Ge/NiGe bilayer applied for the recording film of write-once blu-ray disc

In this study, the Ge/NiGe (3 nm/16 nm) bilayer was deposited by sputtering at room temperature to serve as the recording film for write-once blu-ray disc. The thermal properties, optical characteristics, crystallization mechanisms and recording performance were all investigated in detail. The composition of the NiGe alloy layer was maintained at Ni50Ge50. Based on the results of reflectivity-temperature measurements, it can be observed that the Ge/NiGe bilayer had two temperature ranges of reflectivity increment, i.e. 170-216 °C and 340-352 °C. Microstructural analysis revealed that the NiGe nano-crystalline phase was generated in the as-deposited state. After annealing at 250 °C, the crystallinity of the NiGe phase was improved. Upon further increasing the annealing temperature to 370 °C, the Ge crystallization appeared in this bilayer. Dynamic tests indicate that the blu-ray disc fabricated with the Ge/NiGe recording layer possesses optimum jitter values of 6.4% and 7.1% at 1× and 4× writing speeds, respectively. This implies that the Ge/NiGe bilayer has high potential for write-once blue laser recording applications.