International audienceWe compare the morphological and structural features of SiGe membranes fabricated by three different processes: direct deposition of Si0.5Ge0.5 on. Si(001) nominal substrate, direct deposition Of Si0.5Ge0.5 on silicon on insulator, and deposition of SiGe with low Ge concentration on silicon on insulator followed by Ge enrichment by condensation. We show that the formation of fully strained Ge-rich layers free of defects with a flat surface is possible only by the two-step epitaxy-condensation process. We demonstrate that the condensation based process enables the total inhibition of the morphological instability, together with the hindering of dislocations for critical thickness much greater than those commonly obtained by direct deposition. Those behaviors could be explained by the injection of self-interstitials in the Ge-rich layers during condensation. Such remarkable properties systems using a similar condensation process. could be generalized to many other systems using a similar condensation process

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Core-shell nanowires with radial heterostructures hold great promise in photonic and electronic applications and controlling the formation of these heterostructures in the core-shell configuration remains a challenge. Recently, GaAs nanowires have been used as substrates to create AlGaAs shells. The deposition of the AlGaAs layer leads to the spontaneous formation of Al-rich stripes along certain crystallographic directions and quantum dots/wires near the apexes of the shell. A general two-dimensional model has been developed for the motion of the faceted solid-vapor interfaces for pure materials that accounts for capillarity and deposition. With this model, the growth processes and morphological evolution of shells of nanowires around hexagonal cores (six small facets {112} in the corners of six equivalent facets {110}) are investigated in detail both analytically and numerically. It is found that deposition can yield facets that are not present on the Wulff shape. These small facets can have slowly timevarying sizes that can lead to stripe structures and quantum dots/wires depending on the balances between diffusion and deposition. The effects of deposition rates and polarity (or asymmetry) on planes {112} on the development of the configurations of nanowires are discussed. The numerical results are compared with experimental results giving almost quantitative agreement, despite the fact that only pure materials are treated herein whereas the experiments deal with alloys.

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