Ultrafast Generation of Unconventional{001}Loops in Si

Abstract

Ultrafast laser annealing of ion implanted Si has led to thermodynamically unexpected large {001} self-interstitial loops, and the failure of Ostwald ripening models for describing self-interstitial cluster growth. We have carried out molecular dynamics simulations in combination with focused experiments in order to demonstrate that at temperatures close to the melting point, self-interstitial rich Si is driven into dense liquidlike droplets that are highly mobile within the solid crystalline Si matrix. These liquid droplets grow by a coalescence mechanism and eventually transform into {001} loops through a liquid-to-solid phase transition in the nanosecond time scale.

{001} loops in silicon unraveled

“…These data are collected in In this high temperature regime, the mechanisms for the generation of {001} loops appear to be completely different from the conventional OR process: instead of having ordered and immobile I-defect clusters exchanging mobile point-defect Is, we observe that I-clusters remain completely disordered for sizes of tens or even hundreds of Is. They are of liquid nature, highly mobile and rapidly merge by a coalescence mechanism [29]. Figure 5 shows the measured effective diffusivities as a function of time for all the annealing simulations carried in this work.…”

“…The transformation from a liquid droplet to a fully ordered {001} loop occurs in few nanoseconds (Fig. 6(d)), and it can be described as a firstorder phase transition [29], which needs the prior nucleation of Arai tetra-Is (incubation period) that afterwards act as the seed for the droplet crystallization. From our simulations, we have measured a latent heat of 0.42 eV/I in the transformation, of the order of the latent heat for melting in Si calculated with the Tersoff 3 potential [48].…”

“…4(b) and (c)). Larger loop sizes are favored by higher annealing temperatures [29], which in turn stimulate further atomic agitation within the loop cores, making more likely the unfaulting transformation.…”

“…In a recent letter [29], it has been shown that at such elevated temperatures, I-rich Si is driven into dense liquid-like droplets that are highly mobile within the solid crystalline Si matrix. These liquid droplets merge by a coalescence mechanism and eventually transform into {001} loops through a liquid-to-solid phase transition in the nanosecond timescale.…”

Humble planar defects in SiGe nanopillars

“…Experimentally, {001} planar defects were often observed when H was implanted into Si and Ge [12,13]. In ultrafast laser-annealed ion-implanted Si samples, defects in {001} planes appear as self-interstitial loops [14,15]. Under thermal equilibrium, planar defects in Si and SiGe are primarily found along the {113} planes, and occasionally in {111} planes [16].…”