Atomically resolving the influence of metal-induced gap states on electronic properties of transition metal dichalcogenides

YI-FENG CHEN^1*, HUNG-CHANG HSU², HAO-YU CHEN¹, YA-PING CHIU^1,2

¹Graduate School of Advanced Technology, National Taiwan University, Taipei, Taiwan
²Department of Physics, National Taiwan University, Taipei, Taiwan

* Presenter:YI-FENG CHEN, email:f10222006@ntu.edu.tw

It is well-known that metal-semiconductor junctions form the Schottky barrier, leading to increased contact resistance in electronic devices. Traditionally, this issue has been addressed by heavily doping the semiconductor materials to reduce the width of the Schottky barrier and minimize its impact. However, this method is not widely used when dealing with two-dimensional semiconductor materials like transition metal dichalcogenides (TMD) due to the immature technology. Furthermore, the presence of metal-induced gap states (MIGS) and Fermi-level pinning (FLP) hinder the ability to directly adjust the Schottky barrier by selecting the metals with appropriate work function. Therefore, not only suitable work function, identifying metals that induce fewer MIGS in 2D semiconductors becomes crucial. Nevertheless, accurately measuring MIGS with atomic resolution remains a challenge. In our research, we delve into the interaction between MoS₂ and Au(111) using scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). Through these techniques, we can observe the electronic properties changes influenced by MIGS on the metal substrate. Utilizing scanning tunneling spectroscopy (STS), we identify a series of gap states on MoS₂/Au(111), which are suppressed at specific topographical features that we have identified. Consequently, we- confirm the presence and derive the energy distribution of MIGS. We offer a new approach to atomically clarify the interaction coupling between different metals and the electronic properties of two-dimensional semiconductor materials.

Keywords: Transition metal dichalcogenides, Fermi-level pinning, Metal-induced gap states, Scanning tunneling microscopy