Crystallization growth of layer-controlled ultra-flat hBN single-crystal films with high insulation

Hexagonal boron nitride (hBN), an insulating two-dimensional (2D) material, is widely regarded as an ideal dielectric layer for 2D-based functional devices. Nevertheless, achieving wafer-scale ultra-flat hBN films with uniform thickness and high insulating properties remains a significant challenge. Here, we demonstrate the controlled growth of ultra-flat hBN single-crystal wafers with well-defined layer numbers tuned from one to eight. These hBN films are crystallized from amorphous precursors with predefined thickness, resulting in ultra-flat surfaces, uniform AA’ stacking order and single-crystal features. These ultra-flat films demonstrate excellent insulating performances across the entire wafer, with breakdown fields of 10 – 12 MV/cm and leakage current densities below 10-13 A/cm2. They can be directly employed as dielectric layers for high-performance graphene electronic devices. These highly insulating, wafer-scale ultra-flat hBN wafers will further accelerate the next-generation 2D-based multifunctional devices.