  A concept for the fabrication of highly symmetric quantum dots that are
coherently embedded in a single crystalline matrix is demonstrated. In this
approach, the formation of the quantum dots is induced by a transformation of
an epitaxial 2D quantum well into an array of isolated precipitates with
dimensions of about 25 nm. The formation process is driven by the immiscibility
of the constituent materials resulting from their different lattice structures.
The investigated PbTe/CdTe heterosystem combines two different cubic lattices
with almost identical lattice constants. Therefore, the precipitated quantum
dots are almost strain free and near thermodynamic equilibrium they exhibit the
shape of small-rhombo-cubo-octahedrons. The PbTe/CdTe quantum dots, grown on
GaAs substrates, display intense room temperature luminescence at wavelength
around 3.2 micrometer, which makes them auspicious for applications in
mid-infrared photonic devices.
