Thermoelectric Properties of Zn0.98Al0.02O Thin Films Prepared by RF Magnetron Sputtering

We investigated the microstructure and thermoelectric properties of oriented Zn0.98Al0.02O thin films prepared by RF magnetron sputtering on YSZ(100), YSZ(poly) and MgO(100) substrates. X-ray diffraction studies showed that the c-axis of the crystals was preferentially oriented in the direction perpendicular to the substrate plane. The microstructure and in-plane thermoelectric properties of the films strongly depended on the deposition temperature. The heat-treatment above 550 K in air for the film deposited at room temperature resulted in a marked increase in the electrical resistivity and Seebeck coefficient. This result was explained by a decrease in carrier concentration, which was determined by the Hall effect study. On the other hand, the relative evaluation of the thermal conductivity (κ) for the samples with different average grain sizes suggested that a reduction in κ occurred for the sample with an average grain size of ~50 nm.