Crystallization Time and High Resolution Electron Microscope Lattice Images of Phase Change Optical Discs Dynamically Laser-Annealed

It was demonstrated that a dynamic laser-annealing system (DLAS) could be used for obtaining the crystallization time (tx) for the phase change optical discs. In the DLAS, the laser beams are irradiated onto the discs which are rotating at variable linear velocity (V) with variable power. The measured crystallization time (tx) for the disc ZnS–SiO2/Ge2Sb2.5Te5/ZnS–SiO2/Al–Ti (disc A) monotonously decreased from 480 ns to 206 ns as the laser power increased from 300 mW to 900 mW. tx for Ge2Sb2Te5/ZnS–SiO2 (disc B) more sharply reduced from 400 ns to 200 ns than that for the disc A as the power increased from 200 mW to 400 mW. In the case of the disc B, tx was determined to be 50 ns at an extrapolated 570 mW. The high resolution electron microscope (HREM) of the cross sectional lattice image revealed that the dominant crystallized phase in the active Ge2Sb2Te5 layer was the stoichiometric GeTe. The measured inter-planar spacing of 0.298 nm corresponded to the (202) plane. The Kink bands and edge dislocations were also observed in the crystallized active layer. This was attributed to the thermal stress due to the thermal expansion difference between the active layer and the dielectric layer.