Superior mechanical flexibility and strained-engineered direct-indirect band gap transition of green phosphorene

Most recently, a phosphorus allotrope called green phosphorus has been predicted, which has a direct bandgap up to 2.4 eV, and its single-layer form termed green phosphorene shows high stability. Here, the mechanical properties and the uniaxial strain effect on the electronic band structure of green phosphorene along two perpendicular in-plane directions were investigated. Remarkably, we found that this material can sustain a tensile strain in the armchair direction up to a threshold of 35% which is larger than that of black phosphorene, suggesting that green phosphorene is more puckered. Our calculations also show that the Young's modulus and Poisson's ratio in the zigzag direction are four times larger than those in the armchair direction, which confirms the anisotropy of the material. Furthermore, the uniaxial strain can trigger the direct-indirect bandgap transition for green phosphorene, and the critical strains for the bandgap transition are revealed.