Browsing by Author "Forneris, J"

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    Focused ion beam fabrication and IBIC characterisation of a diamond detector with buried electrodes
    (Elsevier, 2011-10-15) Olivero, P; Forneris, J; Jakšić, M; Pastuovic, Z; Picollo, F; Skukan, N; Vittone, E
    This paper reports on the fabrication and characterization of a high purity monocrystalline diamond detector with buried electrodes realized by the selective damage induced by a focused 6 MeV carbon ion beam scanned over a pattern defined at the micrometric scale. A suitable variable-thickness mask was deposited on the diamond surface in order to modulate the penetration depth of the ions and to shallow the damage profile toward the surface. After the irradiation, the sample was annealed at high temperature in order to promote the conversion to the graphitic phase of the end-of range regions which experienced an ion-induced damage exceeding the damage threshold, while recovering the sub-threshold damaged regions to the highly resistive diamond phase. This process provided conductive graphitic electrodes embedded in the insulating diamond matrix; the presence of the variable-thickness mask made the terminations of the channels emerging at the diamond surface and available to be connected to an external electronic circuit. In order to evaluate the quality of this novel microfabrication procedure based on direct ion writing, we performed frontal Ion Beam Induced Charge (IBIC) measurements by raster scanning focused MeV ion beams onto the diamond surface. Charge collection efficiency (CCE) maps were measured at different bias voltages. The interpretation of such maps was based on the Shockley-Ramo-Gunn formalism. (C) 2011 Elsevier B.V. All rights reserved.
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    Generation of vacancy cluster-related defects during single MeV silicon ion implantation of silicon
    (Elsevier, 2014-08-01) Pastuovic, Z; Capan, I; Siegele, R; Jacimovic, R; Forneris, J; Cohen, DD; Vittone, E
    Deep Level Transient Spectroscopy (DLTS) has been used to study defects formed in bulk silicon after implantation of 8.3 MeV 28Si3+ ions at room temperature. For this study, Schottky diodes prepared from n-type Czohralski-grown silicon wafers have been implanted in the single ion regime up to fluence value of 1 × 1010 cm−2 utilizing the scanning focused ion microbeam as implantation tool and the Ion Beam Induced Current (IBIC) technique for ion counting. Differential DLTS analysis of the vacancy-rich region in self-implanted silicon reveals a formation of the broad vacancy-related defect state(s) at Ec −0.4 eV. Direct measurements of the electron capture kinetics associated with this trap at Ec −0.4 eV, prior to any annealing do not show an exponential behaviour typical for the simple point-like defects. The logarithmic capture kinetics is in accordance with the theory of majority carrier capture at extended or cluster-related defects. We have detected formation of two deep electron traps at Ec −0.56 eV and Ec −0.61 eV in the interstitial-rich region of the self-implanted silicon, before any annealing. No DLTS signal originating from vacancy-oxygen trap at Ec −0.17 eV, present in the sample irradiated with 0.8 MeV neutrons, has been recorded in the self-implanted sample. © 2014, Elsevier B.V.
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    Monte Carlo analysis of a lateral IBIC experiment on a 4H-SiC Schottkey diode
    (Elsevier B.V., 2011-10-15) Olivero, P; Forneris, J; Gamarra, P; Jakšić, M; Lo Giudice, A; Manfredotti, C; Pastuovic, Z; Skukan, N; Vittone, E
    The transport properties of a 4H-SiC Schottky diode have been investigated by the ion beam induced charge (IBIC) technique in lateral geometry through the analysis of the charge collection efficiency (CCE) profile at a fixed applied reverse bias voltage. The cross section of the sample orthogonal to the electrodes was irradiated by a rarefied 4 MeV proton microbeam and the charge pulses have been recorded as function of incident proton position with a spatial resolution of 2 mu m. The CCE profile shows a broad plateau with CCE values close to 100% occurring at the depletion layer, whereas in the neutral region, the exponentially decreasing profile indicates the dominant role played by the diffusion transport mechanism. Mapping of charge pulses was accomplished by a novel computational approach, which consists in mapping the Gunn's weighting potential by solving the electrostatic problem by finite element method and hence evaluating the induced charge at the sensing electrode by a Monte Carlo method. The combination of these two computational methods enabled an exhaustive interpretation of the experimental profiles and allowed an accurate evaluation both of the electrical characteristics of the active region (e.g. electric field profiles) and of basic transport parameters (i.e. diffusion length and minority carrier lifetime). (C) 2011 Elsevier B.V. All rights reserved.
