Effect of partial crystallization on formation of amorphous marks

The reflectivity of an amorphous mark on a first-surface phase-change optical storage disk is shown to vary with the level of crystallization of the GST layer. A static tester with 680-nm laser diode for writing amorphous marks and a 643-nm laser diode for monitoring the reflectivity changes is used for the experiment. An 8% difference in reflectivity is measured between the amorphous marks formed in the fully crystallized, high reflectivity (R equals 43%) state and partially crystallized, low reflectivity (R equals 30%) state.