Growth of Ge dots on templated Si substrates with diffusion-altered holes

Abstract

We have studied the impact of the hole shape on the growth of Ge dots. Si substrates that have been templated by means of electron beam lithography and reactive ion etching have been used to grow Si buffer layers at different substrate temperatures by molecular-beam epitaxy. Atomic-force-microscopy studies show that for high substrate temperatures, the prepatterned holes are smeared out. A model has been employed to quantitatively analyze the smearing out of the holes. The study further shows that the shape of the holes has a substantial impact on the morphology of the subsequently grown Ge dots, i.e. Ge dots grown in smeared out holes show a tendency towards an inhomogeneous size distribution and the formation of multiple dots in one hole.

Structural properties of templated Ge quantum dot arrays: impact of growth and pre-pattern parameters

“…To assure that only the amount of deposited Si is responsible for the shape transformation of the pre-patterned pit and not the temperature, the deposition temperature was set to a fixed value of 300 °C and the deposition rate was set to 0.1 Å s −1 . This allows to avoid pit coarsening due to high substrate temperatures, as observed in our preliminary experiments and described by Rinke et al [33]. During the growth sequences A, B, D and E the Si buffer layer thickness is increased from zero to 10, 100 and 200 Å to determine its influence on the Ge QD nucleation.…”

Recent developments in Ge dots grown on pit‐patterned surfaces

“…This Si buffer layer considerably alters the pit shape and, therefore, also has an influence on the shape and uniformity of Ge dots that nucleate in the pits. While the initial pit shape is a result of the patterning process, it changes during buffer deposition as a function of the amount of Si deposited but also of the buffer growth temperature 37, 38. This is illustrated quailtatively in Fig.…”

“…37, the influence of Si buffer thickness on pit morphology was investigated; higher buffer thickness mainly resulted in shallower facets at the pit bottom. For a fixed Si buffer thickness of 18 nm, an increase in deposition temperatures in steps from 350 to 800 °C leads to a progressive flattening and broadening of the holes, which in turn can lead to increasing size inhomogeneities of the Ge dots as well as the formation of multiple dots in one pit 38. Recent results suggest 39 that holes should be steep and well defined in order to obtain uniform dots.…”

“…Generally, shape and uniformity of the Ge dots are the result of a complex interplay of the adjustable parameters such as pit shape, which is a function of the lithography and etching process 22, 39, of buffer thickness and temperature at deposition 37, 38, and of the amount of Ge deposited and the accompanying process temperatures 37, 43. For a given pit shape after Si buffer growth, the amount of Ge deposited as well as the process temperature have to be adjusted carefully for optimal results, as illustrated in Fig.…”

Investigation of the local Ge concentration in Si/SiGe nanostructures by convergent-beam electron diffraction

“…by Dehlinger et al [1], Grützmacher et al [2], Rinke et al [3], Ross et al [4], Klemenc et al [5], Abstreiter et al [6] and many others. Such devices would have great advantages due to their compatibility with the CMOS-technology.…”