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.

The performance of an active-quenching single-photon avalanche diode (SPAD) array that is based on the tri-state gates of a field programmable gate array (FPGA) is presented. The array is implemented by stacking a bare 4 × 4 N-on-P SPAD array on a bare FPGA die, and the electrodes of the SPAD pixels and the I/O ports of the FPGA are connected through wire bonding within the same package. The active quenching action on each SPAD pixel is performed by using the properties of the tri-state gates of the FPGA. Digital signal processing, such as pulse counters, data encoders, and command interactions, is also performed by using the same FPGA. The breakdown voltage of the SPAD pixels, with an active area of 60 μm × 60 μm, is 47.2–48.0 V. When the device is reverse biased at a voltage of ~50.4 V, a response delay of ~50 ns, a dead time of 157 ns, a dark count rate of 2.44 kHz, and an afterpulsing probability of 6.9% are obtained. Its peak photon detection probability (PDP) reaches 17.0% at a peak wavelength of 760 nm and remains above 10% at 900 nm. This hybrid integrated SPAD array is reconfigurable and cost effective.