Computational discovery of two-dimensional tetragonal group IV–V monolayers

The two-dimensional (2D) hexagonal group IV-V family has attracted significant attention due to their unique properties and potential applications in electronics, spintronics, and photocatalysis. In this study, we report the discovery of a stable tetragonal allotrope, termed the Td4 phase, of 2D IV-V monolayers through a structural search utilizing an adaptive genetic algorithm. We investigate the geometric structures, structural stabilities, and band structures of the Td4-phase 2D IV-V monolayers (where IV = Si, Ge, Sn; V = P, As, Sb) based on the first-principles calculations. All the investigated 2D IV-V monolayers are dynamically and thermodynamically stable, and exhibit metallic behavior in their pristine form. Furthermore, we investigate the effects of surface hydrogenation on the electronic structures of these monolayers. Except for the hydrogenated GeSb monolayer, the remaining 2D IV-V monolayers turn into indirect semiconductors, with band gap values ranging from 0.15 to 1.12 eV. This work expands the known structural motifs within the 2D group IV-V family and contributes to the ongoing exploration of low-dimensional materials.