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
Figure 6.5:
3D surface prole of the high resolution atomic force microscopy (HR-
AFM) measurements of a single hole. (a) Before in-situ surface treatment with L =(70-
75) nm and D =(60-70) nm. (b) After in-situ surface treatment with L =(70-80) nm
and D =(65-70).
the optimized in-situ surface treatment. This in-situ cleaning sequence involving
AH cleaning and 30 min thermal annealing at 750 ◦ C was performed before the
growth on all patterned substrate described in the following.
Two patterned samples were used to study the surface morphology after different
stages of growth of a GaAs/In 0.15 Ga 0.85 As/GaAs heterostructure. The
schematic sequence of growth on patterned samples is shown in Fig. 6.6(a). For
the rst sample, a GaAs buer layer was grown at 600 ◦ C with a nominal thickness
of 2 nm. The AFM prole for this sample (Fig. 6.6(b)) shows that the GaAs
material nucleated in the form of dome like islands with lateral sizes ranging from
120 to 175 nm and exhibits a height variation of 60-115 nm. Moreover, the formation
of these nano-islands has taken place highly selectively in the patterned holes
spaced by 1 µm as compared to the other periods. The second sample was grown
with a nominally identical GaAs buer layer, but with an additional deposition
of 2 MLs of In 0.15 Ga 0.85 As grown at 500 ◦ C and a GaAs capping layer grown at
500 ◦ C with a nominal thickness of 2 nm.
The growth temperature of the GaAs capping layer was kept identical to
the growth temperature of the In 0.15 Ga 0.85 As QDs layer to avoid high indium
desorption, which takes place above 500 ◦ C [100]. The AFM prole of the surface
morphology of this sample (Fig. 6.6(c,d)) conrms the continuation of site-
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