulses can be seen at time zero as 3narrow bands at 1, 2, and 3 avalanches. Cross-talk can be extracteddirectly from the frequency distribution of trigger pulse amplitudeobtained by the projection of these bands onto the y-axis. Cross-talk is calculated as the probability that 1 pixel triggers at least 1avalanche in a neighbor pixel: 1N1/Ntotal with N1 being the

s in Physics Research A 596 (2008) 396401 397number of 1 avalanche pulses and Ntotal the total number oftrigger pulses. The trigger sample is selected by using a 1ns timewindow, which ensures that the contribution of after-pulsing is

ARTICLE IN PRESS

thod25

Y. Du, F. Retie`re / Nuclear Instruments and Me398negligible. Indeed, within 1ns immediately following an ava-lanche, the pixel over-voltage is close to zero. Hence, if a chargecarrier happens to enter or be released within the depleted region1ns or less after the rst avalanche, it will not generate anavalanche.

Time after trigger (ns)0

Pix

el a

vala

nche

0

1

2

3

100 200 300 400

Fig. 2. Amplitude and time distribution of all the pulses found by the pulse nderat 70V bias and 25 1C (1.3V over-voltage).

ns0

AD

C

0

5

10

15

20

AD

C

0

5

10

15

20

25

500 1000 1500 2000

ns0 500 1000 1500 2000

Fig. 1. Two events taken at 70V bias and 25 1C (1.3V overvoltage). The right-hand paneblack curve is the t.25

s in Physics Research A 596 (2008) 3964012.4. Pixel recovery

The over-voltage recovery is clearly visible in Fig. 2 as a bandbelow 1 avalanche between 0 and 40ns after the trigger. Fig. 3presents a clearer view of recovery in a 100ns window following

Time after trigger (ns)0

Pix

el a

vala

nche

0

1

2

3

20 40 60 80 100

Fig. 3. Amplitude and time distribution of the rst pulse following the triggerpulse at 70V and 25 1C (1.3V over-voltage). The solid red curve shows the expectedsingle pixel recovery.

ns250

AD

C

0

5

10

15

20

AD

C

0

5

10

15

20

25

300 350 400 450 500

ns250 300 350 400 450 500

ls are zooms around the trigger pulse. The lled grey histogram is the data and the

the trigger. The recovery behavior is well reproduced by theexpected function 1et/t, with t 100kO8.75 fF 8.75ns.

2.5. Measuring after-pulsing

Each avalanche may result in trapped charge carriers. However,as discussed earlier, it is possible that some of the after-pulseshave nothing to do with trapped carriers but originate insteadfrom charge carriers created by photons in the substrate, in thesame fashion as cross-talk. In order to avoid making unnecessaryassumptions, we will quantify after-pulsing as the averagenumber of delayed carriers triggering an additional avalancheper original avalanche. This nomenclature has the advantage ofaccounting for the fact that a carrier released while the voltage isnot fully recovered will have a smaller probability of triggering anavalanche than at the nominal operating voltage.

We build the timing distribution of the rst pulse following thetrigger pulse, because the probability distribution of the rst pulsearrival time is fairly simple to express mathematically, which isnot the case when multiple after-pulses created by avalanchesfollowing the trigger pulse have to be considered. We selecttrigger pulses with only one simultaneous avalanche, hencediscarding the ones with cross-talk. We also ensure that noavalanche happened within the 270ns before the trigger pulse in

0 0

ARTICLE IN PRESS

Y. Du, F. Retie`re / Nuclear Instruments and Methodorder to avoid selecting avalanches that may themselves be after-pulses. The amplitude and time distribution of the rst pulsefollowing the trigger pulse is shown in Fig. 3. This gure is verysimilar to the one shown in Ref. [18]. Three bands for 1, 2, and 3pixel avalanches are clearly visible when the pulses occur laterthan 40ns after the trigger. Cross-talk is responsible for the2 and 3 pixel avalanche bands. The bands split into two for thepulses within 40ns after the trigger: one constant and the otherfollowing the pixel recovery time constant as discussed earlier.The constant band is unaffected by the pixel recovery, hence mustoriginate from a different pixel than the trigger pulse. It ispresumably due to thermally generated dark pulses. On the otherhand, after-pulses occurring earlier than 40ns after the trigger

Time after trigger (ns)10 102 103

Pro

babi

lity

of th

e ne

xt a

vala

nche

(ns-

1 )

