Single Photon Detection Capability Research Articles

Design of an Electronic Interface for Single-Photon Avalanche Diodes

Single-photon avalanche diodes (SPADs) belong to a family of avalanche photodiodes (APDs) with single-photon detection capability that operate above the breakdown voltage (i.e., Geiger mode). Design and technology constraints, such as dark current, photon detection probability, and power dissipation, impose inherent device limitations on avalanche photodiodes. Moreover, after the detection of a photon, SPADs require dead time for avalanche quenching and recharge before they can detect another photon. The reduction in dead time results in higher efficiency for photon detection in high-frequency applications. In this work, an electronic interface, based on the pole-zero compensation technique for reducing dead time, was investigated. A nanosecond pulse generator was designed and fabricated to generate pulses of comparable voltage to an avalanche transistor. The quenching time constant (τq) is not affected by the compensation capacitance variation, while an increase of about 30% in the τq is related to the properties of the specific op-amp used in the design. Conversely, the recovery time was observed to be strongly influenced by the compensation capacitance. Reductions in the recovery time, from 927.3 ns down to 57.6 ns and 9.8 ns, were observed when varying the compensation capacitance in the range of 5–0.1 pF. The experimental results from an SPAD combined with an electronic interface based on an avalanche transistor are in strong accordance, providing similar output pulses to those of an illuminated SPAD.

Room-temperature waveguide-coupled silicon single-photon avalanche diodes

Single photon detection is important for a wide range of low-light applications, including quantum information processing, spectroscopy, and light detection and ranging (LiDAR). A key challenge in these applications has been to integrate single-photon detection capability into photonic circuits for the realization of complex photonic microsystems. Short-wavelength (λ < 1.1 μm) integrated photonics platforms that use silicon (Si) as photodetectors offer the opportunity to achieve single-photon avalanche diodes (SPADs) that operate at or near room temperature. Here, we report the first waveguide-coupled Si SPAD. The device is monolithically integrated in a Si photonic platform and operates in the visible spectrum. The device exhibited a single photon detection efficiency of >6% for wavelengths of 488 and 532 nm with an excess voltage of <20% of the breakdown voltage. The dark count rate was below 100 kHz at room temperature, with the possibility of improving by approximately 35% by reducing the temperature to −5 °C.

Geiger-Mode Operation 4H-SiC Recessed-Window Avalanche Photodiodes Fabricated by N Ion Implantation

In this work, a 4H-SiC n-i-p avalanche photodiode (APD) with n-layer formed by N ion implantation is demonstrated, in which recessed-window structure is used as termination for reducing electrical field crowding effect around the device edge. The APD with 20 μm diameter active region exhibits low dark current of ~5 pA, high gain of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> , zero-bias peak quantum efficiency of 53.8 % at 265 nm. Two-dimensional avalanche photocurrent mapping indicates that uniform gain is realized across the device central region while edge-located premature breakdown is effectively suppressed. Since there is no shading effect of top contact metal, close to 100% percent of fill factor is achieved in the multiplication region. The APD can operate in Geiger mode by using a passive quenching circuit. A room temperature single photon detection capability is obtained at 280 nm, when the dark count rate is ~ 28.8 Hz/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Study on the time resolution limits of FPMT and SiPM under femtosecond laser

In the past decade, a type of micro-channel-plate based photomultiplier tubes (MCP-PMT) with fast-timing resolution, also called fast-timing PMT(FPMT), has attracted considerable attention in many fields for its single-photon detection capability, good timing performance and magnetic insensitivity. The Silicon Photo-multiplier (SiPM) is another kind of newly developed photodetector with comparable performance to the FPMT. More attention was paid to the single photon time resolution of the photodetectors. However, with the improvement of the temporal performance requirements of photodetectors, the time resolution limit of photodetectors determine the limits of time performance improvement, which worth investigating. In this manuscript, a femtosecond laser is used to calibrate the time resolution limit of FPMT and SiPM. The time resolution limit of FPMT is measured to be 480.4 fs. In addition, the temporal performance of FPMT from single photon to multi-photons under femtosecond laser is also investigated. The time resolution limit of SiPM is measured to be 2.68 ps.

