Epitaxy of FeAl films on GaAs(100) by molecular beam epitaxy

Intermetallics that coexist with III-V's in the bulk are expected to form thermodynamically stable overlayers when deposited as a thin film. To the extent that adsorption kinetics do not play a role, these films should be abrupt and able to withstand high temperature processing. Some of these films have been found to be epitaxial after heating in vacuum. FeAl has been found to form pseudomorphic films on InP(l00) substrates and to grow in a layer-by-layer mode even when code-posited. To explore the role of stoichiometry and crystal strain, we have used reflection high energy electron diffraction (RHEED) to compare the growth of Fe _x -Al_1-x on GaAs(l00) to its growth on InP substrates. In both cases RHEED intensity oscillations are observed at 200° C, indicating two-dimensional island formation and layer-by-layer growth. For both, the growth is pseudomorphic on an AlAs buffer layer, with any lattice constant change less than 0.3%. When the intermetallics were codeposited, the growth proceeded via double layer formation for x < 0.7 and via single layers for large x. The films were stable to 550° C. Subsequent growth of AlAs was three dimensional.