Highly efficient and stable MoS₂FETs with reversible n-doping using a dehydrated poly(vinyl-alcohol) coating

Abstract

Despite rapid progress in 2D molybdenum disulfide (MoS) research in recent years, MoS field-effect transistors (FETs) still suffer from a high metal-to-MoS contact resistance and low intrinsic mobility, which are major hindrances to their future application. We report an efficient technique to dope thin-film MoS FETs using a poly(vinyl-alcohol) (PVA) polymeric coating. This results in a reduction of the contact resistance by up to 30% as well as a reduction in the channel resistance to 20 kΩ sq. Using a dehydration process, we were able to effectively control the surface interactions between MoS and the more electropositive hydroxyl groups (-OH) of PVA, which provided a controllable and yet reversible increase in the charge carrier density to a value of 8.0 × 10 cm. The non-covalent, thus non-destructive, PVA doping of MoS increases the carrier concentration without degrading the mobility, which shows a monotonic increase while enhancing the doping effect. The PVA doping technique is then exploited to create heavily doped access regions to the intrinsic MoS channel, which yields 200% increase of the ON-state source-drain current. This establishes PVA doping as an effective approach to enhance the transport properties of MoS FETs for a variety of applications.

Progress in Contact, Doping and Mobility Engineering of MoS2: An Atomically Thin 2D Semiconductor

“…Moreover, the PVA doping efficiency was enhanced after a dehydration anneal (as H 2 O molecules were found to hinder the electron transfer from the PVA to the MoS 2 surface) which led to the best MoS 2 device performance in this study. Finally, the authors showed that encapsulating the PVA coating with an ALD-grown Al 2 O 3 film can make it robust against the environment with long-lasting doping effects [217]. Other reports on surface charge transfer n-doping of MoS 2 include air-stable doping using hydrazine [218], p-toluene sulfonic acid [219], black phosphorous quantum dots [220], and self-assembled oleylamine (OA) networks [221].…”

Sheet Resistance Reduction of MoS₂ Film Using Sputtering and Chlorine Plasma Treatment Followed by Sulfur Vapor Annealing

“…To intentionally enhance the carrier density in low carrierdensity MoS 2 film for the Seebeck device, intrinsic and extrinsic carrier generations are expected. Although the intrinsic technique such as vacancies and interstitials of the consisting materials generates several energy levels in the band gap [20]- [22], the extrinsic technique is favorable rather than intrinsic one to significantly enhance the carrier density with high controllability [23], for which electrostatic doping [24], molecular adsorption [25]- [27] and substitutional doping [28]- [33] can be considered. Although electrostatic doping has high carrier density, a device structure is complex.…”

Air-stable and efficient electron doping of monolayer MoS2 by salt–crown ether treatment

“…The literature contains numerous accounts of TMDC doping. [22][23][24][25][26][27][28][29][30][31] For example, Fang et al reported degenerate n-type doping of few-layer MoS 2 and WSe 2 via vapor-phase doping of K, resulting in high electron densities of ~1.0 × 10 13 cm −2 and ~2.5 × 10 12 cm −2 for MoS 2 and WSe 2 , respectively. 22 Air-stable n-type doping of few-layer MoS 2 with a high carrier density of ~1.0 × 10 13 cm −2 was also achieved via solution-based doping of benzyl viologen (BV); the BV-doped MoS 2 exhibited stable transport properties in air for ~9 days.…”