Epitaxial Growth of Single Crystalline Hexagonal Boron Nitride on Vicinal Germanium (110) for Atomically Clean Assembly of Twisted Multilayers

Atomically-thin hexagonal boron nitride (hBN) has gained attentions as a material platform for broad applications in nano-photonics and electronics, including near-infrared waveguide, deep-ultraviolet emitter and dielectric film. Recent studies show that the dielectric and electronic properties of multilayers (ML) can be tuned with control of the interlayer rotational angle, θ. While layer by-layer assembly of singly crystalline hBN can enable fabrications of uniform, polytypical structures, large-scale films for atomically clean assembly is still missing. Here, we report the epitaxial growth of single-layer (SL) hBN fims on wafer-scale, which can be exfoliated and assembled by van der Waals interactions. Chemical vapor deposition on a vicinal (110) surface of germanium with miscut toward the <001> direction results in SL films with a single crystallographic orientation. Density functional theory calculations show that it is energetically favorable for the nitrogen-terminated zig-zag edges of hBN to be aligned to the step edges along the <110>, guiding the unidirectional growth. The SL hBN can be repeatedly grown on a same substrate after mechanical exfoliations, and assembled into twisted MLs with controlled θ. Optical absorption spectra show a clear θ-dependency, suggesting effective modulations of the band structures of hBN. Furthermore, the ML films can be integrated with a semiconducting MoS2 channel with tunable dielectric properties by θ.