SiTe monolayers: Si-based analogues of phosphorene

Complementing the group of two-dimensional (2D) binary phosphorene analogues, we carried out first-principles calculations for alpha-SiTe and beta-SiTe monolayers which are, respectively, black-phosphorene-like and blue-phosphorene-like. We show that both the SiTe monolayers are dynamically, thermally and mechanically stable, although alpha-SiTe with significant elastic anisotropy is energetically more favorable than beta-SiTe. Both monolayers exhibit superior mechanical flexibility and are indirect-gap semiconductors with band gaps of 0.57 and 2.36 eV, respectively. What is even more important is that the alpha-SiTe monolayer can be tuned from an indirect band gap semiconductor to a direct band gap semiconductor and eventually to a metal when biaxial strains are applied, showing a high degree of flexibility in band engineering which is absent in non-silicon based analogues.