It is found that many two-dimensional materials are easy to obtain out-of-plane piezoelectric properties because of their Janus structure. Here, based on the monolayer GeSe and SnSe, we study the electronic structure and piezoelectricity of the Janus M ₂ SeX (M=Ge, Sn; X=S, Te) monolayers. Due to the lack of inversion symmetry and mirror symmetry, as well as flexible mechanical properties, the 2D Janus M ₂ SeX monolayers have large in-plane piezoelectric coefficients d ₁₁ (up to 345.08pm/V) and out-of-plane piezoelectric coefficients d ₃₁ (up to 3.83pm/V). All energy band structures of two-dimensional (2D) Janus M ₂ SeX monolayers show indirect bandgap and Zeeman-type spin splitting after considering spin orbit coupling (SOC). The lack of mirror symmetry leads to out-of-plane spin polarization. In addition, the calculation based on the deformation potential theory shows that the 2D Janus M ₂ SeX monolayers have high carrier mobility. The large piezoelectric properties and high carrier mobility show the application potential of 2D Janus M ₂ SeX monolayers in flexible electronic devices and piezoelectric devices.

中文翻译：

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Janus M 2 SeX（M = Ge，Sn; X = S，Te）单层的巨大压电

发现许多二维材料由于其Janus结构而易于获得面外压电特性。在这里，基于单层GeSe和SnSe，我们研究了Janus M ₂ SeX（M = Ge，Sn; X = S，Te）单层的电子结构和压电性 。由于缺乏反演对称性和镜像对称性以及灵活的机械性能，二维Janus M ₂ SeX单层具有较大的面内压电系数d ₁₁（最高345.08pm / V）和面外压电系数d ₃₁（最高3.83pm / V）。二维（2D）Janus M _2的所有能带结构 考虑自旋轨道耦合（SOC）后，SeX单层显示间接带隙和塞曼型自旋分裂。缺乏镜面对称性会导致面外自旋极化。此外，基于变 形势理论的计算表明，二维Janus M ₂ SeX单层具有较高的载流子迁移率。大压电性能和高载流子迁移率表明2D Janus M ₂ SeX单层在柔性电子设备和压电设备中的应用潜力 。