Structural changes and alloying of annealed iron layers on GaAs(001) and GaAs(110)

The nucleation and morphological changes during thermal processing of iron layers on Ga-rich GaAs(001)-(2 x 6) and on GaAs(110) were studied with scanning tunnelling microscopy. At room temperature the initial nucleation is strongly influenced by the rows of the surface reconstruction on GaAs(001), whereas on GaAs(110) larger 3D-islands are formed right away. Further growth above 1 ML is nearly identical for both surfaces showing a granular layer structure with a hindered coalescence of the grains. This behaviour is discussed in terms of the intrinsic growth behaviour of Fe(001) and Fe(I 10). After an initial tendency to form a continuous layer, the Fe-films on both substrates break up around 300 degrees C during thermal processing. On GaAs(I 10) the out-diffusion of substrate material is already seen at 250 degrees C. On GaAs(001) the annealed film shows two types of islands: a mesa-like type with a flat surface, which can be identified as a ternary Fe3Ga2-xAsx alloy, and a second one, whose surface is in-plane with the substrate level which is identified as Fe2As. On the substrate which has been laid open again in the annealing process the initially Ga-rich reconstruction changes to an As-rich (2 x 4). On GaAs(l 10) only one type of islands is present after annealing at 450 degrees C with a roof shaped form which is tentatively also assigned to a ternary Fe-Ga-As alloy. (c) 2008 Elsevier B.V. All rights reserved.