NiGe Thin Films for Write-Once Blue Laser Media

In this paper, Ni₄₁Ge₅₉, Ni₄₆Ge₅₄, Ni₅₀Ge₅₀, Ni₅₈Ge₄₂ thin films with the thickness of 16 nm were deposited at room temperature by cosputtering using Ni and Ge targets. From the result of reflectivity-temperature measurement, it was found the NiGe layers possessed two temperature ranges of reflectivity change, i.e, 180°C-230°C and 360°C-400°C. By measuring the optical reflectivity at a wavelength of 405 nm, the optical contrasts of these films before and after annealing for 400°C were determined to be 35.1%, 39.4%, 40.3%, and 42.5% with the Ni contents of 41, 46, 50, and 58 at%, respectively. Microstructural analysis indicated that the NiGe nanocrystalline phase was formed in the as-deposited state. After annealing at 270°C and 400°C, the crystallinity of NiGe phase was enhanced and the Ge crystallization was formed, respectively. The optimum jitter values of Ni₅₈Ge₄₂ Blu-ray disk were 6.6% at 7 mW and 7.2% at 8.4 mW, respectively, for 1× and 2× recording speeds. It reveals that the NiGe films have high potential in the application of blue laser recording media.