HETEROEPITAXY OF FERROMAGNETIC MNAS THIN-FILMS ON (001)GAAS - TEMPLATE EFFECTS AND EPITAXIAL ORIENTATIONS

We have studied epitaxial orientations and template effects in molecular beam epitaxy (MBE) of ferromagnetic MnAs thin films on (001) GaAs substrates. The MBE-grown MnAs thin films take two different epitaxial orientations, [($) over bar 1100] (type-A) and [($) over bar 1101] (type-B), depending on the surface reconstruction and one monolayer template formation on (001) GaAs surfaces just prior to the growth of MnAs. The easy axis of the magnetization in type-A and type-B MnAs films is along the [110] and the [($) over bar 110] of GaAs, respectively. 90 degrees different with respect to the GaAs substrates. Furthermore, when a very thin epitaxial ErAs template layer was formed on c(4 X 4) GaAs and then MnAs was grown, the growth direction of the MnAs was found to be [($) over bar 1102]. and no strong magnetic anisotropy was observed within the film plane. These results indicate the importance of the first few monolayers and starting surface stoichiometry to control the epitaxial orientation and magnetic properties of the: epitaxial ferromagnetic MnAs thin films.