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    A Monte carlo software for the 1-dimensional simulation of IBIC experiments
    (Science Direct, 2014-08-01) Forneris, J; Jakšić, M; Pastuovic, Z; Vittone, E
    The ion beam induced charge (IBIC) microscopy is a valuable tool for the analysis of the electronic properties of semiconductors. In this work, a recently developed Monte Carlo approach for the simulation of IBIC experiments is presented along with a self-standing software equipped with graphical user interface. The method is based on the probabilistic interpretation of the excess charge carrier continuity equations and it offers to the end-user the full control not only of the physical properties ruling the induced charge formation mechanism (i.e., mobility, lifetime, electrostatics, device’s geometry), but also of the relevant experimental conditions (ionization profiles, beam dispersion, electronic noise) affecting the measurement of the IBIC pulses. Moreover, the software implements a novel model for the quantitative evaluation of the radiation damage effects on the charge collection efficiency degradation of ion-beam-irradiated devices. The reliability of the model implementation is then validated against a benchmark IBIC experiment. © 2014, Elsevier B.V.
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    Radiation hardness of n-type SiC Schottky barrier diodes irradiated with MeV He ion microbeam
    (Elsevier, 2015-04-01) Pastuovic, Z; Capan, I; Cohen, DD; Forneris, J; Iwamoto, N; Ohshima, T; Siegele, R; Hoshino, N; Tsuchida, H
    We studied the radiation hardness of 4H-SiC Schottky barrier diodes (SBD) for the light ion detection and spectroscopy in harsh radiation environments. n-Type SBD prepared on nitrogen-doped (similar to 4 x 10(14) cm(-3)) epitaxial grown 4H-SiC thin wafers have been irradiated by a raster scanning alpha particle microbeam (2 and 4 MeV He2+ ions separately) in order to create patterned damage structures at different depths within a sensitive volume of tested diodes. Deep Level Transient Spectroscopy (DLTS) analysis revealed the formation of two deep electron traps in the irradiated and not thermally treated 4H-SiC within the ion implantation range (E1 and E2). The E2 state resembles the well-known Z(1/2) center, while the E1 state could not be assigned to any particular defect reported in the literature. Ion Beam Induced Charge (IBIC) microscopy with multiple He ion probe microbeams (1-6 MeV) having different penetration depths in tested partly damaged 4H-SiC SBD has been used to determine the degradation of the charge collection efficiency (CCE) over a wide fluence range of damaging alpha particle. A non-linear behavior of the CCE decrease and a significant degradation of the spectroscopic performance with increasing He ion fluence were observed above the value of 10(11) cm(-2). © 2015 Published by Elsevier B.V.
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    Radiation hardness of n-type SiC Schottky diodes
    (Coop Libraria Editrice Universita di padova, 2014-07-07) Pastuovic, Z; Vittone, E; Siegele, R; Ohshima, T; Iwamoto, N; Forneris, J; Cohen, DD; Capan, I
    The results of recent IBIC and DLTS studies of radation damage in silicon carbide (SiC) diodes will be presented. n-type Schottky diodes prepared on an epitaxial grown 4H-SiC thin wafers have been irradiated by a raster scanned alpha particle microbeam (2 & 4 MeV He2+ ions separately) in order to create patterned damage structures at different depths within sensitive volume of tested diodes suitable for Ion Beam Induced Current (IBIC) microscopy. Deep level transient spectroscopy (DLTS) was used to characterize defects created in SiC after implantation of single alpha particles. Robust and proven IBIC experimental protocol [1] has been used to determine a degradation of the charge collection efficiency over a wide fluence range of damaging alpha particle. The radiation hardness of these SiC wafers is compared with the hardness of n-type silicon wafers grown by the Floating zone and Czochralski methods obtained by the same experimental protocol. A suitability of as prepared SiC diodes for the light ion detection and spectroscopy in the MeV range will be discussed from the perspecetive of applications in harsh radiation environments.