Growth kinetics of amorphous interlayers by solid-state diffusion in ultrahigh vacuum deposited polycrystalline Gd thin films on (001) Si

The growth kinetics of amorphous interlayer (a-interlayer) formed by solid-state diffusion in ultrahigh vacuum deposited polycrystalline Gd thin films on (001)Si have been investigated by cross-sectional transmission electron microscopy. The growth of the a-interlayer was found to follow a linear growth law initially. The growth then slows down and deviates from a linear growth law. The result clearly indicated that the growth at early stage is consistent with an interface-reaction-controlled growth model rather than diffusion limited. The activation energy of the linear growth and maximum thickness of the a-interlayer were measured to be about 0.37 eV and 6.6 nm, respectively. Following the growth of amorphous interlayer, epitaxial hexagonal GdSi2-x was found to form at the a-interlayer/(001)Si interface at 225 degrees C. The relatively small lattice mismatch between GdSi2-x and (001)Si compared to other RESi2-x (RE=rare-earth metal) and (001)Si systems facilitates the epitaxial growth of GdSi2-x on (001)Si, which in turn hampers the further growth of a-interlayer. (C) 1998 American Institute of Physics. [S0021-8979(98)01023-8].