A novel multi-anode MCP-PMT with Cherenkov radiator window

With the proposal of the road map of Time-of-Flight positron emission tomography (TOF-PET) with a Coincidence Time Resolution (CTR) of 10 ps by Paul Lecoq et al. in 2020, the technology based on TOF puts forward higher requirements on the performance of its core optical devices. In this manuscript, we developed a kind of Multi-Anode micro channel plate photomultiplier tube (MCP-PMT) based on Cherenkov radiator window. By using the Cherenkov radiator as the optical window of Multi-Anode MCP-PMT directly, the optical interface between the scintillator and the PMT window in conventional TOF-PET is eliminated, reducing light loss and further improve the time resolution of TOF-PET. The anode of this MCP-PMT can be split into a finely spaced array of collecting electrodes to achieve good positional sensitivity. In this paper, the single photon detection capability and time resolution of this kind of MCP-PMT are evaluated. The transit time spread (TTS) at single photon mode can reach 42.9 ps, and the TTS at multi photon mode is less than 10 ps. The CTR based on this kind of MCP-PMT is 156.7 ± 10.6 ps FWHM, which is equivalent to a position resolution of 23.5 ± 1.6 mm along a line of response (LOR). The performance uniformity of this kind MCP-PMT has also been calibrated.

Simulation of FPMT with single chip MCP

Micro-channel plate photomultiplier tube (MCP-PMT) is a kind of photosensitive device with single photon detection capability and great time resolution, which is also called Fast-PMT (FPMT). The MCP is the electron multiplier structure and in order to achieve single photon detection, two layers of MCPs are always used together. Due to the new-generation particle accelerators with high energy and luminosity, the time resolution of the detector is more important than single-photon detection capability. The single-chip-FPMT is expected to have a greater time resolution. Based on the CST STUDIO SUITE, the single-chip-FPMT model is built and the time performances including the rise time and transit time spread are compared with the double-chips-FPMT model under the same parameter setting. The results show that the FPMT model with single chip MCP has better time response and resolution than the traditional double-chips-FPMT.

The R&D of the Ultra-Fast MCP-PMTs for High Energy Physics

Micro-channel plate photomultiplier tube (MCP-PMT) is a kind of photosensitive device with single photon detection capability and great time resolution, which is also called Fast-PMT (FPMT). The characteristic of MCP makes the MCP-PMT capable of reaching great spatial resolution with multi-anodes. With the experience of successfully R&D of the 20-inch MCP-PMT, the researchers in IHEP are now developing the multi-anodes FPMT with great time resolution and spatial resolution. By now, the single-anode, 2×2 anodes, 4×4 anodes and 8×8 anodes FPMT prototypes have been successfully produced. With the fast-timing test system, the performance of these prototypes has been tested. The best TTS can reach 76 ps for single photoelectron and 15 ps for multi photoelectrons.

Sun CubE OnE: A multi-wavelength synoptic solar micro satellite

The Sun cubE onE (SEE) is a 12U CubeSat mission proposed for a phase A/B study to the Italian Space Agency that will investigate Gamma and X-ray fluxes and ultraviolet (UV) solar emission to support studies in Sun-Earth interaction and Space Weather from LEO. More in detail, SEE’s primary goals are to measure the flares emission from soft-X to Gamma ray energy range and to monitor the solar activity in the Fraunhofer Mg II doublet at 280 nm, taking advantage of a full disk imager payload. The Gamma and X-ray fluxes will be studied with unprecedented temporal resolution and with a multi-wavelength approach thanks to the combined use of silicon photodiode and silicon photomultiplier (SiPM) -based detectors. The flare spectrum will be explored from the keV to the MeV range of energies by the same payload, and with a cadence up to 10 kHz and with single-photon detection capabilities to unveil the sources of the solar flares. The energy range covers the same bands used by GOES satellites, which are the standard bands for flare magnitude definition. At the same time SiPM detectors combined with scintillators allow to cover the non-thermal bremsstrahlung emission in the gamma energy range. Given its UV imaging capabilities, SEE will be a key space asset to support detailed studies on solar activity, especially in relation to ultraviolet radiation which strongly interacts with the upper layers of the Earth’s atmosphere, and in relation to space safety, included in the field of human space exploration. The main goal for the UV payload is to study the evolution of the solar UV emission in the Mg II band at two different time scales: yearly variations along the solar cycle and transient variations during flare events. The Mg II index is commonly used as a proxy of the solar activity in the Sun-as-a-star paradigm, in which solar irradiance variations in the UV correlate with the variations in stratospheric ozone concentrations and other physical parameters of the Earth high atmosphere. SEE data will be used together with space and ground-based observatories that provide Solar data (e.g. Solar Orbiter, IRIS, GONG, TSST), high energy particle fluxes (e.g. GOES, MAXI, CSES) and geomagnetic data in a multi-instrument/multi-wavelength/multi-messenger approach.

