Ab Initio Hydrogen Dynamics and the Morphology of Voids in Amorphous Silicon

Abstract

This article presents an ab initio study of hydrogen dynamics inside nanometer‐size voids in amorphous silicon (a‐Si) within the framework of the density‐functional theory for a varying hydrogen load of 10–30 atoms per void at the low and high temperature of 400 and 700 K, respectively. Using the local density approximation (LDA) and its generalized‐gradient counterpart (GGA), the dynamics of hydrogen atoms inside the voids are examined with an emphasis on the diffusion of H atoms/molecules, and the resulting nanostructural changes of the void surfaces. The results from simulations suggest that the microstructure of the hydrogen distribution on the void surfaces and the morphology of the voids are characterized by the presence of a significant number of monohydride SiH bonds, along with a few dihydride configurations. The study also reveals that a considerable number (about 10–45 at%) of total H atoms inside a void can appear as H2 molecules for a hydrogen load of 10–30 H atoms per void. The approximate shape of the voids is addressed from a knowledge of the positions of the void‐surface atoms using the convex‐hull approximation and the Gaussian broadening of the pseudoatomic surfaces of Si and H atoms.