Molecular dynamics simulation of atomic hydrogen diffusion in strained amorphous silica

Understanding hydrogen diffusion in amorphous SiO₂ (a-SiO₂), especially under strain, is of prominent importance for improving the reliability of semiconducting devices, such as metal–oxide–semiconductor field effect transistors. In this work, the diffusion of hydrogen atom in a-SiO₂ under strain is simulated by using molecular dynamics (MD) with the ReaxFF force field. A defect-free a-SiO₂ atomic model, of which the local structure parameters accord well with the experimental results, is established. Strain is applied by using the uniaxial tensile method, and the values of maximum strain, ultimate strength, and Young's modulus of the a-SiO₂ model under different tensile rates are calculated. The diffusion of hydrogen atom is simulated by MD with the ReaxFF, and its pathway is identified to be a series of hops among local energy minima. Moreover, the calculated diffusivity and activation energy show their dependence on strain. The diffusivity is substantially enhanced by the tensile strain at a low temperature (below 500 K), but reduced at a high temperature (above 500 K). The activation energy decreases as strain increases. Our research shows that the tensile strain can have an influence on hydrogen transportation in a-SiO₂, which may be utilized to improve the reliability of semiconducting devices. (paper)