Time-Resolved Investigation of Nanosecond Crystal Growth in Rapid-Phase-Change Materials: Correlation with the Recording Speed of Digital Versatile Disc Media

摘要

The crystallization process in digital versatile disc (DVD) media was investigated using a time-resolved X-ray diffraction apparatus coupled with in situ photoreflectivity measurement. The time profiles of crystallization were found to be consistent with the changes in photoreflectivity. The phase changes were characterized by the start and end time; 90 ± 1 and 273 ± 1 ns for Ge_2Sb_2Te_5, and 85 ± 1 and 206 ± 1 ns for Ag_(3.5)In_(3.8)Sb_(75.0)Te_(17.7), respectively. The faster crystallization time in Ag_(3.5)In_(3.8)Sb_(75.0)Te_(17.7) is ascribed to its characteristic crystallization process; its X-ray diffraction profile shows a significant sharpening during the crystallization process, whereas the peak width of Ge_2Sb_2Te_5 remained unchanged. The present findings suggest that crystal growth control is another key for designing faster phase-change materials.