Defect-Type-Dependent Carrier Lifetimes in Monolayer WS<sub>2</sub> Films

Liu, Yuanshuang; Liu, Huan; Wang, Jiangcai; Liu, Dameng

doi:10.1021/acs.jpcc.1c09603

Cited by 16 publications

(30 citation statements)

References 71 publications

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“…2(d), respectively. On carefully examining the E 1 2g mode at ∼350 cm −1 and the A 1 g mode at ∼420 cm −1 , we observe a slight blue-shift after the treatment, which has been associated with a reduction of the doping in the sample [58,60,61]. This effect is in agreement with the removal of the substitutional oxygen and passivation of the vacancy sites by the TFSI treatment explained earlier.…”

Section: Resultssupporting

confidence: 87%

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Hysteresis-Free High Mobility Graphene Encapsulated in Tungsten Disulfide

Soundarapandian¹,

Fazio²,

Tongay³

2022

Preprint

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High mobility is a crucial requirement for a large variety of electronic device applications. The state-of-the-art for high quality graphene devices is based on heterostructures made with graphene encapsulated in > 80 nm-thick flakes of hexagonal boron nitride (hBN). Unfortunately, scaling up multilayer hBN while precisely controlling the number of layers remains an elusive challenge, resulting in a rough material unable to enhance the mobility of graphene. This leads to the pursuit of alternative, scalable materials, which can be simultaneously used as substrate and encapsulant for graphene. Tungsten disulfide (WS2) is a transition metal dichalcogenide, which was successfully grown in large (∼mm-size) multi-layers by chemical vapour deposition. However, the resistance vs gate voltage characteristics when gating graphene through WS2 exhibit largely hysteretic shifts of the charge neutrality point (CNP) in the order of ∆n ∼2.6•10 11 cm −2 , hindering the use of WS2 as a reliable encapsulant. The hysteresis originates due to the charge traps from sulfur vacancies present in WS2. In this work, we report for the first time the use of WS2 as a substrate and the overcoming of hysteresis issues by chemically treating WS2 with a super-acid, which passivates these vacancies and strips the surface from contaminants. The hysteresis is significantly reduced below the noise level by at least a factor five (to ∆n <5•10 10 cm −2 ) and, simultaneously, the roomtemperature mobility of WS2-encapsulated graphene is as high as ∼6.2•10 4 cm −2 V −1 s −1 at a carrier density n ∼1•10 12 cm −2 . Our results promote WS2 to a valid alternative to hBN as encapsulant for high-performance graphene devices.

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Section: Resultssupporting

confidence: 87%

“…Vacancies represent the main source of trapping/detrapping of charges [48], which in turn results in hysteresis effects [36,37], especially when a TMD is used as a dielectric. Many methods have been proposed to eliminate the substitutional atoms and/or "passivate" the vacancies with the original chalcogen atom species [43][44][45]58].…”

Section: Resultsmentioning

confidence: 99%

Hysteresis-Free High Mobility Graphene Encapsulated in Tungsten Disulfide

Soundarapandian¹,

Fazio²,

Tongay³

2022

Preprint

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“…The results show that HF treatment can effectively reduce the defects of QDs and shorten the carrier recovery time, therefore the mode-locking pulse width is successfully reduced from 635 to 450 fs. This is different from some reported 2D SA materials such as MoS 2 , [31,32] WS 2 , [33,34] and Bi 2 O 2 Se, [35] which can reduce the carrier recovery time by increasing the defect density, which is conducive to reducing the pulse width. Our study will inspire new applications of InP QDs in ultrafast photonics and nonlinear optics.…”

Section: Introductioncontrasting

confidence: 65%

InP/ZnSeS/ZnS Core–Shell Quantum Dots as Novel Saturable Absorbers in Mode‐Locked Fiber Lasers

