Scientists from the Laboratory of Nuclear Problems at JINR, Institute of High Energy Physics of the Chinese Academy of Sciences (CAS), University of CAS, and East China Normal University conducted a study of silicon photomultiplier (SiPM) external cross-talk, including SiPMs to be used in the nEXO and JUNO-TAO Neutrino Experiments. The results reveal a significant presence of external cross-talk in all tested SiPMs.

Optical cross-talk is a critical characteristic of silicon photomultipliers (SiPMs), which represents a significant source of the excess noise factor, exerting a substantial influence on detector performance. During the avalanche process of SiPMs, the generated photons can give rise to both internal cross-talk within the same SiPM and external cross-talk when photons escape from one SiPM and trigger avalanches in others. In scenarios where SiPMs are arranged in a compact configuration and positioned facing each other, the external cross-talk could even dominate the cross-talk phenomenon.

This paper investigates two distinct methods for measuring external cross-talk: the counting method, which involves operating SiPMs face-to-face and measuring their coincident signals, and the reflection method, which employs a highly reflective film attached to the surface of the SiPMs. External cross-talk measurements have been conducted on several types of SiPMs, including Vacuum Ultra-Violet (VUV) sensitive SiPMs that Fondazione Bruno Kessler (FBK) and Hamamatsu Photonics Inc (HPK) produced for nEXO and visible-sensitive SiPMs provided by FBK, HPK, and SensL Technologies Ltd (SenSL) for JUNO-TAO.

The results reveal a significant presence of external cross-talk in all tested SiPMs, with HPK’s SiPMs exhibiting a dominant external cross-talk component due to the implementation of optical trenches that effectively suppress internal cross-talk. Furthermore, the researchers found that the number of fired SPADs resulting from internal cross-talk can be described by combining Geometric and Borel models for all tested SiPMs, while the external cross-talk can be predicted using a pure Borel model. These distinct probability distributions lead to different excess noise factors, thereby impacting the detector performance in varying ways.

The Journal of Instrumentation published an article on this research in June 2024. Among the authors are employees of the DLNP JINR Methodological Research Sector Nikolay Anfimov, Dmitry Fedoseev, Ksenia Kuznetsova, Arseny Rybnikov, Alexander Selyunin, and an engineer of the DLNP Experimental Neutrino Physics Sector Albert Sotnikov.