High performance InGaP Geiger-mode avalanche photodiodes

The Multi-Pixel Photon Counter (MPPC) is a Geiger-mode avalanche photo-diode (APD) developed by Hamamatsu Corp. We propose that it could be a suitable photo-sensor for next-generation time-of-flight PET detectors due to its high photon detection efficiency. We concentrate on the measurement of coincidence timing performance of various MPPCs in conjunction with LYSO crystal scintillators. With 3 mm times 3 mm devices of 50 mum sub-pixels coupled to 3 mm times 3 mm times 10 mm LYSO crystals, we have demonstrated a strong dependence of timing performance on over-voltage and temperature, and analyzed how changes in photon detection efficiency and dark counts would explain the measurements. The best coincidence timing resolution we have achieved between two identical LYSO/MPPC detectors was 240 ps in FWHM. This was worse than the timing resolution of 220 ps obtained with a Hamamatsu H6533 fast PMT, and contradicted the expected improvement from higher photon detection efficiency. The contradiction could be explained by the slow rise-time of MPPC pulse shape, transit time spread, dark counts and electronic noise from the large capacitance of the MPPC. In particular, the slow rise-time of the MPPC pulse suggests the need for a very low trigger threshold on the timing circuit. Since this makes the detector system more sensitive to noise, this poses additional challenges for ganging multiple devices together into a commercially viable time-of-flight PET block detector. We will discuss this work in detail including other challenge imposed by MPPC characteristics.

Single-photon detector (SPD) as an essential building block for detecting and counting photons, plays a fundamental role in quantum technologies. In this work, we propose an efficient workflow of modeling SPDs based on emerging one-dimensional materials, i.e. nanowires, utilizing avalanche breakdown in reverse biased condition. Comparing to another extensively studied platform, superconducting nanowire SPDs, avalanche nanowire device is demonstrated in this work to promise comparable performance (e.g. high photon detection efficiency (PDE) and and low dark count rate (DCR)) but without working at extreme cryogenic temperature (4K). The proposed workflow explored to maximize computational workload and balancing between time-consuming drift-diffusion simulation and fast script-based post-processing, and in timely convergence we were able to predict a suite of key performance metrics for single-photon SPDs, including breakdown voltage, PDE, DCR, and time resolution.

With high specificity for malignant breast lesions, dedicated-breast molecular imaging systems such as positron emission mammography (PEM) have potential to improve the sensitivity of cancer in women with radio-dense breasts and to reduce the false-positive rate of breast screening when used as a diagnostic adjunct. For high signal-to-noise ratio and to minimize the patient dose, scintillation detectors in a PEM system must have high annihilation photon detection efficiency. This efficiency can be increased by accepting annihilation photons from wider incident angles and by using depth-of-interaction (DOI) measurement within a scintillation crystal to minimize parallax blurring. We have developed a dual-ended readout block (DERB) detector that uses asymmetry of signals from photodetectors on either end of a scintillation array to measure DOI and uses Anger Logic with light sharing to identify interacting crystal elements while minimizing the number of photodetectors required. A prototype DERB detector was constructed from two arrays of silicon photomultipliers (SiPM), two glass optical diffusers, and an array of LYSO scintillation crystals. Assembled, each of the 2 × 2 SiPM arrays detect photons that are dispersed via the optical light diffusers originating from either end of 3 × 3 scintillation crystal elements. We evaluated the ability of the detector to identify the crystal index, resolve DOI, and discriminate energy. The DERB detector was able to clearly identify interacting crystal elements, to measure DOI with ̃5mm resolution in 2mm × 2mm × 20mm crystals, and to achieve an average energy resolution of ̃20%. The DERB detector characteristics suggest that it can be used to reduce the parallax effect in PEM systems without increasing the number of required photodetectors. Further investigation is warranted to improve performance with high optical photon detection efficiency photodetectors.

We report large-area, 250-mum-diameter, 4H-SiC avalanche photodiodes with low dark current and high gain. At room temperature, the dark current density is 59.5 nA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at a gain of 1000. An external quantum efficiency of 48% at 280 nm is achieved at unity gain with a recessed-window structure. The differential resistance of the recessed-window device at zero bias is estimated to be 6times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> Omega. As a result of high external quantum efficiency, large area, and large differential resistance, a record high specific detectivity of 4.1times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , has been achieved. In Geiger mode operation, high single photon detection efficiency of 30% with dark count probability of 8times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> is reported.

Studies on a silicon-photomultiplier-based camera for Imaging Atmospheric Cherenkov Telescopes

This paper presented a new detector module consisting of a micropixel avalanche photodiode (MAPD-3NM), LaBr3:Ce scintillator, and a compact read-out interface system for detecting gamma-rays in a wide energy range. The MAPD array (4 × 4 channels) was assembled using a single MAPD-3NM characterized by its high photon detection efficiency (∼25%), pixel density (10 000 pixels/mm2), low operation voltage (74.5 V), and low dark current. An active area of a single MAPD-3NM was 3.7 × 3.7 mm2, while this value was 17 × 17 mm2 for the assembled array with pixel density of 2190 000. The size of the tested LaBr3:Ce scintillator was 15 × 15 × 15 mm3. According to the characteristics of the detector module, a compact read-out interface device (SPECTRIG MAPD) was developed. SPECTRIG MAPD was designed as a miniature device with low power consumption, which continues to provide a wide spectrum of functions needed for measurement and test silicon photomultipliers (SiPM) and scintillation detectors on their basis. The various experiments were implemented to test the detection performance of a detector module to gamma radiation in the range from 30 keV to 4400 keV.

