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

5.3 Results and Discussion
5.3.2 Growth of InAs QDs Directly on Silicon Substrate
In this section the growth conditions are: growth temperature =425 ◦ C , 2 MLs
InAs coverage, V/III ratio of 20 after 15 min thermal desorption at 870 ◦ C . In
the rst section, the inuence of the substrate orientation will be investigated,
then the in-situ Ga surface treatment method.
5.3.2.1 Dependence on Substrate Orientation
It can be seen clearly in Fig. 5.2, the shape and density of InAs QDs show a
signicant dependence on the Si substrate orientation. Dashed-like InAs islands
with a density of 6.8 × 10 10 cm −2 elongated in [1-10] direction were observed on
(111) surfaces (Fig. 5.2(b)) compared to circular shaped QDs with a slightly lower
density of 3.4 × 10 10 cm −2 on (100) planes (Fig. 5.2(a)).
Figure 5.2: (1 × 1 µm 2 ) AFM images of InAs QD structures grown using SK mode by
depositing 2 MLs of InAs (a) Circular QDs on n-doped Si (100) substrate. (b) Elongated
dots on n-doped Si (111).
5.3.2.2 Ga Treatment
Our investigations using pre-growth Ga-assisted thermal treatment have revealed
that the samples exposed to a low Ga ux of 0.1 ML/s at a temperature of
560 ◦ C for 2 minutes followed by thermal desorption at 870 ◦ C for 15 min, allow
an optimization of the lateral size and the homogeneity of QDs.
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