title: Impact and Origin of Interface States in MOS Capacitor with Monolayer MoS2and HfO2High-k Dielectric.
abstract: Two-dimensional layered semiconductors such as molybdenum disulfide (MoS2) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding the interface properties between the atomically thin MoS2channel 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 MoS2and an ultra-thin HfO2high-k gate dielectric. We show that the existence of sulfur vacancies at the MoS2-HfO2interface is responsible for the generation of interface states with a density (Dit) reaching ~7.03 × 1011cm-2eV-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 MoS2bandgap. 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 Ditcould be achieved by thermally diffusing S atoms to the MoS2-HfO2interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS2devices with carrier transport enhancement.
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore.
authors.forename: Pengkun
authors.initials: P
authors.lastname: Xia
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore.
authors.forename: Xuewei
authors.initials: X
authors.lastname: Feng
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore.
authors.forename: Rui Jie
authors.initials: RJ
authors.lastname: Ng
authors.affiliation: Institute of Materials Research and Engineering, 3 Research Link, 117602 Singapore.
authors.forename: Shijie
authors.initials: S
authors.lastname: Wang
authors.affiliation: Institute of Materials Research and Engineering, 3 Research Link, 117602 Singapore.
authors.forename: Dongzhi
authors.initials: D
authors.lastname: Chi
authors.affiliation: Department of Materials Science and Engineering, South University of Science and Technology of China, 1088 Xueyuan Road, Shenzhen, 518055, People Republic of China.
authors.forename: Cequn
authors.initials: C
authors.lastname: Li
authors.affiliation: Department of Materials Science and Engineering, South University of Science and Technology of China, 1088 Xueyuan Road, Shenzhen, 518055, People Republic of China.
authors.forename: Zhubing
authors.initials: Z
authors.lastname: He
authors.affiliation: College of Materials Science and Engineering, Shenzhen Key Laboratory of Special Functional Materials, Nanshan District Key Lab for Biopolymer and Safety Evaluation, Shenzhen University, 3688 Nanhai Ave, Shenzhen, 518060, People Republic of China.
authors.forename: Xinke
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore.
authors.forename: Kah-Wee
authors.initials: KW
authors.lastname: Ang