GAS-SOURCE MOLECULAR-BEAM EPITAXY OF FESI2/SI(111) HETEROSTRUCTURES

Epitaxial iron disilicide thin layers have been grown on silicon by gas source molecular beam epitaxy (GSMBE) in the temperature range 450-550-degrees-C. Fe (CO) 5 and SiH4 are used as sources for the silicide growth on a heated Si(111) surface. The growth phases are characterized in situ by means of high-resolution electron energy loss spectroscopy, ultraviolet and x-ray photoelectron spectroscopies. The formation of an epitaxial metallic gamma-FeSi2 layer at the interface with the silicon substrate is revealed and no complete relaxation of this strained metastable interface layer is observed, as the growth proceeds with the semiconducting equilibrium beta-FeSi2 phase. The coexistence in the GSMBE grown heterostructures of the metallic (CaF2) and semiconducting (orthorhombic) FeSi2 structures is confirmed by cross-section transmission electron microscopy.