Tasnim Kazi Jannatul, Alharbi Safia Abdullah R, Musa Md Rajib Khan, Lovell Simon Hosch, Akridge Zachary Alexander, Yu Ming
Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, United States of America.
Nanotechnology. 2022 Jan 19;33(15). doi: 10.1088/1361-6528/ac475b.
Two-dimensional (2D) polar materials experience an in-plane charge transfer between different elements due to their electron negativities. When they form vertical heterostructures, the electrostatic force triggered by such charge transfer plays an important role in the interlayer bonding beyond van der Waals (vdW) interaction. Our comprehensive first principle study on the structural stability of the 2D SiC/GeC hybrid bilayer heterostructure has found that the electrostatic interlayer interaction can induce the-orbital hybridization between adjacent layers under different stacking and out-of-plane species ordering, with strong hybridization in the cases of Si-C and C-Ge species orderings but weak hybridization in the case of the C-C ordering. In particular, the attractive electrostatic interlayer interaction in the cases of Si-C and C-Ge species orderings mainly controls the equilibrium interlayer distance and the vdW interaction makes the system attain a lower binding energy. On the contrary, the vdW interaction mostly controls the equilibrium interlayer distance in the case of the C-C species ordering and the repulsive electrostatic interlayer force has less effect. Interesting finding is that the band structure of the SiC/GeC hybrid bilayer is sensitive to the layer-layer stacking and the out-of-plane species ordering. An indirect band gap of 2.76 eV (or 2.48 eV) was found under the AA stacking with Si-C ordering (or under the AB stacking with C-C ordering). While a direct band gap of 2.00-2.88 eV was found under other stacking and species orderings, demonstrating its band gap tunable feature. Furthermore, there is a charge redistribution in the interfacial region leading to a built-in electric field. Such field will separate the photo-generated charge carriers in different layers and is expected to reduce the probability of carrier recombination, and eventually give rise to the electron tunneling between layers.
二维（2D）极性材料由于其元素的电负性，会在不同元素之间发生面内电荷转移。当它们形成垂直异质结构时，这种电荷转移引发的静电力在超越范德华（vdW）相互作用的层间键合中起着重要作用。我们对二维SiC/GeC混合双层异质结构的结构稳定性进行的全面第一性原理研究发现，静电层间相互作用可以在不同的堆叠和面外物种排序情况下诱导相邻层之间的轨道杂化，在Si-C和C-Ge物种排序的情况下杂化强烈，而在C-C排序的情况下杂化较弱。特别是，在Si-C和C-Ge物种排序的情况下，有吸引力的静电层间相互作用主要控制平衡层间距离，而vdW相互作用使系统获得较低的结合能。相反，在C-C物种排序的情况下，vdW相互作用主要控制平衡层间距离，而排斥性的静电层间力影响较小。有趣的发现是，SiC/GeC混合双层的能带结构对层层堆叠和面外物种排序敏感。在具有Si-C排序的AA堆叠下（或在具有C-C排序的AB堆叠下）发现间接带隙为2.76 eV（或2.48 eV）。而在其他堆叠和物种排序下发现直接带隙为2.00 - 2.88 eV，表明其带隙可调特性。此外，在界面区域存在电荷重新分布，导致产生内建电场。这样的电场将分离不同层中的光生电荷载流子，预计会降低载流子复合的概率，并最终导致层间电子隧穿。
