Influence of material, surface reconstruction and strain on submonolayer growth at Si(111) and Ge(111) surfaces

The present work is dedicated to the experimental investigation of influence of strain, surface reconstruction, and material on the surface diffusion, nucleation, and growth of two-dimensional islands at the initial stage of the epitaxial growth on the Ge(111) and Si(111) surfaces. A set of the template surfaces, which are different only in one particular feature (reconstruction, strain, material) was prepared to study the dependence of the growth on these properties. The measurements of the densities of 2D island and small cluster by the scanning tunnelling microscopy as the functions of temperature were used to study the peculiarity of the growth on Ge(111) and Si(111) template surfaces. A theoretical model with a unified treatment of the coupled system of small clusters and 2D islands was developed. In this coupled system the densities of 2D islands and small clusters are determined by their competition for the free adatoms. Analysis of the experimental data for the growth of Si on the Si(111)-(7x7) allowed to determine the critical size of the stable small cluster. Using the effective energies extracted from the temperature dependence of the density of 2D islands and small clusters the values of the diffusion barrier on the template surfaces were determined. The energy barrier to remove the stacking fault and the binding energy of adatoms to the small clusters, which are different for different materials, reconstruction, and applied strain, are the important parameters controlling the density of 2D islands and small clusters during epitaxial growth. The barrier for a diffusion jump from one half unit cell to another is found to be smaller on the (5x5) reconstructed surface than on the (7x7) reconstructed surface The difference in the energy barriers for conversion of the faulted HUC to the normal stacking on the (5x5) and (7x7) reconstructed surfaces results in the large difference of the density of the small clusters on these surfaces. The diffusion barrier is found to be the same (within the measurement accuracy) on the compressively strained and relaxed Ge(111)-(7x7) surface both for the Si and Ge. The main effect of the strain is a change of the binding energy of adatoms with the small clusters. In order to study the effect of strain on the attachment of adatoms to the edges of the growing 2D islands a series of measurements of the island size distribution for deposition of Si and Ge on the Si(111)-(7x7) surface was performed. Analysis of the scaling of the size distribution functions was used to study the characteristics of the attachment. The scaling function for island size distribution was found to be the same for Si and Ge 2D islands on the Si(111)-(7x7) indicating that the 4.2% compressive strain does not make a considerable influence on the process of attachment in the regime of submonolayer growth. However depending on the deposition temperature a different scaling law was found for Si and Ge in the surfactant mediated growth with Bi as a surfactant. The main mechanism which results in the difference of the scaling functions was revealed with the help of Kinetic Monte-Carlo simulations. The consequence of the stronger step edge passivation of the Ge islands results in the transition from the growth limited by the surface diffusion to the growth limited by the attachment kinetics. An increase of the deposition temperature vanishes the role of the passivation and the kinetic regime of the island growth changes to the diffusion limited one