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

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110 8. ConclusionsReverse annealing of N eff A study of the initial phase of reverse annealing of N eff ona set of dedicated samples gave clear evidence for a linear dependence of reverse annealingtime constant kYlin on irradiation uence. This means that at least at the initial stage,relevant for the LHC experiments, the reverse annealing rate is governed by a rst orderprocess.Long term annealing of reverse current Study of the long term annealing of reversecurrent showed no saturation up toafewmonths at 60 C. An eective ansatz(t) = E e ;t= E ; L ln(t= L ) (8.1)was found to t the results. Lack of a natural explanation of the logarithmic behaviourhowever indicates the need for better understanding of the processes responsible.Eect of neutron ux Irradiation ux was varied from a few times 10 8 n/cm 2 s to afew times 10 15 n/cm 2 s to check for the eect of neutron ux on defect generation. Nosignicant dierence among samples irradiated with dierent uxes was observed neitherin radiation induced change of N eff nor in generated reverse current [56]. The investigatedux range covers all presently available neutron sources and it seems safe to extrapolateresults from neutron irradiation studies to the expected ux at LHC of about 10 6 n/cm 2 s.Eect of bias voltage Strict control of the biasing condition both during and afterirradiation lead to the discovery of bias inuence on defect development. Its origin wasfound not to be in the creation of defects but in their annealing. Fully biased samplesgave about a factor of two higher N eff values at the plateau after benecial annealingas compared to unbiased ones. The dierence, however, annealed out if the bias voltagewas removed. Decrease of the dierence can be described by two exponentials with timeconstants at 20 C of about 40 h for the fast component ( 45%) and six weeks for theslow one ( 40%). Activation energy of both reactions is around 0.5 eV. The remainingdierence anneals out in less than 4 hours at all measured temperatures (-7, 5 and 20 C).Few ten percent of the dierence however recovers if the sample is biased again. No eectof the bias voltage on time development of reverse current was observed.Comparison with previous results In all parameters, previously studied by othergroups (reverse annealing of N eff and long term annealing of reverse current), a goodagreement of our results with reported values was found. The rst systematic search foran eect of neutron ux on defect creation was performed in this work. Finally, in thescope of this work the eect of bias voltage on annealing of eective dopant concentrationwas discovered.
8. Conclusions 111Implications for LHC experiments Signicant eect of bias voltage on annealingof eective dopant concentration has to be taken into account when estimating radiationinduced changes of detector properties during LHC operation. Decreasing of the dierenceafter switching o the bias implies that detectors should not be biased except duringdata taking. Long time constant of the dierence annealing (about 1 year at -7 C) andlow activation energy for the responsible process ( 0:5 eV) limits its annealing duringintervals with no applied bias. Furthermore, the observed bistability of at least one ofthe defects, responsible for the bias eect, reduces the benet of the annealing of the biasinuenced dierence. Resulting data should be used in a revised operation scenario tominimise combined inuences of bias eect and reverse annealing.
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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
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3. Irradiation Facility 51The full
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3. Irradiation Facility 53percent.
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4Time Development of DefectsIn this
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4. Time Development ofDefects 57* F
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Page 89 and 90: 5Dose Rate Dependence5.1 Motivation
Page 91 and 92: 5. Dose Rate Dependence 83Figure 5.
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Page 117: 8ConclusionsA systematic study of r
Page 121 and 122: 9Povzetek doktorskega dela9.1 UvodS
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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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