Monolithic silicon matrix detector with 50 microns photon counting pixels

A 48-element monolithic matrix detector, designed for parallel fluorescence detection, has been fabricated in silicon and tested. The pixels are single photon avalanche diodes (SPADs) with 50 pm diameter, ordered in a 6 x 8 array with 240 mu m pitch. The photon detection efficiency is remarkably uniform over the array: it has a peak of 48% at 530 nm and it is higher than 30% over all the visible range. Low dark counting rate (DCR) is obtained in operation at moderately low temperature (-15 degrees C with thermoelectric cooling): the individual pixel DCR is 60cs(-1) for about 40% of the elements and it is below 5700cs(-1) in the rest of the array. It was verified that the afterpulsing probability is below 1% and that the optical crosstalk probability between elements is lower than 0.2%. Based on this matrix detector, we have developed a versatile and compact (20cm x 8cm x 4cm) photon counting module that can be easily interfaced to a PC via USB link.