Szabó Áron, Jain Achint, Parzefall Markus, Novotny Lukas, Luisier Mathieu
Integrated System Laboratory , ETH Zürich , 8092 Zürich , Switzerland.
Photonics Laboratory , ETH Zürich , 8093 Zürich , Switzerland.
Nano Lett. 2019 Jun 12;19(6):3641-3647. doi: 10.1021/acs.nanolett.9b00678. Epub 2019 May 14.
In ultrathin two-dimensional (2-D) materials, the formation of ohmic contacts with top metallic layers is a challenging task that involves different processes than in bulk-like structures. Besides the Schottky barrier height, the transfer length of electrons between metals and 2-D monolayers is a highly relevant parameter. For MoS, both short (≤30 nm) and long (≥0.5 μm) values have been reported, corresponding to either an abrupt carrier injection at the contact edge or a more gradual transfer of electrons over a large contact area. Here we use ab initio quantum transport simulations to demonstrate that the presence of an oxide layer between a metallic contact and a MoS monolayer, for example, TiO in the case of titanium electrodes, favors an area-dependent process with a long transfer length, while a perfectly clean metal-semiconductor interface would lead to an edge process. These findings reconcile several theories that have been postulated about the physics of metal/MoS interfaces and provide a framework to design future devices with lower contact resistances.
在超薄二维（2-D）材料中，与顶部金属层形成欧姆接触是一项具有挑战性的任务，其所涉及的过程与块状结构不同。除了肖特基势垒高度外，金属与二维单层之间电子的转移长度也是一个高度相关的参数。对于二硫化钼（MoS₂），已报道了短（≤30纳米）和长（≥0.5微米）两种值，分别对应于接触边缘处的突然载流子注入或在大接触面积上更渐进的电子转移。在此，我们使用从头算量子输运模拟来证明，例如在钛电极的情况下，金属接触与MoS₂单层之间存在氧化层，有利于具有长转移长度的面积依赖性过程，而完全清洁的金属 - 半导体界面会导致边缘过程。这些发现调和了关于金属/MoS₂界面物理的几种假设理论，并为设计具有更低接触电阻的未来器件提供了一个框架。
