Thickness dependences of thermoelectricproperties of PbTe/SnTe/PbTe heterostructures
E.I. Rogacheva1, S.N. Grigorov1,T.V. Tavrina1, O.N. Nashchekina1, Ye.O. Vekhov1,
1National TechnicalUniversity “Kharkov Polytechnic Institute”, 21 Frunze St., Kharkov61002, Ukraine
2Massachusetts Institute of Technology, 77Massachusetts Ave., Cambridge, MA 02139, USA
Thepossibility of an enhancement in ZT in superlattices, predicted theoreticallyand proved experimentally, raises interest in the detailed studying of thelayer growth and the thermoelectric properties not only in superlattices butalso in a separate building block of a superlattice.
Theobjects of this study are PbTe/SnTe/PbTe heterostructures with different signsof dominant carriers in constituent layers (n-type in PbTe and p-type in SnTe),grown on KCl substrates by thermal evaporation in vacuum. The thicknesses ofPbTe layers were kept constant; the SnTe layer thickness was varied (d=0.5-6.0 nm). Theelectron microscopy study of growth mechanisms of PbTe and SnTe layers on oneanother was performed. The critical thickness (d~2 nm) correspondingto the transition from pseudomorphic growth to the formation of misfitdislocations on the interfaces was determined. On the basis of the experimentaldata, the dependence of strains in the SnTe layer on d was plotted andcompared with the theoretical one. The d-dependences of the electricalconductivity, Seebeck coefficient, Hall coefficient were obtained. Thethicknesses at which an inversion of the dominant carrier sign from n to p occurs weredetermined. The observed d-dependences of the thermoelectric properties wereinterpreted within the framework of a model taking into account two sorts ofcarriers.