Amorphous-Crystalline Boundary Dynamics in Laser Crystallization

摘要

Two theoretical descriptions have been developed for the phase boundary dynamics during crystallization of amorphous films by scanning with the slit image of a cw laser or of any cw energy beam. The first reduces the problem to the solution of a one-dimensional integral equation, which allows a choice of initial conditions. Depending on the background temperature, numerical solutions yield either periodic or runaway motion of the amorphous-crystalline (a-c) boundary, as observed in experiments on scanned laser crystallization of thin films of a-Ge on fused-silica substrates. The calculations give a semi-quantitative fit to the experimental results for the spatial periodicity observed in the crystallized films as a function of background temperature. Profiles of film temperature as a function of distance from the laser image at successive times have been computed for both the periodic and runaway cases. The model qualitatively explains many of the effects observed during scanned cw laser crystallization, including periodic fluctuations in light emission. The second theoretical description is a more exact two-dimensional treatment, applicable only to cases of steady-state motion of the a-c boundary, which rigorously handles heat flow into the substrate. This treatment has been used to calculate the boundary velocity during steady-state runaway.