Effects of film thickness on the optical properties of AgInSbTe phase-change films

The optical constants of phase-change films are assumed to be constant regardless of film thickness in conventional optical design and thermal simulation of multilayer structure optical disks. However this assumption is not valid when the phase- change film thickness in the optical disks becomes very small. In this study, the dependence of the optical properties on the thickness of AgInSbTe phase-change films was investigated. The reflectivity, absorptivity, thickness and optical constant of the films were measured. The change of the extinction coefficient and refractive index become significant when the film is very thin, and become larger at shorter wavelengths such as in the blue and green region. These results are very useful in improving the accuracy of optical design and simulation of AgInSbTe phase-change optical disks, as well as in the study of phase-change optical disks at shorter wavelengths.