Study of the breakdown voltage of SiPMs

The breakdown behaviour of SiPMs (Silicon PhotoMultiplier) with pixel sizes of 15×15,25×25,50×50, and 100×100μm2, manufactured by KETEK, has been investigated. From the current-voltage characteristics measured with and without illumination by LED light of 470 nm wavelength, the current-breakdown voltage, VI, and from linear fits of the voltage dependence of the SiPM gain, measured by recording pulse-area spectra, the gain-breakdown voltage, VG, have been obtained. The voltage dependence of the Geiger-breakdown probability was determined from the fraction of zero photoelectron events with LED illumination. By comparing the results to a model calculation, the photodetection-breakdown voltage, VPD, has been determined. Within experimental uncertainties, VI and VPD are equal and independent of pixel size. For VG, a dependence on pixel size is observed. The difference VI−VG is about 1 V for the SiPM with 15μm pixels, decreases with pixel size and is compatible with zero for the SiPM with 100 μm pixels.