Thermoelectric Properties of (ZnO)₅In₂O₃Thin Films Prepared by r.f. Sputtering Method

抄録

We have reported that the thermoelectric figures of merit (Z) of the sintered bodies of layered structured (ZnO)mIn₂O₃, (m=5, 7, and 9) are comparatively large among the semiconducting oxides. In this work, (ZnO)5In2O3 thin films were prepared by r.f. (radio frequency) sputtering method to clarify their anisotropic nature. Under optimum sputtering conditions, (ZnO)₅In₂O₃ thin films developed either (0021) or (110) crystallographic preferred orientation and had dense columnar structures. For c-axis and ab-plane oriented (ZnO)₅In₂O₃ thin films, Seebeck coefficient (α) and electrical conductivity (σ) along the sheet direction were measured at 573-973K. Electrical conductivity of a c-axis oriented thin film was about an order of magnitude higher than that of an ab-plane oriented thin film, while their Seebeck coefficients were substantially the same. This observation suggests that the carrier mobility of (ZnO)₅In₂O₃ along the c-plane is larger than along the ab-plane.