Van der Waals Epitaxy of High-Quality Transition Metal Dichalcogenides on Single-Crystal Hexagonal Boron Nitride

Van der Waals (vdW) heterostructures comprising of transition metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN) are promising building blocks for novel 2D devices. The vdW epitaxy provides a straightforward integration method for fabricating high-quality TMDs/h-BN vertical heterostructures. In this work, the vdW epitaxy of high-quality single-crystal HfSe2 on epitaxial h-BN/sapphire substrates by chemical vapor deposition is demonstrated. The epitaxial HfSe2 layers exhibit a uniform and atomically sharp interface with the underlying h-BN template, and the epitaxial relationship between HfSe2 and h-BN/sapphire is determined to HfSe2 (0001)[12<overline>${\mathrm{\bar{2}}}$10]//h-BN (0001)[11<overline>${\mathrm{\bar{1}}}$00]//sapphire (0001)[11<overline>${\mathrm{\bar{1}}}$00]. Impressively, the full width at half maximum of the rocking curve for the epitaxial HfSe2 layer on single-crystal h-BN is as narrow as 9.6 arcmin, indicating an extremely high degree of out-plane orientation and high crystallinity. Benefitting from the high crystalline quality of HfSe2 epilayers and the weak interfacial scattering of HfSe2/h-BN, the photodetector fabricated from the vdW epitaxial HfSe2 on single-crystal h-BN shows the best performance with an on/off ratio of 1 x 104 and a responsivity up to 43 mA W-1. Furthermore, the vdW epitaxy of other TMDs such as HfS2, ZrS2, and ZrSe2 is also experimentally demonstrated on single-crystal h-BN, suggesting the broad applicability of the h-BN template for the vdW epitaxy. Several high-quality single-crystalline transition metal dichalcogenides are directly grown on an epitaxial h-BN/sapphire substrate via vdW epitaxy, indicating the h-BN is an ideal template for vdW epitaxy. The full width at half maximum of the X-ray diffraction rocking curve for the HfSe2 layers on single-crystal h-BN is only 9.6 arcmin, indicating an extremely high degree of out-plane orientation and high crystallinity. image