Effects of accelerated annealing on p-type silicon micro-strip detectors after very high doses of proton irradiation

Abstract

Miniature (1 cm length) strip detectors have been produced with n-side read-out on p-type substrates to exploit the advantages, after exposure to large fluxes of hadrons, of reading out segmented devices from the n-side. These p-type prototypes have been irradiated with 24 GeV/ c protons to three fluences compatible with the expected doses (at different radii) for the inner tracker at the upgraded LHC (sLHC), namely 1.1, 3.5 and 7.5×10 15 cm −2. We have previously shown that those devices exhibit a signal to noise greater than 8:1 with LHC speed electronics even after the highest dose. The measurements were performed at the minimum of the curve of the annealing of the full depletion voltage after irradiation before the reverse annealing sets in. We have now studied the charge collection performance after accelerated annealing at 80 °C. At this temperature, the effects of the annealing are accelerated by a factor of about 7400 compared to room temperature, and our study spans an equivalent annealing time of several years at room temperature. The results, in terms of charge collection efficiency, are in sharp contrast with the evolution of the full depletion voltage as measured with the capacitance-voltage technique and suggest that these heavily irradiated detectors can be kept at room temperature for long periods without degrading their performance (e.g., during maintenance time). It is also apparent that the description of these heavily irradiated devices in terms of their full depletion voltage is no longer appropriate for the prediction of their charge collection properties.