Neutron, Proton and Gamma Radiation Effects in Candidate InGaAs p-i-n Photodiodes for the CMS Tracker Optical Links

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 1^10nm 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 10^15neutrons/cm2 ( <En>=6MeV), 4x10^14 protons/cm2 ( Ep=24GeV) and 100kGy 60Co 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 ~10^14 p/cm2 or 10^15 n/cm2. Gamma damage was almost negligible in comparison. If the current prototype p-i-n photodiodes are used in the tracker, they should be situated at least 50cm from the beam axis where the hadron fluence is less than 10^14/cm2.