CaP₃: A New Two-Dimensional Functional Material with Desirable Band Gap and Ultrahigh Carrier Mobility

Two-dimensional (2D) semiconductors with direct and modest band gap and ultrahigh carrier mobility are highly desired functional materials for nanoelectronic applications. Herein, we predict that monolayer CaP₃ is a new 2D functional material that possesses not only a direct band gap of 1.15 eV (based on HSE06 computation) but also a very high electron mobility up to 19930 cm² V^-1 s^-1, comparable to that of monolayer phosphorene. More remarkably, contrary to bilayer phosphorene which possesses dramatically reduced carrier mobility compared to its monolayer counterpart, CaP₃ bilayer possesses even higher electron mobility (22380 cm² V^-1 s^-1) than its monolayer counterpart. The band gap of 2D CaP₃ can be tuned over a wide range from 1.15 to 0.37 eV (HSE06 values) through controlling the number of stacked CaP₃ layers. Besides novel electronic properties, 2D CaP₃ also exhibits optical absorption over the entire visible-light range. The combined novel electronic, charge mobility, and optical properties render 2D CaP₃ an exciting functional material for future nanoelectronic and optoelectronic applications.