Time-Resolved Studies of Rapid Solidification in Highly Undercooled Molten Silicon

Abstract

A KrF (248 nm) pulsed laser was used to melt 90-, 190-, and 440-nm thick amorphous silicon layers produced by Si ion implantation into (100) crystalline Si substrates. Time-resolved reflectivity measurements at two different probe wavelengths (633 nm and 1.15 µm) and post-irradiation TEM measurements were used to study the formation of an undercooled liquid Si phase and the subsequent solidification processes. The time-resolved measurements provide new experimental information about the nucleation of fine-grained Si crystallites in undercooled liquid Si, at low laser energy densities (E_ℓ), and about the growth of large-grained Si in the near-surface region at higher E_ℓ. Measurements with the infrared probe beam reveal the presence of a buried, propagating liquid layer at low E_ℓ. Model calculations indicate that this liquid layer is generated in part by the release of latent heat associated with the nucleation and growth process.