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

5.4 Self-Assembled InAs QDs Embedded in Si Matrix
Figure 5.19:
TEM cross-section image of InAs/Si QDs sample (50 nm Si/2 MLs
InAs /10 nm Si/40 nm Si cap) with PGA at 800 ◦ C. (a) AFM image (3 × 3 µm 2 )
of top surface with RMS value of 0.37 nm. (b) The bright eld cross section TEM
image shows the InAs QDs with dismiss wetting and shape dots evolution, and total
disappearance of SFs and bubbles in the cap layer. (c) HR-TEM cross section image
conrmed SFs -free and voids-free structure with improved Si crystal quality growth.
(TEM performed@PDI-Berlin).
Si crystal quality growth with voids-free and SFs-free (defect-free Si) around and
above (capping zone) the InAs layer.
The second cycle of PGA at higher temperature of (800 ◦ C) proved to have
a strong impact on circular-voids kinetics and crystal quality of Si layer, while
the rst PGA cycle (at 700 ◦ C) has a profound inuence on the Si surface reconstruction
and evolution. Therefore, another two samples were needed to conrm
the very interesting model or scenario of Si surface reconstruction and evolution.
The rst sample was prepared by skipping the rst cap layer at low growth temperature
of 400 ◦ C (QDs growth temperature) and start Si overgrowth at 700 ◦ C,
the layer scheme of the intended grown structure is shown in Fig. 5.20(a). The
expectation from this sample is total QDs desorption or no InAs QDs observation.
On the other hand, the second sample was grown with the expectation of
QDs observation, according to our model and explanations. The same growth
conditions and sequence of sample one were rst applied, followed by the growth
of a second layer of InAs QDs, but with two overgrowth steps for the Si cap layer.
However, the rst layer was grown at a QDs growth temperature of 400 ◦ C, while
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