Silicon wafers with two different resistivities were used to produce p
+n junction and bulk samples. Irradiations were performed at high neutron flux and with fluence ranging from 10
13 n/cm
2 to 4 ...10
15n/cm
2. Bulk resistivity and Hall coefficient were measured on bulk samples using the four contact probe method. Measurements of capacitance and current versus voltage characteristics (CV-IV), Thermally Stimulated Currents (TSC), laser induced current Deep Level Transient Spectroscopy (I-DLTS) and Transient Currents by Transient Currents Technique (TCT) were performed on irradiated diodes showing a strong degradation of the detector performances after very high fluences of irradiation. Above 10
15 n/cm
2 the well known monotonic increase of the full depletion voltage seems to have a quadratic dependence on the fluence. In this extreme fluence range, the values calculated for the space charge concentration are of the order of 10
15 cm
−13: the same order of magnitude was found by TSC and I-DLTS analyses for the concentration of the deepest radiation induced traps. Moreover, TCT measurements suggest that it is practically impossible to deplete the most irradiated detectors and that there is virtually no difference between front and back contacts.
The RD48 (ROSE) collaboration has succeeded to develop radiation hard silicon detectors, capable to withstand the harsh hadron fluences in the tracking areas of LHC experiments. In order to reach ...this objective, a defect engineering technique was employed resulting in the development of Oxygen enriched FZ silicon (DOFZ), ensuring the necessary O-enrichment of about 2×10
17 O/cm
3 in the normal detector processing. Systematic investigations have been carried out on various standard and oxygenated silicon diodes with neutron, proton and pion irradiation up to a fluence of 5×10
14
cm
−2 (1
MeV neutron equivalent). Major focus is on the changes of the effective doping concentration (depletion voltage). Other aspects (reverse current, charge collection) are covered too and the appreciable benefits obtained with DOFZ silicon in radiation tolerance for charged hadrons are outlined. The results are reliably described by the “Hamburg model”: its application to LHC experimental conditions is shown, demonstrating the superiority of the defect engineered silicon. Microscopic aspects of damage effects are also discussed, including differences due to charged and neutral hadron irradiation.
The dependence of the displacement damage induced by pions in GaAs has been evaluated, in the energy range 50 –1000 MeV, using the Lindhard theory and parametrised values of the pion-nucleus ...interaction. The curves corresponding to the NIEL produced by protons, neutrons, and pions in Si and in GaAs intersect, in the limit of calculation errors, in the region 50 – 80 MeV, at a NIEL of 2 – 5.5 MeV cm
2/g. The energy dependence of the NIEL of pions in Si and GaAs is discussed in correlation with the simulated pion spectra at new hadron colliders.
Radiation damage on p-type silicon detectors Pirollo, S; Biggeri, U; Borchi, E ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/1999, Letnik:
426, Številka:
1
Journal Article
Recenzirano
Two sets of p-type silicon (high resistivity bulk and low resistivity epitaxial) samples and one set of n
+–p junctions have been irradiated with fast neutrons up to 8×10
13
cm
−2.
I–
V and
C–
V ...characteristics as well as Thermally Stimulated Currents (TSC) and Hall Effect (HE) analyses have been performed on the irradiated samples and diodes in view to determine the radiation-induced damage and the change in the electrical properties. A change in the effective carrier concentration and in the leakage current after irradiation similar to the one found for p
+–n detectors has been observed in p-type diodes. An increase with the fluence of the resistivity and Hall coefficient was measured at room temperature both for the low and high resistivity sets. This evidence has been explained in terms of a two-level model taking into account a linear increase in concentration with the fluence of the main radiation-induced defects observed with TSC, probably related to divacancy and carbon–oxygen complex.
