Journal article
Atomistic-continuum modeling of short laser pulse melting of Si targets



Publication Details
Authors:
Lipp, V.; Rethfeld, B.; Garcia, M.; Ivanov, D.
Publisher:
American Physical Society
Publication year:
2014
Journal:
Physical Review B
Pages range:
245306
Journal acronym:
Phys. Rev.
Volume number:
90
Issue number:
24
Number of pages:
17
ISSN:
1098-0121

Abstract
We present an atomistic-continuum model to simulate ultrashort-pulse laser melting processes in semiconductor solids on the example of silicon. The kinetics of transient nonequilibrium phase transition mechanisms is addressed with a molecular dynamics method at atomic level, whereas the laser light absorption, strong generated electron-phonon nonequilibrium, fast diffusion of and heat conduction due to photoexcited free carriers are accounted for in the continuum. We give a detailed description of the model, which is then applied to study the mechanism of short laser pulse melting of freestanding Si films. The effect of laser-induced pressure and temperature of the lattice on the melting kinetics is investigated. Two competing melting mechanisms, heterogeneous and homogeneous, were identified. Apart from the classical heterogeneous melting mechanism, the nucleation of the liquid phase homogeneously inside the material significantly contributes to the melting process. The simulations showed, that due to the open diamond structure of the crystal, the laser-generated internal compressive stresses reduce the crystal stability against the homogeneous melting. Consequently, the latter can take a massive character within several picoseconds upon the laser heating. Due to the negative volume of melting of modeled Si material, -7.5%, the material contracts upon the phase transition, relaxes the compressive stresses, and the subsequent melting proceeds heterogeneously until the excess of thermal energy is consumed. The threshold fluence value, at which homogeneous nucleation of liquid starts contributing to the classical heterogeneous propagation of the solid-liquid interface, is found from the series of simulations at different laser input fluences. For the example of Si, the laser melting kinetics of semiconductors was found to be noticeably different from that of metals with a fcc crystal structure.


Authors/Editors

Last updated on 2019-25-07 at 11:48