hBN-Layer-Promoted Heteroepitaxy in Reactively Sputter-Deposited MoS_x≈2(0001)/Al₂O₃(0001) Thin Films: Implications for Nanoelectronics

We show that van der Waals (vdW)-bonded hexagonal boron nitride (hBN) promotes heteroepitaxial growth of semiconducting MoS x (0001) ( x = 2.0 ± 0.1) thin films on Al 2 O 3 (0001) substrates. hBN layers are grown on Al 2 O 3 (0001) via pyrolytic cracking of borazine (∼6 × 10 4 L) at 1373 K and the MoS x layers are deposited in an ultrahigh-vacuum system via reactive direct-current magnetron sputtering of Mo in an Ar/H 2 S gas mixture at 1073 K on bare and hBN-covered Al 2 O 3 (0001). Using in situ low-energy electron diffraction and Auger electron spectroscopy along with ex situ X-ray diffraction, X-ray photoelectron and Raman spectroscopies, and transmission electron microscopy, we determine the as-deposited MoS x layer composition and crystallinity. We obtain highly 0001-oriented, ∼20-nm-thick, 2H-structured MoS x multilayers with better crystalline quality on hBN/Al 2 O 3 (0001) than on Al 2 O 3 (0001). We suggest that hBN buffer layer enhances surface diffusion of depositing species, compared to bare Al 2 O 3 (0001), leading to an observed improvement in the crystallinity of MoS x layers. We expect that our results are likely to have broad implications in nanoelectronic device fabrication.