A high-sensitivity rapid acquisition spectrometer for lanthanide(III) luminescence

Detecting luminescence beyond 750–800 nm becomes problematic as most conventional detectors are less sensitive in this range, and as simple corrections stops being accurate. Lanthanide luminescence occurs in narrow bands across the spectrum from 350–2000 nm. The most emissive lanthanide(III) ions have bands from 450 nm to 850 nm, some with additional bands in the NIR. Investigating NIR bands are hard, but the difficulties already start at 700 nm. In general, the photon flux from lanthanide(III) emitters is not great, and the bands beyond 700 nm are very weak, we therefore decided to build a spectrometer based on cameras for microscopy with single-photon detection capabilities. This was found to allieviate all limitations and to allow for fast and efficient recording of luminescence spectra in the range from 450 to 950 nm. The spectrometer characteristics were investigated and the performance was benchmarked against two commercial spectrometers. We conclude that this spectrometer is ideal for investigating lanthanide luminescence, and all other emitters with emission in the target range.

Human Visual System involves macroscopic scaleinvariants and microscopic quantum mechanics single-photon sensitivity

“A half Century has gone by; the general public seems to be lacking a simple Readers’ Digest knowledge about human visual system (HVS). In order to ward off wolf eyesight emitting few photons in a dark cavern, we have evolved to separate the energy from the information, as well as adopt the negation of the converse detection logic. To achieve the sensitivity, HVS uses the dark (no light yet) current, discovered by NIH Hagins, to inhibit 100 rods' bundled together by Ganglion integrator by using its own energy firing. We have applied the dark current to inhibit firing, until a detection of a single photon of wolf eyesight by any of the rod bundle. In this short communication, we shall give 2 theorems: macroscopic scale invariants and microscopic quantum mechanics. Now we know why we can see red color while the other animal cannot and why we can detect a single photon while the other cannot. Given the basic deep learning algorithm and possible experiments to verify Quantum Mechanics Uncertainty Principle for HVS single photon detection capability according to the Gold Standard: Double Blind, Negative Control and Sufficient Statistics.”

Single-Photon Counting with Semiconductor Resonant Tunneling Devices.

Optical quantum information science and technologies require the capability to generate, control, and detect single or multiple quanta of light. The need to detect individual photons has motivated the development of a variety of novel and refined single-photon detectors (SPDs) with enhanced detector performance. Superconducting nanowire single-photon detectors (SNSPDs) and single-photon avalanche diodes (SPADs) are the top-performer in this field, but alternative promising and innovative devices are emerging. In this review article, we discuss the current state-of-the-art of one such alternative device capable of single-photon counting: the resonant tunneling diode (RTD) single-photon detector. Due to their peculiar photodetection mechanism and current-voltage characteristic with a region of negative differential conductance, RTD single-photon detectors provide, theoretically, several advantages over conventional SPDs, such as an inherently deadtime-free photon-number resolution at elevated temperatures, while offering low dark counts, a low timing jitter, and multiple photon detection modes. This review article brings together our previous studies and current experimental results. We focus on the current limitations of RTD-SPDs and provide detailed design and parameter variations to be potentially employed in next-generation RTD-SPD to improve the figure of merits of these alternative single-photon counting devices. The single-photon detection capability of RTDs without quantum dots is shown.

Superconducting nanowire single-photon detectors integrated with tantalum pentoxide waveguides

Photonic integrated circuits hold great potential for realizing quantum technology. Efficient single-photon detectors are an essential constituent of any such quantum photonic implementation. In this regard waveguide-integrated superconducting nanowire single-photon detectors are an ideal match for achieving advanced photon counting capabilities in photonic integrated circuits. However, currently considered material systems do not readily satisfy the demands of next generation nanophotonic quantum technology platforms with integrated single-photon detectors, in terms of refractive-index contrast, band gap, optical nonlinearity, thermo-optic stability and fast single-photon counting with high signal-to-noise ratio. Here we show that such comprehensive functionality can be realized by integrating niobium titanium nitride superconducting nanowire single-photon detectors with tantalum pentoxide waveguides. We demonstrate state-of-the-art detector performance in this novel material system, including devices showing 75% on-chip detection efficiency at tens of dark counts per second, detector decay times below 1 ns and sub-30 ps timing accuracy for telecommunication wavelengths photons at 1550 nm. Notably, we realize saturation of the internal detection efficiency over a previously unattained bias current range for waveguide-integrated niobium titanium nitride superconducting nanowire single-photon detectors. Our work enables the full set of high-performance single-photon detection capabilities on the emerging tantalum pentoxide-on-insulator platform for future applications in integrated quantum photonics.

