STM characterization of defects in MoS2 FET

Fu-Xiang Chen^1*, Pen-Yuan Shih¹, Yong-Cheng Yang¹, Naoya Kawakami¹, Hao-Wei Tu¹, Wen-Bin Jian¹, Chenming Hu², Chun-Liang Lin¹

¹Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²International College of Semiconductor Technology, National Yang Ming Chiao Tung University, Hsinchu, Taiwan

* Presenter:Fu-Xiang Chen, email:fxchen.ep09g@nctu.edu.tw

Recently semiconductor industry is facing the limitation of scaling, and it is urgent to find a new type of material to replace Si. Layered materials solve this problem since the thickness of a monolayer of layered materials can be reduced to only few atoms. Thus, the electronic devices made by layered materials can overcome the current scaling problem and achieve several dreamed properties such as light, thin, and even transparent. MoS₂, a member of transition metal dichalcogenides (TMDs), can be used to fabricate field effect transistors (FETs). It is known that the defects of MoS₂ affect the performance of FET. Although the defects on the as-cleaved surface have been characterized so far, the transferring process on the circuit can cause other types of defects. Thus, we investigated what kinds of defects are present on a MoS₂ thin film after transferring onto a gold circuit by using scanning tunneling microscopy/spectroscopy (STM/STS). We found three kinds of voids corresponding to sulfur vacancies and one kind of impurity. Atomic resolution images and STS spectra indicated that the three types of sulfur vacancies were a missing atom on the top and bottom surface, and two missing atoms on top [1]. Bias-dependent STM images revealed that the impurity was charged, indicating the metallic property. The impurity would be gold atoms adsorbed during the transferring process.

[1] J. Phys. Chem. C 2020, 124, 15076−15084

Keywords: Scanning tunneling microscope, Transition metal dichalcogenides, Field effect transistor