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

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50 3. Irradiation FacilityFigure 3.12: A comparison of a 1/C 2 vs. voltage characteristics as obtained by a a) paralleland b) serial RC model. Straight line ts to the slope at large depletion depths and to theplateau at full depletion are also shown. The intersection of the lines was used to determine thefull depletion voltage.A comparison of results obtained by both models is shown in gure 3.12. As expected,at low depletion voltages better results are obtained with the serial model whileresults at high depletion depths are similar. It can however be noticed that the serialmodel gives a larger error of the value at the plateau for the lowest frequency (1 kHz). Inthat case parallel resistance is no longer negligible compared to capacitor impedance 1!C ,leading to a larger error for the serial model. Full depletion voltages as obtained by bothmodels agree within the errors.The eect of the decoupling capacitors and resistors was taken into account bycalibration. HP4284A enables frequency dependent calibration in a large frequency rangewhile HP4263B can only be calibrated at one frequency, 10 kHz in our case. Calibrationis done at open and closed circuit and with known load 28 .The measurement of the C/V characteristic was run by a custom written LabViewprogram, running on a PC. Bias voltage (DC) was raised in predened steps and samplecapacitance was measured at each step with dierent frequencies of measuring (AC) voltage.Leakage current and sample temperature were also measured at each step. Measuredcapacitance was converted to 1/C 2 and plotted in dependence of the bias voltage.28A capacitor of 44 pF was used since this is an approximate capacitance of fully depleted 300 mthick diodes with an area of 1 cm 2 , used in this study.
3. Irradiation Facility 51The full depleti on voltage was determined as the position of the kink in 1/C 2 vs.voltage curve. The exact position of the kink was determined by the intersection of twolines, one tted to the slope at large depletion depths and the second to the plateauat full depletion (see g. 3.12). Fitted range was determined manually after a visualexamination of the plot.To determine the eective dopant concentration N eff , a homogeneous distributionover the sample was assumed. In such case N eff can be determined from the full depletionvoltage by the equationN eff = 2 Si 0e 0 W 2 V FD : (3.15)The conversion factor depends on sample thickness and for 300 m thick samples equation3.15 can be written with a xed numerical factor N eff =1:44 10 10 V ;1 cm ;3 V FD .The main sources of systematic error on determination of the full depletion voltageare in the selection of the measuring frequency and temperature. While measurementswere performed at dierent frequencies (1 kHz, 3 kHz, 10 kHz, 30 kHz, 100 kHz, 300 kHzand 1 MHz in the laboratory and 100 Hz, 1 kHz, 10 kHz and 100 kHz at the reactor), afrequency of 10 kHz was most usually used to determine FDV. 10 kHz is a compromisebetween a good signal to noise ratio 29 , sensitivity to traps with long trapping times andapplicability of the simple RC model used. Since it is also the most commonly usedfrequency of other groups, it also enables better comparison.In the laboratory, all measurements were performed at 5 Ctoavoid the temperatureeect. This was however not possible at the reactor, where measurements were performedat storage temperature.The systematic error due to the sources listed above is estimated to be below 10%.The variations of FDV due to dierent selections of the tted range for ts of the linearpart at high depletion depths is on a percent level. That means that the largest contributionto the error on introduction rates of dierent defects comes from the 15% systematicerror of the dosimetry.3.5.3 Bulk CurrentThe time development of reverse bulk current has been studied together with N eff . Toseparate bulk-generated current from the surface generated one, only diodes with guardrings were used in the analysis. While both guard ring and the pad were connected tothe same potential, only current owing through the pad was measured to reduce thecontribution of the surface current.29Impedance of capacitor is inversely proportional to the frequency of the measurement voltage.
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UNIVERSITY OF LJUBLJANAFACULTY OF M
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Najprej gre moja zahvala delovnima
Page 8 and 9: PovzetekSevalne poskodbe v siliciju
Page 10 and 11: 3.5 Measurement Setup, Methods and
Page 13 and 14: 1IntroductionSilicon detectors play
Page 15 and 16: 1. Introduction 7Figure 1.2: Schema
Page 17 and 18: 1. Introduction 9R(cm)Z(cm)Figure 1
Page 19 and 20: 2Operation and Radiation Damage of
Page 21 and 22: 2. Operation and Radiation Damage o
Page 43 and 44: 3Irradiation Facility3.1 The Reacto
Page 45 and 46: 3. Irradiation Facility 373.3 Irrad
Page 47 and 48: 3. Irradiation Facility 39Fission p
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Page 51 and 52: 3. Irradiation Facility 43Figure 3.
Page 53 and 54: 3. Irradiation Facility 45Figure 3.
Page 55 and 56: 3. Irradiation Facility 47the inuen
Page 57: 3. Irradiation Facility 49width of
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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6. Inuence of Bias Voltage 101(abou
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6. Inuence of Bias Voltage 103Figur
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7Comparison with Other GroupsWhile
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7. Comparison with Other Groups 107
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8ConclusionsA systematic study of r
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8. Conclusions 111Implications for
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9Povzetek doktorskega dela9.1 UvodS
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9. Povzetek doktorskega dela 115Ski
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9. Povzetek doktorskega dela 117sre
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9. Povzetek doktorskega dela 1199.2
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9. Povzetek doktorskega dela 121Sli
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9. Povzetek doktorskega dela 123Ce
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9. Povzetek doktorskega dela 127Cep
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9. Povzetek doktorskega dela 129Mer
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9. Povzetek doktorskega dela 131Sam
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9. Povzetek doktorskega dela 1379.6
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10Appendix: List of Symbols and Abb
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10. Appendix: List of Symbols and A
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References[1] J. Straver et al., Nu
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[27] A.M. Ougang et al.: Dierential
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[57] M. Huhtinen et al, HU-SEFT-R-1
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