A combinatorial approach to solution-processed InGaO3(ZnO)m superlattice films: growth mechanisms and their thermoelectric properties

Abstract

Multicomponent amorphous InGaZnO thin films with several metal cations have been synthesized with flexible chemical composition control based on a sol–gel process, and a combinatorial approach through a sol–gel process enables us to perform a systematic survey to fluently find the best film properties. Contrary to amorphous films, crystalline InGaO₃(ZnO)_m requires a refined chemical composition ratio among metal cations. These ratios are expected to affect the growth evolution and thermoelectric properties of two-dimensional InGaO₃(ZnO)_m superlattice structures with various compositional combinations. Here, we explore a combinatorial approach to the ratio of metal cations using various mole fractions of metal precursors in InGaZnO sol for amorphous InGaZnO films fabricated on an epitaxial ZnO buffer layer, and then, they were crystallized with various chemical compositions. The crystallized InGaO₃(ZnO)_m films can be classified as strong single-phase InGaO₃(ZnO)_m, double-phase InGaO₃(ZnO)_m/InGaO₃(ZnO)_m+1, and weak single-phase InGaO₃(ZnO)_m with excess metal ions. Among them, the strong single-phase InGaO₃(ZnO)_m films with superlattice structures showed superior thermoelectric power factors. The detailed microstructural growth evolution of single- and double-phase InGaO₃(ZnO)_m films was investigated using transmission electron microscopy.