Understanding the band alignment at metal/2D semiconductor (SC) contacts is essential for electrical characterizations of 2D SC materials and for fabrication of high performance 2D SC devices. Many researchers have attempted to understand the electrical properties of metal/2D SC contacts and have revealed that they have unique features distinct from those of 3D SC counterparts. In this work, we investigated the surface potential (Vsurf) of exfoliated MoS2 flakes on bare and Au-coated SiO2/Si substrates using Kelvin probe force microscopy. The Vsurf of MoS2 single layers was larger on the Au-coated substrates than on the bare substrates; our theoretical calculations indicate that this may be caused by the formation of a larger electric dipole at the MoS2/Au interface leading to a modified band alignment. Vsurf decreased as the thickness of the flakes increased until reaching the bulk value at a thickness of ~20 nm on the bare and ~80 nm on the Au-coated substrates, respectively. This thickness-dependence of Vsurf was attributed to electrostatic screening in the MoS2 layers. Thus, a difference in the thickness at which the bulk Vsurf appeared suggests that the underlying substrate has an effect on the electric-field screening length of the MoS2 flakes. This work provides important insights to understand the band alignment and the charge transport at the metal/2D SC interfaces.
Dong-Wook Kim, Ahrum Sohn, Hankyoul Moon, Jayeong Kim, Miri Seo, Kyung-Ah Min, Sang Wook Lee, Seokhyun Yoon, and Suklyun Hong, "Band alignment at Au/exfoliated-MoS2-flake contacts (Conference Presentation)," Proc. SPIE 10534, 2D Photonic Materials and Devices, 105340T (Presented at SPIE OPTO: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289426.5751536503001.
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