(001) loops in silicon unraveled

LA Marques and M Aboy and M Ruiz and I Santos and P Lopez and L Pelaz, ACTA MATERIALIA, 166, 192-201 (2019).

DOI: 10.1016/j.actamat.2018.12.052

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 self-interstitial 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. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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