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Title: Impact and Origin of Interface States in MOS Capacitor with Monolayer MoS 2 and HfO 2 High-k Dielectric
Authors: Xia, P
Feng, X 
Ng, R.J
Wang, S 
Chi, D
Li, C
He, Z
Liu, X
Ang, K.-W 
Issue Date: 2017
Citation: Xia, P, Feng, X, Ng, R.J, Wang, S, Chi, D, Li, C, He, Z, Liu, X, Ang, K.-W (2017). Impact and Origin of Interface States in MOS Capacitor with Monolayer MoS 2 and HfO 2 High-k Dielectric. Scientific Reports 7 : 40669. ScholarBank@NUS Repository.
Abstract: Two-dimensional layered semiconductors such as molybdenum disulfide (MoS 2) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding the interface properties between the atomically thin MoS 2 channel and gate dielectric is fundamentally important for enhancing the carrier transport properties. Here, we investigate the frequency dispersion mechanism in a metal-oxide-semiconductor capacitor (MOSCAP) with a monolayer MoS 2 and an ultra-thin HfO 2 high-k gate dielectric. We show that the existence of sulfur vacancies at the MoS 2 -HfO 2 interface is responsible for the generation of interface states with a density (D it) reaching ?7.03 × 10 11 cm â '2 eV â '1. This is evidenced by a deficit S:Mo ratio of ?1.96 using X-ray photoelectron spectroscopy (XPS) analysis, which deviates from its ideal stoichiometric value. First-principles calculations within the density-functional theory framework further confirms the presence of trap states due to sulfur deficiency, which exist within the MoS 2 bandgap. This corroborates to a voltage-dependent frequency dispersion of ?11.5% at weak accumulation which decreases monotonically to ?9.0% at strong accumulation as the Fermi level moves away from the mid-gap trap states. Further reduction in D it could be achieved by thermally diffusing S atoms to the MoS 2 -HfO 2 interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS 2 devices with carrier transport enhancement. © The Author(s) 2017.
Source Title: Scientific Reports
ISSN: 20452322
DOI: 10.1038/srep40669
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