  Optical crosstalk seriously limits the photon-counting resolution of silicon
photomultipliers. In this work, realistic analytical models to describe the
crosstalk effects on the response of these photodetectors are presented and
compared with experimental data. The proposed models are based on the
hypothesis that each pixel of the array has a finite number of available
neighboring pixels to excite via crosstalk. Dead-time effects and geometrical
aspects of the propagation of crosstalk between neighbors are taken into
account in the models for different neighborhood configurations. Simple
expressions to account for crosstalk effects on the pulse-height spectrum as
well as to evaluate the excess noise factor due to crosstalk are also given.
Dedicated measurements were carried out under both dark-count conditions and
pulsed illumination. Moreover, the influence of afterpulsing on the measured
pulse-height spectrum was studied, and a measurement of the recovery time of
pixels was reported. High-resolution pulse-height spectra were obtained by
means of a detailed waveform analysis, and the results have been used to
validate our crosstalk models.
