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

MBE Growth of Self-Assembled InAs and InGaAs Quantum Dots Embedded in
Silicon Matrix
observed to have very low density compared to the InAs QDs and no detectable
wetting layer has been detected in the rst measurement in TEM cross section
image Fig. 5.12(a). Mist dislocations loops were observed to form at the InAs/Si
interface consisting of perfect 60 ◦ -type dislocations and partial dislocation with
SFs inside the InAs QDs observed to start moving from the dots to the Si surface
(Fig. 5.12).
Figure 5.12: TEM cross-section image of InAs/Si QDs sample (50 nm Si/2 ML InAs
QDs/ 50 nm Si cap/2 ML InAs) showing; (a) stacking faults defects start at InAs
QDs running to the top surface; (b) HR-TEM of single InAs QD shows spherical to
ellipsoidal QDs shape embedded in Si matrix and at shape InAs islands on the top
layer of the grown structure; (c) HR-TEM of single InAs QD in Si matrix with 20 nm
lateral size and 6 nm height the red arrows point to mist dislocation and the white
arrow represents pure edge dislocation. (TEM performed@PDI-Berlin).
The inuence of substrate o-cut has been found to have a strong impact on
InAs dots shape and geometry. Depending on the dot diameter (D) dierent dot
shapes were observed on exactly oriented substrates in case of InAs QDs grown
with 2 MLs (Fig. 5.12(b)). They can be classied to: spherical shape when D
< 10 nm, ellipsoidal shape, if 10 nm < D < 25 nm and plate-like shape when D
> 25 nm. In contrast to that, a semi-coherent and multi-faceted InAs QDs with
very homogeneous size distribution were observed in the sample of 2 ML InAs
coverage embedded in Si matrix on mis-oriented Si substrates. A cross-section
TEM image in Fig. 5.13(a) illustrates the very homogeneous and narrow size dots
distribution with diameter D in the range of 5 - 8 nm.
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