First-principle studies on the metal/semiconductor properties and strain-tuned electronic structures of SnP3 monolayer

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Using first-principles calculations, we found several energetically stable structures of monolayer SnP3, which include metal (M−SnP3) and semiconductor (S-SnP3). The structural difference between M−SnP3 and S-SnP3 lies in the buckling angle, which is the reason for the metal–semiconductor transition of SnP3 from bulk to monolayer. When the biaxial strain is applied from −5% to 5%, the buckling decreases and the bond angle increases, leading to the weakened (enhanced) hybridization of the pz (px) orbital and the increase (decrease) of the energy of the corresponding bonding state. Although the biaxial strain of 6% or − 6% does not change the structure of monolayer SnP3 from S-SnP3 to M−SnP3, a large enough compressive strain will close the band gap of semiconductor SnP3. The uniaxial tensile strain has the same effects, but exhibits anisotropic behaviors on the band near the Fermi level. There are similar situations for GeP3 and GeSnP6, which have the same valence electrons. By the investigation of structural characteristics and atomic orbital compositions, this work reveals the mechanism of strain-tuned band structures and metal–semiconductor properties, which is useful for band engineering of two-dimensional materials.