Hybrid solution processed InGaO3(ZnO)m thin films with periodic layered structures and thermoelectric properties

Abstract

Short period superlattices comprising alternating InO₂⁻ 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 InGaO₃(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 InGaO₃(ZnO)₂ and other InGaO₃(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 InO₂⁻ 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.