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Recording Characteristics, Microstructure, and Crystallization Kinetics of Ge/GeCu Recording Film Used for Write-Once Blu-Ray Disc

by Sin-Liang Ou, Feng-Min Lai, Wei-Kai Wang, Shih-Yung Huang, An-Cheng Sun, Ching-Ho Tien, Zhi-Jia Xu, Chin-Yen Yeh and Kuo-Sheng Kao

Materials 2016, 9(11), 953; https://doi.org/10.3390/ma9110953 - 23 Nov 2016

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Abstract

A Ge₆₇Cu₃₃ (16 nm) layer and a Ge (3 nm)/Ge₆₇Cu₃₃ (16 nm) bilayer were grown by sputtering at room temperature and used as the recording films for write-once blue laser media. In comparison to the crystallization temperature of Ge in a GeCu film (380.7 °C–405.1 °C), the crystallization temperature of Ge in a Ge/GeCu bilayer could be further decreased to 333.7 °C–382.8 °C. The activation energies of Ge crystallization were 3.51 eV ± 0.05 eV and 1.50 eV ± 0.04 eV for the GeCu and the Ge/GeCu films, respectively, indicating that the Ge/GeCu bilayer possesses a higher feasibility in high-speed optical recording applications. Moreover, the lower activation energy would lead to a larger grain size of Ge crystallization in the Ge/GeCu bilayer after the annealing process. Between the as-deposited and the annealed states, the optical contrasts (@ 405 nm) of the GeCu and the Ge/GeCu films were 26.0% and 47.5%, respectively. This reveals that the Ge/GeCu bilayer is more suitable for the recording film of a write-once blu-ray disc (BD-R) in comparison with the GeCu film. Based on the dynamic tests performed for 2× and 4× recording speeds, the optimum jitter values of the BD-R with the Ge/GeCu recording film were 7.4% at 6.3 mW and 7.6% at 8.6 mW, respectively. Full article

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Figure 1

Figure 1
Layer structures of the write-once blu-ray discs (BD-Rs) with (a) Ge67Cu33 (16 nm) and (b) Ge (3 nm)/Ge67Cu33 (16 nm) recording films. PC: polycarbonate. Full article ">Figure 2
Relationships between reflectivity and temperature of (a) Ge67Cu33 (16 nm) and (b) Ge (3 nm)/Ge67Cu33 (16 nm) films measured at the heating rates of 5, 10, 20, and 50 °C/min. Full article ">Figure 3
Transmission electron microscopy (TEM) bright field images and electron diffraction patterns of (a) as-deposited and (b) 450 °C-annealed Ge67Cu33 (16 nm) films. Full article ">Figure 4
(a) TEM image and electron diffraction pattern of as-deposited Ge (3 nm)/Ge67Cu33 (16 nm) film; (b) TEM image and electron diffraction pattern of annealed Ge/GeCu film; (c) TEM image of region 2 of the annealed film; (d) TEM bright field image and selected area electron diffraction pattern of parallelogram-shaped grain formed in the 450 °C-annealed Ge/GeCu film; (e) TEM bright field image and selected area electron diffraction pattern of hexagon-shaped grain formed in the 450 °C-annealed Ge/GeCu film. Full article ">Figure 5
Plots of ln[A/(Tx)2] versus (1/Tx) of (a) Ge67Cu33 (16 nm) and (b) Ge (3 nm)/Ge67Cu33 (16 nm) films for the Ge crystallization. Full article ">Figure 6
Reflectivity spectra of the as-deposited and the 450 °C-annealed states for (a) Ge67Cu33 (16 nm) and (b) Ge (3 nm)/Ge67Cu33 (16 nm) films. Full article ">Figure 7
Jitter values and modulations as a function of writing power at 2× and 4× recording speeds for the BD-Rs with (a) Ge67Cu33 (16 nm) and (b) Ge (3 nm)/Ge67Cu33 (16 nm) recording films. Full article ">

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