2D edge-seeded heteroepitaxy of ultrathin high-κ dielectric CaNb₂O₆ for 2D field-effect transistors

The experimental realization of single-crystalline high-κ dielectrics beyond two-dimensional (2D) layered materials is highly desirable for nanoscale field-effect transistors (FETs). However, the scalable synthesis of 2D nonlayered high-κ insulators is currently limited by uncontrolled isotropic three-dimensional growth, hampering the achievement of simultaneous high dielectric constants and low trap densities for small film thicknesses. Herein, we show a 2D edge-seeded heteroepitaxial strategy to synthesize ultrathin nonlayered 2D CaNb₂O₆ nanosheets by chemical vapor deposition, exhibiting high-crystalline quality, thickness-independent dielectric constant (~ 16) and breakdown field strength up to ~ 12 MV cm⁻¹. The MoS₂/CaNb₂O₆ FETs exhibit an on/off ratio of over ~ 10⁷, a subthreshold swing down to 61 mV/dec and a negligible hysteresis. This work suggests a universal 2D edge-seeded heteroepitaxy and slow kinetic strategy for the scalable growth of 2D nonlayered dielectric and demonstrates 2D CaNb₂O₆ nanosheets as promising dielectrics for facilitating 2D electronic applications.