Thickness-dependent formation of Gd-silicide compounds

Abstract

Gd-silicide phases were investigated by x-ray diffraction. The results showed that not only one phase exists in a Gd thin-film and silicon substrate reactions. The first phase formed was hexagonal GdSi≊1.7, the second orthorhombic GdSi2. The ratio of the two phases depends on temperature of the heat treatment, and at a given temperature and time of annealing, a dependence of the thickness of the evaporated Gd layer was found. At ∼100-nm Gd thickness the dominant phase was orthorhombic GdSi2, at ∼250 nm hexagonal GdSi≊1.7. In the 300–1000-nm interval orthorhombic GdSi2 was the main component again. Rutherford backscattering analysis showed that the phases were found mixed within the layer. This thickness-dependent formation could be described with a simple model proposed by Gösele and Tu [J. Appl. Phys. 53, 3252 (1982)].

Formation of GdSi2 film on Si(111) via phase transformation assisted by interfacial SiO2 layer

“…The XPS data were collected in a Physical Electronics PHI 5700 ESCA spectrometer using Al-K␣ ͑h = 1486.6 eV͒ x-ray source, with an energy resolution of 0.86 eV. 17,21 Figure 2(a) indicates that the hexagonal GdS 1.7 phase is formed after the deposition at 400°C, as expected. The detailed film structure and crystallinity at the interfacial region were analyzed by using high-resolution transmission electron microscopy (HRTEM).…”

Epitaxial Growth and Electrical Properties of Thick SmSi2 Layers on (001) Silicon

“…We note that XRD measurements do not show significant variations in bulk structure and strain across the growth temperature range, from 350 to 700 C. In particular, we did not observe a phase transformation by increasing the temperature, as reported for the Gd-Si system (from hexagonal to orthorhombic). 30,31) Using RBS the Sm/Si ratio is found to be 1 : 2 within AE5%, independent of film thickness ranging from 250 nm to 1.2 mm. The ratio does not vary significantly from the interface to the surface, in contrast to reports for ErSi 1:7 layers.…”

Formation of Ytterbium Silicide Thin Films by Solid-Phase Crystallization

“…The aforementioned discrepancy might result from the high density of Si vacancies contained in the YbSi 2--x phase (similar to other hexagonal rare-earth silicides) [15]. Moreover, it can be seen that, in order to reach such a stoichiometry, some Si atoms in the substrate diffuse into the film, forming a thicker YbSi 1.7 layer [16].…”

“…Therefore, the Si substrate enhances the nucleation of YbSi 1.7 and a relative low temperature is sufficient to form a hexagonal phase of YbSi 1.7 . Another possible reason that cannot be ruled out is that, because of the strong affinity of rare-earth metals for O [16], a small amount of O from the silica-silicide interface might react with the excess Yb to form Yb oxides, which slows down the nucleation and retards the growth of Yb silicides. However, it should be noted that no Yb oxide was observed from the XRD spectrum (no list) in the irradiated film deposited on silica.…”