Nature of intrinsic and extrinsic electron trapping in SiO2

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 characterize 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 (≥132 • ) 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 ≈ 4 × 10 19 cm −3 . The structure of these centers is similar to that of Ge and Li electron centers in α-quartz.

Hydrogen-Induced Rupture of Strained Si─O Bonds in Amorphous Silicon Dioxide

“…The distributions of Si-O bonds and Si-O-Si angles in our samples are described in detail in Ref. [36] and agree well with previous calculations by other authors [41]. We have calculated the neutron structure factors for our models and they show excellent agreement with experiment [42], indicating that our models describe both the short-and long-range order and are indeed representative of a-SiO 2 .…”

“…This center is thought to result from the interaction of H 0 with electronically excited strained Si-O bonds [30]. Strained Si-O bonds in amorphous silica, that is those bonds whose length deviates strongly from the crystalline equilibrium value of 1.61Å, have been the focus of many other studies due to their relatively high reactivity [30,[32][33][34][35][36]. However, reactions of atomic hydrogen with strained Si-O bonds have not been investigated theoretically, except in [32], and the perception that atomic hydrogen interacts only weakly with the silica network still prevails in the literature [1, 7,37].…”

“…We used classical molecular dynamics and a melt and quench procedure described in detail in Ref. [36]. Densities of the ReaxFF a-SiO 2 structures ranged from 1.99 to 2.27 g cm −3 , averaging at 2.16 g cm −3 .…”

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

“…The ReaxFF force-field 43,44 and a classical MD melt and quench procedure are used with the LAMMPS code 45 to generate starting structures representing non-defective continuous random networks of a-SiO 2 . 46 These structures containing 216 atoms each were evaluated 46 by comparing the distributions of Si-O bonds, Si-O-Si angles, and neutron structure factors to prior theoretical and experimental studies before being used for DFT calculations. DFT calculations of the electronic and geometric structures and nudged elastic band calculations 47,48 of adiabatic barriers were performed using the Gaussians and Plane Waves method 49 implemented in the CP2K code.…”

Intrinsic electron traps in atomic-layer deposited HfO2 insulators

“…Clustering of vacancies 35 or their interaction with hydrogen, as recently revealed in the case of a-SiO 2 , 36 represent feasible models deserving further theoretical and experimental analysis. Second, self-trapping of electrons on oxide network sites under strained bonding geometries may also provide deep acceptor states in the amorphous phases 37 or inside the grain boundary region in polycrystalline HfO 2 . Considerable site-to-site variations in the trapping geometry expected in this case may explain the relatively wide energy distributions of the trapped electrons as well as the mentioned failure of ESR to detect the corresponding paramagnetic state because of excessive line broadening.…”