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We present an overall impression of the present state of knowledge on the formation, via a modified Stranski-Krastanov growth mode, of InAs quantum dots (QDs) on GaAs substrates. We will begin with the substrate orientation and surface reconstruction specificity of QD formation, which demonstrates that QDs are the exception rather than the rule in this system, with the implication that a second process, in addition to strain relaxation, is involved in the driving force. We then discuss the formation of an alloy wetting layer, and although it may not be unique to growth on the GaAs(001) c(4 × 4) surface, it is very much more marked than on any other. This is an important effect, in that QD formation is effectively limited to the same surface reconstruction. The next stage involves this formation process and we will review the experimental evidence, including dot composition, size (volume) distribution (including scaling behaviour), and two-dimensional to three-dimensional transition effects, with some comments on possible experimental artefacts in this area. We conclude with some comments on QD shape, based mainly on reflection high energy electron diffraction (RHEED) results, but including a comparison with results from transmission electron microscopy (TEM) and scanning tunnelling microscopy (STM).

Density-functional theory calculations are employed to obtain important information about the morphology of III–V semiconductor surfaces and kinetics of epitaxial growth. In this way, insight into the microscopic processes governing quantum dot formation in InAs/GaAs(001) heteroepitaxy is gained. First, we investigate theoretically the atomic structure and thermodynamics of the wetting layer formed by InAs deposition on GaAs(001), including the effect of strain in our discussion. Secondly, we present results about In adatom diffusion both on the wetting layer and on the c(4 × 4)-reconstructed GaAs(001) surface. In the latter case, we demonstrate the importance of mechanical stress for the height of surface diffusion barriers. Implications for the growth of InAs quantum dots on GaAs(001) are discussed.

The growth of kinetically self-organized two-dimensional (2D) islands is described for Si/Si(111) epitaxy. The island size distribution for this system was measured using scanning tunneling microscopy (STM). The potential formation of thermodynamically stable strained islands of a specific size is discussed. The formation of 2D Si/Ge nanostructures at preexisting defects is studied. The step-flow growth mode is used to fabricate Si and Ge nanowires with a width of 3.5 nm and a thickness of one atomic layer (0.3 nm) by self-assembly. One atomic layer of Bi terminating the surface is used to distinguish between the elements Si and Ge. A difference in apparent height is measured in STM images for Si and Ge, respectively. Additionally, different kinds of 2D Si/Ge nanostructures, such as alternating Si and Ge nanorings having a width of 5–10 nm, were grown.

Experimental, theoretical and computer simulation studies of growth of thin metal films in molecular-beam epitaxy are presented. Starting from a flat high symmetry surface such as Cu(001), a beam of Cu atoms is deposited on the surface. Within a broad range of experimental conditions, the adsorbed atoms diffuse and nucleate into islands. The process of island nucleation and growth in the sub-monolayer regime is studied using both rate equations (mean field) and kinetic Monte Carlo simulations. As additional layers grow, mounds form and the surface becomes three-dimensional in nature. The mounds effectively partition the surface into small sections with little diffusion of atoms between them. As the atomic flux continues, new islands form on the top layer of each mound. Recent studies have shown that the nucleation on the top terraces cannot be described by rate equations. We discuss the relation between the next layer nucleation and other processes in confined geometries, such as the formation of molecules on small dust grains.

For strained-layer epitaxy, a detailed examination is carried out of the way in which strain changes due to elemental segregation within the initially-formed flat “wetting” layer can control the Stranski—Krastanov epitaxial islanding transition. Based upon these considerations, it is shown that a new segregation-based mechanism is fully compatible with the transition in both the InGaAs/GaAs and SiGe/Si systems grown over wide ranges of conditions. Quantitative segregation calculations allow critical “wetting” layer thicknesses to be derived and it is demonstrated that for the InGaAs/GaAs system (=0.25−1) such calculations show good agreement with experimental measurements. The strain energy associated with the segregated surface layer is determined for the complete range of deposited In concentrations using atomistic simulations. The segregation-mediated driving force is considered to be important, also, for all other epitaxial systems which comprise chemically-similar but substantially misfitting materials and which exhibit the Stranski—Krastanov transition.

We investigate strained heteroepitaxial crystal growth in the framework of a simplifying (1+1)-dimensional model by use of off-lattice kinetic Monte Carlo simulations. Our modified Lennard—Jones system displays the so-called Stranski—Krastanov growth mode: initial pseudomorphic growth ends by the sudden appearance of strain induced multilayer islands upon a persisting wetting layer.

We study the mechanisms of strain-induced InAs quantum dot (QD) formation using theoretical and experimental techniques with focus on the influence of the growth parameters such as temperature and flux. The QDs are grown using solid-source molecular-beam epitaxy on GaAs and AlAs substrates and investigated with electron diffraction, x-ray diffraction techniques, and atomic force microscopy. The experimental data of the critical time up to quantum dot formation and of the QD structural properties are modelled in terms of a kinetic rate-equations-based growth model. We distinguish three main temperature regimes. At low temperatures ( ≤ 420°C), QD formation is assumed to be mainly controlled by kinetic migration of adatoms on the surface. At higher temperatures, the additional process of intermixing of the QDs with substrate material is observed, which crucially modifies the QD formation process. Due to this intermixing, the strain energy inside the dots is significantly reduced and, accordingly, the driving force for QD formation. As a consequence, the critical time for QD formation increases. At > 520°C for InAs on GaAs and > 540°C for InAs on AlAs, desorption of In from the QDs becomes important and yields a further delay of QD formation.

The existence of a wetting layer in strained films is not well understood, despite extensive studies of the stability of strained films. In this paper we show that the dependence of the reference state free energy on film thickness leads to a finite thickness wetting layer, which decreases with increasing lattice mismatch strain. We also show that anisotropic surface tension gives rise to a metastable enlarged wetting layer.

Scanning tunneling microscopy (STM) experiments were performed to study growth modes induced by hyperthermal Ge ion action during molecular-beam epitaxy (MBE) of Ge on Si(100). Continuous and pulsed ion-beams were used. STM studies have shown that ion-beam action during heteroepitaxy leads to decrease in critical film thickness for transition from two-dimensional (2D) to three-dimensional (3D) growth modes, enhancement of 3D island density and narrowing of size distribution, as compared with conventional MBE experiments. The crystal perfection of Ge/Si structures with Ge islands embedded in Si was analyzed by the Rutherford backscattering/channeling technique (RBS) and transmission electron microscopy (TEM). The studies of Si/Ge/Si(100) structures indicated defect-free Ge dots and Si layers for the initial stage of heteroepitaxy (5 monolayers of Ge) in pulsed ion beam action growth mode at 350°C. Continuous ion-beam irradiation was found to induce dislocations around Ge dots. The results of kinetic Monte Carlo (KMC) simulations have shown that two mechanisms of ion-beam action can be responsible for stimulation of 2D-3D transition: (i) surface defect generation by ion impacts, and (ii) the enhancement of surface diffusion.

The work reported here focuses on the role of nanopatterning in strained heteroepitaxy. This study makes use of an atomistic description. Two types of prepatterning are considered: