High carrier mobility and moderate band gap are two key properties of electronic device applications. Two ultrathin two-dimensional (2D) semiconductors, namely, Bi₂Te₂S and Bi₂Te₂Se nanosheets, with novel electronic and optical properties are predicted based on first-principles calculations. The Bi₂Te₂S and Bi₂Te₂Se monolayers own moderate band gaps (∼0.7 eV) and high electron mobilities (∼20 000 cm² V^–1 s^–1), and they can absorb sunlight efficiently through the whole incident solar spectrum. Meanwhile, layer-dependent exponential decay band gaps are also unveiled. The relatively low interlayer binding energies suggest that these monolayers can be easily exfoliated from bulk structures. Their high dynamical and thermal stabilities are further verified by phonon dispersion calculations and ab initio molecular dynamics simulations. The exceptional properties render Bi₂Te₂X (X = S, Se) monolayers promising candidates in future high-speed (opto)electronic devices.

中文翻译：

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具有高电子迁移率的超薄半导体Bi ₂ Te ₂ S和Bi ₂ Te ₂ Se

高载流子迁移率和适度的带隙是电子设备应用程序的两个关键特性。基于第一性原理计算，预测了具有新颖的电子和光学特性的两种超薄二维（2D）半导体，即Bi ₂ Te ₂ S和Bi ₂ Te ₂ Se纳米片。Bi ₂ Te ₂ S和Bi ₂ Te ₂ Se单层具有中等的带隙（〜0.7 eV）和高的电子迁移率（〜20 000 cm ² V ^–1 s ^–1）），它们可以在整个入射太阳光谱中有效吸收太阳光。同时，还揭示了依赖于层的指数衰减带隙。相对较低的层间结合能表明，这些单层很容易从整体结构上剥落。它们的高动力学和热稳定性已通过声子色散计算和从头算分子动力学模拟得到了进一步验证。优异的性能使Bi ₂ Te ₂ X（X = S，Se）单层有望成为未来高速（光电）电子设备的候选材料。