2D Indium Oxide at the Epitaxial Graphene/SIC Interface: Synthesis, Structure, Properties, and Devices

Scaled and high-quality insulators are crucial for fabricating 2D/3D hybrid vertical electronic devices such as metal-oxide-semiconductor (MOS) based Schottky diodes and hot electron transistors, the production of which is constrained by the scarcity of bulk layered wide bandgap semiconductors. In this research, the synthesis of a new 2D insulator, monolayer InO₂, which differs in stoichiometry from its bulk form is presented, over a large area (>300 µm²) by intercalating at the epitaxial graphene (EG)/SiC interface. By adjusting the lateral size of graphene through optical lithography prior to the intercalation, the thickness of InO₂ is tuned such that it is 85% monolayer. The preference for monolayer formation of InO₂ is explained using molecular dynamics and density functional theory (DFT) calculations. Additionally, the bandgap of InO₂ is calculated to be 4.1 eV, differing from its bulk form (2.7 eV). Furthermore, MOS-based Schottky diode measurements on InO₂ intercalated EG/n-SiC demonstrate that the EG/n-SiC junction transforms from ohmic to a Schottky junction upon intercalation, with a barrier height of 0.87 eV and a rectification ratio of ≈10⁵. These findings introduce a new addition to the 2D insulator family, demonstrating the utility of monolayer InO₂ as a barrier in vertical electronic devices.