Diplomarbeit Diplom-Ingenieur - Institut für Halbleiter

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4.3 Precipitation from different layer thicknesses
4.3.1 Annealed 5nm layer
The best specimen of an originally 5nm thick layer resulted from sample #11, which
is the double QW sample. It was possible to record more than 100 dots in one row,
which allows significant dot size statistics. The double quantum well samples were
annealed at 350°C for 10 min. The height (along the growth direction) and the width
of the dots were evaluated with the program package Gatan Digital Micrograph.
Digital Micrograph is a control and analysis software for the Gatan Multi-Scan CCD
camera employed on our TEM [41]. The specimen itself shows dots with almost the
same height, but the width of the dots varies significantly (see fig. 4.5). Smaller dots
with a decreased high show always a high symmetry with comparable height and
widths. Dots with the maximum height have lengths of up to twice their height. This
is a strong indication that not all dots have reached there thermodynamic equilibrium
shape.
Figure 4.5: (a) Cross sectional, dark field image over a large area. The sample contains a
double row of QDs. The bottom row was used to analyse the dimensions of the dots. (b)
Typical QDs found in the sample, recorded as bright field image. The left-hand image
shows two highly symmetric QDs. The crystal orientation is indicated. The QDs show
sharp interfaces. The kind of the interfaces indicated in the right-hand images, which
show two elongated, centro-symmetric dots.