Identification of paramagnetic centers in irradiated Sn-doped silicon dioxide by first-principles.

We present a first-principles investigation of Sn paramagnetic centers in Sn-doped vitreous silica based on calculations of the electron paramagnetic resonance (EPR) parameters. The present investigation provides evidence of an extended analogy between the family of Ge paramagnetic centers in Ge-doped silica and the family of Sn paramagnetic centers in Sn-doped silica for SnOconcentrations below phase separation. We infer, also keeping into account the larger spin-orbit coupling of Sn atoms with respect to Ge atoms, that a peculiar and highly distorted three-fold coordinated Sn center (i.

Deep Levels and Electron Paramagnetic Resonance Parameters of Substitutional Nitrogen in Silicon from First Principles.

Nitrogen is commonly implanted in silicon to suppress the diffusion of self-interstitials and the formation of voids through the creation of nitrogen-vacancy complexes and nitrogen-nitrogen pairs. Yet, identifying a specific N-related defect via spectroscopic means has proven to be non-trivial. Activation energies obtained from deep-level transient spectroscopy are often assigned to a subset of possible defects that include non-equivalent atomic structures, such as the substitutional nitrogen and the nitrogen-vacancy complex.

Collective dipole effects in ionic transport under electric fields.

In the context of ionic transport in solids, the variation of a migration barrier height under electric fields is traditionally assumed to be equal to the classical electric work of a point charge that carries the transport charge. However, how reliable is this phenomenological model and how does it fare with respect to Modern Theory of Polarization? In this work, we show that such a classical picture does not hold in general as collective dipole effects may be critical. Such effects are unraveled by an appropriate polarization decomposition and by an expression that we derive, which defines the equivalent polarization-work charge.

v-PO micro-clustering in P-doped silica studied by a first-principles Raman investigation.

Synthetic vitreous silica is currently the preferred material for the production of optical fibres because of the several excellent properties of this glass, e.g. high transmission in the visible and IR domains, high mechanical strength, chemical durability, and ease of doping with various materials.

Photoactivated processes in optical fibers: generation and conversion mechanisms of twofold coordinated Si and Ge atoms.

In this work we present an extensive investigation of nanoscale physical phenomena related to oxygen-deficient centers (ODCs) in silica and Ge-doped silica by means of first-principles calculations, including nudged-elastic band, electron paramagnetic resonance parameters calculations, and many-body perturbation theory (GW and Bethe-Salpeter equation) techniques. We show that by neutralizing positively charged oxygen monovacancies we can obtain model structures of twofold Si and Ge defects of which the calculated absorption spectra and singlet-to-triplet transitions are in excellent agreement with the experimental optical absorption and photo-luminescence data. In particular we provide an exhaustive analysis of the main exciton peaks related to the presence of twofold defects including long-range correlation effects.