Pion Radiation Damage in InGaAs p-i-n Photodiodes

Fully packaged InGaAs p-i-n photodiodes for use in CMS Tracker optical digital timing and control links have been irradiated at room temperature with 330MeV positive pions. Measurements of the leakage current and photocurrent response were made in-situ for pion fluences up to 3.9x10 14pi+/cm2. The leakage current increases from <1nA to 40 muA at 5V reverse bias and the photocurrent for 100 muW incident optical power decreases from 90 muW to 18 muW after 2x10 14 pi+/cm2. 330MeV pions cause a similar level of damage to 24GeV protons and several times more damage than 6MeV neutrons. The leakage current damage anneals slowly and no significant recovery of the photocurrent damage occurs at temperatures up to 80 degree C. Although the damage effects are relatively large they are tolerable in the CMS tracker digital timing/control optical link system.