Using evolutionary structure search combined with ab initio theory, we investigate the electronic, thermal, and mechanical properties of two-dimensional (2D) A₂B (A = Cu, Ag, Au, and B = S, Se) auxetic semiconductors. Two types of structures are found to have low energy, namely, s(I/II)-A₂B, which have direct bandgaps in the range 1.09–2.60 eV and high electron mobilities. Among these semiconductors, Cu₂B and Ag₂B have light holes with 2 orders of magnitude larger mobility than the heavy holes, up to 9.51 × 10⁴ cm² V^–1 s^–1, giving the possibility of achieving highly anisotropic hole transport with the application of a uniaxial strain. Due to the ionic bonding nature, s-A₂B structures have unusually low lattice thermal conductivities down to 1.5 W m^–1 K^–1 at 300 K, which are quite promising for new generation thermoelectric devices. Besides, s-A₂B structures show extraordinary flexibility with ultralow Young’s moduli (down to 20 N/m), which are lower than most previously reported 2D materials. Moreover, under strain along the diagonal direction, five of the structures have in-plane negative Poisson’s ratios.

中文翻译：

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二维Square-A ₂ B（A = Cu，Ag，Au和B = S，Se）：具有高载流子迁移率和异常低的晶格热导率的辅助半导体

使用进化结构搜索结合从头算理论，我们研究了二维（2D）A ₂ B（A = Cu，Ag，Au和B = S，Se）半导体的电子，热和机械性能。发现两种类型的结构具有低能量，即s（I / II）-A ₂ B，它们的直接带隙在1.09–2.60 eV范围内，并且电子迁移率高。在这些半导体中，Cu ₂ B和Ag ₂ B的轻孔的迁移率比重孔大2个数量级，最高达9.51×10 ⁴ cm ² V ^–1 s ^–1通过施加单轴应变，可以实现高度各向异性的空穴传输。由于离子键的性质，sA ₂ B结构在300 K时具有异常低的晶格热导率，低至1.5 W m ^–1 K ^–1，这对于新一代热电器件是非常有前途的。此外，sA ₂ B结构具有超低的杨氏模量（低至20 N / m），显示出非凡的柔韧性，比以前报道的大多数2D材料要低。而且，在沿对角线方向的应变下，五个结构具有面内负泊松比。