CaP: 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 CaP 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 19 930 cm V s, comparable to that of monolayer phosphorene. More remarkably, contrary to bilayer phosphorene which possesses dramatically reduced carrier mobility compared to its monolayer counterpart, CaP bilayer possesses even higher electron mobility (22 380 cm V s) than its monolayer counterpart. The band gap of 2D CaP can be tuned over a wide range from 1.15 to 0.37 eV (HSE06 values) through controlling the number of stacked CaP layers. Besides novel electronic properties, 2D CaP also exhibits optical absorption over the entire visible-light range. The combined novel electronic, charge mobility, and optical properties render 2D CaP an exciting functional material for future nanoelectronic and optoelectronic applications.