10-4

10-3

10-2

69.4 V

70.0 V

70.6 V

Fig. 4. Timing distribution of the rst pulse following the trigger. The dotted lines

are ts with a single after-pulsing time constant, while the solid lines included two

time constants. The dashed lines show the two exponential function behaviors

beyond the t range.The dotted curve in Fig. 4 shows a t using this function. Thequality of the t is poor, so a second after-pulse time constant hasto be introduced to obtain a good t. The t is limited to time laterthan 10ns because the pulse nder is not very accurate for ndingpulses with signicantly reduced gains, which typically occurwithin 10ns after the trigger. While the pulse nding efciencyremains fair (except for low bias voltage), the t parameters (timeand amplitude) become less accurate, especially the pulse time,which tends to be shifted later due to an artifact in the pulsender algorithm.

3. Parameterization of cross-talk and after-pulsing as a functionof over-voltage

The parameters extracted from the t using the 2 timeconstant after-pulsing models are summarized in Fig. 5, asfunctions of over-voltage. The VBD was found to be 68.7V byextrapolating the gain down to zero. The after-pulsing parametershown in this gure is 1el, the probability that an avalanche isfollowed by at least one after-pulsing avalanche. The errors areboth statistical and systematic. The statistical errors dominate atlow over-voltage whereas systematic ones dominate at above 1V.The main source of systematic error comes from the lack ofefciency for nding the pulses in the 010ns time interval.Indeed the probability distribution used in the t assumes thatthe rst pulse is always found. However, if it occurs too early to bedetected, the second pulse will be substituted as the rst pulseand distort the experimental time distribution. We performedsimulations to estimate this effect. Assuming that all the pulsesoccurring 10ns or less after the trigger pulse are missed, we foundthat the dark noise rate, the number of after-pulses per avalanche,and the long after-pulse time constant were overestimated by asmuch as 40%, 15%, and 15%, respectively, when those parametersare large, i.e. corresponding to an over-voltage of 1.9V. On theother hand, the short time constant appears to be underestimatedby as much as 15%. This effect was found to be small for thehave reduced gains because the over-voltage is not recovered toits original level.

Fig. 4 shows the time distribution of the rst pulse followingthe trigger for three different bias voltages. The rst pulsefollowing the trigger pulse comes either from after-pulsing orfrom dark noise. The probability of the rst pulse occurring in thetime interval t and t+dt, is an after-pulse is

PAPt X1i1

li

i!el

i

t eti=t

with l being the average number of delayed carriers triggering anavalanche per original avalanche, t, the carrier release or diffusiontime constant. The probability for a thermally generated darkpulse is

PDNt ReRt

with R being the dark noise rate. The sum over the Poissonprobability accounts for the possibility of having more than onedelayed carrier created per avalanche, which was not taken intoaccount in Ref. [4]. When combining after-pulses and thermallygenerated dark pulses, the probability must be mutually exclusive,i.e. a dark (after) pulse occurring at t with no after (dark) pulseoccurring between 0 and t, which leads to the probability

Pt Z t

1 PAPxdxPDNt Z t

1 PDNx dxPAPt.

s in Physics Research A 596 (2008) 396401 399parameters corresponding to over-voltages o1.3V. The error onthe over-voltage is primarily due to day-to-day temperaturevariation.

ARTICLE IN PRESS

thodOver-voltage (V)0.5

Dar

k no

ise

rate

(kH

z)

0

100

200

300

400

afte

r-pu

lsin

g tim

e co

nsta

nt (n

s)

5

10

15

20

1 1.5 2

Y. Du, F. Retie`re / Nuclear Instruments and Me400The data shown in Fig. 5 were tted to extract trends as afunction of over-voltage. The dark noise rate rises linearly withover-voltage at a rate of 21279kHz/V. The dark noise remainsbelow 500kHz even at 2V over-voltage. The after-pulsing andcross-talk probabilities vary quadratically with over-voltage in thefollowing fashion: Prob(APshort) 0.07370.003V2, Prob(APlong) 0.05470.003V2, and Prob(cross-talk) 0.04470.002V2.Cross-talk is smaller than the sum of both short and long after-pulsing probabilities by roughly a factor of 3. At 1.9V over-voltage(70.6V at 25 1C), the average number of late carriers per avalancheis 0.5. At that level after-pulsing may become problematic. It isindeed not uncommon to see trains of avalanches produced by asingle dark noise pulse. The average after-pulsing time constantsare 15.070.6 and 83.573.9 ns. There appears to be a slightdecrease of the time constants with over-voltage, which runscontrary to the expectation that the trap release time constant isindependent of the bias voltage. As mentioned earlier, therobustness of the method has been veried by simulations andthe necessary systematic errors have been included in thereported results. Nevertheless, the systematic errors on the longtime constant are likely underestimated. Indeed calculating thelong time constant with only the three lowest over-voltage pointsyields 92.775.8 ns. The time constants measured for the MPPCsare consistent with the ones reported for single photon avalanchediode in Ref. [10], which suggests that after-pulsing can beinterpreted solely as being due to trapping. In Ref. [10], a thirdtime constant of about 1ms has been found as well. However, ourmeasurement method is not sensitive to it because thermallygenerated dark pulses dominate the timing distribution beyond500ns after the trigger.

