Statistically Robust Characterization of Polaron and Bipolaron Intrinsic Traps in Amorphous Silica Reveals the Role of Network Flexibility in Electron Localisation
Abstract
Intrinsic electron localization in amorphous silica (a-SiO2) contributes to charge trapping and defect generation in silica-based electronic materials - a phenomenon that degrades logic-device performance but can be exploited for memory applications. However, the structural distribution of one- and two-electron traps remains incompletely characterized, largely because the disordered covalent network of a-SiO2 spans a vast configurational space. To address this, we perform statistical sampling to select a representative 200-model subset of defect-free bulk a-SiO2 structures from a structurally converged parent set of 2512 models, generated via classical melt-quench molecular dynamics simulations. We then characterize the intrinsic one- and two-electron traps in this subset using HSE06 density functional theory calculations. Analysis of neutral precursor sites shows that trapping propensity is not determined by a universal O-Si-O angle or Si-O bond length; it is controlled by the accessibility of the relaxed trap geometry, requiring both local strain and medium-range network flexibility. Single electrons predominantly form edge-centred polarons on distorted SiO4 tetrahedra, with occupied states 3.1-4.3 eV below the conduction band minimum. Injection of a second electron drives stronger lattice relaxation, most commonly Si-O bond elongation leading to rupture, thereby forming threefold-coordinated-Si (Si3) bipolarons and, in some cases, Si-Si-bonded bipolaron configurations. The calculated bipolaron energy ranges are consistent with optical absorption features at 3.7, 4.7, and 6.4 eV associated with intrinsic electron localization.
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BibTeX
@misc{delhomme2026statistically,
title = {{Statistically Robust Characterization of Polaron and Bipolaron Intrinsic Traps in Amorphous Silica Reveals the Role of Network Flexibility in Electron Localisation}},
author = {Robin Delhomme and Jonathon Cottom and Emilia Olsson},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.04652},
eprint = {2611.04652},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.04652},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Statistically Robust Characterization of Polaron and Bipolaron Intrinsic Traps in Amorphous Silica Reveals the Role of Network Flexibility in Electron Localisation
AU - Robin Delhomme
AU - Jonathon Cottom
AU - Emilia Olsson
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.04652
UR - https://arxiv.org/abs/2611.04652
AB - Intrinsic electron localization in amorphous silica (a-SiO2) contributes to charge trapping and defect generation in silica-based electronic materials - a phenomenon that degrades logic-device performance but can be exploited for memory applications. However, the structural distribution of one- and two-electron traps remains incompletely characterized, largely because the disordered covalent network of a-SiO2 spans a vast configurational space. To address this, we perform statistical sampling to select a representative 200-model subset of defect-free bulk a-SiO2 structures from a structurally converged parent set of 2512 models, generated via classical melt-quench molecular dynamics simulations. We then characterize the intrinsic one- and two-electron traps in this subset using HSE06 density functional theory calculations. Analysis of neutral precursor sites shows that trapping propensity is not determined by a universal O-Si-O angle or Si-O bond length; it is controlled by the accessibility of the relaxed trap geometry, requiring both local strain and medium-range network flexibility. Single electrons predominantly form edge-centred polarons on distorted SiO4 tetrahedra, with occupied states 3.1-4.3 eV below the conduction band minimum. Injection of a second electron drives stronger lattice relaxation, most commonly Si-O bond elongation leading to rupture, thereby forming threefold-coordinated-Si (Si3) bipolarons and, in some cases, Si-Si-bonded bipolaron configurations. The calculated bipolaron energy ranges are consistent with optical absorption features at 3.7, 4.7, and 6.4 eV associated with intrinsic electron localization.
ER -