A new physical model of Geiger-mode avalanche photodiodes

A new physical model of avalanche process with single photon detection capabilities is presented. The model describes the avalanche process, taking into account the resistance of space charge, parasitic capacitance as well as the changes of electric field during avalanche process caused by internal discharge and external recharge currents. The results of simulation are compared with the experimental data obtained with photodiodes from different manufacturers. It was determined that at a fixed value of overvoltage, the signal gain decreases significantly, depending on the resistance of the space charge region. This paper presents also the possibilities for improving the parameters of silicon photomultipliers.

Development of a novel neutron tracker for the characterisation of secondary neutrons emitted in Particle Therapy

The MONDO (MOnitor for Neutron Dose in hadrOntherapy) project addresses the technical challenges posed by a neutron tracker detector: high detection efficiency and good backtracking precision. The project main goal is to develop a tracking device capable of fully reconstructing the four-momentum of the ultra-fast secondary neutrons produced in Particle Therapy treatments via double elastic scattering interactions. The tracker – a 16×16×20cm3 matrix – is made by a matrix of thin squared scintillating fibres (250 μm) arranged in layers orthogonally oriented. A custom readout system called SBAM (SPAD-Based Acquisition readout for MONDO experiment), matched to the MONDO needs of single photon detection capability, high spatial resolution and compactness, has been developed in collaboration with Fondazione Bruno Kessler (FBK). A small detector prototype (4×4×4.8cm3) has been built and tested with a sensor prototype, SPADnet-I, in order to experimentally evaluate the light output expected and consequently optimise the final readout. The simulation characterisation of the detector response with monochromatic neutrons in the [20-300] MeV will be presented together with the expected performances of MONDO as neutron beam monitor. The preliminary measurements at electron and proton beams of the prototype with the SPAD array readout will be reported.

A SPAD-based random number generator pixel based on the arrival time of photons

A quantum random generator based on photon detection is here presented. The system consists of a photon source, typically a commercial LED, coupled with a detector with single photon detection capability. The detector is composed of a Single-Photon Avalanche Diode (SPAD) and a time stamp circuit, which samples the arrival time of impinging photons within a predefined temporal window. The proposed implementation optimizes the area, allowing embedding all circuitry into a single pixel, and increases the efficiency of random bit extraction. Moreover, the adopted fast pre-charge mode of the SPAD quenching circuit reduces the afterpulsing probability, and hence possible undesirable correlation in the resulting random bit sequence. Thanks to the implemented random bit extraction, experimental results show that the pixel has a flat behavior for a significant range of light intensity, which makes the pixel robust against variations of external PVT parameters. The maximum achievable bit rate has been measured equal to 1 Mbps, while random sequences are shown to pass NIST tests without any post-processing.

Preliminary test of the MONDO project secondary fast and ultrafast neutrons tracker response using protons and MIP particles

The risk of developing a second malignant cancer as a late time consequence of undergoing a treatment, is one of the main concerns in particle therapy (PT). Since neutrons can release a significant dose far away from the tumour region, a precise characterisation of their production point, kinetic energy and abundance is eagerly needed. The treatment planning system (TPS) software that predicts the normal tissue toxicity in the target region and the risk of late complications in the whole body is currently based on the poorly known production cross-sections and will greatly benefit from improved precision double differential measurements. The MONDO (MOnitor for Neutron Dose in hadrOntherapy) project aims to build an ultrafast neutron tracker that could be used to characterise the production of secondary neutrons with energies in the 20–400 MeV range. The neutron tracking will proceed via the detection of recoil protons produced in two consecutive (n, p) elastic scattering interactions. The MONDO detector consists of a 10 × 10 × 20 cm3 matrix of thin scintillating fibres, arranged in orthogonally oriented layers. A compact read-out sensor with single photon detection capabilities employing the CMOS SPAD technology has been developed in collaboration with Fondazione Bruno Kessler (FBK). The detector will be completed by the end of 2018. A 4 × 4 × 4.8 cm3 prototype has been built using 250 μ m thick scintillating fibres of squared section and was tested using a proton beam and minimum ionising particles. In this contribution we present the experimental results related to the prototype test performed with a proton beam at the Proton Therapy Centre of the Trento Hospital (PTC) in May 2017. The results are compared with the results of a Monte Carlo simulation performed with the FLUKA software.

