Effect of elastic stresses on the thermoelectric properties of Pb1-xGexTe epitaxial layers

The temperature dependence of the thermopower of Pb-1_xGexTe (x = 0.01-0.05) epitaxial films grown on BaF2(111) substrates was measured. The temperature of the ferroelectric phase transition was found to disagree with that obtained for bulk single crystals of the same composition. This disagreement was explained as resulting from the effect of elastic stresses arising in the crystal lattice of the Pb1-xGexTe compound due to the difference between the thermal expansion coefficients of the film and the substrate during cooling of the layers from the growth temperature to the temperature of measurement.