Prediction and synthesis of novel ultra-wide-band-gap semiconducting oxides

Ultra-wide-band-gap (UWBG) semiconductors with band gaps ranging from 3.5 eV to 6.2 eV have emerged as the next frontier in power electronics and UV optoelectronics research. However, state-of-the-art materials such as AlGaN/AlN, diamond, β-Ga₂O₃, and c-BN, suffer from doping asymmetry and/or thermal management. Here I will discuss the theoretical framework that we developed to understand the chemical and structural origins of semiconducting behavior in UWBG semiconductors, and to uncover new UWBG semiconductors that can alleviate the challenges of established materials. Among the UWBG materials surveyed, we identified rutile GeO₂ as an UWBG (4.68 eV) semiconductor with ambipolar dopability and high thermal conductivity. To synthesize the UWBG materials identified by theory, we employed molecular-beam epitaxy using molecular beams from novel suboxide precursors to navigate kinetic pathways and synthesize new phases with narrow phase stability windows. I will present the details of single-crystalline rutile GeO₂ film growth that navigates competing amorphous and hexagonal phases, as well as potential high-mobility p-type oxides with oxidation states that are difficult to synthesize such as SnO and PbO. The findings provide opportunities to realize new materials for UWBG semiconductor research.