SnxPy Monolayers: a New Type of Two-Dimensional Materials with High Stability, Carrier Mobility, and Magnetic Properties

Searching for two-dimensional (2D) group V materials with ferromagnetism, elastic anisotropy, and carrier mobility and tunable band structure is one key to developing constantly developing nanodevices. The 2D monolayers Sn_xP_y with x/y (1/1, 1/2, 1/3, and so on) coordination number are studied based on the particle-swarm optimization technique combined with the density functional theory optimization. Its thermal stability can be confirmed by molecular dynamics at 70K and 300K, indicating that the novel 2D materials have a stable existence. The electronic band structures of four stable structures suggest that all the monolayers of Sn_xP_y are fully adjustable and flexible tunable band gaps semiconductors under the biaxial strain. The monolayer of P4¯21m-SnP₂ with unique valence band structure can go from nonmagnetic to ferromagnetic by the hole doping because of the "Stoner criterion," and Pmc2₁-SnP₂ is a direct-like gap semiconductor with in-plane elastic anisotropy to possess a high electron mobility as high as 800 cm²V^‑1 s^‑1 along the k_b direction, which is much higher than that of MoS₂ (∼ 200 cm²V^‑1 s^‑1). The optical absorption peak of the material is in the ultraviolet region. These discoveries expand the potential applications of the emerging field of 2D Sn_xP_y structures in nanoelectronics.