The role of defects during amorphization and crystallization processes in ion implanted Si

Amorphization and crystallization processes in ion implanted Si have been investigated using cross-sectional transmission electron microscopy (XTEM) measurements and molecular dynamics (MD) simulations. Amorphization mechanisms in 5 MeV Si+ ion implanted Si were analyzed using XTEM measurements. High-resolution XTEM images of the amorphous/crystalline (a/c) Si interface region indicate that the a/c interface is very sharp and the amorphous Si transition occurs within a few atomic layers. Image simulations based on the divacancy and di-interstitial (D-D) pair model (Phys. Rev. B49 (1994) 16367) suggest that an accumulation of the D-D pairs gives rise to homogeneous amorphization in ion implanted Si and the threshold number of the D-D pairs is ∼0.3 per atom. MD calculations have been performed to simulate solid phase epitaxial growth of Si at a/c interfaces based on the ordinary Langevin equation employing the Tersoff potential for Si. It was found that crystal growth in the [001] direction occurred by attaching Si atoms in the amorphous phase at kink sites associated with {111} facets formed at the a/c interface, while in the [111] direction two-dimensional nucleation was first created on the flat (111) interface and then followed by layer-by-layer growth.