A comparison on radiation tolerance of microstrip detectors built on 〈1 0 0〉 and 〈1 1 1〉 silicon substrates after proton irradiation

A comparative study on silicon microstrip detectors of the same geometry built on 〈1 0 0〉 low resistivity and 〈1 1 1〉 high resistivity substrates has been carried out. Leakage current, depletion voltage and interstrip capacitance have been measured before and after irradiation with 34 MeV protons at regular intervals during the beneficial annealing period. The samples were irradiated at four different fluences up to ≃2×1014 n/cm2. The measurements after irradiation show that leakage current does not depend on substrate resistivity and crystal orientation. Above type inversion also, the depletion voltage does not depend substantially on the initial resistivity. The interstrip capacitance is damaged both for 〈1 0 0〉 and 〈1 1 1〉 silicon substrates, even if in the first case the interstrip capacitance increase is lower, as expected from the known difference in charge trapping effects. The results of this work are compared with previous measurements performed on identical structures irradiated with neutrons.