Yu. B. Bolkhovityanov

Molecular beam epitaxy of silicon–germanium nanostructures

Abstract The current status of the research in the field of synthesis and application of silicon and germanium-based nanostructures formed by the process of 3D island self-organization is reviewed in the present paper. There was an obvious conclusion that elastic deformations in epitaxial films and 3D islands are the key factor which is not only the reason of the transition from planar to Stranski–Krastanow mechanism of growth, but also influences the next stages of islands evolution including their shape, size and spatial distributions. There are many cases when this factor makes crucial changes to the classical set of phase-formation mechanisms right up to an equilibrium coexistence of islands on a surface. Various types of ordering were classified in the nanocluster systems under consideration: in cluster shape, in its size, in the distance between nearest islands, as well as ordering through vertical, i.e. in successively growing multilayer structures containing quantum dots. The results of recent original investigations of electrical and optical properties of self-assembled arrays of Ge quantum dots are presented.

The initial growth stages of III–V lattice-mismatched films grown by liquid phase epitaxy

Abstract It is shown that the liquid phase must be supersaturated (supercooled) in quasi-equilibrium with the substrate if the resulting film and the seed are lattice mismatched; otherwise the substrate dissolves. The following characteristics of the film formation are observed: (1) etch-back of the seed and the growth of centers occur simultaneously, and as a result the composition of the centres varies continuously; (2) the centres of a new phase or even a continuous film may grow at constant temperature if the mismatch is large.

Solid solutions GeSi grown by MBE on a low temperature Si (001) buffer layer: specific features of plastic relaxation

Abstract The role of a low temperature Si buffer layer (LT-Si) in the process of plastic relaxation of MBE grown GeSi/Si (001) is studied. Probable sources and mechanisms of a generation of misfit dislocations (MD) are discussed. Transmission electron microscopic and X-ray diffraction techniques are used for studying 100 nm GexSi1−x films with LT-Si and those free of such a buffer layer. The MD density is found to be much lower in the former than in the latter and the level of the film plastic relaxation is not higher than 20% in both as-grown and annealed films with LT-Si. As the thickness of the solid solution layer reaches 400 nm, the plastic relaxation of the films increases to almost 100%. Therefore, the determining role of the MD multiplication is supposed. We assume the double role of the LT-Si buffer layer. Firstly, the diffusion flux of vacancies from the LT-Si layer to the GeSi/Si interface may cause erosion of the interface and as a result a decrease in the rate of MD generation at the early stages of epitaxy. Secondly, the generation of intrinsic defect clusters in the LT-Si, which are potential sources of MDs, occurs in the field of mechanical stresses of the growing pseudomorphic layer. This process is thought to be the key feature of plastic relaxation of GeSi/LT-Si/Si (100) films which promotes MD self-organization.

The initial stages of heteroepitaxy from the liquid phase at a low misfit: InGaAsP on GaAs

The initial stages of liquid phase heteroepitaxial growth of InGaAsP on GaAs(111)A substrates were studied. The room temperature lattice misfit (Δaa)⊥ was controlled in the range from −3.5 × 10−3 to +4 × 10−3. It was observed that for |(Δaa)⊥| ⪅ 10−3 the growth proceeds via a layer-by-layer mechanism, while for larger misfits three-dimensional nucleation occurs and the quaternary epi-islands are disk shaped. The experimental results suggest that in this case nucleation occurs on some “active” sites on the substrate surface, the density of these actives sites being 104–105 cm-2. For non-zero mismatch (|(Δaa)⊥| ⩾ 3 × 10−3) and small super-coolings (or step coolings with steps of less than 1 K) of the quaternary melt the epi-island shape evolution is very peculiar; initially smooth and continuous islands later become dissolved in a “fjord-like” pattern. It is suggested that stress accumulation in growing epi-islands is responsible for this behaviour.

Experimental observation of the dislocation walls in heterostructures with two interfaces: Ge/Ge0.5Si0.5 10 nm/Si(001) as an example

Abstract High-resolution electron microscopy (HREM) at the atomic scale has been applied to study the edge dislocation redistribution between interfaces in Ge/Ge0.5Si0.5/Si(0 0 1) heterostructures. Our results provide a direct explanation that plastic relaxation of the GeSi buffer layer proceeds owing to motion of Lomer-type dislocation complexes consisting of a pair of complementary 60° dislocations with the ends of the {1 1 1} extra planes being located at a distance of ~2–12 interplanar spacings from each other. It is demonstrated that edge dislocations belonging to the upper and lower interfaces become arranged one under the other and dislocation walls are formed. The distributions of tension and compression in the [0 0 1] direction between two edge dislocations, obtained by processing the HREM image, testify to superposition of strain fields.