Laser-induced crystallization phenomena in GeTe-based alloys. I. Characterization of nucleation and growth

The laser-induced crystallization behavior of GeTe-based amorphous alloy thin films has been quantitatively studied by local reflection measurements with a focused 780 nm laser. The use of multiple laser pulse sequences enables the nucleation rate and crystal-growth speed to be separately deduced, allowing the compositional variation of both these processes to be followed. This not only gives detailed information on the crystallization mechanism, but also allows the fine tuning of phase change alloy compositions for use in erasable optical recording. The differences between the as-deposited and melt-quenched amorphous phases are also discussed. In particular, it is shown that the crystallization speed of the as-deposited layer can differ by over an order of magnitude from that of the melt-quenched amorphous layer. The as-deposited state can, however, be transformed into a modified amorphous state equivalent to that obtained by melt quenching a previously crystalline layer. This allows the determination of the optical constants and crystallization speeds of the amorphous state written during optical recording.