Three types of SiPMs (Silicon Photomultiplier) with an active area of 3 × 3 mm 2 manufactured by KETEK with cell sizes of 50 µm (PM3350), 60 µm (PM3360) and 75 µm (PM3375) have been investigated. All devices have optical trenches in between the cells to suppress direct crosstalk. Their breakdown voltage at room temperature is about 23 V and the gain at an overvoltage U over = 3.4 V is > 6 • 10 6 . The temperature variation of the breakdown voltage is < 16 mV/K and the gain coefficient with temperature is < 1% for overvoltages U over > 1.7 V. The photodetection efficiency (PDE) at 420 nm and U over = 3.4 V is 51% for PM3350, 55% for PM3360 and 58% for PM3375. At U over = 3.4 V, the dark count rates are < 470 kHz/mm 2 at 20 • C and the afterpulse probability is < 9% at −20 • C. Single photon timing of 230 ps FWHM for PM3350, 320 ps for PM3360 and 375 ps for PM3375 have been achieved. To test their performance in PET (Positron Emission Tomography), energy spectra of 22 Na with LYSO (Lutetium Yttrium Oxyorthosilicate, Lu 1.8 Y .2 SiO 5 :Ce) and GAGG (Gadolinium Aluminum Gallium Garnet, Gd 3 (Ga,Al) 5 O 15 :Ce) scintillators with a size of 2×2×6 mm 3 have been acquired. The saturation corrected energy resolution (FHWM) at 511 keV was with LYSO 12.3% for PM3350, 13.4% for PM3360, 12.4% for PM3375 and with GAGG 10.8% for PM3350. Coincidence timing (FWHM) at U over = 3.4 V was with LYSO 174 ps for PM3350, 178 ps for PM3360, 157 ps for PM3375 and with GAGG 430 ps for PM3350.

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The Silicon Photomultiplier (SiPM) is a novel device for low level light detection in various applications, for example scintillator-and fiber readout. 1,2 The SiPM is insensitive to magnetic fields and has a high photon detection efficiency. Current devices have a high optical crosstalk probability, which causes a significant increase of the excess noise factor. 3 It may replace traditional Photo Multiplier Tubes (PMT) when the optical crosstalk is reduced to a lower level of below 10%.Depending on the quantity of hot electrons in the Geiger discharge approximately three to fifty secondary photons (in average three photons per 10 5 avalanche electrons 4 ) with a wavelength range from 450nm to 1600nm are emitted from the excited cell in all directions. 5 Some of those secondary photons cause the discharge of the neighboring cell. 6,7 The different mechanism of optical crosstalk are categorized as direct and indirect crosstalk.To reduce direct crosstalk an optical barrier has to be implemented between the single micro cells. 8 Thus, we have investigated different technological concepts with regard to the trench shape, the trench etching process as well as the trench fill material.

The design of a positron emission tomography (PET) scanner is specially challenging since it should not compromise high spatial resolution, high sensitivity, high count-rate capability, and good energy and time resolution. The geometrical design of the system alongside the characteristics of the individual PET detector modules contributes to the overall performance of the scanner. The detector performance is mainly influenced by the characteristics of the photo-detector and the scintillation crystal. Although silicon photomultipliers (SiPMs) have already proven to be promising photo-detectors for PET, their performance is highly influenced by micro-cell structure and production technology. Therefore, five types of SiPMs produced by KETEK with an active area size of 1.2 × 1.2 mm 2 were characterized in this study. The SiPMs differed in the production technology and had micro-cell sizes of 25, 50, 75, and 100 µm. Performance of the SiPMs was evaluated in terms of their breakdown voltage, temperature sensitivity, dark count rate, and correlated noise probability. Subsequently, energy resolution and coincidence time resolution (CTR) of the SiPMs were measured with five types of crystals, including two Ce:LYSO, two Ce:GAGG, and one Pr:LuAG. Two crystals with a geometry of 1.5 × 1.5 × 6 mm 3 were available from each type. The best CTR achieved was ∼240 ps, which was obtained with the Ce:LYSO crystals coupled to the 50 µm SiPM produced with the trench technology. The best energy resolution for the 511 keV photo-peak was ∼11% and was obtained with the same SiPM coupled to the Ce:GAGG crystals.

Abstract. Despite several advantages of Silicon Photomultipliers (SiPM) over Photomultiplier Tubes (PMT) like the increased photon detection efficiency (PDE), the compact design and the insensitivity to magnetic fields, the dark count rate (DCR) of SiPM is still a large drawback. Decreasing of the SiPM dark count rate has become a modern task, which could lead to an enormous enhancement of the application range of this promising photo-detector. The main goal of this work is to gain initial information on the dark generation and identify the dominating contributions to dark currents. The chosen approach to fulfill this task is to extract characteristic activation energies of the contributing mechanisms from temperature dependent investigations of dark currents and DCR. Since conventional methods are not suited for a precise analysis of activation energies, a new method has to be developed. In this paper, first steps towards the development of a reliable method for the analysis of dark currents and dark events are presented. IntroductionThe dark count rate (DCR) of the Silicon Photomultiplier (SiPM) is still a limiting factor for the extension of its application range and requires a significant reduction. In order to achieve this requirement, a distinction of contributions determining the DCR is needed to be able to identify the dominating mechanisms. As reported in [1,3,4,5] the extraction of characteristic activation energies from the temperature dependence of the dark current is able to provide information on the dominating mechanisms. Unfortunately these methods are not suited for a precise determination of the needed energy levels, since the investigated dark currents are determined by a mixture of effects depending on voltage on the one hand (e.g. generation current, electric field effects) and overvoltage on the other hand (e.g. gain, crosstalk, afterpulsing). In this paper, we propose a new method to separate the mentioned effects using the responsivity of the detector as an appropriate reference for the measured dark current. This approach allows us