Ge 2 Sb 2 Te 5 thin film is a promising candidate for recording material of phase-change optical disks, and nitrogen is doped into this film to increase overwrite characteristics. In this study, the crystal structure and the microstructure of nitrogen-doped Ge 2 Sb 2 Te 5 thin film were investigated. In the annealed nitrogen-doped thin film, the characteristic face-centered cubic peaks on the X-ray diffraction pattern were broadened and shifted to a smaller angle with the increase of nitrogen content. In addition, a remarkably reduced grain size and a highly strained structure are seen in the transmission electron microscopy image. Doped nitrogen in Ge 2 Sb 2 Te 5 thin film plays two roles. One is to distort the crystal lattice and induce a strain field in the film. The other is to refine the grain size of the film through precipitation. The crystal lattice is transformed from face-centered cubic to a hexagonal structure in nitrogen content above 20 at.%.

The crystallization behavior of amorphous Ge2Sb2Te5 thin films were investigated by using differential scanning calorimetry, x-ray diffraction, and optical reflectivity measurements. The analysis of in situ ellipsometry isotherm Ge2Sb2Te5 films based on the Johnson–Mehl–Avrami equation revealed that the crystallization process near 150 °C was a two-step process. In this alloy thin film, the kinetic exponents in the Johnson–Mehl–Avrami equation were about 4.4 for the first stage and 1.1 for the second stage. A kinetic model based on the cascaded crystallization is proposed. The proposed model showed good agreement with the experimental results obtained by transmission electron microscopy and x-ray diffraction.

No abstract

No abstract

With the increasing demand of the cost effective optical recording system, the optical media based on the phase-change phenomena have attracted an extensive research interest. One of the commonly used recording material for the phase-change optical disk is Ge-Sb-Te (GST) alloys which show a reversible phase transformation between the crystalline and the amorphous, thus the corresponding reflectivity change.[1,2] It has been reported that GST-alloys near to the stoichiometric compound are suitable for high speed application while other alloys like In-Sb-Te and Ag-In-Sh-Te are reported to be appropriate for low -speed applications.[3,4] The main purpose of this research is to study the feasibility of GST-alloys for the blue wavelength region for both high density recording and linear velocity applications. Variation of the complex refractive indices with Sb-addition in GST-alloy and their wavelength dependence were studied in the present research by using spectroscopic ellipsometry (SE) and atomic force microscopy (AFM). The reflectivity spectra of GST with different chemical compositions were calculated using these optical constants, and compared with the measured spectra.