Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA.
Department of Physics and Astronomy, University of California, Riverside, California 92521, USA.
J Chem Phys. 2017 Feb 14;146(6):064701. doi: 10.1063/1.4975178.
Two-dimensional (2D) heterostructures and all-2D contacts are of high interest for electronic device applications, and the SnS/HfSe bilayer heterostructure with graphene contacts has some unique, advantageous properties. The SnS/HfSe heterostructure is interesting because of the strong intermixing of the two conduction bands and the large work function of the SnS. The band lineup of the well separated materials indicates a type II heterostructure, but the conduction band minimum of the SnS/HfSe bilayer is a coherent superposition of the orbitals from the two layers with a spectral weight of 60% on the SnS and 40% on the HfSe for AA stacking. These relative weights can be either increased or reversed by an applied vertical field. A 3×3 supercell of graphene and a 2×2 supercell of SnS/HfSe have a lattice mismatch of 0.1% and both the SnS/HfSe conduction band at M and the graphene Dirac point at K are zone-folded to Γ. Placing graphene on the SnS/HfSe bilayer results in large n-type charge transfer doping of the SnS/HfSe bilayer, on the order of 10/cm, and the charge transfer is accompanied by a negative Schottky barrier contact for electron injection from the graphene into the SnS/HfSe bilayer conduction band. Binding energies and the anti-crossing gaps of the graphene and the SnS/HfSe electronic bands both show that the coupling of graphene to the HfSe layer is significantly larger than its coupling to the SnS layer. A tunneling Hamiltonian estimate of the contact resistance of the graphene to the SnS/HfSe heterostructure predicts an excellent low-resistance contact.
二维（2D）异质结构和全 2D 接触对于电子器件应用具有很高的兴趣，而具有石墨烯接触的 SnS/HfSe 双层异质结构具有一些独特的优势。SnS/HfSe 异质结构之所以有趣，是因为两个导带之间的强混合以及 SnS 的大功函数。这些材料的能带排列表明这是一种 II 型异质结构，但 SnS/HfSe 双层的导带最小值是两个层的轨道的相干叠加，其中 SnS 的谱权重为 60%，HfSe 的谱权重为 40%，对于 AA 堆叠。这些相对权重可以通过施加垂直场来增加或反转。石墨烯的 3×3 超胞和 SnS/HfSe 的 2×2 超胞的晶格失配为 0.1%，并且 SnS/HfSe 的导带在 M 和石墨烯的狄拉克点在 K 处都被折叠到 Γ 处。将石墨烯放置在 SnS/HfSe 双层上会导致 SnS/HfSe 双层的 n 型电荷转移掺杂，掺杂程度约为 10/cm，并且电荷转移伴随着从石墨烯到 SnS/HfSe 双层导带的电子注入的负肖特基势垒接触。石墨烯和 SnS/HfSe 能带的结合能和反交叉间隙都表明，石墨烯与 HfSe 层的耦合明显大于其与 SnS 层的耦合。对石墨烯与 SnS/HfSe 异质结构接触电阻的隧道哈密顿估计预测了一个出色的低电阻接触。
