Formation of homologous In2O3(ZnO) m thin films and its thermoelectric properties

Homologous In2O3(ZnO)5 thin films were produced on a synthetic quartz glass substrate by thermal annealing of magnetron sputtered In2O3-ZnO compound films. When the annealing temperature was increased to 700 °C, the sputtered In2O3-ZnO film with In2O3 microcrystalline changed to a c-oriented homologous In2O3(ZnO)5 structure, for which the crystallization is suggested to begin from the surface and proceed along with the film thickness. The annealing temperature of 700 °C to form the In2O3(ZnO)5 structure was substantially lower than temperatures of conventional solid state synthesis from In2O3 and ZnO powders, which is attributed to the rapid diffusional transport of In and Zn due to the mixing of In2O3 and ZnO in the atomic level for sputtered In2O3-ZnO compound films. The homologous structure collapsed at temperatures above 900 °C, which is attributed to (1) zinc vaporization from the surface and (2) a gradual increase of zinc silicate phase at the interface. This c-oriented layer structure of homologous In2O3(ZnO)5 thin films along the film thickness allowed the thin film to reach a power factor of 1.3 × 10−4 W/m K2 at 670 °C, which is comparable with the reported maximum value for the textured In2O3(ZnO)5 powder (about 1.6 × 10−4 W/m K2 at 650 °C).