Multifunctional Binary Monolayers GexPy: Tunable Band Gap, Ferromagnetism, and Photocatalyst for Water Splitting

The most stable structures of two-dimensional GexPy and GexAsy monolayers with different stoichiometries (e.g., GeP, GeP2, and GeP3) are explored systematically through the combination of the particle-swarm optimization technique and density functional theory optimization. For GeP3, we show that the newly predicted most stable C2/m structure is 0.16 eV/atom lower in energy than the state-of-the-art P (3) over bar m1 structure reported previously (Nano Lett. 2017, 17, 1833). The computed electronic band structures suggest that all the stable and metastable monolayers of GexPy are semiconductors with highly tunable band gaps under the biaxial strain, allowing strain engineering of their band gaps within nearly the whole visible-light range. More interestingly, the hole doping can convert the C2/m GeP3 monolayer from nonmagnetic to ferromagnetic because of its unique valence band structure. For the GeP2 monolayer, the predicted most stable Pmc2(1) structure is a (quasi) direct-gap semiconductor that possesses a high electron mobility of similar to 800 cm(2) V-1 s(-1) along the k(a) direction, which is much higher than that of MoS2 (similar to 200 cm(2) s(-1)). More importantly, the Pmc2(1) GeP2 monolayer not only can serve as an n-type channel material in field-effect transistors but also can be an effective catalyst for splitting water.