Rediscovering the MP15 Family (M = Li, Na, and K) as an Anisotropic Layered Semiconducting Material.

The binary alkaline metal phosphides family MP15 (M = Li, Na, K) exhibiting a layered structure nature and in-plane anisotropy is discussed through first principles. Their thickness-dependent bandstructures are reported for the first time. Furthermore, the transport studies demonstrate that single-layer MP15 exhibits a large anisotropic ratio for carrier mobility (both electron and hole) (∼101-102 magnitude) between two special crystal directions, which is the record high value among the reported two-dimensional anisotropic materials. Additionally, the chemical stability under ambient conditions and the binding energy which relates to experimental exfoliation are also investigated. The high anisotropy of the layered semiconducting MP15 family could open up considerable promise for anisotropic optics, electronics, optoelectronics devices, and energy storage applications.