A Novel Measurement Method for SiPM External Crosstalk Probability at Low Temperature

Silicon photomultipliers (SiPMs) are being considered as potential replacements for conventional photomultiplier tubes (PMTs). However, a significant disadvantage of SiPMs is crosstalk (CT), wherein photons propagate through other pixels, resulting in secondary avalanches. CT can be categorized into internal crosstalk (iCT) and external CT (eCT) based on whether the secondary avalanche occurs within the same SiPM or a different one. Numerous methods exist for quantitatively estimating the percentage of iCT. However, eCT has not been extensively studied. This article presents a novel measurement method for the probability of emitting an eCT photon during a single-pixel avalanche, using a setup involving two identical SiPMs facing each other, and without the need for complex optical designs. The entire apparatus is enclosed within a stainless-steel (SS) chamber, functioning as a light-tight enclosure, and maintained at liquid nitrogen temperature. The experimental setup incorporates two Sensl J-60035 SiPM chips along with two 0.5-in Hamamatsu Photonics (HPK) VUV4 S13370-6050CN SiPM arrays. The findings show a linear relationship between the probability of emitting an eCT photon and the SiPM overvoltage for both SiPM samples. Surprisingly, this novel measurement method also provides measurements of the SiPM photon detection efficiency (PDE) for eCT photons at low temperature.