Epitaxial Growth of α-FeSi2 on Si(111) at Low Temperature

Epitaxial α-FeSi2 phase has been observed on silicon (111) face after growth at T = (500 ÷ 550) °C by Molecular Beam Epitaxy (MBE). In situ Reflection High-Energy Electron Diffraction (RHEED) enabled us to identify its crystallographic structure. Quantitative measurements of the lattice parameters parallel to the interface were obtained from ex situ X-ray diffraction experiments at grazing incidence. The existence of three domains was also observed. These results are shown to be fully consistent with the growth of tetragonal α-FeSi2. Compared to the bulk orthorhombic β-FeSi2 state which is mainly determined by a solid-state Jahn-Teller effect, this change of the FeSi2 structure appears to be directly induced by the epitaxial growth on the (111) silicon surface. During the growth, the relaxation α-FeSi2 towards β-FeSi2 has been found. During in situ thermal annealing, the transition of another pseudomorphic cubic-FeSi2 toward α-FeSi2 has also been observed. These two irreversible transformations suggest a hierarchy of stability between the various phases of FeSi2 epitaxially grown on silicon (111) from cubic-FeSi2 to α-FeSi2 and finally β-FeSi2.