Kinetic and thermodynamic studies of pulsed laser irradiation

Simultaneous measurements of the transient conductance, to determine the molten layer thickness versus time, and the time-dependent surface reflectance, to determine the melt duration at the surface during pulsed laser irradiation, are reviewed. These real-time measurements have been applied in a variety of studies of Si and Si-based alloys. In crystalline Si, melt initiates at the surface and propagates to some depth, whereupon the motion of the liquid/solid interface reverses and the material solidifies. In amorphous Si, these measurements were used to determine the melting temperature of the amorphous phase and the mechanism by which explosive crystallization occurs. In Si implanted with impurities, combined transient conductance and reflectance measurements reveal the occurrence of such novel melt and solidification scenarios as internal nucleation of melt and surface nucleation of solid on molten Si. Internal melts, which were previously unexpected, appear to be quite common and explain unusual microstructures observed by TEM.