Size and electron hole pair effects on the melting of phase-change optical memory materials

Abstract

A great variety of reversible phase change optical recording materials have been extensively investigated. These alloy films are mainly composed of the IV-VI group (GeTe) and V group (Sb) in the periodic table. For achieving fast crystallization and stable cyclic operation, the excess Sb component of pseudo ternary alloy of GeTe-Sb2Te3-Sb has been investigated. At the melt-quenched process from the crystalline to the amorphous phase, the problem is to know if the laser pulse is essentially heating the sample which simply melts or if the electron-hole pairs created by the laser generate a new fluidlike state. The research on the electron-phonon interaction has shown that if a certain fraction of the valence-band electrons are excited into the conduction band, then the frequency of TA phonon, responsible for the stability of the crystal, goes to zero and crystal should become fluid. On the other hand, thin film surface becomes unstable before the bulk and the process of melting consists in the unstable surface at the film thickness of 10 - 50 nm. The inclusion of surface effects that self-consistently accounts for anharmonicity reduces the temperature at which an instability occurs. Both effects of electron-phonon instability and surface instability reduced the melting temperature of the phase change optical memory materials cooperatively. Therefore, the phase change optical disk is stable for the cyclic operation of 106 - 107.