Study of radiation damage in silicon detectors for high ... - F9

76 4. Time Development of 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 of diodes used to study long term annealing of bulk current. All samples areplanar p + -n-n + 11 cm 2 diodes, 3005 m thick with three guard rings. In the rst part of thetable are given irradiation ux and uence normalised to 1 MeV neutrons. In the second part arevalues of the t parameters according to ansatz 4.12. Values of the parameters are normalisedto 20 C to simplify comparison with other results. Time constants E and L are given for 60 C.Errors on E , E and L are about 20% and on L as large as 50%. The systematic error of thedosimetry is not included in the given errors.Results from the present ts show no systematic behaviour with no clear temperaturedependence while measured leakage currents agree within about 20%. Discrepanciesbetween samples may be explained by contribution of surface current, high irradiationenvironment and long, partially unshielded, measurement cables. Measurements of theleakage current at the laboratory with shorter cables give the same value for all samplesafter a time equivalent toafewweeks at 20 C (see next section on long term annealing).For LHC experiments short term annealing is irrelevant anyway. It is however importantto be aware of its extent when results from dierent sources are compared.4.4.2 Long Term AnnealingLong term annealing of the bulk current has been studied on diodes K3, K0, I3, B3, G3,G2, U3A and U3B. Their irradiation conditions are given in table 4.10. To accelerateannealing, the samples were heated to 60 C for increasing time periods, intermited withC/V and I/V measurements at 5 C. As can be seen in gure 4.16, after almost threemonths at 60 C there was still no evidence of reaching a plateau.A constant slope in log-lin plot at large heating times (over 10 h at 60 C) indicatedthat a logarithmic time dependence could parametrise the late stage of annealing. An