Crystallization kinetics and recording mechanism of a-Si/Ni bilayer for write-once blue-ray recording

摘要

For the a-Si/Ni bilayer with a thickness ratio of 4:1, the formation of NiSi and NiSi_2 phases took place in the temperature range between 200 and 350 ℃ and only —9% of unreacted a-Si would crystallize to c-Si, which will not cause appreciable reflectivity change. As the thickness ratio of a-Si to Ni was increased to 20:1, the formation of NiSi_2 phase and subsequent crystallization of a-Si mediated by NiSi_2 precipitates were clearly observed. The crystallization temperature of a-Si in the a-Si/Ni bilayer with a thickness ratio of 20:1 was significantly reduced to around 350 ℃, which was 130 ℃ lower than that in the a-Si/Cu bilayer. The activation energies for NiSi_2 phase formation and crystallizations of a-Si for the a-Si/Ni bilayer with a thickness ratio of 20:1 were determined to be 1.12±0.09 and 2.19±0.08 eV, respectively. The crystallization behavior of the a-Si(20 nm)/Ni(l nm) bilayer recording film under pulsed laser irradiation is similar to that under thermal annealing. During the recording process, the NiSi_2 phase will precipitate first and serve as the nucleation sites for the following crystallization of the remaining amorphous Si. The maximum value of carrier to noise ratio for 3 T could reach 43 dB for the write-once blue-ray disk with layer structure of a-Si(20 nm)/Ni(l nm), demonstrating a high potentiality for practical use.