Interface chemistry, band alignment, and thermal stability study of Sn metal contact on bulk and monolayer MoS2

Two-dimensional semiconductors such as transition metal dichalcogenides (TMDs) are making impressive strides in a short duration compared to other candidates. However, to unlock their full potential for advanced logic transistors, attention must be given to improving the contacts or interfaces they form. One approach is to interface with a suitable low work function metal contact to allow the surface Fermi level (EF) movement toward intended directions, thereby augmenting the overall electrical performance. In this work, we implement physical characterization to understand the tin (Sn) contact interface on monolayer and bulk molybdenum disulfide (MoS2) via in situ x-ray photoelectron spectroscopy and ex situ atomic force microscopy. A Sn contact exhibited a van der Waals type weak interaction with the MoS2 bulk surface where no reaction between Sn and MoS2 is detected. In contrast, reaction products with Sn—S bonding are detected with a monolayer surface consistent with a covalentlike interface. Band alignment at the interface indicates that Sn deposition induces n-type properties in the bulk substrate, while EF of the monolayer remains pinned. In addition, the thermal stability of Sn on the same substrates is investigated in a sequential ultrahigh vacuum annealing treatment at 100, 200, 300, and 400 °C. Sn sublimated/desorbed from both substrates with increasing temperature, which is more prominent on the bulk substrate after annealing at 400 °C. Additionally, Sn significantly reduced the monolayer substrate and produced detectable interface reaction products at higher annealing temperatures. The findings can be strategized to resolve challenges with contact resistance that the device community is having with TMDs.