School of Materials Science and Engineering , Gwangju Institute of Science & Technology (GIST) , 123 Cheomdangwagi-ro , Buk-gu, Gwangju 61005 , Republic of Korea.
ACS Appl Mater Interfaces. 2020 Jan 22;12(3):4129-4134. doi: 10.1021/acsami.9b19681. Epub 2020 Jan 8.
Contact engineering for two-dimensional (2D) transition metal dichalcogenides (TMDCs) is crucial for realizing high-performance 2D TMDC devices, and most studies on contact properties of 2D TMDCs have mainly focused on Fermi level unpinning. Here, we investigated electrical and photoelectrical properties of chemical vapor deposition (CVD)-grown molybdenum disulfide (MoS) monolayer devices depending on metal contacts, Ti/Pt, Ti/Au, Ti, and Ag, and particularly demonstrated the essential role of defects in MoS in contact properties. Remarkably, MoS devices with Ag contacts show a field-effect mobility of 12.2 cm V s, an on/off current ratio of 7 × 10, and a photoresponsivity of 1020 A W, which are outstanding compared to similar devices with other metal contacts. These improvements are attributed to a reduced Schottky barrier height, thanks to the small work function of Ag and Ag-MoS orbital hybridization at the interface, which facilitates efficient charge transfer between MoS and Ag. Interestingly, X-ray photoelectron spectroscopic analysis reveals that AgS was formed in our defect-containing CVD-grown MoS monolayer, but such orbital hybridization is not observed in a nearly defect-free exfoliated MoS. This distinction shows that defects existing in MoS enable Ag to effectively couple to MoS and correspondingly enhance multiple electrical and photoelectrical properties.
二维（2D）过渡金属二卤化物（TMDCs）的接触工程对于实现高性能 2D TMDC 器件至关重要，大多数关于 2D TMDC 接触特性的研究主要集中在费米能级钉扎上。在这里，我们研究了化学气相沉积（CVD）生长的二硫化钼（MoS）单层器件的电学和光电性能，取决于金属接触，Ti/Pt、Ti/Au、Ti 和 Ag，并特别证明了 MoS 中的缺陷在接触特性中的重要作用。值得注意的是，具有 Ag 接触的 MoS 器件具有 12.2 cm V s 的场效应迁移率、7×10 的导通/关断电流比和 1020 A W 的光响应率，与具有其他金属接触的类似器件相比，这些性能都非常出色。这些改进归因于肖特基势垒高度的降低，这要归功于 Ag 的小功函数和界面处的 Ag-MoS 轨道杂化，这有利于 MoS 和 Ag 之间的有效电荷转移。有趣的是，X 射线光电子能谱分析表明，在我们含有缺陷的 CVD 生长的 MoS 单层中形成了 AgS，但在几乎无缺陷的剥离 MoS 中没有观察到这种轨道杂化。这种区别表明，MoS 中的缺陷使得 Ag 能够有效地与 MoS 结合，并相应地增强多个电学和光电性能。
