Step-Edge-Guided Growth of Single-Crystalline γ-Bi ₂ O ₃ with Unidirectional Orientation as a High-κ Dielectric for 2D Transistors

2D dielectrics are promising for next-generation integrated circuits, yet the development of high-performance 2D dielectrics is hindered by challenges such as a low crystallinity, insufficient dielectric constant, and lack of scalable synthesis. Here, we present a chemical vapor deposition technique that enables step-edge-guided growth of single-crystalline γ-Bi 2 O 3 with unidirectional orientation on the C/M sapphire substrate with a miscut angle of 0.2 ± 0.05°. The obtained γ-Bi 2 O 3 films exhibit exceptional dielectric properties, including a high dielectric constant of 39.38 and an ultralow leakage current density of 2.5 × 10 –5 A cm –2 . With integration into top-gated γ-Bi 2 O 3 /MoS 2 field-effect transistors, the devices achieve a high on/off ratio exceeding 10 6, a near-ideal subthreshold swing of 80 mV dec –1, and a small hysteresis window of 19 mV, along with excellent thermal stability over 300–450 K and prolonged environmental stability over 4 months. These results establish γ-Bi 2 O 3 as a compelling high-κ dielectric candidate to address scaling challenges in low-power nanoelectronics.