Studies of propagation mechanism of optical crosstalk in silicon photomultipliers

Silicon photomultipliers (SiPMs) are now replacing photomultiplier tubes where low voltage operations, compactness, and cost per channel are important. However, optical crosstalk (OCT) is still one of the major disadvantages of SiPMs since it increases accidental triggers and degrades the accuracy of photon counting. Previously, we reported that OCTs can be suppressed by either thicker or no protection resin coating. Although no resin coating heavily suppresses OCTs, we still observe some OCTs at a few % levels. In this study, we have investigated the properties of OCTs and delayed OCTs for several types of SiPMs with different device sizes, cell sizes, and resin coating thickness. We observe that delayed OCTs have very similar properties compared with OCTs with no resin coating. Furthermore, we find that the sizable amount of delayed OCTs is overlapping with the original pulse and may be treated as OCTs when the delay is less than 8 ns in our analysis. Since the properties and rate of overlaps of delayed OCTs match those of OCTs with no resin coating, we conclude that the remaining OCTs for SiPMs with no coating can be fully explained by overlaps of delayed OCTs.