The effects of a high background count and a microsecond dead time interval on a gated InGaAs/InP single-photon avalanche photodiode (SPAD) during microsecond luminescence decay registration are discussed. It is shown that the background count rate of the SPAD limits its use for time-resolved and steady-spectral measurements, and that a “pile-up” effect appears in the microsecond range

Baranov, A. V.

Berwick, Kevin

Fedorov, A. V.

Gonchar, K. A.

Litvin, A. P.

Onishchuk, D. A.

Parfenov, P. S.

English

Arrow@TUDublin

Technological University Dublin ARROW@TU Dublin Articles School of Electrical and Electronic Engineering 2020 The Effect of High Background and Dead Time of an InGaAs/InP Single-Photon Avalanche Photodiode on the Registration of Microsecond Range Near-Infrared Luminescence P. S. Parfenov A. P. Litvin D. A. Onishchuk See next page for additional authors Follow this and additional works at: https://arrow.tudublin.ie/engscheleart2  Part of the Electrical and Electronics Commons This Article is brought to you for free and open access by the School of Electrical and Electronic Engineering at ARROW@TU Dublin. It has been accepted for inclusion in Articles by an authorized administrator of ARROW@TU Dublin. For more information, please contact arrow.admin@tudublin.ie, aisling.coyne@tudublin.ie, gerard.connolly@tudublin.ie. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License Funder: Russian Science Foundation Authors P. S. Parfenov, A. P. Litvin, D. A. Onishchuk, K. A. Gonchar, Kevin Berwick, A. V. Fedorov, and A. V. Baranov 674ISSN 0030-400X, Optics and Spectroscopy, 2020, Vol. 128, No. 5, pp. 674–677. © Pleiades Publishing, Ltd., 2020.The Effect of High Background and Dead Time of an InGaAs/InP Single-Photon Avalanche Photodiode on the Registrationof Microsecond Range Near-Infrared LuminescenceP. S. Parfenova,*, A. P. Litvina, D. A. Onishchuka, K. A. Goncharb, K. Berwickc, A. V. Fedorova, and A. V. BaranovaaCenter of Information Optical Technology, ITMO University, St. Petersburg, 197101 RussiabDepartment of Physics, Lomonosov Moscow State University, Moscow, 119991 RussiacSchool of Electrical and Electronic Engineering, Technological University Dublin, Dublin, Ireland*e-mail: qrspeter@gmail.comReceived January 27, 2020; revised January 27, 2020; accepted February 6, 2020Abstract—The effects of a high background count and a microsecond dead time interval on a gatedInGaAs/InP single-photon avalanche photodiode (SPAD) during microsecond luminescence decay regis-tration are discussed. It is shown that the background count rate of the SPAD limits its use for time-resolvedand steady-spectral measurements, and that a “pile-up” effect appears in the microsecond range.Keywords: near-infrared detector, photon counting, single-photon avalanche diode (SPAD), pile-up, count-ing lossDOI: 10.1134/S0030400X20050100INTRODUCTIONSingle photon counting is one of the most sensitivemethods to register low intensity light signals with highresolution. For many years it has been used primarilyto record visible luminescence decay curves with char-acteristic decay times from several to hundreds ofnanoseconds [1], using instruments such as the Pico-quant MicroTime system. However, many samples ofinterest luminesce in the near infrared (NIR) regionand have decay times of dozens of micro- or millisec-onds. These include PbS and PbSe nanocrystals, sin-glet oxygen and porous silicon [2, 3]. NIR lumines-cence is measured by InGaAs and Ge photodiodesusing an oscilloscope and InGaAs photomultipliertubes (PMT). The most sensitive type of NIR single-photon detector is a single-photon avalanche photodi-ode (SPAD) based on Ge or InGaAs. These deviceshave a very high background count rate due to the nar-row bandgap of InGaAs and a relatively long deadtime. A typical InGaAs SPAD has a background countrate of about 104 s–1 and a dead time of about 10 μs.Typical data is available in the References [5]. Docu-mentation on the ID221 SPAD, provided by IDQuantique, is also readily available. Comparable val-ues for a typical Si SPAD are 100 s–1 and tens of ns,respectively.Photon counting in time intervals up to hundredsof nanoseconds is usually carried out in time-cor-related single photon counting mode (TCSPC),because TCSPC is insufficient for longer periods,those longer than 100–500 ns, and starts to require avery long accumulation time. Measurement of longertimes requires the use of gated mode, in which thedelay curve is divided into intervals and the total num-bers of photons is counted in each interval. Anotherway to do this is by dividing the curve into TCSPCintervals, which are then merged. This provides a hightemporal resolution. A more suitable method for mea-surements in the micro- and millisecond range is mul-tiscalar counting (MSC), that theoretically allows reg-istration of most of the photons within the