Measurements of the reverse current of highly irradiated silicon sensors

Abstract

The reverse current of irradiated silicon sensors depends, among other variables, on sensor temperature and irradiation fluence. The temperature dependency is parameterized by the effective energy Eeff and the fluence dependency by the current related damage rate α. The literature values for Eeff and α were obtained from previous measurements, but α was only measured directly to a fluence up to 1×10151MeV neutron equivalent fluence per cm2 (neq/cm2).Miniature micro-strip sensors (≈1×1cm2) were irradiated with protons to fluences from 1×1012 to 1×1015 neq/cm2 and with neutrons from 5×1015 to 2×1016 neq/cm2 to investigate the reverse current at higher fluences. Precise temperature and current measurements of sensors from Hamamatsu Photonics K.K. (293μm thick) and Micron Semiconductor Ltd. (143μm and 108μm thick) were carried out. The sensors were measured shortly after irradiation and after room temperature annealing. These measurements allow the determination of the evolution of Eeff. Instead of α the geometric current related damage rate α⁎ is used, which depends on the geometric thickness rather than the depletion depth. For low fluences they are in good agreement while for high fluences α⁎ is smaller.