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Silicon-hydrogen bonds play a crucial role in modern microelectronics, especially regarding reliability. At the semiconductor-oxide interface these bonds are broken via interaction with energetic charge carriers, which spoils a MOSFET's performance, for example. This study develops a consistent physical picture of that phenomenon through a bottom-up approach based on quantum mechanical formulations, and also unravels the disparity of that effect in $n\ensuremath{-}$ and $p\ensuremath{-}$MOSFETs. The model is free of empirical parameters and can easily be extended to emerging material combinations.

We used density functional theory (DFT) calculations to model the interaction of hydrogen atoms and molecules with strained bonds and neutral oxygen vacancies in amorphous silica $({\text{a-SiO}}_{2})$. The results demonstrate that the interaction of atomic hydrogen with strained Si--O bonds in defect-free ${\text{a-SiO}}_{2}$ networks results in the formation of two distinct defect structures, which are referred to as the ${[{\text{SiO}}_{4}/\text{H}]}^{0}$ and the hydroxyl ${\text{E}}^{\ensuremath{'}}$ center. To study the distribution of each defect's properties, up to 116 configurations of each center were calculated. We show that the hydroxyl ${E}^{\ensuremath{'}}$ center can be thermodynamically stable in the neutral charge state. In order to understand the origins and reactions of this defect, different mechanisms of formation, passivation, and depassivation have been investigated. The interaction of H with a single-oxygen vacancy in ${\text{a-SiO}}_{2}$ was studied in 144 configurations, all resulting in the hydrogen bridge defect. The reaction of the hydrogen bridge defect with the second H atom is barrierless and fully passivates the O vacancy. The latter defect reacts with atomic H with a small barrier, restoring the hydrogen bridge defect. These results provide a better understanding of how atomic and molecular hydrogen can both passivate existing defects and create new electrically active defects in amorphous-silica matrices.

Using ab initio modeling we demonstrate that H atoms can break strained Si{O bonds in continuous amorphous (a)-SiO2 networks, resulting in a defect consisting of a 3-coordinated Si atom with an unpaired electron facing a hydroxyl group, adding to the density of dangling bond defects, such as E0 centres. The barriers to form this defect from interstitial H atoms range between 0.5 and 1.3 eV. This discovery of unexpected reactivity of atomic hydrogen may have signifcant implications for our understanding of processes in nano-scaled silica, e.g., in porous low-permittivity insulators, and strained variants of a-SiO2. ispartof: Physical Review Letters vol:114 issue:11 pages:1-5 ispartof: location:United States status: published

Using classical and ab initio calculations we demonstrate that extra electrons can be trapped in pure crystalline and amorphous SiO2 (a-SiO2) in deep band gap states. The structure of trapped electron sites in pure a-SiO2 is similar to that of Ge electron centers and so-called [SiO4/Li]0 centers in α quartz. Classical potentials were used to generate amorphous silica models and density functional theory to characterize the geometrical and electronic structures of trapped electrons in crystalline and amorphous silica. The calculations demonstrate that an extra electron can be trapped at a Ge impurity in α quartz in six different configurations. An electron in the [SiO4/Li]0 center is trapped on a regular Si ion with the Li ion residing nearby. Extra electrons can trap spontaneously on pre-existing structural precursors in amorphous SiO2, while the electron self-trapping in α quartz requires overcoming a barrier of about 0.6 eV. The precursors for electron trapping in amorphous SiO2 comprise wide (≥132∘) O–Si–O angles and elongated Si–O bonds at the tails of corresponding distributions. Using this criterion, we estimate the concentration of these electron trapping sites at ≈4×1019 cm−3.