Oxygen Vacancy Driven Sub-Band Gap Luminescence in Multilayer SnSe ₂ /Graphene Heterostructures

High Resolution Image Download MS PowerPoint Slide The synergy between interfacial interactions and defect states in two-dimensional (2D) heterojunctions plays a critical role in determining their optoelectronic performances. Herein, we investigate the optoelectronic and charge transport properties of chemical vapor deposition-grown multilayer SnSe 2 /graphene heterostructures. Temperature-dependent photoluminescence (PL) and X-ray photoelectron spectroscopy reveal an anomalous, highly efficient visible-range sub-band gap luminescence in multilayer heterojunctions. Detailed analysis indicates that this phenomenon originates from environmental surface oxidation, where a thin SnO x interfacial layer introduces deep-level oxygen vacancy-induced defect states. These defect states effectively trap and pin photoexcited carriers, thereby competing with the steady-state temperature-dependent PL quenching process typically expected at the graphene Dirac point. Overall, this study clarifies the complex physical origins of defect-mediated radiative recombination in SnSe 2 and provides critical insights into utilizing defect engineering to tailor the macroscopic optical and electrical performance of 2D heterostructures for next-generation optoelectronic and quantum devices.