Radiation hardness and lifetime studies of photodiodes for the optical readout of the ATLAS semiconductor tracker

A large sample (96) of epitaxial Si PIN photodiodes has been irradiated by ~1 MeV neutrons and 24 GeV protons with fluences up to 10E15 equivalent 1 MeV neutrons per square cm in order to test their suitability for use in the optical readout of the ATLAS semiconductor tracker and pixel detector at the CERN Large Hadron Collider. After an initial reduction of 30the responsivity remains constant up to the maximum fluence. The rise and fall times are not significantly affected and remain below 1 ns. Although the dark current increases linearly with increasing neutron fluence, its level remains below 100 nA which is negligible in comparison to the operating photocurrent which is above 100 microamps. Enhance ageing studies at 60 degrees C have also been carried out and no failure has occurred after an equivalent of 360 years of operation.