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

5.4 Self-Assembled InAs QDs Embedded in Si Matrix
5.4.5 Geometric Phase Analysis Strain vs. Material Strain
The sample with 4 MLs InAs coverage underwent dierent strain analysis. The
layer scheme of the grown structure with the growth conditions are shown in
Fig. 5.10(b). However, this sample underwent an intensive structural and strain
analysis in order to understand the dierent strain types. Fig. 5.25(a) shows
the cross-section TEM image of the grown structure, which is consistent with
intended one in Fig. 5.10(b). The HR-TEM image of a single InAs QD after
plastic relaxation, with half lens shape and at interface on the top layer of the
grown structure is shown in Fig. 5.25(b). On the other hand, the dark eld straincontrast
image in Fig. 5.25(c) conrmed the existence of unstrained Si layers with
no extended defects in the Si matrix.
Figure 5.25:
TEM cross-section image of InAs/Si QDs sample (50 nm Si/ 4 MLs
InAs /10 nm Si/40 nm Si cap) showing; (a) bright eld cross section TEM image of
the grown structure, consistent with intended layer scheme; (b) HR-TEM cross-section
of typical InAs QD with half lens shape and at interface on top Si (100) surface; (c)
dark eld strain-contrast image with buried InAs layer, shows unstrained Si layer with
no extended defects in Si matrix. (TEM performed@PDI-Berlin).
For this intensive strain analysis and study, it is important to distinguish
between dierent types of strain. There are two main types of strain, the rst
type referred as material strain (ε ii ) described by Eq. 5.7, while the second type
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