The silicon photomultiplier (SiPM) is a promising semiconductor device for low-level light detection. The recovery time, or the photon-counting rate of the SiPM is essential for high-flux photon detection in such applications as photon counting computer tomography (CT). A SiPM with epitaxial quenching resistors (EQR SiPM) has advantages in fabricating small APD microcells connected in series with lower quenching resistors, therefore, APD cells with a low RC time constant and a short recovery time can be expected. In this report, the recovery time of EQR SiPM has been investigated using both the double light pulse method and the waveform analysis method. The results show that the recovery time of EQR SiPM is strongly dependent on the size of the active area and the number of fired pixels. For a 3 × 3 mm² device, while total about 90,000 pixels were fired, the recovery time was 31.1 ± 1.8 ns; while fired pixels were controlled to about 2000, the recovery time decreased significantly to 6.5 ± 0.4 ns; and the recovery time of one fired pixel was 3.1 ± 0.2 ns. For 1.4 × 1.4 mm² device, the recovery time was 15.2 ± 0.5 ns, while a total of about 20,000 pixels were fired. Effects that may affect the recovery time of the SiPM, including strength of the pulse light, signal transmission time delay, and the readout electronics are discussed.

A two-dimensional (2D) square-bordered position-sensitive (PS) silicon photomultiplier (SiPM) toward distortion-free performance with high spatial resolution is reported in this letter. The device, based on SiPM technology of an epitaxial quenching resistor, contains a central cap resistive region enclosed by a narrow square-shaped metal ring contact located at the surface periphery. Four small output metal pads are connected to the metal ring at each corner to read out signal charges. With an active area of 6.14 mm × 6.14 mm, the PS-SiPM demonstrated an average position measurement error (PME) of 86.9 μm without correction, which accounted for 1.4% of the side length of the active area. The average position resolutions were demonstrated to be ~130.7 μm and ~135.6 μm in the X and Y directions, respectively, for incident light with a spot diameter of 80 μm and a mean photoelectron number (MPEN) of ~600. In addition, an intrinsic radioactive-light image of a pixelated 12×12 lutetium-yttrium oxyorthosilicate (LYSO) array with each element volume of 0.475 × 0.475 × 6 mm3 was clearly resolved by the 2D square-bordered PS-SiPM.

The thickness of the high-resistivity layer (active layer) is a crucial factor affecting the timing resolution of low gain avalanche diodes (LGADs). We studied the potential improvement of the timing resolution of charge particles based on LGADs with different active layer thicknesses. The Institute of High Energy Physics (IHEP) and the Novel Device Laboratory (NDL) jointly designed two types of LGAD sensors with active layer thicknesses of 33 and 50 $\mu \text{m}$ . The timing resolution is given by contributions from the time walk, jitter, and nonuniform charge deposition (Landau term). The jitter and the Landau term contributions in the timing resolution are extracted by the combination of the ${^{90}{Sr}}$ beta source test and the picosecond laser test. The Landau contribution is found to be the dominant contribution for both types of LGAD sensors, and the Landau contribution of the 33 $\mu \text{m}$ sensor is lower than that of the 50 $\mu \text{m}$ sensor. Based on the experimental results, we perform the simulation for thinner active layer LGAD with the WeightField2 program. The timing resolution can be further improved by reducing the active layer thickness from 33 to 20 $\mu \text{m}$ .

An ultralow level light detection module, the time-correlated photon counter, is proposed and evaluated for fluorescence analysis. The time-correlated photon counter employs a silicon photomultiplier as a photon counting sensor in conjunction with a Poisson statistics algorithm and a double time windows technique, and therefore it can accurately count the photon number. The time-correlated photon counter is compatible with the time-correlated single photon counting technique and can record the arrival time of very faint light signals. This low-cost and compact instrument was used to analyze the intensity and lifetime of fluorescein isothiocyanate; a limit of detection of 16 pg/ml with a large linear dynamic range from 2.86 pg/ml to 0.5 µg/ml was obtained, and the lifetime of fluorescein isothiocyanate was measured to be 3.758 ns, which agrees well with the results of a sophisticated commercial fluorescence analysis instrument. The time-correlated photon counter may be useful in applications such as point-of-care testing.