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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76 4. Time Development <strong>of</strong> DefectsSample eq eq E E L L[n/cm 2 s] [n/cm 2 ] [10 ;17 A/cm] [h] [10 ;17 A/cm] [years]K3 1:9 10 9 1:03 10 14 1.4 0.7 0.32 2.K0 1:6 10 12 1:04 10 14 1.1 1.8 0.26 6.I3 1:9 10 9 4:4 10 13 1.3 1.8 0.26 14.B3 1:9 10 9 4:4 10 13 1.4 1.3 0.29 8.G3 1:8 10 9 8:3 10 12 1.2 1.6 0.28 9.G2 1:8 10 10 8:7 10 12 1.2 1.9 0.24 12.U3A 1:8 10 9 4:1 10 13 1.2 2.1 0.31 2.U3B 1:8 10 9 4:1 10 13 1.2 2.1 0.32 3.Table 4.10: List <strong>of</strong> diodes used to study long term anneal<strong>in</strong>g <strong>of</strong> bulk current. All samples areplanar p + -n-n + 11 cm 2 diodes, 3005 m thick with three guard r<strong>in</strong>gs. In the rst part <strong>of</strong> thetable are given ir<strong>radiation</strong> ux and uence normalised to 1 MeV neutrons. In the second part arevalues <strong>of</strong> the t parameters accord<strong>in</strong>g to ansatz 4.12. Values <strong>of</strong> the parameters are normalisedto 20 C to simplify comparison with other results. Time constants E and L are given <strong>for</strong> 60 C.Errors on E , E and L are about 20% and on L as large as 50%. The systematic error <strong>of</strong> thedosimetry is not <strong>in</strong>cluded <strong>in</strong> the given errors.Results from the present ts show no systematic behaviour with no clear temperaturedependence while measured leakage currents agree with<strong>in</strong> about 20%. Discrepanciesbetween samples may be expla<strong>in</strong>ed by contribution <strong>of</strong> surface current, <strong>high</strong> ir<strong>radiation</strong>environment and long, partially unshielded, measurement cables. Measurements <strong>of</strong> theleakage current at the laboratory with shorter cables give the same value <strong>for</strong> all samplesafter a time equivalent toafewweeks at 20 C (see next section on long term anneal<strong>in</strong>g).For LHC experiments short term anneal<strong>in</strong>g is irrelevant anyway. It is however importantto be aware <strong>of</strong> its extent when results from dierent sources are compared.4.4.2 Long Term Anneal<strong>in</strong>gLong term anneal<strong>in</strong>g <strong>of</strong> the bulk current has been studied on diodes K3, K0, I3, B3, G3,G2, U3A and U3B. Their ir<strong>radiation</strong> conditions are given <strong>in</strong> table 4.10. To accelerateanneal<strong>in</strong>g, the samples were heated to 60 C <strong>for</strong> <strong>in</strong>creas<strong>in</strong>g time periods, <strong>in</strong>termited withC/V and I/V measurements at 5 C. As can be seen <strong>in</strong> gure 4.16, after almost threemonths at 60 C there was still no evidence <strong>of</strong> reach<strong>in</strong>g a plateau.A constant slope <strong>in</strong> log-l<strong>in</strong> plot at large heat<strong>in</strong>g times (over 10 h at 60 C) <strong>in</strong>dicatedthat a logarithmic time dependence could parametrise the late stage <strong>of</strong> anneal<strong>in</strong>g. An