E. Zoethout

The influence of strain on the diffusion of Si dimers on Si(001)

The influence of lattice mismatch-induced tensile strain on the diffusion of Si dimers on Si(001) has been studied. The rate of surface diffusion of a Si dimer along the substrate dimer rows is relatively insensitive to tensile strain, whereas the rate of diffusion for a Si dimer across the substrate dimer rows is significantly enhanced. The insensitivity of the along row diffusion rate for tensile strain is attributed to the presence of a dissociative intermediate state of the ad-dimer during diffusion rather than diffusion as a solid unit.

Origin of roughening in epitaxial growth of silicon on Si(0 0 1) and Ge(0 0 1) surfaces

It is shown that the formation of (2×1) reconstructed islands during the growth of Si on Si(0 0 1) and Ge(0 0 1) surfaces at moderate temperatures and the consequent anisotropic diffusion and sticking lead to roughening. As Si islands nucleate and expand, the dimer rows in neighboring rows need not, in general, align with each other. An anti-phase boundary (APB) will be found if two growing islands meet, but their internal dimer rows are not in the same registry. One type of APB runs perpendicular to the substrate rows, whereas the other runs along the substrate rows. As has been pointed out by Hamers et al. [J. Vac. Sci. Technol. A 8 (1990) 195] this first type of APB is a preferential center for nucleation of next layer islands and thus naturally leads to roughening. Here we show that the other type of APB leads, in combination with the anisotropy in sticking and diffusion of dimers, to the formation of long B-type double layer steps and narrow trenches. We argue that it is the kinetic suppression of filling of these trenches and not, as previously suggested the existence of step edge barrier for the double layer step edge that leads to roughening.

Adatom assisted stabilization of ad dimers on Ge(001)

The early stage of silicon heteroepitaxial growth and germanium homoepitaxial growth on Ge(001) has caused a discrepancy between experimental and theoretical work. Previously a dimer configuration was identified experimentally, which theoretically has been predicted to be unfavorable: the D dimer. Upon careful reinvestigation this cluster turns out to be not a two-atom, but a three-atom cluster. The three-atom cluster of Ge or Si on Ge(001) is shown to differ from a C dimer, a small epitaxial island (BD) or the three-atom cluster of Si on Si(001)

Antiphase boundary network: A route to extract the island nucleation density

Epitaxial growth of Si or Ge on Si(001) and Ge(001) surfaces leads to the formation of an antiphase boundary network because adjacent (2×1) reconstructed islands can either be in-phase or out-of-phase with each other. We show that this antiphase boundary network can be used to extract the saturation island nucleation density well after the onset of coalescence. This method is more accurate than the commonly used method of counting the islands in the low coverage regime

Diffusion of Dimers on Silicon and Germanium (001) Surfaces

Atomic resolved imaging techniques have provided us with an exciting view on how atoms or clusters of atoms diffuse on surfaces. Here the stability and diffusion of Si and Ge dimers on elementary semiconductor (001) surfaces is briefly reviewed. It will be shown that, for these systems, in principle three diffusion pathways are active: diffusion of on-top dimers over the substrate rows, diffusion across the substrate rows, and diffusion in the troughs. Furthermore, we will report on a heretofore unknown phenomenon, namely, diffusion-driven concerted motion of substrate atoms. During diffusion of a dimer in the trough or across the substrate rows the substrate atoms in the proximity of the diffusing dimer exhibit a collective rearrangement. In retrospect, the occurrence of this concerted motion is not surprising at all, but is a direct consequence of the rearrangement of substrate atoms in the proximity of an adsorbed trough dimer.