  This paper presents a rigorous calculation of the figure of merit of
superlattice thermoelectric material (SL TEM) with regard to real
three-dimensionality and nonparabolicity of its energy spectrum with the
arbitrary level of openness of its Fermi surface (FS).It is shown that the
figure of merit of SL TEM in the temperature range of 300-500K is drastically
increased with increasing level of openness of FS. However, due to the presence
of lattice component of thermal conductivity the figure of merit of SL TEM is
rather responsive to the distance between the layers and drastically drops with
its increase. Besides, for the same material, coefficient of performance of a
refrigerator in the framework of its simplest model was calculated. It was
established that if material band spectrum is described by the Fivaz model, the
coefficient of performance is drastically increased with increasing the level
of openness of FS and in case of transient FS it reaches 1.9 between the
temperatures of 300 and 230K. However, as the distance between the layers of SL
TEM increases 2 times, it drops to 0.4 Based on the obtained criteria, four
methods of search for promising SL TEM with the use of quantizing magnetic
fields are proposed.
