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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.
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Effect of physical vapor deposition on contacts to 2D MoS2
Two-dimensional (2D) molybdenum disulfide (MoS2) holds immense promise for next-generation electronic applications. However, the role of contact deposition at the metal/semiconductor interface remains a critical factor influencing device performance. This study investigates the impact of different metal deposition techniques, specifically electron-beam evaporation and sputtering, for depositing Cu, Pd, Bi, Sn, Pt, and In. Utilizing Raman spectroscopy with backside illumination, we observe changes at the buried metal/1L MoS2 interface after metal deposition. Sputter deposition causes more damage to monolayer MoS2 than electron-beam evaporation, as indicated by partial or complete disappearance of first-order E′(Γ)α and A′1(Γ)α Raman modes post-deposition. We correlated the degree of damage from sputtered atoms to the cohesive energies of the sputtered material. Through fabrication and testing of field-effect transistors, we demonstrate that electron-beam evaporated Sn/Au contacts exhibit superior performance including reduced contact resistance (~12×), enhanced mobility (~4.3×), and lower subthreshold slope (~0.6×) compared to their sputtered counterparts. Our findings underscore the importance of contact fabrication methods for optimizing the performance of 2D MoS2 devices and the value of Raman spectroscopy with backside illumination for gaining insight into contact performance.
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- PAR ID:
- 10584899
- Publisher / Repository:
- AIP Publishing
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 136
- Issue:
- 22
- ISSN:
- 0021-8979
- Page Range / eLocation ID:
- 224303
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1063/5.0231261
