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 MoSx(0001) (x = 2.0 ± 0.1) thin films on Al2O3(0001) substrates. hBN layers are grown on Al2O3(0001) via pyrolytic cracking of borazine (∼6 × 104 L) at 1373 K and the MoSx layers are deposited in an ultrahigh-vacuum system via reactive direct-current magnetron sputtering of Mo in an Ar/H2S gas mixture at 1073 K on bare and hBN-covered Al2O3(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 MoSx layer composition and crystallinity. We obtain highly 0001-oriented, ∼20-nm-thick, 2H-structured MoSx multilayers with better crystalline quality on hBN/Al2O3(0001) than on Al2O3(0001). We suggest that hBN buffer layer enhances surface diffusion of depositing species, compared to bare Al2O3(0001), leading to an observed improvement in the crystallinity of MoSx layers. We expect that our results are likely to have broad implications in nanoelectronic device fabrication.