Hybrid solution processed InGaO ₃(ZnO) _m thin films with periodic layered structures and thermoelectric properties

Short period superlattices comprising alternating InO ₂ ^- and GaO ⁺(ZnO) ₂ layers were fabricated by a simple hybrid solution process and reactive solid-phase epitaxy at high temperature. The epitaxial ZnO buffer layer deposited by sputtering, and an amorphous IGZO layer fabricated from a solution mixture of 1:1:1.0 (In nitrate:Ga nitrate:Zn acetate) produced pure, single-phase InGaO ₃(ZnO) ₂ films with a well-ordered layered structure and smooth surfaces, which showed intense periodic diffraction peaks. Deviation from the stoichiometric sol condition induced coexisting InGaO ₃(ZnO) ₂ and other InGaO ₃(ZnO) _m phases and very rough surface morphologies. The solid-phase epitaxy of a single phase decreased electrical resistivity, increased the Seebeck coefficient, and significantly improved the power factor. An extremely low thermal conductivity (1.11 W m ^-1 K ^-1) was also obtained due to phonon scattering at the InO ₂ ^- and GaO ⁺(ZnO) ₂ interfaces by the formation of the superlattice structure. This solution-based fabrication of superlattice structures could aid the development of advanced multicomponent oxides due to its simple growth process and the adaptability of compositions.