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Performance Limiting Factors
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
Displacement damage results from non-ionizing energy loss (NIEL) interactions of a primary particle with the atoms of the bulk material. Unlike ionization, it results in permanent damage to the lattice structure by displacing atoms from their equilibrium position. If the displaced atom escapes, a vacancy is created. If however it assumes an interstitial position in the lattice, a vacancy-interstitial complex is created, known as a Frenkel defect (see Chapter 3, section 3.5.2). As well as altering the structural properties of the lattice these defects change the electronic characteristics of the crystal by introducing additional energy levels within the bandgap. These levels facilitate the transition of electrons from the valence to the conduction band, which in the active depletion layers of a detector leads to a generation current and in turn electronic shot noise. The effect can be particularly acute in indirect bandgap semiconductors, since these levels can act as a conduit to facilitate electronic transitions between the conduction and valence bands – again leading to a generation current. In addition, those states created close to the band edges act as efficient trapping centers, facilitating charge loss if de-trapping times are longer than amplifier time constants. A measure of the effectiveness of creating a Frenkel defect is given by the threshold displacement energy Ed, which is the minimum kinetic energy an atom in a solid needs, to be permanently displaced from its lattice site to a defect position.
Enhancing neutron radiation resistance of silicon-based semiconductor devices through isotope separation and enrichment
Published in Radiation Effects and Defects in Solids, 2021
Ying Bai, Zeng-Hua Cai, Yu-Ning Wu, Shiyou Chen
Incident neutron transfers its energy to the struck atom through elastic or inelastic scattering, and the struck atom gains kinetic energy. If this kinetic energy exceeds the threshold displacement energy , the atom displaces from its original position, forming a primary knock-on atom (PKA). PKAs may cause a series of cascade collisions and lead to the radiation-induced vacancies that evolve into more complex defects, which is the main reason of the displacement damage (10). Therefore, higher threshold displacement energy generally means better resistance against the neutron irradiation of a semiconductor material. For example, GaN has good resistance against the neutron irradiation because of its high average threshold displacement energy (11–14).
Evaluating Quantities of Interest Other Than Nuclide Densities in the Bateman Equations
Published in Nuclear Science and Engineering, 2023
Olin W. Calvin, Micah D. Gale, Sebastian Schunert
At high neutron energies, a neutron scattering event transfers sufficient energy to cause these displacements, but a neutron at low energies cannot transfer enough energy to cause a displacement via scattering because of the kinematics of the reaction. At these low energies, all displacements are driven by exothermic capture reactions. In many of these reactions, the target nucleus will recoil with enough energy to cause displacements as well as produce a secondary particle with sufficient mass and energy to cause displacements. The minimum energy required to remove an atom from its lattice site in this way is referred to as the average threshold displacement energy . This value is generally on the order of 40 eV but can vary significantly between different elements (e.g., 17 eV for rubidium to 90 eV for tungsten6) and be a source of controversy because of conflicting models and experimental data, particularly for polyatomic materials.7 Intuitively, this value is the property of a specific crystal lattice and crystal phase. Since measuring the difference between two crystal phases, say ferritic and martensitic steels, is beyond the current state-of-the-art technology, displacement energies are calculated on an elemental level. The first recoiling atom is referred to as the primary knock-on atom (PKA) and generally has kinetic energy between 1 and 100 keV in fission reactor applications for nonfuel materials. Reactor fuel materials, which experience the production of high-energy fission product nuclei with tens of mega-electron-volts of kinetic energy, as well as materials used outside of fission reactors may experience PKAs with larger energies, but we are concerned with only nonfuel reactor materials in this work