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We have studied the relative adhesion (the wetting) of dislocation-free three-dimensional (3D) islands belonging to an array of islands to the wetting layer in the Stranski-Krastanov growth mode. The array has been simulated as a chain of islands in 1+1 dimensions placed on top of a wetting layer. In addition to the critical size of the two-dimensional (2D) islands for the 2D-3D transformation to occur, we find that the wetting depends strongly on the density of the array, the size distribution and the shape of the islands.

This work describes an effort to seek for new materials capable of selfassembly of nanostructures, such as dots and wires, for electron-confined devices. A good candidate is a metal-semiconductor compounds group, most notably metal silicides. As will be shown below, the disilicides of cobalt and titanium form distinct nanodot arrays on silicon, of a significantly smaller mean size, and substantially improved size and shape uniformity, as compared to Ge/Si arrays. In order to achieve that, not only the deposition parameters were carefully controlled, but the Sisubstrate orientation seemed to play an important role, as well. In the case of CoSi2, small and uniform dots resulted from reactive deposition epitaxy at 800 K on Si(001), whereas TiSi2 dots required Si(111) substrate orientation to form even more uniform, small and isotropic nanodot array. In both cases reacting the metal with silicon in a solid state, and/or on differently oriented substrates did not produce the desired result.

Several x-ray diffraction methods are presented to determine the local chemical composition of self-assembled islands and to discriminate them from strain gradients. Two different routes are followed: in the first approach, the scattered intensities are simulated using numerical fitting to a suitable structure model for the islands (indirect methods). In the second one, the structural data are directly derived from the experimental ones. This direct approach is based on the so-called iso-strain scattering method and/or on the anomalous diffraction technique, which uses the strong enhancement and suppression of the scattered intensity close to the absorption edge of one of the chemical elements in the island. We show that for Ge dome-shaped islands the different techniques give similar results.

Carbon system plays a twofold role in the SiGe, inducing both high stress fields and strong chemical effects. Our Monte Carlo simulations, based on a novel algorithm enabling C-insertion and equilibration, shed light on the stress field and composition of C-induced Ge islands on Si(100), a prototypical case where these two effects operate. It is shown that the dots do not contain C under any conditions of temperature and coverage, but have a gradual composition profile from SiGe at the bottom to Ge at the apex. The average compressive stress in the islands is considerably reduced, compared to the pure Ge/Si case. At low Ge coverage, the terrace around the dots is enriched with Si-C dimers. At high Ge contents, Ge wets the surface and covers the pre-deposited C geometries. We predict enhancement of Ge content in the islands upon C incorporation.

Scientific and technological developments have made it possible to grow materials with different properties onto each other, and this way we can build quantum wells, quantum islands, quantum dots (QDs), etc., which leads to the possibility of creating novel devices and applications. Molecular-beam-epitaxy (MBE) is the nearly exclusive technique of growth of the above mentioned low-dimensional structures. The technology of growth under UHV made the observation of the growth process possible, which is widely realized by reflection high-energy electron-diffraction (RHEED). The growth of perfect crystal layers and low-dimensional structures is basically conditioned by the control of epitaxy. We need the knowledge and understanding of the growth mechanism for this, and the RHEED pattern and its intensity oscillations carry information to help us attain this goal. We will briefly deal with the basic information that is carried by RHEED. After that we investigate the dependence of mechanical strain appearing in the layer, material dependence, and other particular behaviour on RHEED. Finally, we discuss the relation between observed RHEED and the QD formation.

An efficient method for calculation of self-assembled dot states within the effective mass approximation is described and its application to the calculation of Auger relaxation rates is detailed. The method is based on expansion of the dot states in a harmonic oscillator basis whose parameters are optimised to improve the convergence rate. This results in at least an order of magnitude reduction in the number of basis states required to represent electron states accurately compared to the conventional plane wave approach. Auger relaxation rates are calculated for harmonic oscillator model states and exact states for various pyramidal models. The dipole approximation, previously used to calculate Auger rates, is found to be inaccurate by a factor of around 2–3. The harmonic oscillator states do not reproduce the rates for the more realistic pyramidal models very well and even within the set of pyramidal models variations in the dot shape and size can change the rates by up to an order of magnitude. Typical Auger relaxation rates are on a picosecond timescale but the actual value is strongly dependent on the density of electrons outside the dot.

A review of results from theoretical investigations of several systems composed of two or more coupled quantum dots (known as or ) is presented. All the calculations are performed within an empirical tight-binding theory. It is shown that coupling between nanocrystals can split and reorder energy levels and change state symmetries. The results help to understand and explain differences observed in optical spectra of arrays of quantum dots in comparison to the spectra obtained for non-interacting nanocrystals. We show also how an external electric field influences the properties of coupled quantum dots.

We discuss the properties of few electrons and electron-hole pairs confined in coupled semiconductor quantum dots, with emphasis on correlation effects and the role of tunneling. We discuss, in particular, exact diagonalization results for biexciton binding energy, electron-hole localization, magnetic-field induced Wigner molecules, and spin ordering.

Electrons confined in quantum dots can form island-like space structures called . We discuss the ground-state properties of two-dimensional Wigner molecules. In particular, we consider the formation of different phases (isomers) of the Wigner molecules at high magnetic fields. The -electron system, confined in the quantum dot and subject to a sufficiently strong magnetic field, forms a fully spin-polarized maximum density droplet (MDD). At high enough magnetic field the MDD decays and the Wigner molecule is formed with an island-like electron distribution. For ≥6 several different phases of the -electron Wigner molecule have been predicted. At extremely high magnetic fields, the spatial distribution of the electrons is the same as that in a classical system of equal point charges. Possible mechanisms of MDD breakdown, i.e. hole formation in the occupation number distribution and an edge reconstruction, are addressed. We also consider the creation of Wigner molecules without applying an external magnetic field in an electron system confined within a single quantum dot of large enough size and compare these Wigner molecules with artificial molecules formed in coupled quantum dots. Possible experimental evidence is examined for the formation of different phases of Wigner molecules.

We study the kinetics of confined carrier-phonon system in a quantum dot under fast optical driving and discuss the resulting limitations to fast coherent control over the quantum state in such systems.