Silicon photomultipliers (SiPMs) are arrays of many single-photon avalanche diodes (SPADs), all connected in parallel. Each SPAD is sensitive to single photons and the SiPM gives an output proportional to the number of detected photons. These sensors are becoming more and more popular in different applications, from high-energy physics to spectroscopy, and they have been significantly improved over last years, decreasing the noise, increasing the cell fill-factor (FF) and thus achieving very high photon-detection efficiency (PDE). In FBK (Trento, Italy), we developed new SiPM technologies with high-density (HD) and, more recently, ultra-high-density (UHD) of cells (i.e. density of SPADs). These technologies employ deep-trenches between cells, for electrical and optical isolation. As an extreme case the smallest-cell, SiPM, i.e. with 5μm cell pitch, has about 40000 SPADs per squared millimeter. Such small SPAD dimensions gives a significantly high dynamic range to the SiPM. These small-cells SiPM have a lower correlated noise (including lower afterpulsing probability) and a faster recharge time (in the order of few nanoseconds), and they also preserve a very good detection efficiency (despite the small SPAD dimension).

Wide Field of View Cherenkov Telescope Array (WFCTA) has 16 image air Cherenkov telescopes and is one of the main detectors of LHAASO. The main scientific goal of WFCTA is to measure the ultra-high energy cosmic ray energy spectrum and composition from 30 TeV to a couple of EeV. Each Cherenkov telescope has an array of 32 \(\times \) 32 SiPM and covers a field of view \(14^{\circ }\times 16^{\circ }\) with a pixel size of \(0.5^{\circ }\). Because SiPM cannot be aging under strong light exposure, SiPM-based camera can be operated in the moon night and achieve a longer duty cycle than PMT-based camera, e.g. the duty cycle of SiPM-based camera is about 30%, while the PMT-based camera is about 10%. A square SiPM with photosensitive area of 15 mm \(\times \) 15 mm and Geiger-APD size of 25 \(\upmu \)m is used in the SiPM-based camera. Each SiPM has 360,000 APDs, which can meet the required dynamic range from 10 photoelectrons (pes) to 32000 pes of WFCTA. SiPM has higher photon detection efficiency than quantum efficiency \(\times \) collection efficiency of PMT, so SiPM-based camera has the same signal to noise ratio with PMT-based camera, although SiPM has higher dark count rate.

Planar semiconductor InGaAs/InP single photon avalanche diodes with high responsivity and low dark count rate are preferred single photon detectors in near-infrared communication. However, even with well-designed structures and well-controlled operational conditions, the performance of InGaAs/InP SPADs is limited by the inherent characteristics of avalanche process and the growth quality of InGaAs/InP materials. It is difficult to ensure high detection efficiency while the dark count rate is controlled within a certain range at present. In this paper, we fabricated a device with a thick InGaAs absorption region and an anti-reflection layer. The quantum efficiency of this device reaches 83.2%. We characterized the single-photon performance of the device by a quenching circuit consisting of parallel-balanced InGaAs/InP single photon detectors and single-period sinusoidal pulse gating. The spike pulse caused by the capacitance effect of the device is eliminated by using the characteristics of parallel balanced common mode signal elimination, and the detection of small avalanche pulse amplitude signal is realized. The maximum detection efficiency is 55.4% with a dark count rate of 43.8 kHz and a noise equivalent power of 6.96 × 10−17 W/Hz1/2 at 247 K. Compared with other reported detectors, this SPAD exhibits higher SPDE and lower noise-equivalent power at a higher cooling temperature.

In this study, we present the gamma-ray detection performance of LYSO, YSO(Ce) and BGO scintillators read out by a 9 ch. micropixel avalanche photodiode (MAPD) array with a high pixel density (PD) and photon detection efficiency (PDE). The array with an active area of 11.5 × 11.5 mm2 was assembled using single MAPDs with an active area of 3.7 × 3.7 mm2. It had a single output signal and was developed for gamma spectroscopy. Breakdown voltage measurements were carried out for each channel, as a result of which the optimal operating voltage for the array was found. The linearity range and energy resolution for each crystal were determined in the energy range from 30 to 1770 keV . The high pixel density of the array allowed to achieve good linearity in the studied energy range.

