Abstract：
Based on the first-principles calculations, ferroelectricBi2O2X(X=S,Se,Te)monolayers with unequivalent in-plane lattice constants are confirmed to be the ground state, which is consistent with the experiment result (Ghoshet al2019Nano Lett.195703-09), and the anisotropic optical property is firstly investigated. We find that the polarizations ofBi2O2Xmonolayers points along the direction ofa-axis, andBi2O2Temonolayer process the largest polarization. Furthermore, both the biaxial and uniaxial strains are favor for the enhancement of polarization ofBi2O2Xmonolayers. It should be mentioned that the type of band gap will convert from indirect to direct forBi2O2Temonolayer when thea-axial tensile strain is larger than 2%. At last, the optical absorption coefficient forBi2O2Xmonolayers are calculated, and we obtain thatBi2O2Temonolayer has the strongest optical absorption within the range of visible light, the anisotropy and possible strain engineering to improve the optical absorption are discussed in detail. Our findings are significant in fields of optoelectronics and photovoltaics.
摘要：
基于fi第一原理计算，铁电Bi2O2X(X=S，Se,Te)具有不相等的面内晶格常数的单层被认为是基态，这与实验结果(NanoLett。19，5703（2019）），并对fi的各向异性光学特性进行了初步研究。我们发现Bi2O2X单层的极化指向a轴方向，而Bi2O2Te单层过程中极化最大。此外，双轴和单轴应变均有利于增强Bi2O2X单层的极化。应该提到的是，当a轴拉伸应变大于2％时，Bi2O2Te单层的带隙类型将从间接转变为直接。最后,计算了Bi2O2X单层的光吸收系数，我们得到Bi2O2Te单层在可见光范围内具有最强的光吸收，详细讨论了改善光吸收的各向异性和可能的应变工程。我们的fi编码在光电和光伏领域具有重要意义。
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