We have studied the early stages of self-interstitial clustering in silicon using molecular dynamics simulation techniques. We have generated silicon samples of over 200000 atoms where we introduced a 0.5% extra concentration of self-interstitials. Then samples were annealed at several temperatures. During the simulations we observed the formation of interstitial clusters with different atomic structures, ranging from spherical and amorphous-like clusters, to highly ordered extended configurations such as (110) chains, {111} rod-like defects and dislocation loops, and {100} planar defects. This last type of defects, while common in germanium, have not been observed in silicon until very recently, in ultra-fast laser annealing experiments. The particular morphology of formed interstitial clusters is found to be related to the annealing temperature, as it is observed in the experiments. From the molecular dynamics simulations we have analyzed the atomic mechanisms leading to the formation and growth of interstitial clusters, with special attention to the newly found {100} planar defects.
By using classical molecular dynamics simulations and a novel technique to identify defects based on the calculation of atomic strain, we have elucidated the detailed mechanisms leading to the anomalous generation and growth of {001} loops found after ultra-fast laser annealing of ion-implanted Si. We show that the building block of the {001} loops is the very stable Arai tetra-interstitial [N. Arai, S. Takeda, M. Kohyama, Phys. Rev. Lett. 78, 4265 (1997)], but their growth is kinetically prevented within conventional Ostwald ripening mechanisms under standard processing conditions. However, our simulations predict that at temperatures close to the Si melting point, Arai tetra-interstitials directly nucleate at the boundaries of fast diffusing selfinterstitial agglomerates, which merge by a coalescence mechanism reaching large sizes in the nanosecond timescale. We demonstrate that the crystallization of such agglomerates into {001} loops and their subsequent growth is mediated by the tensile and compressive strain fields that develop concurrently around the loops. We also show that further annealing produces the unfaulting of {001} loops into perfect dislocations. Besides, from the simulations we have fully characterized the {001} loops, determining their atomic structure, interstitial density and formation energy.
In this work we propose a methodology to analyze the elastic energy interaction at the atomic level between Si self-interstitials and extended defects in crystalline Si. The representation of this energy in maps in 2D planes shows the anisotropic nature of the elastic interaction. This elastic energy maps can be used to understand diffusion trajectories of Si self-interstitials around extended defects obtained from classical molecular dynamics simulations. The combined analysis of these trajectories and the elastic energy maps shows preferential capture directions around extended defects.
We used atomistic simulation tools to correlate experimental transmission electron microscopy images of extended defects in crystalline silicon with their structures at atomic level. Reliable atomic configurations of extended defects were generated using classical molecular dynamics simulations. High-resolution transmission electron microscopy (HRTEM) simulated images of obtained defects were compared to experimental images reported in the literature. We validated the developed procedure with the configurations proposed in the literature for {113} and {111} rod-like defects. We also proposed from our procedure configurations for {111} and {001} dislocation loops with simulated HRTEM images in excellent agreement with experimental images.
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