This work presents the development and experimental characterization of a compact ultraviolet (UV) telescope based on silicon photomultipliers (SiPMs) designed for the detection of faint atmospheric optical tracks. Such transient optical phenomena include meteors, transient luminous events (TLEs), space debris reentries, and other faint atmospheric emissions. Nuclearite-induced atmospheric emission is considered as a benchmark case for evaluating the expected signal levels of rare luminous track events. We detail the fabrication, assembly, and testing of the SiPM sensor array, comprising parallel Geiger-mode avalanche diodes with high fill factor and photon detection efficiency, alongside custom readout electronics using self-triggering ASICs, precision optical components, and a stable mechanical mount. This photon-counting telescope provides a compact and mechanically robust alternative to conventional PMT-based systems, with demonstrated capability for detecting low-light atmospheric tracks under controlled laboratory conditions.

In the last decades much effort has been addressed to realize novel solid state photo-detectors with a high quantum efficiency in the UV wavelength region to be used in experiments detecting Cherenkov or fluorescence radiation even at cryogenic temperatures. Among the possible devices with these characteristics, the large-area solid detectors made of n-doped silicon substrate coated with Multi-Walled Carbon Nanotubes (MWCNTs) appear to be particularly promising since they combine the great UV radiation absorbance of MWCNTs (at about 200 nm) with their unique characteristics for electrical conductivity and mechanical resistance at low temperatures. In this work we present the cryogenic characteristics of a MWCNT-Si large-area (1 cm2) photo-detector, in which a UV photo-sensitive heterojunction is obtained growing, by Chemical Vapour Deposition (CVD), multi-walled carbon nanotubes on an n-type silicon substrate. Measurements have been made at various temperatures in the range from 5K to 300K by illuminating the photo-detector with a 378 nm UV continuous laser light source. Results demonstrate the capability of such device to be successfully employed in cryogenic experiments as well at room temperature with high stability and high photon detection efficiency in the UV region.

We present a high-speed Single-Photon Camera for demanding applications in biology, astrophysics, telecommunications, 3D imaging and security surveillance. The camera is based on a 32-by-32 array of "smart pixels" processed in a standard high-voltage technology. Every pixel is a completely independent photon-counting channel. Sensitivity is at the single-photon level and no readout noises affect the measure. The camera has high Photon-Detection Efficiency (PDE) in the blu/green visible spectrum (45% at 450 nm) and low Dark-Counting Rate (DCR) even at room temperature (usually lower than 2 kcps). The use of microlenses makes it possible to further increase the effective pixel fill-factor. The camera can be configured by means of a cross-platform user-friendly software that communicates with the camera through a fast USB link. The integration time window may range from few tens of nanoseconds to milliseconds. The maximum frame rate for the whole 1,024 pixels is about 100 kframe/s, while the minimum 20 ns dead-time between frames boosts the sensor dynamic range. The camera is equipped with a standard C-Mount connector. A gating input pin can be used to quickly gate on/off the integration. The camera works in One-Shot mode for the maximum acquisition speed, Real-Time mode for very long measurements and Live mode for setups alignment purposes.

The high light output and fast decay time of LaBr3:Ce scintillation detectors leads to excellent timing performance. To realize the potential of timing resolution with LaBr3:Ce we have investigated the performance with SiPMs, which enable 1-to-1 coupling to individual crystals, and which have been optimized for the near-ultraviolet (NUV) scintillation light emission of LaBr3:Ce. Coincidence timing resolution (CTR) of 100 ps was measured for a 4×4×5 mm3 LaBr3:30%Ce crystal directly coupled to a large-area 4×4 mm2 NUV-SiPM. Results show very little dependence on temperature, in the range of -20° to 20°C, and bias voltage, from 2 V to 5 V over breakdown. Optimal performance was achieved at an over-voltage (OV) range of 3 V - 5 V, at which high gain and high photon detection efficiency are achieved. Though saturation was evident at 511 keV, an energy resolution of 6.8% was measured after correcting for non-linearity. We also measured a CTR of 110 ps for a 4×4×5mm3 LaBr3:5%Ce crystal and 245 ps for a 4×4×30 mm3 LaBr3:5%Ce crystal using the NUV-SIPM. The poorer timing measurement for the 30-mm long crystal is due mainly to a systematic shift in the time pick-off as a function of the depth-of-interaction. The excellent temperature stability, fast rise time, high gain, and low noise of the NUV-SiPM make it a practical and highly appealing photodetector for the readout of a LaBr3:Ce TOF-PET detector.

Silicon Photomultipliers are state-of-the-art solid state sensors of light with single photon sensitivity, unprecedented photon number resolving capability and high photon detection efficiency. SiPM are cost effective, compact, magnetic field insensitive and with an extreme flexibility in the design to cope with different applications in fundamental and applied science and industry. As a rapidly evolving technology, new generation of sensors are being continuously proposed by different producers, requiring the development of reliable and efficient SiPM characterisation methods to perform a quick assessment and comparison. The procedure presented here is based on post-processing of digitised SiPM waveforms recording the response of the sensor to an ultra-fast light pulse. For every pulse, the signal is synchronously sampled, digitised and recorded on the timescale of a few microseconds with the objective of extracting from a single set of waveforms a full picture of the sensor characteristics in terms of Gain, Breakdown Voltage, Dark Count Rate , Optical Cross-Talk and After Pulse probability. The need of a unique and consistent data-set guarantees a fast and robust characterisation, stable against environmental condition changes, notably temperature.