Détecteur à semi-conducteur | EPFL Graph Search

Un détecteur à semi-conducteur est un détecteur de particules ou de rayons X ou gamma qui s'appuie sur la technologie des semi-conducteurs. Principe Détection Une particule ayant une énergie suffisante, rencontrant un semi-conducteur, va arracher un électron à un atome du cristal en lui cédant une partie ou la totalité de son énergie sous forme d'énergie potentielle (ionisation) et cinétique. Par exemple, un photon créera des électrons libres dans le milieu par effet photoélectrique, effet Compton ou création de paires. Le semi-conducteur a la particularité de se comporter comme un conducteur lorsqu'il y a interaction du rayonnement et comme un isolant lorsqu'il n'y a pas interaction. Le gap est l'énergie minimale qui doit être apportée au cristal pour qu'un électron de la bande de valence (participant aux liaisons entre les atomes) soit libéré dans la bande de conduction. Le semi-conducteur est particulièrement bien adapté à la mesure de rayonnements gamma, car

Transient Current Technique characterization of bonded interfaces for monolithic silicon radiation detectors

Jacopo Bronuzzi

This thesis aims at demonstrating a novel technique for the characterization of interfaces obtained by a CMOS-compatible Surface Activated Bonding (SAB) process between silicon wafers. This enables the optimization of the two main components of monolithic silicon detectors, the CMOS circuitry for the read-out and the sensing layer, by fabricating them in different substrates and then by bonding them together. Therefore, to be collected by the read-out circuitry, charges generated by radiation in the bulk have to traverse the bonding interface, whose electrical properties need to be characterized. The first part of this thesis is focused on the evaluation of Transient Current Technique (TCT) for this purpose. TCT is largely used for the study of radiation damage in silicon detectors, and consists in the injection of a localized cloud of electrons inside a detector based on a reverse-biased diode, that is drifted by the electric field. A transient current signal is generated, whose shape is related to the electric field profile that may be affected by lattice defects generated by radiation. In this context, the bonding process is expected to generate a thin amorphous silicon interface between the two bonded substrates. This layer can be seen as full of defects and therefore it is expected to influence the electric field, and the TCT current signal. This is demonstrated by means of Sentaurus TCAD numerical simulations and an analytical model, using a diode with the bonding interface in the middle of the bulk as test structure. The second part of the thesis describes the characterization of the interface, generated by bonding high resistivity wafers at CEA-Leti in Grenoble. For this purpose, Schottky diodes are fabricated on these stacks at EPFL, and then characterized with CV, IV and TCT techniques. The results obtained are compared to simulation data, to show that the electric field did not extend to the bulk, preventing charges to be collected. This is an issue for the fabrication of radiation detectors, since there would not be collection of charges generated at the sensing bulk. Following these conclusions, two solutions are proposed. First, the optimization of the bonding process to reduce the number of traps. Second, a modification of the detector design in such a way that the bonding interface is located at the PN junction, since the electric field is maximum at this position, and therefore the influence of traps is less important. The last part of this thesis is devoted to the description of a new charge injection technique for TCT measurements. Instead of using a laser, charges are injected by means of nanosecond voltage pulses, applied to dedicated wells fabricated on the PN junction contact. Injection occurs by thermionic emission, while the charges drift, as in standard TCT measurements. This novel method of charge injection is called electrical injection TCT (el-TCT). It could allow to perform on-line TCT measurements during experiments.

EPFL2018

CROCUS Concrete Activation Study by γ-ray Spectrometry and TLD Neutron Flux Measurements

Isabelle Tanseri

The semester project was under the course Physics lab IVb at EPFL. At EPFL site, the experimental fission reactor CROCUS is shielded by concrete which becomes radioactive as a result of neutron interaction. The activation is of interest to study for validation of models and cal- culations, and to quantify the amount of radioactive waste when the reactor will be recycled. In this project, measurements on concrete ac- tivation by NaI- and HPGe-detectors were performed on an in-cavity concrete block, together with TLD measurements on neutron flux in- side the core of CROCUS and in the cavity. The concrete activation and neutron flux allows for comparison and validation of models. The in-cavity concrete block had a low activation, trace elements of 60Co and 65Zn seem to be existing. The relative flux was the highest for structures close to the core and at the ceiling. In future projects, more experimental data on both concrete activation and neutron flux would be performed to acquire uncertainty estimations and correction factors.

2017

Modeling the response of a diamond detector in the zero power reactor CROCUS

Pavel Frajtag, Mathieu Hursin, Vincent Pierre Lamirand, DongHyuk Lee, Andreas Pautz

The present manuscript documents the development of a practical calculation scheme to model the response of a diamond detector in the mixed (neutron and gamma) radiation field of the CROCUS experimental reactor at EPFL. The model is shown to perform reasonably well in terms of energy spectra shapes for the limited amounts of irradiations considered; the relative magnitude of the neutron and gamma contributions to the detector output is, however, not properly captured. The gamma contribution is underestimated by a factor of four if the neutron contribution is correctly captured. A sensitivity study to three parameters (the azimuthal position of the detector, the magnitude of the neutron and gamma sources, and the threshold voltage used in the detector) is also carried out to analyze the effect of modeling assumptions and experimental choices on the results. Then, a detailed analysis of the computational results is carried out to provide quantitative information about the response of a diamond detector in a mixed radiation field. It is shown that the low-energy interactions are mainly produced by gamma interactions; that the high energy interactions are generated by proton recoil interactions; and that 60% of the recorded neutron interactions are produced by thermal neutron captures in Li-6, while the rest come from scattering interactions with fast neutrons. Finally, it is demonstrated that considering some of the effects of the electronics on the pulses (RC time constant) is required to reproduce the trends observed in the experimental results, especially the increased detection rate within the diamond crystal.

SPRINGER HEIDELBERG2021

Transient Current Technique characterization of bonded interfaces for monolithic silicon radiation detectors

Jacopo Bronuzzi

EPFL2018