Li Ze-Yu, Liu Ming-Yang, Huang Yang, Chen Qing-Yuan, Cao Chao, He Yao
Department of Physics, Yunnan University, Kunming, Yunnan 650091, People's Republic of China.
Phys Chem Chem Phys. 2017 Dec 20;20(1):214-220. doi: 10.1039/c7cp06727e.
As the isoelectronic counterpart of phosphorene, monolayer group IV-VI binary MX (M = Ge, Sn; X = Se, S) compounds have drawn considerable attention in recent years. In this paper, we construct four high-symmetry stacking models for bilayer MX to tune their electronic properties. We systematically explore the dynamical and thermal stabilities of all bilayer MX. It is found that five of them are possible at room temperature. Then, we perform first-principles calculations to study how the bilayer structure affects their electronic properties. The results demonstrate that the electronic properties of MX materials can be modulated by forming bilayer structures. Their bandgap can be tuned over a wide range from 0.789 to 1.617 eV, and an indirect-to-direct transition occurs in three cases. Considering the flexibility of bilayer MX, we utilize in-plane uniaxial tensile strain to adjust their band structures and achieve much more indirect-to-direct bandgap transitions. The realization of direct bandgaps will be helpful for their application in next-generation high-efficiency modern nano-optoelectronic and photovoltaic devices. We also study the responses of different bilayer MX to an external vertical electric field. It is found that their bandgaps decrease rapidly with the increase of the electric field.
作为磷烯的等电子对应物，单层IV - VI族二元MX（M = Ge，Sn；X = Se，S）化合物近年来受到了广泛关注。在本文中，我们构建了四种双层MX的高对称堆叠模型以调控其电子性质。我们系统地探究了所有双层MX的动力学和热稳定性。结果发现其中五种在室温下是可能存在的。然后，我们进行第一性原理计算来研究双层结构如何影响其电子性质。结果表明，通过形成双层结构可以调制MX材料的电子性质。它们的带隙可以在0.789至1.617 eV的宽范围内调节，并且在三种情况下会发生间接带隙到直接带隙的转变。考虑到双层MX的柔韧性，我们利用面内单轴拉伸应变来调整它们的能带结构，并实现更多的间接带隙到直接带隙的转变。直接带隙的实现将有助于它们在下一代高效现代纳米光电器件和光伏器件中的应用。我们还研究了不同双层MX对外部垂直电场的响应。结果发现，它们的带隙随着电场的增加而迅速减小。
