Study of detection efficiency distribution and areal homogeneity of SiPMs

The analog hadron calorimeter for the International Linear Collider (ILC) of the CALICE collaboration utilized novel silicon detectors, the Sillicon Photomultipliers (SiPMs), for the detection of scintillation light coming from very small scintillator cells 3x3x0.5 cm^3. This technology allows the construction of highly granular calorimeters used for excellent shower separation and therefore outstanding jet energy resolution using the particle flow concept. Since the SiPMs still have potential for further improvements, we developed a setup dedicated to the measurement of parameters like the areal distribution of relative photon detection efficiency and crosstalk probability which are used to characterize and compare different devices. Thanks to the precise positioning system together with excellent focusing of the light source we are capable of scanning whole SiPMs with an area of ca. 1 mm^2 at a sub-pixel resolution of 1-2 \mu{}m. A further alignment compensation feature allows us to conduct separate analysis on each single pixel of a SiPM. We present the technical description of our measurement setup and results obtained for two types of SiPMs. The first one is a commercial Hamamatsu MPPC with 50 \mu{}m pixel size, the second one was the second iteration series SiMPl device developed and manufactured in the Semiconductor Laboratory of the Max Planck Institute.