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

MBE Growth of Self-Assembled InAs and InGaAs Quantum Dots Embedded in
Silicon Matrix
reconstruction with bubbles (spherical or circular-voids without material inside)
and vacancy stacking faults (V-SF) formation above the InAs QDs has been
observed. The vacancy SFs and circular-voids formation are very logical traces of
the possible route of lling the voids. The dark eld cross-section TEM image of
the grown structure in Fig. 5.17(b) shows the InAs QDs with a missing wetting
layer and the shape transition evolution from pyramidal and at to spherical and
faceted dots. The V-SF and the circular-voids above the InAs QDs are clearly
shown in the HR-TEM image Fig. 5.17(c). The further growth of 40 nm Si
cap layer (sample 4) after PGA at 700 ◦ C resulted in high circular-voids density
localized above dots layer (Fig. 5.18(b)). However, the SFs density observed to
have low density after 40 nm Si capping. The HR-TEM image in Fig. 5.18(c)
shows spherical QDs shapes evolution, some with facets and obviously with higher
density and random size distribution compared to sample 3.
Figure 5.18: TEM cross-section image of InAs/Si QDs sample (50 nm Si/2 MLs InAs
/10 nm Si/40 nm Si cap). (a) (3 × 3 µm 2 ) AFM image 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 layer with low density SFs and high density circular-voids. (c)
HR-TEM cross-section image of high density circular-voids above InAs QDs. (TEM
performed@PDI-Berlin).
The inuence of the nal PGA step at 800 ◦ C for 5 minutes of the whole
structure was invigilated by sample 5 (Table 5.2). Bright eld cross-section TEM
image in Fig. 5.19(b) conrmed a total disappearance of circular-voids and SFs
defects in the Si cap layer. A HR-TEM image in Fig. 5.19(c) shows an improved
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