All In-Plane Thermoelectric Properties of Atomic Layer Deposition-Grown Al₂O₃/ZnO Superlattice Film in the Temperature Range from 300 to 500 K

We report in-plane thermoelectric (TE) properties of Al₂O₃ (AO)/ZnO superlattice films at high temperatures. The films were prepared at 523 K on a 300-nm-thick SiO₂/Si substrate by atomic layer deposition (ALD), and their in-plane electrical and TE properties were evaluated. The measurement of the in-plane TE properties such as Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (κ) of the AO/ZnO superlattice were carried out in the temperature range from 300 to 500 K. The S, σ, and κ were found to be approximately –22.3 and –39.9 μV/K, 856 and 851 (Ω·cm)^–1, and 1.04 and 1.04 W/m · K at 300 K and 500 K, respectively, indicating that σ and κ remained unchanged with increasing temperature up to 500 K. In contrast, S linearly increased to ∼39.9 μV/K with increasing temperature. Finally, the in-plane TE figure of merit (ZT) of the superlattice films at 500 K was calculated as ∼0.013, which is ∼3.3 times more than that of the AO/ZnO films (ZT ∼0.004) at 300 K. Our results clearly exhibit that the in-plane TE performance of the AO/ZnO films was significantly enhanced as compared to that of the bulk materials due to the enhanced phonon scattering at the interface of the films and the formation of nanograin columnar structure in the film. We strongly believe that the AO/ZnO superlattice films can be applied to high-temperature TE devices such as cooling and power generation devices.