Time-resolved TEM of pulsed crystallization of amorphous Si and Ge films

Pulse crystallization is investigated by time-resolved TEM in amorphous Ge and Si films close to the threshold (resolution 3 ns in specimen areas above 0.4 μm ø). A threefold structure originates with non-monotonic dynamics. The centre grows slowly (≈ 0.05 m/s) and polycrystalline. Next comes a ring where the amorphous phase transforms into a large-grain structure of radially elongated crystals, either directly with ≈ 100 m/s, or via a slowly growing (≈ 0.1 m/s) polycrystalline stage which recrystallizes with ≈ 100 m/s. Finally, large-grain shells with a finegrained intercalate spiral out of the irradiated area with ≈ 20 m/s. Dynamics and structure possibly result from competition of crystal growth and nucleation, modified by expulsion of mpurities.