Characterization of avalanche photodiodes (APDs) for the electromagnetic calorimeter in the ALICE experiment

The Electromagnetic Calorimeter (EMCal) of the ALICE experiment at LHC will extensively make use of avalanche photodiodes (APDs) for the readout of scintillation light. The large sensitive area, high quantum efficiency and low dark current make this type of photosensors well-suited for the EMCal requirements. A testing activity is currently in progress in order to characterize the main properties of these APDs and find the best working conditions. Fundamental tasks are the individual test of all APDs after presetting their nominal gain via the bias control and the study of APD gain coefficients as a function of the applied bias voltage and temperature. An overview of the adopted procedure will be presented, together with a description of preliminary results obtained on a first sample of APDs during the testing activity.