Two-dimensional (2D) ultra-wide bandgap (UWBG) semiconductors have attracted tremendous attention because of their unique electronic properties and promising applications. Using first-principles calculations, monolayer (bilayer) CaFCl has a cleavage energy of 0.93 J m⁻² (0.72 J m⁻²), suggesting that the exfoliation of monolayer and few-layer materials from the bulk phase could be feasible. The CaFCl monolayer is an UWBG semiconductor with a direct bandgap of 6.62 eV. In addition to the dynamic and thermodynamic stability, it can remain thermally stable at 2200 K, suitable for operation in high-temperature environments. The bandgap of monolayer CaFCl can be tuned by external strain and layer thickness. The decrease of the layer thickness leads to not only a bandgap increase but also an indirect-to-direct bandgap transition, suggesting a strong interlayer quantum confinement effect. Under biaxial strain, the direct bandgap can also be turned into an indirect one. The adsorption of a tetrathiafulvalene (TTF) molecule introduces deep donor states in the gap of CaFCl. Under an external electric field with direction from CaFCl to TTF, the TTF-derived donor states move closer to the conduction band edge of CaFCl and then the adsorption complex becomes effectively n-doped. Furthermore, monolayer CaFCl exhibits pronounced optical absorption in the ultraviolet range of the solar spectrum. These results render CaFCl an attractive 2D material for applications in flexible nanoelectronic and optoelectronic devices.

中文翻译：

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二维CaFCl：超宽带隙，强层间量子限制和n型掺杂。

二维（2D）超宽带隙（UWBG）半导体因其独特的电子特性和广阔的应用前景而备受关注。使用第一性原理计算，单层（双层）CaFCl的裂解能为0.93 J m ^-2（0.72 J m ^-2），表明从本体相中剥离单层和几层材料可能是可行的。CaFC1单层是UWBG半导体，其直接带隙为6.62 eV。除了动态和热力学稳定性外，它还可以在2200 K下保持热稳定，适合在高温环境下运行。单层CaFCl的带隙可以通过外部应变和层厚来调整。层厚度的减小不仅导致带隙增大，而且导致间接至直接的带隙跃迁，这表明强的层间量子约束效应。在双轴应变下，直接带隙也可以变成间接带隙。四硫富瓦烯（TTF）分子的吸附在CaFCl的间隙中引入了深供体态。在从CaFCl到TTF方向的外部电场下，TTF衍生的供体态更靠近CaFCl的导带边缘，然后吸附复合物被有效地n掺杂。此外，单层CaFCl在太阳光谱的紫外线范围内表现出明显的光吸收。这些结果使得CaFC1成为用于柔性纳米电子和光电器件中的有吸引力的2D材料。