Evidence for charge collection efficiency recovery in heavily irradiated silicon detectors operated at cryogenic temperatures

Charge collection efficiency of 300 μm thick silicon detectors, previously irradiated at 2.23×1015 n/cm2, has been measured at 4.2, 77 and 195 K. The recovery measured at a bias voltage of 250 V leads to a most probable signal for minimum ionizing particles of 13 000 electrons, preserving its fast characteristics (<5 ns). Negligible difference is observed between 77 and 4.2 K operation, while no recovery is measurable at 195 K. The samples were stored at room temperature and cooled only when operated.