Cryogenic readout for multiple VUV4 Multi-Pixel Photon Counters in liquid xenon

We present the performances and characterization of an array made of S13370-3050CN (VUV4 generation) Multi-Pixel Photon Counters manufactured by Hamamatsu and equipped with a low power consumption preamplifier operating at liquid xenon temperature (∼175 K). The electronics is designed for the readout of a matrix of maximum dimension of 8×8 individual photosensors and it is based on a single operational amplifier. The detector prototype presented in this paper utilizes the Analog Devices AD8011 current feedback operational amplifier, but other models can be used depending on the application. A biasing correction circuit has been implemented for the gain equalization of photosensors operating at different voltages. The results show single photon detection capability making this device a promising choice for future generation of large scale dark matter detectors based on liquid xenon, such as DARWIN.

QLog Solar-Cell Mode Photodiode Logarithmic CMOS Pixel Using Charge Compression and Readout.

In this paper, we present a new logarithmic pixel design currently under development at New Imaging Technologies SA (NIT). This new logarithmic pixel design uses charge domain logarithmic signal compression and charge-transfer-based signal readout. This structure gives a linear response in low light conditions and logarithmic response in high light conditions. The charge transfer readout efficiently suppresses the reset (KTC) noise by using true correlated double sampling (CDS) in low light conditions. In high light conditions, thanks to charge domain logarithmic compression, it has been demonstrated that 3000 electrons should be enough to cover a 120 dB dynamic range with a mobile phone camera-like signal-to-noise ratio (SNR) over the whole dynamic range. This low electron count permits the use of ultra-small floating diffusion capacitance (sub-fF) without charge overflow. The resulting large conversion gain permits a single photon detection capability with a wide dynamic range without a complex sensor/system design. A first prototype sensor with 320 × 240 pixels has been implemented to validate this charge domain logarithmic pixel concept and modeling. The first experimental results validate the logarithmic charge compression theory and the low readout noise due to the charge-transfer-based readout.

First results on DEPFET Active Pixel Sensors fabricated in a CMOS foundry—a promising approach for new detector development and scientific instrumentation

DEPFET Active Pixel Sensors (APS) have been introduced as focal plane detectors for X-ray astronomy already in 1996. Fabricated on high resistivity, fully depleted silicon and back-illuminated they can provide high quantum efficiency and low noise operation even at very high read rates. In 2009 a new type of DEPFET APS, the DSSC (DEPFET Sensor with Signal Compression) was developed, which is dedicated to high-speed X-ray imaging at the European X-ray free electron laser facility (EuXFEL) in Hamburg. In order to resolve the enormous contrasts occurring in Free Electron Laser (FEL) experiments, this new DSSC-DEPFET sensor has the capability of nonlinear amplification, that is, high gain for low intensities in order to obtain single-photon detection capability, and reduced gain for high intensities to achieve high dynamic range for several thousand photons per pixel and frame. We call this property “signal compression”.Starting in 2015, we have been fabricating DEPFET sensors in an industrial scale CMOS foundry maintaining the outstanding proven DEPFET properties and adding new capabilities due to the industrial-scale CMOS process. We will highlight these additional features and describe the progress achieved so far. In a first attempt on double-sided polished 725 μm thick 200 mm high resistivity float zone silicon wafers all relevant device related properties have been measured, such as leakage current, depletion voltage, transistor characteristics, noise and energy resolution for X-rays and the nonlinear response. The smaller feature size provided by the new technology allows for an advanced design and significant improvements in device performance. A brief summary of the present status will be given as well as an outlook on next steps and future perspectives.

Performance of InGaAs short wave infrared avalanche photodetector for low flux imaging

Opto-electronic performance of the InGaAs/i-InGaAs/InP short wavelength infrared focal plane array suitable for high resolution imaging under low flux conditions and ranging is presented. More than 85% quantum efficiency is achieved in the optimized detector structure. Isotropic nature of the wet etching process poses a challenge in maintaining the required control in the small pitch high density detector array. Etching process is developed to achieve low dark current density of 1 nA/cm2 in the detector array with 25 µm pitch at 298 K. Noise equivalent photon performance less than one is achievable showing single photon detection capability. The reported photodiode with low photon flux is suitable for active cum passive imaging, optical information processing and quantum computing applications.