Epitaxial Zinc-Blende CdTe Antidots in Rock-Salt PbTe Semiconductor Thermoelectric Matrix

The formation of zinc-blende CdTe antidots (bandgap of 1.5 eV at room temperature) embedded in a rock-salt PbTe semiconductor matrix with a narrow bandgap of 0.3 eV in properly annealed epitaxial CdTe/PbTe multilayers grown by molecular beam epitaxy on a GaAs(001) substrate is reported. Transmission microscopy and X-ray diffraction characterization revealed the monocrystalline zinc-blende crystal structure of the CdTe antidots. The CdTe antidots have a highly symmetric shape and size varying in a controlled way in the range from 5 to 30 nm, depending on the layer thicknesses in the initial multilayer CdTe/PbTe stack. The presented results indicate that the CdTe antidot growth mechanism is similar to that of PbTe dots embedded in a CdTe matrix and is driven by the nanoscale phase separation due to qualitative differences in the chemical bonding and crystal structure of PbTe and CdTe. The electrical characterization in terms of Hall effect, electrical conductivity, and Seebeck effect measurements showed that both n- and p-type conductivities can be obtained in these nanocomposite thermoelectric materials with carrier concentrations of 1017–1018 cm–3 and mobilities of about 200 cm2/(V s) at room temperature. About a 25% increase of the thermoelectric power as compared to that of the reference bulk thermoelectric PbTe crystals was found in heterostructures with the smallest CdTe antidots.