The emergence of metallic conduction in layered dichalcogenide semiconductor materials by chemical doping is one of key issues for two-dimensional (2D) materials engineering. At present, doping methods for layered dichalcogenide materials have been limited to an ion intercalation between layer units or electrostatic carrier doping by electrical bias owing to the absence of appropriate substitutional dopant for increasing the carrier concentration. Here, we report the occurrence of metallic conduction in the layered dichalcogenide of SnSe 2 by the direct Se-site doping with Cl as a shallow electron donor. The total carrier concentration up to ∼10 20 cm ' '3 is achieved by Cl substitutional doping, resulting in the improved conductivity value of ∼170 S·cm ' '1 from ∼1.7 S·cm ' '1 for non-doped SnSe 2. When the carrier concentration exceeds ∼10 19 cm ' '3, the conduction mechanism is changed from hopping to degenerate conduction, exhibiting metal-insulator transition behavior. Detailed band structure calculation reveals that the hybridized s-p orbital from Sn 5s and Se 4p states is responsible for the degenerate metallic conduction in electron-doped SnSe 2.
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