measure-ment period simultaneously [6]. It is known thatTCSPC is affected by a pile up effect [1] whichbecomes negligible when measuring longer time inter-vals using MSC. These methods of photon countingare widely used in the visible range, both for PMT andAPD detectors.The use of NIR SPAD experimentally for longluminescence decay times is subject to pile-up andrequires a reconsideration of the applicability ofcounting methods. Additionally, the high backgroundcount significantly reduces the dynamic range, neces-sitating a reevaluation of the impact of counting losses.In this article, we describe how a high backgroundcount rate and a long dead time affect experimentaldata using a gated InGaAs/InP SPAD, supplied byMicro Photon Devices.OPTICAL SENSORS AND TRANSDUCERSOPTICS AND SPECTROSCOPY  Vol. 128  No. 5  2020THE EFFECT OF HIGH BACKGROUND AND DEAD TIME 675EXPERIMENTSNIR SPAD devices are of two types—gated andfree-running. Synchronized gating allows a reductionin noise and an improved dynamic range, but thecount is limited by gate width, with a maximum ofabout 500 ns, much shorter than the decay time in ourcase. An application note for an InGaAs/InP SPAD(MPD) [7] describes three ways in which the gatedNIR detector can operate—two synchronous methodsand one asynchronous. In the first method, the decaycurve is divided into consecutive TCSPC/MSC inter-vals, no longer than the gate width, which are thenmerged. The second method uses MSC over the wholedecay curve, the SPAD opens the gates with a fre-quency at least 100 times greater than the excitationlaser pulse repetition rate. The laser, MSC and SPADare synchronized with a frequency divider.The third asynchronous method, also called“equivalent” free running mode, is the simplest,because it does not require additional equipment andremains gated. In this method, MSC is over the wholedecay curve, but the SPAD is synchronized by its ownfrequency generator that is not connected to the laserpulse frequency generator. Photons are registered inMSC mode and the decay curve appears randomlyscanned. The asynchronous mode increases theacquisition time because the SPAD continues to countphotons between measured decay curves, when no sig-nal is present. We chose this last mode because of itssimplicity. A schematic diagram of the asynchronousmethod is shown in Fig. 1. Photon counting was car-ried out with a DPC-230 photon correlator, suppliedby Becker and Hickl, in multiscalar mode. Defaultinstrument settings are 168 ns gate width, 3.5 V bias,15 μs dead time, and a background count of 104 s–1.Background SaturationIt is known that at levels above 10% of the maxi-mum count rate, the efficiency becomes noticeablynonlinear due to photon overlap. This leads to satura-tion when measuring the intensity of spectra. Withtime-resolved measurements, the maximum usefulcount rate is 50% of the maximum count rate if pile-up effects are absent [1]. The SPAD under consider-ation has a dead time of 15 μs and a background countof 104 s–1. Therefore, the background count is about15% of the maximum count rate (67 × 103 s–1 for 15 μsdead time) and nonlinearity and saturation are alreadypresent when recording spectra. It is possible toincrease the dynamic range of linear sensitivity byadjusting the gate width. The smaller the gate width,the lower the sensitivity and the wider the dynamicrange. The maximum possible change of sensitivity is225 times when the gate width is reduced from 450 to2 ns. The background is decreased by the same factorand is now less than 0.2% of the maximum count rate.At gate repetition rates of the order of MHz, thismethod does not lead to signal distortion and has beenuseful for spectral calibration using a black bodysource.The high background level of the detector has onemore important consequence, viz. a very high sensitiv-ity to background illumination. An increase in thelevel of background light reduces the time remainingfor registration of the useful signal, since each regis-tered photon leads to a long shutdown of the receiverfor the dead time. This leads to an increase in theacquisition time required to register the initial signallevel. A further increase in acquisition time is requiredto get a sufficient initial signal-to-noise ratio, even fortime-resolved measurements.We measured the influence of the background illu-mination on the registration of a laser pulse. The laserdiode used, a PicoQuant LDH-P-C-980, producedpulses with a duration of 0.3 ns, a wavelength of980 nm and a 2 MHz repetition rate. The laser wasattenuated so that the amplitude of the pulse was equalto the background level and was sufficient for registra-tion in one minute. The dark count rate without addi-tional illumination was 1.2 × 104 s–1. Doubling of thebackground had almost no effect on the signal level. Afurther doubling of the background count to 4.8 ×104 s–1 led to a reduction