CV and Hall effect analysis on neutron irradiated silicon detectors Biggeri, U; Borchi, E; Bruzzi, M ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/1997, Letnik:
388, Številka:
3
Journal Article
Recenzirano
Four contact bulk samples and p
+ n junction diodes produced from high resistivity n-type silicon wafers of the same ingot have been irradiated with 1 MeV-neutron fluences between 10
12 and 3 × 10
...13cm
−2. The effective impurity concentration
N
eff has been calculated from CV measurements in irradiated diodes, and bulk resistivity has been measured with the Van der Pauw method on four contact samples. The experimental resistivity and
N
eff dependence on the irradiation fluence, self-annealing time and storage temperature have been modeled considering the exponential shallow donor decay and the creation of acceptor traps in the irradiated silicon. A numerical fit to the experimental data, based on the solution of the neutrality and Poisson equations, has been carried out considering an equivalent deep acceptor defect created during and after irradiation in the silicon lattice. The energy level and the introduction rate of this defect, evaluated as best-fit parameters in the numerical procedure, are
E
t = 0.60–0.65eV above the valence band edge defect, evaluated as best-fit parameters in the numerical procedure, are
E
t = 0.60–0.65eV above the valence band edge and
b ∼ 0.06 cm
−1.
The radiation damage in 100
μm thick Schottky diodes made on semi-insulating undoped GaAs materials, were studied using α-, β-, proton- and γ-spectroscopy as well as
I–
V measurements. The results ...have been analysed within the framework of the Hecht model to investigate the influence of the plasma produced by short-range strongly ionising particles on the detector performance after 24
GeV proton irradiation. It has been found that with the mean free drift lengths for electrons and holes determined from α-spectra in overdepleted detectors, the charge collection efficiency for β-particles, cce
β, is well predicted in the unirradiated detectors, while in the most irradiated ones, the cce
β is underestimated by more than 40%. The observed disagreement can be explained by assuming that the charge carrier recombination in the plasma region of such detectors, becomes significant.
Electrical properties of high (4–6kΩcm) and medium (1–1.5kΩcm) resistivity p+/n/n+ silicon detectors irradiated with very high fluence neutrons, up to 4×1015neutrons/cm2, have been studied. Some new ...results are presented and discussed.
Hall effect analysis on neutron irradiated high resistivity silicon Biggeri, U.; Borchi, E.; Bruzzi, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/1995, Letnik:
360, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
The electrical conductivity and the Hall coefficient of high resistivity n-type silicon have been measured before and after irradiation with high fluences of fast neutrons. A model based on the ...dopant concentration changes observed after irradiation is proposed to describe the sample resistivity dependence on the neutron fluence. From the fit of the experimental data, the initial dopant concentrations and the parameters describing donor and acceptor modifications have been determined.
Non-ionising energy loss of pions in thin silicon samples Lazanu, I; Lazanu, S; Biggeri, U ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/1997, Letnik:
388, Številka:
3
Journal Article
Recenzirano
The dependence of the displacement damage induced by pions in silicon has been calculated as a function of their kinetic energy, between 50 and 1000 MeV, using data on pion-silicon interaction. The ...region of the delta resonance has been carefully considered, because it corresponds to a sharp maximum in the spectra of simulated pion production in the central cavity of LHC. Results are reported on previous calculations and on experimental damage data measured in silicon detectors irradiated with pions.
Model predictions for the NIEL of high energy pions in Si and GaAs Lazanu, S.; Lazanu, I.; Biggeri, U. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/1997, Letnik:
394, Številka:
1
Journal Article
Recenzirano
The concept of NIEL (Non Ionising Energy Loss) is usually considered to correlate the effects of the displacement damage produced in the material bulk by different particles in different energy ...ranges. An evaluation of the NIEL is especially important for those semiconductors which are planned to be used in the extreme radiation environment of the new generation of colliders as LHC. In the present work, a calculation of the pion NIEL in silicon and GaAs, in the energy region up to 50 GeV is reported and discussed. The energy dependence of the NIEL is found to follow the resonant structures of the pion-nuclei interactions, where the strongest effect is due to the
Δ
33 resonance. Above 1 GeV a slight monotonic decreasing behaviour of the NIEL has been found, both for Si and GaAs.
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