The evolution of the size and shape of individual ͕105͖ faceted Ge islands on Si(001) is measured with a high temperature scanning tunneling microscope during growth. A slower growth rate is observed when an island grows to larger sizes. This behavior can be explained by kinetically self-limiting growth. A kinetic growth model involving a nucleation barrier for each repeated growth of a new atomic layer on the ͕105͖ facets agrees with the experimental results for the evolution of the island volume. The experimentally observed shape transition from nearly square shaped islands to elongated islands is described by the kinetic growth model. [S0031-9007(99)

The spin injection into GaAs has been studied for the ferromagnetic metal MnAs. Evidence for preferential minority-spin injection is obtained from the circular polarization of the electroluminescence in GaAs/͑In,Ga͒As light-emitting diodes ͑LED͒. The spin-injection efficiency of 6% at the MnAs/GaAs interface is estimated on the basis of spin-relaxation times extracted from time-resolved photoluminescence measurements. This efficiency, as well as the preferential spin orientation, resembles very much the injection behavior found for epitaxial Fe layers. The results do not depend on the azimuthal orientation of the epitaxial MnAs injection layer.

The surface topography of epitaxial MnAs films on GaAs(001) is studied by scanning probe microscopy. We provide direct experimental evidence for temperature-dependent elastic domains of the coexisting ferromagnetic αMnAs and paramagnetic βMnAs phases. The results agree well with a theoretical model for the elastic equilibrium of periodic domains.

The surface of epitaxial MnAs layers grown on GaAs͑001͒ substrates by molecular beam epitaxy is studied by atomic force microscopy and scanning tunneling microscopy ͑STM͒. A periodic array of alternating ridges and grooves is observed. The periodicity ranges from 200 to 900 nm and increases with increasing layer thickness. The terrace-step morphology and the surface reconstruction on the ridges and in the grooves are imaged by STM. It is found that both are independent from the ridge-groove structure, supporting the idea that the formation of the ridge-groove structure is due to elastic distortion of the film during cooling after growth.

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