Neutron , proton and gamma radiation effects in candidate InGaAs pi-n photodiodes for the CMS tracker optical

InGaAs p-i-n photodiodes will be used in the CMS tracker to receive the digital timing and control signals transmitted from the Front End Controller (FEC) boards by 1310nm wavelength lasers. These devices should be sufficiently rad-hard to survive the fluences/doses encountered in the tracker during a ten year operational period. Candidate p-i-n diodes have been irradiated, in a fully packaged, fibre-pigtailed form, with up to 10neutrons/cm (=6MeV), 4x10 protons/cm 2 (Ep=24GeV) and 100kGy Co photons. Displacement damage from the neutron and proton irradiation caused the leakage current to increase by 6-7 orders of magnitude and the responsivity to decrease by 90% after ~10p/cm 2 or 10n/cm. Gamma damage was almost negligible in comparison.