Explosive Crystallization in Eutectic Materials of Phase Change Optical Memory
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Okuda Technical Office, 1-chome 2-27 Mozu Umemachi sakai, Osaka 591-8032, Japan phone:+81-72-257-9244, fax:+81-72-257-9244, e-mail:[email protected] 2 Osaka Prefecture University, 1-1 Gakuen-cho Sakai, Osaka 599-8531, Japan 3 Osaka Prefectural College of Technology, 26-12 Saiwai-cho Neyagawa Osaka 572-0017, Japan ABSTRACT
The excess Sb effect for the dynamics of rapid crystallization in eutectic amorphous films are discussed. This crystallization mechanism describe the propagation with high velocity in the interface separating the crystalline and amorphous phase for InSb and AgInSbTe materials. From these analysis, it is clear that the crystallization is grown up in the boundary of crystalline-amorphous region of eutectic materials, which is different from the stoichiometric GeSbTe media. Also, the quantum effect on the melting, crystallization and solidification of phase change media has been discussed. 1. INTRODUCTION
For the materials of eutectic composition (GaSb, GeSb, GaSbSn, AgInSbTe and InSbTe) using as the phase change optical memory, Sb rich recording layer have been utilized in order to the rapid crystallization. But, the mechanism of excess Sb addition has not been clear, because a eutectic material is thought to cause the phase separation in its solidification process. Recently, it was reported that a melt-quenched crystalline states of eutectic AgInSbTe and SbTe with excess Sb has a quasi-equilibrium sate with single phase hexagonal structure based Sb(R3m) and some Sb atoms are randomly replaced with Te atoms.1, 2) In this paper, we report the excess Sb effect for the dynamics of rapid crystallization in eutectic amorphous films. This crystallization mechanism describe the propagation with high velocity in the interface separating the crystalline and amorphous phase for GaSb, GaSbSn and GeSb materials. From these analysis, it is clear that the crystallization is grown up in the boundary of amorphous-crystalline region of eutectic materials, which is different from the stoichiometric Ge2Sb2Te5 media. Under favorable conditions, an explosive crystalline process results by laser irradiation. Then, once crystallization has been initiated in the amorphous-crystalline region, the entire amorphous films has been crystallized. Also, the quantum effect on the melting, crystallization and solidification has been investigated for the eutectic materials of phase change memory.
2. EXPLOSIVE CRYSTALLIZATION MECHANISM OF EUTECTIC MATERIALS
Crystallization of eutectic materials is reasonable for phase change optical disk, because it is well known that the smaller marks corresponds to the shorter the crystallization time. And, the rich Sb compositions in GaSb, GeSb and GaSbSn recording materials were available for the improvement of crystallization velocity. These circumstance is shown in Table 1 and 2. For the recording materials of the low linear velocity (linear velocity 1.2 10m/s), the materials contained about 55-70% Sb content was used, but for high linear velocity (linear velocity 10 - 50 m/s), ab
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