Study of radiation damage in silicon detectors for high ... - F9
Study of radiation damage in silicon detectors for high ... - F9
Study of radiation damage in silicon detectors for high ... - F9
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5Dose Rate Dependence5.1 MotivationIr<strong>radiation</strong> <strong>of</strong> <strong>silicon</strong> <strong>detectors</strong> <strong>in</strong> the environment <strong>of</strong> future <strong>detectors</strong> will be a slow process,tak<strong>in</strong>g many years to accumulate the predicted uence <strong>of</strong> the order <strong>of</strong> 10 14 n/cm 21 MeV neutrons equivalent. For obvious reasons it is unpractical, if not impossible, toper<strong>for</strong>m studies <strong>of</strong> ir<strong>radiation</strong> <strong>damage</strong> eects with uxes that low. Most <strong>of</strong>ten samplesare irradiated to those uences <strong>in</strong> a few hours or days. It is thus important tocheck <strong>for</strong> apossible ux eect. Even more so because results on ion implantation with Br, Si and Care show<strong>in</strong>g considerable decrease <strong>in</strong> trap generation rates <strong>for</strong> uxes above a threshold <strong>of</strong>about 10 7 cm ;2 s ;1 , 10 8 cm ;2 s ;1 and few times 10 8 cm ;2 s ;1 , respectively [52]. This canbe expla<strong>in</strong>ed by clusters overlapp<strong>in</strong>g at <strong>high</strong> uxes, enhanc<strong>in</strong>g prompt vacancy-<strong>in</strong>terstitial<strong>silicon</strong> recomb<strong>in</strong>ation, thus reduc<strong>in</strong>g <strong>radiation</strong> <strong>in</strong>duced <strong>damage</strong>.The reactor where the present ir<strong>radiation</strong>s were per<strong>for</strong>med can cover a wide range<strong>of</strong> uxes. The maximal ux is determ<strong>in</strong>ed by a uence <strong>of</strong> about 10 14 n/cm 2 that can beobta<strong>in</strong>ed <strong>in</strong> an about 20 ms long pulse, giv<strong>in</strong>g a ux <strong>of</strong> about 510 15 n/cm 2 s. The lowerux was limited by practical reasons (about 150 h <strong>for</strong> 10 14 n/cm 2 )toabout210 8 n/cm 2 s.Thus, a range <strong>of</strong> more than seven orders <strong>of</strong> magnitude <strong>in</strong> ux can be <strong>in</strong>vestigated.A set <strong>of</strong> 7 samples was used to study the ux <strong>in</strong>uence. They were all irradiated toabout 10 14 n/cm 2 with neutron uxes cover<strong>in</strong>g the above mentioned range. All sampleswere 11 cm 2 p + -n-n + planar Micron diodes. Except <strong>for</strong> samples SA1 and SA2 that had1 and 2 guard r<strong>in</strong>gs respectively, all diodes had 3 guard r<strong>in</strong>gs. Details about ir<strong>radiation</strong>and storage are listed <strong>in</strong> table 5.1. For samples K0, K1 and K3, about a week afterir<strong>radiation</strong>, the time development was accelerated by heat<strong>in</strong>g to 60 C. In case <strong>of</strong> SA andP0 diodes, heat<strong>in</strong>g started 8 and 4 months after the ir<strong>radiation</strong>. In the meanwhile they81