Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

6.3 Further Results: Site-Controlled Growth of InGaAs QDs Embedded in GaAs
Matrix on Pre-Patterned Silicon Substrate
size of nucleated QDs during the MBE growth. The uctuation of beam uxes
during the growth could also partially contribute to the non-uniformity of the
nucleated QDs. The lack of nucleation of QDs in some of the holes could be
due to the surface degradation after the processing steps, the local surface inhomogeneities
would aect the diusion of ad-atoms to certain crystal directions,
which would result in a non-uniform distribution of nucleation sites during the
growth. A tilted scanning electron microscope image (Fig. 6.6(e)) displays the
cross section of the QDs localized in the patterned holes obtained after cutting
through the localized QDs with focused ion beam (FIB). The cross sectional
view exhibits a good interface between QDs and silicon in the patterned hole.
The selective formation of GaAs/ In 0.15 Ga 0.85 As/GaAs nanostructures inside the
patterned holes with 1 µm spacing after dierent stages of the growth can be
explained based on the lower chemical potential inside the etched holes than the
plane surface [121]. This gradient of chemical potential provides the driving force
for the group-III ad-atoms to diuse to the holes and preferentially nucleate there
[121, 122]. The growth of GaAs/InAs/GaAs nanostructures on pre-patterned Si
masked with SiO 2 has been demonstrated in reference [12] with thick nominal
depositions. But we have demonstrated here for the rst time the site-controlled
growth of GaAs/In 0.15 Ga 0.85 As/GaAs nanostructures with very low nominal deposition
thicknesses directly on pre-patterned Si without the use of SiO 2 masks.
These results are highly encouraging for the realization of III/V optical devices
on the pre-patterned Si surfaces for potential applications.
113