Identification of intrinsic electron trapping sites in bulk amorphous silica from ab initio calculations

Abstract

Using ab initio calculations we demonstrate that extra electrons in pure amorphous SiO2 can be trapped in deep band gap states. Classical potentials were used to generate amorphous silica models and density functional theory to characterise the geometrical and electronic structures of trapped electrons. Extra electrons can trap spontaneously on pre-existing structural precursors in amorphous SiO2 and produce ≈3.2 eV deep states in the band gap. These precursors comprise wide (⩾130°) O–Si–O angles and elongated Si-O bonds at the tails of corresponding distributions. The electron trapping in amorphous silica structure results in an opening of the O-Si-O angle (up to almost 180). We estimate the concentration of these electron trapping sites to be ≈ 5 X 1019cm-3. © 2013 Elsevier Ltd. All rights reserved

A microscopic mechanism of dielectric breakdown in SiO2 films: An insight from multi-scale modeling

“…38 This mechanism stems from the recent discovery that extra electrons can be trapped in the a-SiO 2 network and form deep electron states in the band gap of a-SiO 2 . 36 These trapping sites correspond to wide O-Si-O angles (>132 ) in the otherwise continuum random network a-SiO 2 structure and can accommodate up to two electrons. As a result, the energy barrier to break the Si-O bonds adjacent to the trapped bi-electron is lowered to around 0.7 eV on average.…”

“…55 The estimated concentration of these intrinsic electron traps is at least 4 Â 10 19 in a-SiO 2 . 36 and they are used as a starting point for simulations performed in this work.…”

Nature of intrinsic and extrinsic electron trapping in SiO2

“…30 The geometric structure of these centers is similar to that of electrons trapped by Ge impurities in a-SiO 2 , 31 where the key to the electron trapping is the wide opening of the O-Ge-O angle, or Li centers in quartz where it is facilitated by the opening of the O-Si-O angle. It turns out that the precursor Si sites with wide enough O-Si-O angles naturally present in a-SiO 2 structure can facilitate spontaneous electron trapping at these sites.…”

Highly Resistant Zero‐Order Waveplates Based on All‐Silica Multilayer Coatings

“…Three materials were picked for production of thin films with optical anisotropy: LaF 3 , Al 2 O 3 , and SiO 2 . All these materials have low absorption for the wavelength of 355 nm due to their wide band gaps (9.4, 7.0, and 8.9 eV, respectively) and are widely used in optical coatings for UV spectral region.…”