Half-Hydrogenated Monolayer Group III Monochalcogenides: Wide Direct Band Gaps and Potential Photocatalysts for Water Splitting

We have theoretically proposed previously unknown half-hydrogenated nanosheets, monolayer H-MX (M = Ga and In, X = S, Se, and Te) via first-principles simulations. The analysis of phonon model and cohesive energy indicates that these monolayer H-MX are stable both in dynamics and in energy. On the basis of hybrid functional methods, we find that the systems are wide-direct-band gap semiconductors with their band structures satisfying the requirement of photocatalytic water splitting. Furthermore, our calculations show that the systems have major optical absorption in ultraviolet region. Through applying the biaxial strain to monolayer H-GaSe, we obtain that biaxial strain can effectively tune their optical and electronic properties and even induce transition from direct band gap to indirect band gap, which reveals that biaxial strain is a feasible way to improve the potential application of monolayer H-MX. Our research paves the way for developing the high-energy and high-frequency optoelectronic devices as well as improving the potential photocatalysts for water splitting based on these half-hydrogenated nanosheets.