A Layered Wide-Bandgap BiOF Gate Dielectric with a High Dielectric Constant.

The ongoing downscaling of semiconductor devices necessitates gate dielectric materials that simultaneously possess a wide bandgap and ultrahigh dielectric constant to ensure efficient gate control. However, such materials remain scarce due to the inherent trade-off between bandgap widening and dielectric response enhancement in conventional insulators. Here, we demonstrate bismuth oxyfluoride (BiOF) as a promising dielectric candidate with a wide bandgap (Eg ≈ 4.5 eV) and a high out-of-plane dielectric constant (κ = 22.5). Moreover, we develop a scalable solid-state route for synthesizing phase-pure BiOF powder and achieve the chemical vapor deposition (CVD) growth of ultrathin BiOF nanosheets. The free-standing characteristic, temperature-stable dielectric properties, and inert van der Waals (vdW) surface of BiOF facilitate its seamless integration with two-dimensional (2D) materials to enhance device performance. Few-layer graphene double-encapsulated by BiOF demonstrates superior electron Hall mobility (μe,2K ≈ 134,000 cm2 V-1 s-1) and pronounced Shubnikov-de Haas (SdH) oscillations at 2 K. Our work not only expands the library of high-κ vdW materials but also overcomes the intrinsic trade-off between dielectric constant and bandgap.