Van der Waals epitaxy and composition control of layered SnS x Se 2− x alloy thin films

Epitaxial SnS x Se 2− x films with tunable band gap energies (1.0–2.2 eV) are of growing interest for photodetectors and 2D heterostructures for nanoscale electronics. In this study, powder vapor transport growth of SnS x Se 2− x was investigated on c -plane sapphire and epitaxial graphene (EG)/6H–SiC substrates using tin, sulfur, and selenium powder sources in a heated tube furnace. The SnS x Se 2− x composition was controlled by varying the sulfur and selenium source temperatures and the corresponding chalcogen vapor pressure ratio. Raman spectroscopy was used to determine the alloy composition of the films, and the optical properties were characterized using UV-Vis-NIR spectroscopy. SnS x Se 2− x grown on sapphire consisted of vertically oriented platelets. By contrast, large-area, planar coalesced SnS x Se 2− x films grew on EG with low surface roughness indicative of a van der Waals growth mode. High-resolution X-ray diffraction θ–2θ scans and pole figure analysis confirm that the SnS x Se 2− x films are c -axis oriented with epitaxial relation being $\left[ {11\bar{2}0} \right]$ SnS x Se 2− x ‖ $\left[ {10\bar{1}0} \right]$ 6H–SiC.