Percolation threshold in annealed ultrathin SiOx films by 2D Monte Carlo simulations

Abstract

In this work, the kinetics of phase separation in ultrathin non-stoichiometric Si oxide (SiO_x, x < 2) films during high-temperature annealing is studied by Monte Carlo simulations on a two-dimensional lattice. The separation of Si and Si oxide phases by redistribution of oxygen atoms between the neighboring Si–O_aSi_4−a (0 ≤ a ≤ 4) complexes composing the SiO_x microstructure is considered. The net direction of oxygen redistribution corresponds to the decrease of the penalty energy of the participating complexes, which is taken into account by applying the Metropolis algorithm. As a result, the dependence of the morphology of the Si nano-structures formed in the Si oxide matrix on the initial SiO_x stoichiometry is obtained. Isolated Si nanoparticles with irregular shapes form at x = 1. A progressive increase of the excess Si content leads to the formation of noodle-like and branched Si particles, local Si networks and finally fully percolated Si structures at the percolation threshold x ∼ 0.7.