Feasibility Study of ZnO/Ge Bilayer Recording Medium in Blue Laser Recordable Disc

Abstract

In this paper, a new recording medium (ZnO/Ge bilayer film) used for a write-once blue laser disc is reported. By differential scanning calorimeter technique (DSC), a new endothermic peak of the bilayer was observed at 385 °C. Simultaneously the optical contrast of the ZnO/Ge bilayer film at a wavelength of 405 nm was observed to be higher than 77%. X-ray diffraction (XRD) spectra showed that this film has three major components (ZnO, Zn, and Ge), and an additional component (Zn2GeO4) observed after annealing at 500 °C. From the results of the dynamic tests of the entire disc structure of PC/ZnS–SiO2 (30 nm)/ZnO (13 nm)/Ge (5 nm)/ZnS–SiO2 (20 nm)/Ag (120 nm), the carrier-to-noise ratio (CNR) with a writing power of 10 mW was determined to be 49 dB for a numerical aperture (NA) of 0.65 at a wavelength of 405 nm. In this study, the key to recording in this ZnO/Ge bilayer film was mainly due to the production of Zn2GeO4 between the layers of ZnO and Ge under illumination with the blue laser.