Direct Probing of Cross-Plane Thermal Properties of Atomic Layer Deposition Al ₂ O ₃ /ZnO Superlattice Films with an Improved Figure of Merit and Their Cross-Plane Thermoelectric Generating Performance

There is a recent interest in semiconducting superlattice films because their low dimensionality can increase the thermal power and phonon scattering at the interface in superlattice films. However, experimental studies in all cross-plane thermoelectric (TE) properties, including thermal conductivity, Seebeck coefficient, and electrical conductivity, have not been performed from these semiconducting superlattice films because of substantial difficulties in the direct measurement of the Seebeck coefficient and electrical conductivity. Unlike the conventional measurement method, we present a technique using a structure of sandwiched superlattice films between two embedded heaters as the heating source, and electrodes with two Cu plates, which directly enables the investigation of the Seebeck coefficient and electrical conductivity across the Al ₂ O ₃ /ZnO superlattice films, prepared by the atomic layer deposition method. Used in combination with the promising cross-plane four-point probe 3-ω method, our measurements and analysis demonstrate all cross-plane TE properties of Al ₂ O ₃ /ZnO superlattice films in the temperature range of 80 to 500 K. Our experimental methodology and the obtained results represent a significant advancement in the understanding of phonons and electrical transports in nanostructured materials, especially in semiconducting superlattice films in various temperature ranges.