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Condensed Matter Physics

Thermal stability of monolayer WS2 in BEOL conditions

Profile image of Camilla ColettiCamilla Coletti

Journal of Physics: Materials

https://doi.org/10.1088/2515-7639/ABD4F2
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21 pages

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Abstract

Monolayer tungsten disulfide (WS2) has recently attracted large interest as a promising material for advanced electronic and optoelectronic devices such as photodetectors, modulators, and sensors. Since these devices can be integrated in a silicon (Si) chip via back-end-of-line (BEOL) processes, the stability of monolayer WS2 in BEOL fabrication conditions should be studied. In this work, the thermal stability of monolayer single-crystal WS2 at typical BEOL conditions is investigated; namely (i) heating temperature of 300 °C, (ii) pressures in the medium-(10-3 mbar) and high-(10-8 mbar) vacuum range; (iii) heating times from 30 minutes to 20 hours. Structural, optical and chemical analyses of WS2 are performed via scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). It is found that monolayer single-crystal WS2 is intrinsically stable at these temperature and pressures, even after 20 hours of thermal treatment. The thermal stability of WS2 is also preserved after exposure to low-current electron beam (12 pA) or low-fluence laser (0.9 mJ/m 2), while higher laser fluencies cause photo-activated degradation upon thermal treatment. These results are instrumental to define fabrication and in-line monitoring procedures that allow the integration of WS2 in device fabrication flows without compromising the material quality.

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Artem Mishchenko

Dalton Transactions, 2014

Atomically thin layers of materials, which are just a few atoms in thickness, present an attractive option for future electronic devices. Herein we characterize, optically and electronically, atomically thin tungsten disulphide (WS 2 ), a layered semiconductor. We provide the distinctive Raman and photoluminescence signatures for single layers, and prepare field-effect transistors where atomically thin WS 2 serves as the conductive channel. The transistors present mobilities μ = 10 cm 2 V −1 s −1 and exhibit ON/OFF ratios exceeding 100 000. Our results show that WS 2 is an attractive option for applications in electronic and optoelectronic devices and pave the way for further studies in this two-dimensional material. Fig. 3 (a) Optical image of a WS 2 transistor. (b) Logarithmic conductance as a function of gate voltage with I on /I off = 100 000 at V b = 0.1 V. Inset: drain current I ds versus drain voltage V ds for various gate voltages.

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Disentangling the effects of doping, strain and defects in monolayer WS2 by optical spectroscopy
Pavel V . Kolesnichenko

2019

Monolayers of transition metal dichalcogenides (TMdC) are promising candidates for realization of a new generation of optoelectronic devices. The optical properties of these two-dimensional materials, however, vary from flake to flake, or even across individual flakes, and change over time, all of which makes control of the optoelectronic properties challenging. There are many different perturbations that can alter the optical properties, including charge doping, defects, strain, oxidation, and water intercalation. Identifying which perturbations are present is usually not straightforward and requires multiple measurements using multiple experimental modalities, which presents barriers when attempting to optimise preparation of these materials. Here, we apply highresolution photoluminescence and differential reflectance hyperspectral imaging in situ to CVD-grown WS2 monolayers. By combining these two optical measurements and using a statistical correlation analysis we are able to di...

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Temperature dependence of optical properties of monolayer WS2 by spectroscopic ellipsometry
Kyung Hee University

The complex dielectric function ɛ = ɛ 1 + iɛ 2 of monolayer tungsten disulfide (WS 2) is investigated for the energy range from 1.5 to 6.0 eV and temperatures from 41 to 300 K. Measurements were performed under ultra-high vacuum conditions to avoid degradation and overlayer contamination. Fourteen critical-point (CP) energies were observed and their origins in Brillouin-zone were identified by band structure calculations. At low temperature the A and B excitonic peaks split into four CPs, which is understood as the neutral and charged exciton states of monolayer WS 2. At low temperatures the CP energies show blue shifts with enhanced structure due to the reduction of electron-phonon interaction. The temperature dependence of these data was obtained by a phenomenological expression with Bose-Einstein statistical factor.

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Synthesis and Optical Properties of Large-Area Single-Crystalline 2 D Semiconductor WS 2 Monolayer from Chemical Vapor Deposition
Bingchen Cao
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Related topics

  • Physics
  • Computational materials physics

    • Cited by

    Unexpected Electron Transport Suppression in a Heterostructured Graphene–MoS2 Multiple Field-Effect Transistor Architecture
    Camilla Coletti

    ACS Nano, 2021

    We demonstrate a graphene−MoS 2 architecture integrating multiple field-effect transistors (FETs), and we independently probe and correlate the conducting properties of van der Waals coupled graphene−MoS 2 contacts with those of the MoS 2 channels. Devices are fabricated starting from high-quality single-crystal monolayers grown by chemical vapor deposition. The heterojunction was investigated by scanning Raman and photoluminescence spectroscopies. Moreover, transconductance curves of MoS 2 are compared with the current−voltage characteristics of graphene contact stripes, revealing a significant suppression of transport on the n-side of the transconductance curve. On the basis of ab initio modeling, the effect is understood in terms of trapping by sulfur vacancies, which counterintuitively depends on the field effect, even though the graphene contact layer is positioned between the backgate and the MoS 2 channel.

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