The microcrystalline mode of solidification in pulsed-laser-melted ultra-thin films of silicon.

摘要

In the present work, it has been found that the controlled super-lateral growth (C-SLG) of ultra-thin films exhibits a breakdown in the lateral epitaxial growth, after which the solidification proceeds via defective growth. This regime of growth has been termed the defective and/or microcrystalline growth mode, and through experimental observations of the microstructure has been found to correspond to extreme undercooling of the solidification interface. The defective mode of growth is also manifested in the transition from interfacial amorphization to crystalline growth, as well as the microcrystalline microstructures formed via explosive crystallization and nucleation. The parametric condition for the onset of this mode of growth has been derived from considerations of the growth kinetics, whereby a threshold interface temperature of 1550 K and a velocity of 13.8 m/s were suggested on the basis of previously used assumptions. Furthermore, an interface response function attempting to incorporate the effects of a large defect population in the interface was formulated. Lateral explosive crystallization experiments confirm the correlation between solidification interface temperature, velocity, and defectiveness of the resulting microstructure implicit in the proposed model. It was also revealed by C-SLG experiments in SIMOX films that the breakdown morphology is dependent on the crystallographic orientation, which affects the onset of the critical threshold of defect-mediated solidification. The origin of the orientation-dependence of breakdown is explained by the difference in interface roughness present among different crystal interfaces.