Kinetic evolution of self-organised SiGe nanostructures

The Si1yxGexrSi growth usually proceeds by a layer by layer growth of the first monolayers followed by 3D growth of islands on the top of the uniform layer Stranski–Krastanov mode.. Self-organisation of these islands is very attractive to create large arrays of nanoscale structures. This paper deals with the self-organisation of Si1yxGex nanostructures by way of kinetic and thermodynamic manipulations. Solid source-molecular beam epitaxy SS-MBE.and gas source-MBE GS-MBE. grown heterostructures are characterised by atomic force microscopy AFM.and grazing incidence X-ray diffraction GIXRD.. The results concentrate on the role of the atomic configuration of substrates on the metastable shape of islands. By comparing the Si1yxGex layers grown on 111., 001.and misoriented substrates, we prove that the different Si1yxGex morphologies obtained can be explained by different mechanisms of step redistribution on the two nominal orientations. Misoriented surfaces from 111. and from 001. lead to step-bunching roughening and to anisotropic undulations perpendicular to the atomic steps, respectively. The influence of concentration stress., thickness and annealing on the island-shaped transition is evidenced. Qualitatively, these three parameters induce the same shape evolution: after the onset of ‘‘hut’’ islands, first the island density increases, then a shape transition going through a bimodal distribution of island sizes is observed which leads to the complete transformation into ‘‘dome’’-shaped islands in the end. The results show that whatever is the underlying mechanism, the onset of the shape transition is related to a critical aspect ratio hrL.of the islands and to typical level of stress relaxation as shown by GIXRD analysis. q2000 Elsevier Science B.V. All rights reserved.