Diplomarbeit Diplom-Ingenieur - Institut für Halbleiter

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seen in Fig. 2.4, where also the structure of the HQ buffer is shown. Fig. 2.5 shows a
TEM image of an annealed sample, where also the buffer structure can be seen.
Essential for the growth of a high quality PbTe SQW is a high-quality CdTe buffer
with low surface roughness and low lattice defects. The lattice constants of GaAs and
CdTe differ by ~15% which lead to CdTe growth with a high dislocation density. To
grow a high-quality CdTe buffer, fist a 100 nm thick low temperature (LT) CdTe film
was grown at 280°C on a sulphur treated GaAs substrate, followed by 300 nm CdTe
at 320°C providing a (100) oriented CdTe surface. This was capped with a 100 nm
thick MnTe layer to suppress the re-evaporation during the following thermal
annealing step at 380°C for 30min. On the CdTe/MnTe buffer a superlattice of twenty
5 nm thick MnTe / 2 nm thick CdTe sublayers were grown at 280°C and then
finalised with a CdTe layer (300nm-900nm) at 320°C [28]. Such high-quality buffers,
or similar ones, were used for all samples investigated within this thesis. The root-
mean-square roughness of such a HQ buffer is less than 0.5nm in an area of
3μm × 3μm (measured by atomic force microscopy).
Figure 2.5: A typical PbTe/CdTe heterostructure recorded with the TEM along the [110]
zone axis. The layers with Mn content are brighter and clearly visible. The HQ buffer
was finalised with 900nm CdTe. The image shows an annealed sample. The PbTe dots
can be seen beneath the surface of the sample at the top of the image.
On such high quality CdTe buffers the PbTe SQWs were grown at temperatures
from 220°C to 280°C with different thickness. The CdTe (100) surface is polar,