Lou

et al. 2022

Advanced Optical Materials

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In this study, red light emitting InP/ZnSeS/ZnS quantum dots (QDs) are prepared by thermal injection method. The results show that the InP/ZnSeS/ZnS QDs saturable absorbers (SA) have good nonlinear saturable absorption properties with modulation depth of 24.2% and saturation intensity of 0.08 KW cm−2. Then the QD SAs are applied to the erbium‐doped fiber laser (EDFL) ring cavity system, and a mode‐locked laser pulse with a pulse width of 635 fs is generated. In addition, the pulse width is determined by the carrier recovery time, which is closely related to the defect density in the material. A large number of defects are eliminated in the QDs by hydrogen fluoride (HF) treatment, and the pulse width is reduced from 635 to 450 fs. Results of time‐resolved photoluminescence and ultrafast transient absorption spectroscopy (TAS) show that HF treatment indeed reduces defects in InP/ZnSeS/ZnS QDs, indicated by the decrease of the carrier recovery time. This is different from the reported 2D SA materials, which usually reduce the carrier recovery time by increasing the defect density. This study will inspire new applications of QDs in ultrafast photonics and nonlinear optics.

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“…Transition metal dichalcogenides (TMDs), such as MoSe 2 and WSe 2 , are promising candidates in novel high-performance nanoelectronic and optoelectronic devices due to their alluring properties. − In general, intrinsic defects and unintentional impurities during the growth of the materials are unavoidable, and they dramatically affect the physical and chemical properties of the materials. − On the other hand, the functionality of semiconductors depends essentially on whether enough free carriers can be introduced by doping. ,− Therefore, the prerequisite for designing and optimizing high-performance devices is to have deep understanding of the properties of defects in materials.…”

Section: Introductionmentioning

confidence: 99%

First-Principles Study of the Origin of the Distinct Conductivity Type of Monolayer MoSe₂ and WSe₂

et al. 2022

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Monolayer (ML) MoSe2 and WSe2 are promising materials for novel two-dimensional high-performance electronic and optoelectronic devices. Although ML MoSe2 and WSe2 possess the same crystal structure and similar chemical composition and band gap, they are experimentally observed to have distinct carrier types in conduction, i.e., ML MoSe2 is usually a n-type and ML WSe2 usually a p-type semiconductor. The reasons for such distinction are not fully understood so far. In this paper, by first-principles systematic investigation of the properties of intrinsic point defects and some inevitable unintentional extrinsic impurities under normal growth environments for ML MoSe2 and WSe2, we find that intrinsic defects are neither efficient p-type nor n-type dopants in these materials. Instead, hydrogen interstitial (H i inside ) is a shallow donor in both ML MoSe2 and WSe2, while nitrogen-substituting host selenium (N Se ) is a relatively shallow acceptor in both ML MoSe2 and WSe2. However, in the presence of both H and N doping, the compensation between the two type dopants pinned the Fermi energy close to the conduction band edge for ML MoSe2 and close to the valence band edge for ML WSe2. Our study, therefore, provides insights into the origin of the distinct types of conduction of ML MoSe2 and WSe2 and provides guidelines on how to dope transition metal dichalcogenides.

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Defect-Type-Dependent Carrier Lifetimes in Monolayer WS₂ Films

Cited by 16 publications

References 71 publications

Hysteresis-Free High Mobility Graphene Encapsulated in Tungsten Disulfide

Hysteresis-Free High Mobility Graphene Encapsulated in Tungsten Disulfide

InP/ZnSeS/ZnS Core–Shell Quantum Dots as Novel Saturable Absorbers in Mode‐Locked Fiber Lasers

First-Principles Study of the Origin of the Distinct Conductivity Type of Monolayer MoSe₂ and WSe₂

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Defect-Type-Dependent Carrier Lifetimes in Monolayer WS2 Films

Cited by 16 publications

References 71 publications

Hysteresis-Free High Mobility Graphene Encapsulated in Tungsten Disulfide

Hysteresis-Free High Mobility Graphene Encapsulated in Tungsten Disulfide

InP/ZnSeS/ZnS Core–Shell Quantum Dots as Novel Saturable Absorbers in Mode‐Locked Fiber Lasers

First-Principles Study of the Origin of the Distinct Conductivity Type of Monolayer MoSe2 and WSe2

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Defect-Type-Dependent Carrier Lifetimes in Monolayer WS₂ Films

First-Principles Study of the Origin of the Distinct Conductivity Type of Monolayer MoSe₂ and WSe₂