Combinatorial Co-Sputtering of Mg-Bi-O Thin Films: Structural Evolution and Tunable Optoelectronic Properties

Abstract

Binary and ternary metal oxides offer diverse functionalities, enabling their use in photovoltaics, transparent conductors, water-splitting catalysts, and topological insulators. Despite this potential, many novel oxide systems remain underexplored for thin film solar energy applications. In this work, we present the first high-throughput investigation of magnesium bismuth oxide (Mg_xBi_yO_z) thin films using combinatorial co-sputtering across a wide compositional space. An integrated characterization workflow combining synchrotron-based grazing-incidence wide-angle X-ray scattering (GIWAXS) and spectroscopic ellipsometry is employed to systematically map their structural and optical properties. The as-deposited films are predominantly amorphous, with post-deposition annealing up to 450 °C revealing a strong correlation between Mg content and crystallization behavior. These structural transitions directly influence the optical properties, with absorption coefficients and band gaps adjustable between 1.7 and 2.3 eV. This study establishes Mg_xBi_yO_z thin films as a compositionally versatile and optically tunable material system, and demonstrates the potential of combinatorial co-sputtering workflows to accelerate discovery and optimization in complex thin films.