of the signal intensity by400 times. The intensity fell from 2900 to 110 s–1 andthe acquisition time increased from 1 to 16 min.Clearly, the maximum, practically achievable, countrate is much lower than 4.8 × 104 s–1, since the back-ground overwhelms the receiver, while an assumptionof a uniform distribution gives a rate of 6.7 × 104 s–1.Since a small increase in the background causes sucha dramatic decrease in the signal intensity, it is advis-able not to exceed a background level of 2 × 104 s–1 fortime-resolved measurements. For spectral steady-state measurements, the external background illumi-nation should be excluded and a reduction in the gatewidth is recommended. So, the free-running photodi-ode is not useful for steady-state measurements.Fig. 1. Schematic diagram of devices during the experi-ment. SPAD—InGaAs/InP single photon avalanche pho-todiode (Micro Photon Devices), MSC—multiscalar pho-ton counter DPC-230 (Becker & Hickl). Laser—pulsedlaser (980 nm LDH-P-C-980 by PicoQuant, 1053/527 nmDTL-339QT by Laser-Export via pulse inverter).Control unitPhoton outSPADSampleLaserStopMSCStartSyncout676OPTICS AND SPECTROSCOPY  Vol. 128  No. 5  2020PARFENOV et al.Distortion of the Decay CurvesIt is known that the loss of a second photondetected in the same signal period as the initial photoncauses an error in the detected f luorescence lifetime.This is a classic pile-up effect. The loss of the secondphoton within the dead time interval creates a “count-ing loss,” a nonlinearity in the recorded intensities,and causes signal distortion. Ending the dead timecauses a step change in the probability of recording aphoton, leaving the lifetime unaffected [1]. Theseeffects manifest themselves in unusual ways due to themicrosecond timescale and the high background level.One example of this is when the wavelength of theexcitation pulsed laser is in the spectral range of theSPAD, and these pulses reach the detector due to scat-tering or insufficient filtration. The initial large shortpulse corresponding to laser excitation is followed byseveral small negative “dips” within the dead time andpositive “peaks” outside the dead time (Fig. 2). Theirrepetition rate is equal to the gate repetition rate. Thisodd distribution of photons is due to the fact that ahigh-intensity pulse during an open gate causes a pile-up effect in the gate. In addition, it decreases the prob-ability of detecting background pulses within the deadtime. This leads to a noticeable reduction in counts forthe next gate periods, which are compensated after thedead time period, forming dips and peaks. The effectis greatest when the peak arrives just after the gateopens.Solving this pile-up problem is straightforward.Either reduce the intensity of the radiation (the usualway to eliminate the pile-up effect) or reduce the gatewidth. Reducing the gate width is less effective,because the duration of the laser pulses normally doesnot exceed a few ns. This is an example of where syn-chronization with the laser offers significant advan-tages, since it can allow opening of the gates with somedelay after the pulse to avoid registration of the laserpulse during the initial few nanoseconds. It is possibleto modify the asynchronous mode using an externalgating pulse generator instead of an internal one, adelay scheme, an additional sampling pulse generatorand a simple logic circuit that passes gating pulses tothe “Trigger In” input of the SPAD during the activesampling pulse level only. The sampling intervalshould be set by the first generator, while the time shiftshould be determined by the delay.A second example of decay curve distortion relatesto “counting loss” and is observed when measuringintense luminescence. The measurement time isdecreased due to losses in the signal during the longdead time and also because of background losses. Thislatter effect can even cause the decay curve to fallbelow the normal background level. The ability todetect photons is restored after the dead time and it isdisplayed on the decay curve as a sudden signalincrease. If a measurement is carried out over a smallerrange than the dead time interval, you may not noticethe step, causing severe signal loss and lower decaytimes. This effect cannot be corrected. Ideally, thereshould be no more than one open gate registering pho-tons during the dead time to prevent this distortion. Inpractice, the gate period depends on the duration andintensity of the luminescence and can be determinedexperimentally. In order to address this, it is necessaryto decrease the gate frequency until the secondary sig-nal increase disappears. This approach increases themeasurement time in proportion to the gate period,but maintains the signal-to-noise ratio at the samelevel. In contrast, the customary advice to decrease thesignal intensity to address this problem leads to adecrease in the