Growth mechanism and thermoelectric properties of PbTe/SnTe/PbTe heterostructures

An electron microscopy study of the mechanism of SnTe and PbTe layer growth in PbTe/SnTe/PbTe heterostructures prepared by thermal evaporation in vacuum onto a KCl substrate was performed. It is established that PbTe and SnTe grow on one another in a layer-by-layer fashion with the introduction of misfit dislocations on the interface at a critical thickness dc ≈ 2 nm. The experimentally determined dependence of the elastic stress in a growing layer (either PbTe or SnTe) on the layer thickness and the critical thickness are in good agreement with those calculated theoretically. The dependences of the thermoelectric properties of PbTe/SnTe/PbTe heterostructures on the SnTe layer thickness (dSnTe = 5-100 nm) at fixed thicknesses of the PbTe layers were studied at room temperature. It was found that in the thickness range of dSnTe ≈ (10-15) nm, an inversion of the dominant carrier sign from n to p takes place. The d-dependences of the thermoelectric properties were interpreted within the framework of a three-layer model, treating a PbTe/SnTe/PbTe heterostructure as three conductors connected in a parallel fashion, each characterized by its specific electrophysical parameters.