Novel two-dimensional Janus β-Ge 2 XY (X/Y = S, Se, Te) structures: first-principles examinations.

Two-dimensional (2D) structures can stably exist in different allotropes. In this manuscript, we propose a new series of Janus structures based on the β-phase of germanium monochalcogenides, namely, β-Ge 2 XY (X/Y = S, Se, and Te) monolayers. Our calculations indicate that Janus β-Ge 2 XY monolayers have a stable crystal structure and possess anisotropic mechanical properties. At the ground state, β-Ge 2 XY monolayers are semiconductors with a large bandgap and their electronic properties depend strongly on a biaxial strain. Strains not only change the bandgap but can also lead to a change in the bandgap characteristic, namely transitions from indirect to direct bandgap. Our findings not only introduce a new structure of germanium chalcogenide compounds but also show that they have superior physical properties suitable for applications in nanoelectronics.