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

60 4. Time Development of DefectsSample V 0 FD [V] T eq [n/cm 2 s] eq [n/cm 2 ]K3 6 5 C 1:9 10 9 1:03 10 14K1 32 5 C 3:7 10 11 1:02 10 14K0 32 5 C 1:6 10 12 1:04 10 14P0A,B 8 -10 C 5 10 15 1:12 10 14I3 24 5 C 1:9 10 9 4:4 10 13D3 16 15 C 1:8 10 9 4:2 10 13B3 20 0 C 1:9 10 9 4:4 10 13G3 23 0 C 1:8 10 9 8:3 10 12G2 20 0 C 1:8 10 10 8:7 10 12Table 4.3: List of diodes used in the study of reverse annealing of N eff with model ts.Full depletion voltage before irradiation, irradiation/storage temperature, irradiation ux anduence normalised to 1MeV neutrons are given for each sample. The thickness of samples was3005 m.heating periods 34 . Though not all samples were irradiated at the same temperature theseeects could be neglected after a few hours at 60 C. Nevertheless, this was accounted for,using equationgivingk(T )=k 0 e ; Eak BT (4.4)k(T 2 )=k(T 1 )e Eak B( 1T 1; 1T 2 ) : (4.5)Value of the activation energy E a for the reverse annealing of N eff is about 1.3 eV [13, 14,15] and for annealing of reverse current about 1.1 eV [15]. Thus, the time development ofN eff at 60 C is almost 500 times faster than at 20 and for time development of reversecurrent this factor is about 190.Since annealing time constants are much shorter than those for the reverse annealingit is possible to study reverse annealing independently by waiting for annealing tocomplete. The eect of reverse annealing during the time interval of benecial annealingis negligible as can be seen from gures 4.7, 4.5. Thus, assuming annealing to be completedand using equations 2.65, 2.57 and 2.61 one can set an ansatz for both processesasN eff (t) =g C eq + g Y eq (1 ; e ;kY 1 t ) (4.6)34Due to voltage-source current limit of 3 mA for some highly irradiated samples the bias voltageduring heating was somewhat lower, but never below 140 V.