Liquid-amorphous and liquid-crystalline phase transformation and impurity segregation phenomena in silicon during pulsed dye laser irradiation

Abstract

We have studied microstructural changes and impurity segregation phenomena associated with liquid-amorphous (l-α) and liquid-crystalline (l-c) phase transformations as a function of pulse energy density across a laser spot in indium implanted silicon. The specimens were irradiated with a dye laser pulse (wavelength 0.485 μm, energy density 0.7 J cm−2, pulse duration 9×10−9 s). At an energy density (0.2 J cm−2), we observed a liquid to amorphous phase transformation and concomitant segregation of indium due to interface motion from the bulk and the surface, resulting in a band of indium below the surface. At a higher energy density, explosive recrystallization from the surface is triggered, where a thin layer of liquid moves from the surface resulting in a band of indium at the end of the crystallized front. At a still higher energy density, epitaxial (liquid to crystalline) crystallization occurs below the surface followed by liquid to amorphous phase transformation near the surface. At the highest energy density near the center of the laser spot, epitaxial layer followed by the formation of constitutional/supercooling cells in the top region is observed as a result of interfacial instability of the planar crystallizing interface.