Enhanced Cross-Plane Thermoelectric Figure of Merit Observed in an Al2O3/ZnO Superlattice Film by Hole Carrier Blocking and Phonon Scattering

Abstract

We experimentally investigate the cross-plane figure of merit (ZT) for an Al2O3/ZnO (AO/ZnO) superlattice film by measuring cross-plane electrical and thermal conductivity and Seebeck coefficient using the 3-omega method and an in-house Seebeck coefficient measurement system recently developed for 300-500 K and examine how ZT factors depend on the AO layer inside the AO/ZnO superlattice film using measured thermoelectric properties. The AO/ZnO superlattice film exhibited maximum power factor of similar to 276.2 mu W/m K-2 with low thermal conductivity (similar to 0.31 W/m K), producing ZT >= 0.45 at 500 K, which is approximately 2,650% improvement compared with an undoped ZnO film (similar to 0.017). The enhanced ZT performance of the AO/ZnO superlattice film can be explained by enhanced phonon scattering at the interface and minority carrier blocking at the interfacial barrier due to the AO layer, suggesting that the interfacial AO layer is important to enhance ZT in oxide-based films. These results open new applications for micro- or nanoscale thin film-based thermoelectric devices.