Laser-induced crystallization in Ge-Sb-Te optical recording materials

Laser-induced crystallization behaviour in Ge-Sb-Te optical recording thin film materials, that are sandwiched between dielectric layers, was studied by a multipulse laser technique. The reflection changes at 780 nm laser wavelength caused by local heating by a pulsed high-power laser beam are monitored. Both the nucleation time and the complete crystallization time are found to decrease significantly with increasing phase change layer thickness up to about 25 nm, above which both tend to become constant. Furthermore, the maximum crystallization speed depends on the type of dielectric material. The strong dependence of crystallization speed on layer thickness is explained in terms of competing interface and bulk processes. This finding is of practical use because it allows the design of phase change optical recording media which can be used at high linear recording speeds.