We have investigated by atomic force microscopy and scanning tunneling microscopy subsequent stages of the heteroepitaxy of InAs on GaAs(001) from the initial formation of the strained two-dimensional wetting layer up to the development of three-dimensional quantum dots. We provide evidence of structural features that play a crucial role in the two- to three-dimensional transition and discuss their contribution to the final morphology of the self-assembled nanoparticles. A model is suggested for the strained phase at the critical thickness consisting of an intermixed InxGa1 - xAs surface layer of composition x = 0.82 and InAs "floating" on top. Such "floating" phase participate to the large mass transport along the surface during the two- to three-dimensional transition that accounts quantitatively for the total volume of dots
To investigate the effect of surface patterning on island growth, a real-time study by scanning tunneling microscopy (STM) of Ge deposition on nanostructured Si(001) surfaces is presented. The substrate is nanopatterned by the STM tip and the subsequent evolution of a Ge layer deposited at 500 degreesC is recorded. The formation of the wetting layer, a transition stage and the growth of three-dimensional (3D) Ge huts are examined dynamically. The 2D-3D transition is described in terms of the nucleation and evolution of pre-pyramids consisting of (001) oriented terraces, which eventually transform into pyramids by successive introduction of {105} facets. Substrate patterning strongly affects the positioning of 3D islands, and represents a route toward ordering of Ge islands
The morphology of the InAs/GaAs(001) system has been imaged by atomic force microscopy (AFM) at different stages of the epitaxial growth from the initial formation of a pseudomorphic two-dimensional (2D) interace up to the self-aggregation of InAs quantum dots (QDs). The substrate texture and the dependence of the cation diffusion on the elastic strain field fully control the lateral ordering of the nanoparticles in the self assembling process and determine the final morphology of multistacked InAs QD arrays. (C) 2002 American Institute of Physics
We analyzed by atomic force microscopy self-assembled quantum dots of InAs on GaAs(001) in a series of samples prepared by molecular beam epitaxy (MBE). Two different growth procedures have been applied, namely, the usual continuous growth and the migration-enhanced growth. At equal depositions of InAs, larger than the critical thickness for the two- to three-dimensional transition, marked differences are found in the evolution of the nanoparticle density and volume, despite of the same set of growth parameters were used. Above 2 ML, a small fraction of ripened islands is also present, which is responsible for the nonlinear increase of the total volume of the dots with InAs coverage caused by an anomalous participation of the underlying layers. The different morphologies obtained substantiate the overwhelming role of kinetics on thermodynamics in the nonequilibrium MBE growth. (C) 2001 American Institute of Physics
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