Van der Waals Epitaxy Growth and Characterization of 7:7:8 Commensurate Heterointerfaces between h-AlN and Two-Dimensional WS₂/c-Al₂O₃

Abstract

In this study, hexagonal AlN (h-AlN) thin films were grown on a two-dimensional (2D)-WS 2 /Al 2 O 3 substrate by radio frequency−metalorganic molecular beam epitaxy at 800 °C. We examined the influence of various RF plasma powers on the synthesis and characterization of AlN/WS 2 heterostructures, as well as their properties, for optoelectronic applications. In-plane grazing incidence X-ray diffraction results indicated that the h-AlN thin films grown on 2D-WS 2 /Al 2 O 3 (0001) are oriented along (100) and ( 110) planes, indicating epitaxial growth with orientation relationships between AlN(101̅ 0)//WS 2 (101̅ 0)//Al 2 O 3 (112̅ 0) and AlN(112̅ 0)//WS 2 (112̅ 0)//Al 2 O 3 (112̅ 0). The full width at half-maximum values of the AlN thin film at 300 W of RF power were measured to be 260 and 1400 arcsec for (0002) and (101̅ 0) reflections, respectively. Transmission electron microscopy images show that the AlN (0002) films can grow epitaxially with the WS 2 /Al 2 O 3 substrate and that the film structure is nearly stoichiometric in composition. In addition, the AlN film was measured to be approximately 50 nm thick. The AlN surface corresponds to the (0002) plane of AlN, and a direct measurement based on the lattice image yielded a lattice parameter of c = 4.98 Å. Additionally, the high-resolution cross-sectional transmission electron microscopy images show that the 50 nm-thick AlN film on WS 2 has relaxed lattice parameters and is a layered structure with an in-plane lattice match aligned with the underlying WS 2 lattice. This is evidence of domain-matching epitaxy with an atomic ratio of 7:7:8, demonstrating a commensurate match among AlN, WS 2 , and Al 2 O 3 . These results will have a significant impact on the heteroepitaxy of high-quality thin AlN films with a WS 2 buffer and will facilitate the preparation of nitride-based optoelectronic devices at low growth temperatures.