Optimal Growth Conditions for Selective Ge Islands Positioning on Pit-Patterned Si(001)

We investigate ordered nucleation of Ge islands on pit-patterned Si(001) using an original hybrid Kinetic Monte Carlo model. The method allows us to explore long time-scale evolution while using large simulation cells. We analyze the possibility to achieve selective nucleation and island homogeneity as a function of the various parameters (flux, temperature, pit period) able to influence the growth process. The presence of an optimal condition where the atomic diffusivity is sufficient to guarantee nucleation only within pits, but not so large to induce significant Ostwald ripening, is clearly demonstrated

continuum modelling of semiconductor heteroepitaxy an applied perspective

Semiconductor heteroepitaxy involves a wealth of qualitatively different, competing phenomena. Examples include three-dimensional island formation, injection of dislocations, mixing between film and substrate atoms. Their relative importance depends on the specific growth conditions, giving rise to a very complex scenario. The need for an optimal control over heteroepitaxial films and/or nanostructures is widespread: semiconductor epitaxy by molecular beam epitaxy or chemical vapour deposition is nowadays exploited also in industrial environments. Simulation models can be precious in limiting the parameter space to be sampled while aiming at films/nanostructures with the desired properties. In order to be appealing (and useful) to an applied audience, such models must yield predictions directly comparable with experimental data. This implies matching typical time scales and sizes, while offering a satisfactory description of the main physical driving forces. It is the aim of the present review to show tha..

intermixing in heteroepitaxial islands fast self consistent calculation of the concentration profile minimizing the elastic energy

We present a novel computational method for finding the concentra- tion profile which minimizes the elastic energy stored in heteroepitaxial islands. Based on a suitable combination of continuum elasticity theory and configura- tional Monte Carlo, we show that such profiles can be readily found by a simple, yet fully self-consistent, iterative procedure. We apply the method to SiGe/Si islands, considering realistic three-dimensional shapes (pyramids, domes and barns), finding strongly non-uniform distributions of Si and Ge atoms, in qualitative agreement with several experiments. Moreover, our simulated selective-etching profiles display, in some cases, a remarkable resemblance to the experimental ones, opening intriguing questions on the interplay between kinetic, entropic and elastic effects

Impact-driven effects in thin-film growth: steering and transient mobility at the Ag(110) surface

Low-energy atomic impacts on the Ag(110) surface are investigated by molecular dynamics simulations based on reliable many-body semiempirical potentials. Trajectory deflections (steering) caused by the atom-surface interaction are observed, together with impact-following, transient-mobility effects. Such processes are quantitatively analysed and their dependence on the initial kinetic energy and on the impinging direction is discussed. A clear influence of the surface anisotropy on both steering and transient mobility effects is revealed by our simulations for the simple isolated-atom case and in the submonolayer-growth regime. For the latter case, we illustrate how steering and transient mobility affect the film morphology at the nanoscale.Comment: 7 pages, 9 figure

Effects of deposition dynamics on epitaxial growth

The dynamic effects, such as the steering and the screening effects during deposition, on an epitaxial growth (Cu/Cu(001)), is studied by kinetic Monte Carlo simulation that incorporates molecular dynamic simulation to rigorously take the interaction of the deposited atom with the substrate atoms into account. We find three characteristic features of the surface morphology developed by grazing angle deposition: (1) enhanced surface roughness, (2) asymmetric mound, and (3) asymmetric slopes of mound sides. Regarding their dependence on both deposition angle and substrate temperature, a reasonable agreement of the simulated results with the previous experimental ones is found. The characteristic growth features by grazing angle deposition are mainly caused by the inhomogeneous deposition flux due to the steering and screening effects, where the steering effects play the major role rather than the screening effects. Newly observed in the present simulation is that the side of mound in each direction is composed of various facets instead of all being in one selected mound angle even if the slope selection is attained, and that the slope selection does not necessarily mean the facet selection.Comment: 9 pages, 10 figure

Atomic structure of Ge quantum dots on the Si(001) surface

In situ morphological investigation of the {105} faceted Ge islands on the Si(001) surface (hut clusters) have been carried out using an ultra high vacuum instrument integrating a high resolution scanning tunnelling microscope and a molecular beam epitaxy vessel. Both species of hut clusters--pyramids and wedges--were found to have the same structure of the {105} facets which was visualized. Structures of vertexes of the pyramidal clusters and ridges of the wedge-shaped clusters were revealed as well and found to be different. This allowed us to propose a crystallographic model of the {105} facets as well as models of the atomic structure of both species of the hut clusters. An inference is made that transitions between the cluster shapes are impossible.Comment: 6 pages, 6 figures. Accepted to JETP Letters (publication date 2010-03-25

The formation of a Sn monolayer on Ge(1 0 0) studied at the atomic scale

The growth of multi-layer germanium-tin (GeSn) quantum wells offers an intriguing pathway towards the integration of lasers in a CMOS platform. An important step in growing high quality quantum well interfaces is the formation of an initial wetting layer. However, key atomic-scale details of this process have not previously been discussed. We use scanning tunneling microscopy combined with density functional theory to study the deposition of Sn on Ge(1 0 0) at room temperature over a coverage range of 0.01 to 1.24 monolayers. We demonstrate the formation of a sub-2% Ge content GeSn wetting layer from three atomic-scale characteristic ad-dimer structural components, and show that small quantities of Sn incorporate into the Ge surface forming two atomic configurations. The ratio of the ad-dimer structures changes with increasing Sn coverage, indicating a change in growth kinetics. At sub-monolayer coverage, the least densely packing ad-dimer structure is most abundant. As the layer closes, forming a two-dimensional wetting layer, the more densely packing ad-dimer structure become dominant. These results demonstrate the capability to form an atomically smooth wetting layer at room temperature, and provide critical atomic-scale insights for the optimization of growth processes of GeSn multi-quantum-wells to meet the quality requirements of optical GeSn-based devices

Steering effect on the shape of islands for homoepitaxial growth of Cu on Cu(100)

The steering effect on the growth of islands is investigated by combining molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations. Dynamics of depositing atoms and kinetics of atoms on a substrate are realized by MD and KMC, respectively. The reported experimental results on the asymmetric island growth [van Dijken {\it et al.}, Phys. Rev. Lett. {\bf 82}, 4038 (1999).] is well reproduced. A salient phenomenon, the reversal of the asymmetry, is found as the island size increases, and attributed to the asymmetric flux on the lower terrace of island.Comment: 5 figur