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Silicon Photomultipliers (SiPMs) are fabricated in two different configurations: p-on-n and n-on-p junctions. More particularly p-on-n SiPMs turn out to be more suitable in nuclear medical imaging applications like Positron Emission Tomography (PET), due to their higher sensitivity in blue wavelength range where common PET scintillators have their emission spectrum. Here we report on the preliminary results of the electro-optical characterization performed on the first STMicroelectronics p-on-n SiPMs with standard (45%) and enhanced (62%) fill factor. The performances of these devices are compared with standard n-on-p technology. The inversion of the junction results in a remarkable improvement of PDE in blue wavelength range. Moreover all the tested devices show very good single photoelectron resolution also for high overvoltage values confirming the excellent single photon detection capability of SiPM technology. In this work a comprehensive SiPM model integrating the electrical and statistical behavior of the device is also presented. We used a Monte Carlo model for statistical and a SPICE circuit model for the electrical behavior description of the SiPM.

In this paper we report the results relative to the design and fabrication of Single Photon Avalanche Detectors (SPAD) operating at low voltage in planar technology. These silicon sensors consist of pn junctions that are able to remain quiescent above the breakdown voltage until a photon is absorbed in the depletion volume. This event is detected through an avalanche current pulse. Device design and critical issues in the technology are discussed. Experimental test procedures are then described for dark-counting rate, afterpulsing probability, photon timing resolution, quantum detection efficiency. Through these experimental setups we have measured the electrical and optical performances of different SPAD technology generations. The results from these measurements indicate that in order to obtain low-noise detectors it is necessary to introduce a local gettering process and to realize the diode cathode through in situ doped polysilicon deposition. With such technology low noise detectors with dark counting rates at room temperature down to 10c/s for devices with 10mm diameter, down to 1kc/s for 50mm diameter have been obtained. Noticeable results have been obtained also as far as time jitter and quantum detection efficiency are concerned. This technology is suitable for monolithic integration of SPAD detectors and associated circuits. Small arrays have already been designed and fabricated. Preliminary results indicate that good dark count rate uniformity over the different array pixels has already been obtained.