We present a statistical study of silicon and oxygen neutral defects in a silica glass model. This work is performed following two complementary approaches: first-principles calculations and empirical potential molecular dynamics. We show that the defect formation energies and structures are distributed and that the energy distributions are correlated with the local stress before the defect formation. Combining defect energies calculated from first principles and local stresses from empirical potential calculations in undefected silica, we are able to predict the formation energy distributions in larger systems, the size of which precludes the use of ab initio methods. Using the resulting prediction we will show that the cell size used in our modeling contains all the formation energy fluctuations needed to describe a real glass.

first principles study of the defects generated by displacement cascades in silicon is performed. This work is particularly focused on two defect configurations; the di-vacancy and the triinterstitial, both identified in previous Molecular Dynamics (MD) and kinetic Activation Relaxation Technique (k-ART) simulations [1, 2]. By combining structural, energy and migration properties evaluated within the framework of the standard Density Functional Theory (DFT) and electronic properties calculated within the G0W0 approximation, a reconstruction of the corresponding thermallyactivated electrical signal generated by each defect is obtained. Their contribution to Dark Current (DC) and Dark Current Random Telegraph Signal (DC-RTS) measured in image sensors is then discussed.

This paper investigates the Total Ionizing Dose (TID) sensitivity of NanoWire Field Effect Transistors (NWFET). Both x-ray irradiations and self-consistent calculations of charge trapping in dielectrics are performed to study their TID response. First of all, the impact of the nanowire geometry is investigated. The NWFET TID behavior exhibits a strong dependence as a function of the nanowire’s width while shortening the gate length does not significantly change the TID characteristics of optimized narrow NWFETs. Furthermore, the effect of the bias configuration used during irradiation is discussed to state if NMOS NWFETs could withstand significant amount of TID in several operation conditions.

The electronic and optical properties of neutral oxygen vacancies, also called oxygen deficient centers (ODC(I)s), have been investigated in pure and germanium doped silica (both amorphous and α-quartz) through first-principles calculations. By means of density functional theory and many-body perturbation theory (GW approximation and the solution of the Bethe–Salpeter equation), we obtain the atomic and electronic structures as well as the optical absorption spectra of pure and Ge-doped silica in the presence of ODCs (SiODC(I)s and GeODC(I)s); our study allows us to interpret and explain the very nature of the optical features in experimental absorption spectra. The theoretical optical absorption signatures of these defects show excellent agreement with experiments for the SiODC(I)s, i.e. two absorption bands arise around 7.6 eV due to transitions between the defect levels. Our theoretical results also explain the experimental difficulty in measuring the GeODC(I) absorption band in Ge-doped silica, which was in fact tentatively assigned to a broad and very weak absorption signature, located between 7.5 and 8.5 eV. The influence of Ge-doping induced disorder on the nature of the defect-related optical transitions is discussed. We find that even if the atomic and electronic structures of SiODC(I) and GeODC(I) defects are relatively similar, the slight network distortion induced by the presence of the Ge atom, together with the increase in the Ge–Si bond asymmetry, completely changes the nature of the optical absorption edge.

The inclusion of sophisticated density-dependent electronic stopping and electron-phonon coupling calculated with first-principles methods into molecular dynamics simulations of collision cascades has recently become possible thanks to the development of the so-called electron-phonon (EPH) model. This paper aims at employing the EPH model in molecular dynamics simulations of collision cascades in Si. In this context, the electronic stopping power is investigated in Si at low energies with Ehrenfest dynamics calculations. Also, the parametrization of the EPH model for Si, from first-principles Ehrenfest dynamics simulations to actual molecular dynamics simulations of collision cascades is performed and detailed. We demonstrate that the EPH model is able to reproduce very closely the density-dependent features of the energy lost to electrons obtained with ab initio calculations. Molecular dynamics collision cascade simulations results obtained in Si using the EPH model and the simpler but widely employed two-temperature model are compared, showing important discrepancies in the collision cascades results obtained depending on the model employed.