Composition controlled superlattice InGaO₃(ZnO)_m thin films by thickness of ZnO buffer layers and thermal treatment

Single crystal InGaO₃(ZnO)_m compound films with a superlattice structure for thermoelectric applications were fabricated on sapphire substrates with epitaxial ZnO buffer layers. Using a buffer layer with an appropriate thickness allows us to form InGaO₃(ZnO)_m films with complete superlattice structures along the c-axis at annealing temperatures below 1000 °C. The crystal phases of the InGaO ₃(ZnO)_m films annealed at 900 °C were assigned to InGaO₃(ZnO)₁ and InGaO₃(ZnO)₂, depending on the thickness of the buffer layer and annealing time. When compared to the as-grown films, these InGaO₃(ZnO)_m films with superlattice structures exhibited both a lower electrical resistivity and higher Seebeck coefficient, due to the quantum confinement effect, resulting in improved thermoelectric properties.