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

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102 6. Inuence of Bias Voltageunbiased. It is thus not possible yet to determine the portion of the initial dierence thatrecovers after restoration of the bias voltage.The bistable nature of the defect is also shown in the time development of thedierence of the diode D2A (g. 6.10), where reverse bias was replaced by a small (about10 V) forward bias. One can see that the initial dierence between the biased (D2A) andunbiased (D2B) sample was annealing out at the beginning, but started to increase againafter afewdays at 20 C.Bistable behaviour of all presented samples could also be explained by reaction 6.1,assuming it can proceed both waysA + B $ C (6.5)the equilibrium balance being distorted by the electric eld sweeping out the mobilereaction ingredient. Two time constants of the bias eect annealing indicate two suchreactions responsible for its annealing. In that case results of the sample D2 are consistentwith an assumption that the fast reaction can proceed both ways (6.5) while the slow onecan not be reversed (reaction 6.1) and is thus, contrary to the fast one, not signicantlyaected by a weak forward bias.Bias dependent annealing of bistable defects has also been reported by M. Moll etal. [54]. There are however a few major dierences between the observed properties, indicatingdierent defects compared to those reported in this work. First, defects reportedin [54] are only seen in irradiated samples, activated by heat treatment, charge injectionby forward bias or illumination. The eect reported in this work are present since theirradiation and no special treatment is needed to activate them. Second, though bothanneal only if no reverse bias is applied, there is a big dierence in time constants. While[54] reports simple exponential annealing with a time constant of about 10h at 20 C andan activation energy of 1.040.06 eV we observe annealing with two exponentials. Thetime constants of the fast component at 20 C is four times higher (40 h) and its activationenergy about two times lower (0.5 eV). The slow component is even further o(about 1000 h at 20 C) with about the same activation energy as the fast component. Allthose dierences indicate that processes responsible for the reported phenomena are notidentical.6.3 Inuence on Reverse CurrentSince diodes, dedicated to the study of the dierence between biased and unbiased samples,had no connectable guard rings they could not be used to study the bias voltageeect on the reverse current. However, results presented in section 4.4.2, where time
6. Inuence of Bias Voltage 103Figure 6.13: Comparison of reverse current time development for biased (black) and unbiased(red) diodes.development of reverse current is discussed, can give conclusive results also on the bias effect.While no measurements of the short term annealing were performed for the unbiaseddiodes U3A and U3B, results on annealing at 60 C have been used to study long termannealing of the leakage current. Results presented there show no systematic dierenceamong the samples. They are summarised in gure 6.13 where the identical behaviour ofbiased and unbiased samples is clearly shown.6.4 ConclusionThe inuence of bias voltage on defect development was studied on neutron irradiated p + -n-n + diodes. It was shown that the presence of electric eld aects annealing of N eff whileno inuence on the reverse current was observed. Dierence in N eff between fully biasedand unbiased samples amounts to a factor of two after the end of benecial annealingwith the higher value for biased samples. The dierence scales with total irradiationuence and persists also during reverse annealing. Results on comparison of dierent
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UNIVERSITY OF LJUBLJANAFACULTY OF M
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Najprej gre moja zahvala delovnima
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PovzetekSevalne poskodbe v siliciju
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3.5 Measurement Setup, Methods and
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1IntroductionSilicon detectors play
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1. Introduction 7Figure 1.2: Schema
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1. Introduction 9R(cm)Z(cm)Figure 1
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2Operation and Radiation Damage of
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2. Operation and Radiation Damage o
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3Irradiation Facility3.1 The Reacto
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3. Irradiation Facility 373.3 Irrad
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3. Irradiation Facility 39Fission p
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3. Irradiation Facility 413.4 Irrad
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3. Irradiation Facility 43Figure 3.
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3. Irradiation Facility 45Figure 3.
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3. Irradiation Facility 47the inuen
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3. Irradiation Facility 49width of
Page 59 and 60: 3. Irradiation Facility 51The full
Page 61 and 62: 3. Irradiation Facility 53percent.
Page 63 and 64: 4Time Development of DefectsIn this
Page 65 and 66: 4. Time Development ofDefects 57* F
Page 67 and 68: 4. Time Development ofDefects 59val
Page 69 and 70: 4. Time Development ofDefects 61for
Page 71 and 72: 4. Time Development ofDefects 63Fig
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Page 89 and 90: 5Dose Rate Dependence5.1 Motivation
Page 91 and 92: 5. Dose Rate Dependence 83Figure 5.
Page 93 and 94: 5. Dose Rate Dependence 85Figure 5.
Page 95 and 96: 5. Dose Rate Dependence 87could be
Page 97 and 98: 6Inuence of Bias VoltageIt was a ge
Page 99 and 100: 6. Inuence of Bias Voltage 91energy
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Page 113 and 114: 7Comparison with Other GroupsWhile
Page 115 and 116: 7. Comparison with Other Groups 107
Page 117 and 118: 8ConclusionsA systematic study of r
Page 119 and 120: 8. Conclusions 111Implications for
Page 121 and 122: 9Povzetek doktorskega dela9.1 UvodS
Page 123 and 124: 9. Povzetek doktorskega dela 115Ski
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Page 147 and 148: 10Appendix: List of Symbols and Abb
Page 149 and 150: 10. Appendix: List of Symbols and A
Page 151 and 152: References[1] J. Straver et al., Nu
Page 153 and 154: [27] A.M. Ougang et al.: Dierential
Page 155 and 156: [57] M. Huhtinen et al, HU-SEFT-R-1
Page 158: Izjavljam, da je disertacija rezult
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