Sho

rt

0

Over-voltage (V)0.5 1 1.5 2

Fig. 5. Parameters extracted from the ts to the distributionOver-voltage (V)0.5

Pro

babi

lity

per p

ixel

ava

lanc

he

0

0.05

0.1

0.15

0.2

0.25 1 after-pulse, short 1 after-pulse, long 1 cross-talk

fter-

puls

ing

time

cons

tant

(ns)

40

60

80

100

1 1.5 2

s in Physics Research A 596 (2008) 3964014. Impact of after-pulsing and cross-talk on the T2K ND280detector performance

In order to estimate the impact of cross-talk and after-pulsing,we have developed a Monte Carlo simulation code that allowsturning each effect on and off. The simulations include analgorithm that tracks the operating voltage of every pixeldropping down the voltage to VBD as avalanches occur andrecovering according to the 8.75ns time constant. This algorithmis important because it introduces avalanches with reduced gains,which are clearly visible in the dark noise spectrum or for lowlight level (o20 avalanches). The simulations use a model for thephoto-detection efciency, consistent with preliminary datashowing a linear increase up to 1.5V over-voltage followed byan onset of saturation. Light is injected onto the MPPC followingan exponential with a 9ns decay constant emulating the emissionof the WLS ber. The time zero of the light pulse is chosenrandomly within 540ns, which corresponds to the beam bunchwidth. Signal amplitude and time are calculated by mocking upthe electronics response. The signal amplitude is given by theintegral of the avalanche charge within the 540ns gate. Timing isobtained by generating a discriminator output when the inte-grated charge goes above a programmable threshold. The T2K negrain detector uses different set of electronics, based on waveformdigitization at 50MHz. However, the conclusions drawn below forthe gate and discriminator electronics remain qualitatively thesame.

The number of pixels red is chosen to be about 20 at 1V over-voltage, according to beam test measurements for a minimumionizing particle [4]. Cross-talk and after-pulsing increase the

Long

a

0

20

Over-voltage (V)0.5 1 1.5 2

of the arrival time of the rst hit following the trigger.

average number of pixels avalanching from 20 to 23.2 and 29.3 to49.3 at 1 and 2V over-voltage, respectively. However, suchincrease does not help the photo-detection efciency becausethe number of avalanches generated by dark noise also increasesin the same fashion. At 1V over-voltage, the energy resolutiondegrades from 21.3% without cross-talk and after-pulsing to 22.1%when they are turned on. At 2V over-voltage, the energyresolution goes from 17.8% to 21.2%. Cross-talk and after-pulsinghence have a marginal impact on the energy resolution up to 2Vover-voltage. However, the energy resolution does not improveand eventually worsens beyond 1.5V over-voltage as the photo-detection efciency saturates, while cross-talk and after-pulsingkeep on increasing rapidly. Nevertheless, in the T2K detectors, theMPPCs will be operated between 0.5 and 1.5V over-voltage, whichmeans that cross-talk and after-pulsing will not affect the energyresolution signicantly.

The simulations also show that cross-talk and after-pulsing

5. Conclusions

operating voltage that is expected to be used by the ND280detectors.

In the future, it would be benecial to redesign the MPPCs byincreasing the quenching resistor from 100 to 500kO or moreeffectively by changing the quenching circuit from a passive oneto an active circuit. If avalanches were followed by a 50ns voltagedrop to the VBD, then after-pulsing would be reduced by morethan a factor of 2.

The authors wish to thank the ND280 photosensor group forfruitful discussions, Thomas Lindner and Antonin Vacheret forproviding many useful suggestions regarding the experiment andthe manuscript, Thomas Lindner and Scott Oser for providing thesimulation code, Roman Tacik for pioneering the use of singleavalanche response functions, the TRIUMF DAQ group for settingup the waveform digitizer and Leonid Kurchaninov for providingthe low noise amplier and the TRIUMF pienu experiment forsupporting Yubo Dus work.

