Controlled Ge quantum dots positioning with nano‐patterned Si(001) substrates

Abstract

A square nanometric patterned substrate (period 20 nm) is obtained by direct twist bonding of two twin Si(001) surfaces, thinning and preferential chemical etching. Molecular beam epitaxy of Ge is carried out on a sample having heterogeneous trench depths to analyse islands positioning as a function of the surface morphology. Scanning electron microscopy observations show that small single dots per mesa or large dots covering several mesas can be observed. It highlights the influence of the mesa aspect ratio on the control of Ge islands self-organization, and suggests the occurrence of an effective activation barrier depending on the surface profile. The position-dependent energy stored in a dot for a given surface profile is estimated from a very simple model based on the balance between capillarity and elastic relaxation terms. By choosing a cycloid-like profile, experimental observations can be explained without fitting parameters.

On the Mechanisms Governing Aluminum-Mediated Solid-Phase Epitaxy of Silicon

“…5, indicate a reduction of the Al thin-film elastic energy field by a partial transfer of deformation to the oxide along the edges of the contact window. If it is assumed that the incoming Si is kinetically capable of traveling across the whole Al-to-Si window surface, the SiO 2 /Si interface would correspond, from a lattice deformation point of view, to a local minimum of the Si chemical potential found in the contact window, 21 and this results in a preferential diffusion direction for the Si atoms. Moreover, the nucleation of c-Si at the window perimeter corresponds to the substitution of an SiO 2 /Al interface with an SiO 2 /SPE-Si plus an SPE-Si/Al interface.…”

Metal positioning on silicon surfaces using the etching of buried dislocation arrays

“…without dislocation), μ can be written as a function of the surface tension (capillarity) and of the elastic strain (see, for example, the formulation of Mullins-Herring [28]) and the island positioning depends directly on the competition between these two contributions. This has been already shown by the deposition of Ge on nanopatterned Si for which the influences of the mesa aspect ratio and of the amount of deposited materials has been pointed out [21,8].…”

“…The etching of twist bonded silicon films reveals a nanotrench network with the fourfold symmetry and the period of the underneath cross grid of screw dislocation lines (an example is given in figure 3). After the Yang-etching, the mesa height is in the 1.5-2 nm range, but this value is too small to guide efficiently the self-organization of epitaxial islands as shown by Ge depositions [20,21].…”

Recent developments in Ge dots grown on pit‐patterned surfaces

“…Hirai and Itoh 28 prepared shallow pits by scanning probe microscope anodic oxidation and subsequent oxide removal with HF solution. Another method consists of direct twist bonding of two Si(001) surfaces, thinning and selective etching of the resulting dislocation network 29. A focused ion beam can also be used for direct surface patterning 30, 31.…”