Spectroscopic Ellipsometry Studies on Optical Constants of Ge2Sb2Te5 Used for Phase Change Optical Disks

Spectroscopic ellipsometry has been applied to Ge2Sb2Te5, which is commonly used as a recording layer for phase change optical disks, and the optical constants have been measured for a wavelength range from 400 to 900 nm. We have improved the accuracy of this measurement by means of inserting a transparent film between a Ge2Sb2Te5 film and a Si substrate. A calculation of the reflectivity change, due to the phase transition between the amorphous and the crystalline states, shows that the change is sufficient for optical optimization of the disk structure, down to the 400 nm wavelength.