Self-organization of nanostructures in semiconductor heteroepitaxy

in semiconductor heteroepitaxy the growing film frequently undergoes a series of strain relief mechanisms that may include surface reconstruction, step bunching, faceting, and finally formation of misfit dislocations. Under certain conditions, these mechanisms and their interplay result in self-organized nanostructure arrays with a high degree of uniformity. Using atomic force microscopy and X-ray diffraction investigations, the following mechanisms are analyzed in the model system of Si1-xGex molecular beam epitaxy Si(001): (i) formation of ripple patterns by bunching of the preexisting steps on vicinal substrates, (ii) step bunch faceting on high miscut substrates, (iii) correlated ripple propagation in heteroepitaxial superlattices, (iv) interplay of three-dimensional island arrangement and step-bunched ripple patterns, (v) interplay of island arrangement and cross-hatched dislocation network, (vi) formation of three-dimensionally ordered island arrays in multilayer films. The driving forces of these self-organization mechanisms-that are not restricted to a particular growth system-are discussed in the framework of continuum elasticity theory. Besides optoelectronic applications (not extensively considered here) a novel use of self-organized semiconductor nanostructures is proposed, namely the utilization as large-area templates to grow various materials on them. This is demonstrated for the case of magnetic thin films that can be nanostructured by this way. (C) 2002 Elsevier Science B.V. All rights reserved.