HIGH-RESOLUTION ELECTRON-MICROSCOPY STUDY OF ALPHA-FESI2 HETEROEPITAXY ON SI(111)

During the course of orthorhombic beta-FeSi2 heteroepitaxy on Si substrates under molecular beam epitaxy conditions, several ultra-thin pseudomorphic metastable silicide layers have been observed, e.g. a cubic CsCl phase, a cubic CaF2 phase and tetragonal alpha-FeSi2, recently and surprisingly stabilized at low temperature. We report here on their phase transition towards the stable beta-FeSi2 phase via two main kinetic paths, clearly demonstrated for the first time thanks to high-resolution electron microscopy measurements and image simulation. Our results emphasize the relevant influence of the local morphology at the interface in favoring one or another kinetic path, although the common general behavior of the interface development is well reflected in the sequential formation on Si substrate of: epitaxially strained FeSi2 layer; relaxed FeSi2 layer mediated by dislocation formation; stable beta-FeSi2.