APD properties and recovery from radiation damage

Avalanche photodiodes will be used to detect scintillation light from PbWO4 crystals in the CMS electromagnetic calorimeter. Properties of Hamamatsu APD are reported and special attention has been devoted to the study of radiation hardness and room temperature annealing. We found a fast recovery with a time constant of 1.3 days, a medium fast recovery with of the order of 10 days and indication of a third component with very long time constant of the order of 300 days. 1 APD (batch B) T'18oC (summer 1996) APD C(pF) Front Window V(V) ID(nA) Area (cm2) BA 120 130 SiO2 193 20 .2 BC 130 140 SiO2 182 2 .2 BD 420 430 SiO2 119 2.5 .2 BE 470 480 SiO2 113 10 .2 BA-N 120 130 Si3N4 193 2 .2 Table 1 Parameters of the new APD’s from Hamamatsu : capacitance, front window layer, bias for a gain of 50, dark current for a gain of 50, area.