References

ARTICLE IN PRESS

Y. Du, F. Retie`re / Nuclear Instruments and Methods in Physics Research A 596 (2008) 396401 401We have measured after-pulsing probabilities and time con-stants for 400 pixel MPPCs at room temperature with goodaccuracy. At 2V over-voltage, the average number of delayedcarriers that can trigger and after-pulse is larger than 0.5. Thecross-talk probability remains below 0.2 at 2V over-voltage.While such large after-pulsing and to a lesser extent cross-talkprobabilities appear to be a concern, simulations show that theydo not affect the energy nor timing resolution signicantly at theif the threshold is set low and the light pulse occurs late withinthe integration window. When using the electronics with slowpreamplier shapers, effect of after-pulsing on the timingresolution can be successfully mitigated by tting only the risetime of the pulse and not the full waveform. Overall, thesimulations show that cross-talk and after-pulsing do have visibleeffects in the charge and timing distributions, and thus must betaken into account, but they do not affect the detector perfor-mances signicantly.[1] Y. Itow, et al., The JHF-Kamioka neutrino project, hep-ex/0106019, 2001.[2] T2K ND280 Conceptual Design Report, T2K Internal Document;/http://www.

nd280.org/infoS.[3] A. Vacheret, M. Noy, M. Raymond, A. Weber, First results of the Trip-t based

T2K front end electronics performance with GM-APDs, PoS(PD07)027.[4] F. Retie`re, Using MPPCs for T2K ne grain detector, PoS(PD07)017.[5] D. Renker, Nucl. Instr. and Meth. A 571 (2007) 1.[6] P. Buzhan, et al., Nucl. Instr. and Meth. A 504 (2003) 48.[7] P. Buzhan, et al., Nucl. Instr. and Meth.A 567 (2006) 78.[8] R.J. McIntyre, IEEE Trans. Electron Devices ED-20 (1973) 637.[9] W.J. Kindt, H.W. van Zeijl, S. Middelhoek, in: Proceedings of the 28th ESSDERC

(1998) p. 192.[10] I. Rech, A. Ingargiola, R. Spinelli, I. Labanca, S. Marangoni, M. Ghioni, IEEE

Photonics Technol. Lett. 20 (2008) 330.[11] S. Cova, A. Lacaita, G. Ripamonti, IEEE Electron Devices Lett. 12 (1991) 685.[12] A.C. Giudice, M. Ghioni, S. Cova, F. Zappa, in: Proceedings of the 28th ESSDERC

(2003) p. 347.[13] A. Lacaita, S. Cova, M. Ghioni, F. Zappa, IEEE Electron Device Lett. (USA) 14

(1993) 360.[14] K. Yamamoto, K. Yamamura, K. Sato, S. Kamakura, S. Ohsuka, T. Ota, H. Suzuki,

IEEE NSS Conf. Rec. 2 (2007).[15] K. Yamamoto, K. Yamamura, K. Sato, S. Kamakura, S. Ohsuka, T. Ota, H. Suzuki,

Proc. Int. Workshop New Photon-Detectors (2007) (PoS(PD07)004).[16] S. Gomi, T. Nakaya, M. Yokohama, H. Kawamuko, T. Nakadeira, T. Murakami,

R&D of MPPC for T2K experiment, PoS(PD07)015.[17] O. Mineev, et al., Nucl. Instr. and Meth. A 577 (2007) 540.[18] H. Oide, H. Otono, S. Yamashita, T. Yoshiota, H. Hano, T. Suehiro, Study of

afterpulsing of MPPC with waveform analysis, PoS(PD07)008.discriminator does not trigger on noise, which is likely to happenhave very little impact on the timing resolution obtained with theTRIP-t electronics as long as the programmable threshold isselected carefully. Indeed, it is crucial to ensure that the

After-pulsing and cross-talk in multi-pixel photon countersIntroductionThe T2K near detector experimentPixelated Geiger-mode avalanche photon detectorsMulti-pixel photon counters (MPPCs)

Measuring cross-talk and after-pulsingTest setupWaveform analysis: pulse findingExtracting cross-talkPixel recoveryMeasuring after-pulsing

Parameterization of cross-talk and after-pulsing as a function of over-voltageImpact of after-pulsing and cross-talk on the T2K ND280 detector performanceConclusionsReferences