signal-to-noise ratio. This effect is notnoticeable when working with time intervals shorterthan the dead time, so it is important to check theshape of the decay curve at longer time intervals.To illustrate this experimentally, measurements ofthe luminescence of silicon nanowires [3] at 1150 nmwere performed. We used excitation at 1057 nm. Vari-ous gate frequencies—200 kHz, 2 MHz, and 20 MHzwere used. The signal at 20 MHz was attenuated by20- and 200-times using filters. From Fig. 3 it isapparent that the attenuation is insufficient, leading toa decrease in the useful signal, while the backgroundremains the same. Attenuation leads to a longer acqui-sition time to obtain a similar signal-to-noise ratio. Incontrast, a decrease in gate frequency gives a result at200 kHz that corresponds to a 5 μs gate period, whilethe dead time is 15 μs. If the lifetime is much less thanthe dead time, the distortion turns into an ordinary“counting loss” (Fig. 4).It is worth discussing how these effects manifestthemselves in other modes. When using a free-runningdiode, the regular peaks inside the dead time periodwill not be observed because there are not regular gatesexcept the first large peak, which can be reduced bydecreasing the signal. The main problem is pile-upwithin the dead time. The only way to reduce this pile-Fig. 2. Pile-up within the gate—luminescence of siliconnanowires at 1150 nm with different gate frequencies:500 kHz (gate period is 2 μs) and 100 kHz (gate period is10 μs).10 000Dead time500 kHz100 kHzGate periodsIntensity, counts1000100102011510Time, μs50OPTICS AND SPECTROSCOPY  Vol. 128  No. 5  2020THE EFFECT OF HIGH BACKGROUND AND DEAD TIME 677up is to decrease the intensity. This is far less effectivethan reducing the gate width.The method of merged intervals is associated withlong measurements due to the sequential measure-ment of intervals, a general feature of gated counting.The method allows the influence of insufficient filtra-tion of the laser to be mitigated since the measurementbegins with a short time delay. Any pile-up effectwithin the dead time will be observed only within theinitial interval.Both pile-up effects will be present in the frequencydividing method as in the asynchronous method.Again, pile-up can be avoided in this method withinthe gate by also using a time delay.CONCLUSIONIn summary, the influence of background countrate and dead time on a NIR SPAD was discussed. Itis shown that control of the level of background illumi-nation is critical. We demonstrated how the “pile-up”effect can further distort the signal and how “countingloss” can reduce the measured lifetime.ACKNOWLEDGMENTSThis work was supported by the Russian Science Foun-dation (agreement no. 18-13-00200).REFERENCES1. W. Becker, The bh TCSPC Handbooks (Becker andHickl, Berlin, 2014).2. A. P. Litvin, S. A. Cherevkov, A. Dubavik, A. A. Ba-baev, P. S. Parfenov, A. L. Simtoes Gamboa, A. V. Fe-dorov, and A. V. Baranov, J. Phys. Chem. C 122, 20469(2018). https://doi.org/10.1021/acs.jpcc.8b060593. V. Yu. Timoshenko, K. A. Gonchar, L. A. Golovan,A. I. Efimova, V. A. Sivakov, A. Dellith, and S. H. Chris-tiansen, J. Nanoelectron. Optoelectron. 6, 519 (2011). https://doi.org/10.1166/jno.2011.12054. P. S. Parfenov, A. P. Litvin, E. V. Ushakova, A. V. Fe-dorov, A. V. Baranov, and K. Berwick, Rev. Sci.Instrum. 84, 116104 (2013). https://doi.org/10.1063/1.48297175. A. Tosi, F. Acerbi, M. Anti, and F. Zappa, IEEE J.Quantum Electron. 48, 1227 (2012). https://doi.org/10.1109/JQE.2012.22080976. A. Jiménez-Banzo, X. Ragàs, P. Kapusta, and S. Non-ell, Photochem. Photobiol. Sci. 7, 1003 (2008). https://doi.org/10.1039/B804333G7. TCSPC Measurements with the InGaAs/InP Single-Photon Counter, Application Note 4. http://www.micro-photon-devices.com/Docs/Appli-cation-note/InGaAs.pdf. Accessed January 16, 2020.Fig. 3. Pile-up within the dead time—luminescence of sil-icon nanowires at 1150 nm with different gate frequencies:200 kHz (1), 2 MHz (2), 20 MHz (3), and the 20 MHz sig-nal attenuated by 20 (4) and 200 times (5). Time constantsare 6.2, (6.0 + 1.0), (2.0 + 0.46), 4.5, and 4.5 μs, respec-tively.1000Intensity, counts100102013010Time, s032Dead time451Fig. 4. Pile-up within the dead time—luminescence of sil-icon nanowires at 1150 nm at different gate frequencies:500 kHz (1), 5 MHz (2), and 25 MHz (3). Time constantsare 267, 269, and 272 ns, respectively.10 0001000100Dead timeIntensity, counts201510Time, μs50123

The Effect of High Background and Dead Time of an InGaAs/InP Single-Photon Avalanche Photodiode on the Registration of Microsecond Range Near-Infrared Luminescence

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The Effect of High Background and Dead Time of an InGaAs/InP Single-Photon Avalanche Photodiode on the Registration of Microsecond Range Near-Infrared Luminescence

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