[en] Thermally stimulated current analysis has been performed on silicon detectors irradiated with high fast neutron fluences. The complexity of the TSC spectra required the development of a numerical procedure to deconvolute peak components. The numerical code has been used to directly calculate trap parameters: a comparison between numerical and experimental results is shown. Twentyone peaks related to various lattice defects have been found for the highest fluence of irradiation of 10¹⁴ n/cm². ((orig.))

[en] The photoluminescence (PL), thermoluminescence (TL) and thermally stimulated currents (TSC) of four high-quality CVD diamond films have been investigated in the range of temperatures between 300 and 700 K. The sample excitation has been carried out by means of an UV xenon lamp and UV laser lines. The features of the signals have been found equal to those obtained from particle excitation. The TL analysis shows the existence of several deep traps with activation energies between 0.6 and 1.0 eV. The contribution to the TL signal from different traps has been singled out by means of successive annealing processes. The TL results are in good agreement with those obtained from TSC measurements. The combined use of the two techniques allows a precise determination of the trap parameters. The spectral content of the TL response has also been compared with the PL signal in order to investigate the recombination process. This analysis shows that, in this temperature range, the TL signal is likely due to recombination from bound states rather than due to radiative free to bound transitions, as generally assumed in TL theory. The TSC signal is likely to arise from impurity band rather than from free carriers conduction

[en] New TCT measurements reveal the existence of a strong electric field, before full depletion, near both p⁺ and n⁺ side of high- and medium-resistivity silicon detectors, irradiated over space-charge sign inversion. More, by injecting carriers near the low-field side, double-peaked TCT current pulses are observed. This fact can be justified by assuming the presence of two deep levels in the gap, an acceptor like above mid-gap, and a donor like in the lower half of the gap, which can support the existence of two depleted regions. Particularly, the theoretical analysis of the TCT current profiles has been developed, and the second peak existence has been explained as the effect of carriers re-injection from ENB inside depleted regions

[en] Bulk samples obtained from two wafers of a silicon monocrystal material produced by Float-Zone refinement have been analyzed using the four-point probe method. One of the wafers comes from an oxygenated ingot; two sets of pure and oxygenated samples have been irradiated with 24 GeV/c protons in the fluence range from 10¹³ p/cm² to 2x10¹⁴ p/cm². Van der Pauw resistivity and Hall coefficient have been measured before and after irradiation as a function of the temperature. A thermal treatment (30 minutes at 100C) has been performed to accelerate the reverse annealing effect in the irradiated silicon. The irradiated samples show the same exponential dependence of the resistivity and of the Hall coefficient on the temperature from 370K to 100K, corresponding to the presence of radiation-induced deep energy levels around 0.6-0.7eV in the silicon gap. The free carrier concentrations (n, p) have been evaluated in the investigated fluence range. The inversion of the conductivity type from n to p occurred respectively at 7x10¹³ p/cm² and at 4x10¹³ p/cm² before and after the annealing treatment, for both the two sets. Only slight differences have been detected between the pure and oxygenated samples

[en] CVD diamond films have been irradiated with electrons, ⁶⁰Co photons and protons in order to study the dose response to exposure to different particles and energies and to investigate linearity with dose. The Thermally Stimulated Current (TSC) has been studied as a function of the dose delivered to polymethilmetacrilate (PMMA) in the range from 1 to 12 Gy with 20 MeV electrons from a linear accelerator. The TSC spectrum has revealed the presence of two components with peak temperatures of about 470 and 520 K, corresponding to levels lying in the diamond band gap with activation energies of the order of 0.7 - 1 eV. After the subtraction of the exponential background the charge emitted during the heating scan has been evaluated and has been found to depend linearly on the dose. The thermally emitted charge of the CVD diamond films has also been studied using different particles. The samples have been irradiated with the same PMMA dose of about 2 Gy with 6 and 20 MeV electrons from a Linac, ⁶⁰Co photons and 21 MeV protons from a TANDEM accelerator. A similar TSC response has been found at different irradiation conditions

[en] In the present work, the bulk degradation of SiC in hadron (pion and proton) fields, in the energy range between 100 MeV and 10 GeV, is characterised theoretically by means of the concentration of primary defects per unit fluence. The results are compared to the similar ones corresponding to diamond, silicon and GaAs

[en] Thermally stimulated current measurement of neutron irradiated silicon detectors have been performed. Several energy levels have been observed, revealing in particular the presence of the vacancy-oxygen complex (A center) in its double configuration, the divacancy in single (V₂^-) and double (V₂^--) minus charge state and the vacancy-phosphorous complex (E center). The increase of the leakage current of the irradiated diodes seems to be caused mainly by the presence of the E and V₂^- defects. The E centers give the main contribution to this effect, nearly 25 times higher than the V₂^- one, while the current terms related to the other defects are almost irrelevant in the generation of the total leakage current of the device. A general agreement with leakage current constant measurements and annealing behaviours has been observed. (orig.)

[en] High band-gap semiconductor materials can represent good alternatives to silicon in relative dosimetry. Schottky diodes made with epitaxial n-type 4 H SiC and Chemical Vapor Deposited diamond films with ohmic contacts have been exposed to a ⁶⁰Co γ-source, 20 MeV electrons and 6 MV X photons from a linear accelerator to test the current response in on-line configuration in the dose range 0.1-10 Gy. The released charge as a function of the dose and the radiation-induced current as a function of the dose-rate are found to be linear. No priming effects have been observed using epitaxial SiC, due to the low density of lattice defects present in this material

[en] Detectors made on the silicon wafers with high concentration of thermal donors (TD), which were introduced during the high temperature long time (HTLT) oxygenation procedure, have been investigated in the study of radiation hardness with regard to neutron irradiation and donor removal problems in irradiated high resistivity Si detectors. Two facts have been established as the evidence of radiation hardness improvement of HTLT(TD) Si detectors irradiated below ∼10¹⁴ n/cm² compared to detectors made on standard silicon wafers: the increase of space charge sign inversion fluence (of 1 MeV neutrons) due to lower initial Si resistivity dominated by TD, and the gain in the reverse annealing time constant τ favourable for this material. Coupled with extremely high radiation tolerance to protons observed earlier ('beta zero' behaviour in a wide range of fluence), detectors from HTLT(TD) Si may be unique for application in the experiments with multiple radiations. The changes in the effective space charge density (N_eff) in as-irradiated detectors as a function of neutron fluence have been fitted using three different models. It has been shown that a new model with a universal donor removal rate for both materials, and considering the contribution of non-removable TD to the N_eff provides good fit to the experimental data. A defect level related to TD has been observed in DLTS spectra of HTLT Si(TD) near T∼75 K. The physics of donor removal in irradiated silicon detectors is discussed

[en] We performed a study of charge collection distance (CCD) on medium to high-quality prototypes of diamond sensors prepared by Chemical Vapor Deposition (CVD). We studied the Charge Collection Efficiency in these materials supposing that it is limited by the presence of a recombination level and a distribution of trap levels centered at 1.7 eV from the band-edge. We also supposed that the exposition to ionizing radiation can make the trap levels ineffective (pumping effect). We have shown that these assumptions are valid by correlating the CCD to the pumping efficiency. Moreover, we have shown that the pumping efficiency is bias-dependent. We have explained our experimental results assuming that trapped carriers generate an electric field inside the diamond bulk