Spontaneous van der Waals epitaxy of high-quality 2D chalcogenide thin film

Explosive interests have been focused on layer structured two-dimensional (2D) chalcogenides due to the discoveries of exotic physical properties, such as high-performance thermoelectricity, superior carrier mobility, ultrafast charge transfer, topological insulator, and superconductivity. In parallel, the demands on high-quality 2D chalcogenide films for device applications are increasing since such properties originate from their unique structural ordering and depend on crystal quality. However, the difficulties in controlling epitaxy with defect density, the lack of suitable substrate, and the limited understanding of growth mechanism for 2D chalcogenide film have been major obstacles for the further advances of these materials. We demonstrate new approaches enabling the vdWE of 2D chalcogenide epitaxial films on conventional substrates. As a proof of concept, highly-oriented bismuth antimony telluride thermoelectric films were epitaxially grown on 2D (graphene) and 3D (α-Al₂O₃) substrates by pulsed laser deposition via vdWE utilizing the natural surface reaction of the substrate with chalcogen. It was confirmed that this unusual vdWE renders the high-quality 2D chalcogenide film with high carrier mobility, low defect density, and exceptionally low thermal conductivity.