Controllable Synthesis of δ′-Ta₂O₅ Single Crystals as a High-κ Dielectric for 2D Transistors

The continued scaling of integrated transistors faces fundamental limitations, primarily due to severe gate leakage and reliability degradation at sub-nanometer dielectric thicknesses. High-quality, wide-bandgap high-κ dielectrics are therefore essential to enable further device miniaturization and energy-efficient operation. Here, we report the synthesis of a novel hexagonal δ′-tantalum pentoxide (δ′-Ta₂O₅) via a molten-salt-assisted chemical vapor deposition (CVD) method combined with a spatial confinement strategy. This material exhibits single-crystalline characteristics with an exceptionally high dielectric constant (κ ≈ 42.8), a large breakdown field (>7.23 MV cm⁻¹), and a wide bandgap (∼3.78 eV). When integrated as a top-gate dielectric in graphene and molybdenum disulfide (MoS₂) field-effect transistors (FETs), δ′-Ta₂O₅ enables outstanding device performance: an equivalent oxide thickness (EOT) as low as 2.03 nm, a near-Boltzmann-limit subthreshold swing of 62.4 mV dec⁻¹, and gate leakage currents on the order of 10⁻⁶ A cm⁻². These results establish δ′-Ta₂O₅ as a promising high-κ dielectric platform for low-power, high-performance electronics beyond the silicon scaling roadmap.