ZnO/Silicon-Rich Oxide Superlattices with High Thermoelectric Figure of Merit: A Comprehensive Study by Experiment and Molecular Dynamic Simulation.

Abstract

ZnO is a direct band gap material that has numerous optoelectronic applications. Recently, the thermoelectric behavior of ZnO has drawn much attention because it is expected to enrich the multifunctional application of ZnO. However, the high thermal conductivity nature of ZnO (∼50 W/(m·K)) is a challenge to further increase its thermoelectrtic figure of merit ( ZT). In this paper, a way to increase the ZT of ZnO thin films by insertion of silicon-rich oxide (SRO) interlayers is reported. All of the constituents are earth-abundant and environmental friendly. The effects of the number of SRO layers, thickness, grain size, heat treatment, and crystallinity of ZnO of the superlattices on the thermoelectric behaviors of ZnO were investigated. The thermoelectric ZT was determined by the transient Harman method by measuring the Seebeck voltage. The thermal conductivity of the ZnO/SRO superlattices that is crucial to elucidate the ZT behaviors is calculated using molecular dynamic simulation, in which the Zn-O and Zn-Zn interactions were described by the Born-Mayer potential and the short-range non-Coulombic O-O interaction was described by the Morse potential. For a given total ZnO/SRO thickness, the grain size of the ZnO decreases monotonically with the increasing number of SRO layers, thus leading to a decrease of the thermal conductivity and an increase of the ZT of the superlattices. As the best result, the annealed 45 nm thick ZnO thin film with three SRO interlayers presents a high ZT of ∼0.16 at room temperature. A comprehensive study on the ZnO/SRO superlattice-based thermoelectrtic devices was carried out by the experiment and theoretical simulation. The results imply potential thermoelectric application of the ZnO/SRO superlattices.