Covalent nitrogen doping in molecular beam epitaxy-grown and bulk WSe2

Khosravi, Ava; Addou, Rafik; Smyth, Christopher M.; Yue, Ruoyu; Cormier, Christopher R.; Kim, Jiyoung; Hinkle, Christopher L.; Wallace, Robert M.

doi:10.1063/1.5002132

Cited by 24 publications

(19 citation statements)

References 29 publications

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“…A clear blue shift of E 1 2g/A1g and 2LA(M) was observed after the 250 °C treatment. According to previous studies 37,39 , the blue shift (~ 1.3 cm -1 ) in the E 1 2g/A1g peak is correlated to p-type doping effect in WSe2 flakes, which is consistent with our XPS analysis and electrical characterizations discussed in the later paragraph. Therefore, we have confirmed that both atomically precise layer control and doping level modulation can be achieved through different treatment temperatures.…”

Section: Materials Analysessupporting

confidence: 91%

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Atomically Controlled Tunable Doping in High‐Performance WSe₂ Devices

Pang

Hung

Khosravi

et al. 2020

Adv Elect Materials

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Two-dimensional transitional metal dichalcogenide (TMD) field-effect transistors (FETs) are promising candidates for future electronic applications, owing to their excellent transport properties and potential for ultimate device scaling. However, it is widely acknowledged that substantial contact resistance associated with the contact-TMD interface has impeded device performance to a large extent. It has been discovered that O2 plasma treatment can convert WSe2 into WO3-x and substantially improve contact resistances of p-type WSe2 devices by strong doping induced thinner depletion width. In this paper, we carefully study the temperature dependence of this conversion, demonstrating an oxidation process with a precise monolayer control at room temperature and multilayer conversion at elevated temperatures. Furthermore, the lateral oxidation of WSe2 under the contact revealed by HR-STEM leads to potential unpinning of the metal Fermi level and Schottky barrier lowering, resulting in lower contact resistances. The p-doping effect is attributed to the high electron affinity of the formed WO3-x layer on top of the remaining WSe2 channel, and the doping level is found to be 2 dependent on the WO3-x thickness that is controlled by the temperature. Comprehensive materials and electrical characterizations are presented, with a low contact resistance of ~528  m and record high on-state current of 320 A/m at -1V bias being reported.

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Section: Materials Analysessupporting

confidence: 91%

“…Lower binding energy suggests that more prominent doping effect can be achieved at higher temperature treatment. 37,38 The doping effect in WSe2 was also examined by Raman spectroscopy. Figure 2g compares the Raman spectra of WSe2 flakes before and after the O2 plasma treatment at 250 °C.…”

Section: Materials Analysesmentioning

confidence: 99%

Atomically Controlled Tunable Doping in High‐Performance WSe₂ Devices

Pang

Hung

Khosravi

et al. 2020

Adv Elect Materials

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“…Two prominent Raman peaks at 150.2 cm −1 and 211.0 cm −1 are assigned to E g -like and A g -like vibrational modes, respectively [51]. In TMDs, Raman active modes have been reported to shift with changes in strain [52], temperature [53], and doping [54]. Figure 2d confirms that ReS 2 remains unaffected following the annealing and the ALD process.…”

Section: Resultsmentioning

confidence: 81%

High-κ Dielectric on ReS2: In-Situ Thermal Versus Plasma-Enhanced Atomic Layer Deposition of Al2O3

et al. 2019

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We report an excellent growth behavior of a high-κ dielectric on ReS2, a two-dimensional (2D) transition metal dichalcogenide (TMD). The atomic layer deposition (ALD) of an Al2O3 thin film on the UV-Ozone pretreated surface of ReS2 yields a pinhole free and conformal growth. In-situ half-cycle X-ray photoelectron spectroscopy (XPS) was used to monitor the interfacial chemistry and ex-situ atomic force microscopy (AFM) was used to evaluate the surface morphology. A significant enhancement in the uniformity of the Al2O3 thin film was deposited via plasma-enhanced atomic layer deposition (PEALD), while pinhole free Al2O3 was achieved using a UV-Ozone pretreatment. The ReS2 substrate stays intact during all different experiments and processes without any formation of the Re oxide. This work demonstrates that a combination of the ALD process and the formation of weak S–O bonds presents an effective route for a uniform and conformal high-κ dielectric for advanced devices based on 2D materials.

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“…[39] Notably, Raman peak shift is usually inevitable for TMD materials when carrier doping or strain is introduced, so the unchanged eigen-peak positions revealed that the possibility of carrier concentration variation or lattice strain induced by air-exposure can be ruled out. [19,[40][41][42] The wavenumber difference between the two eigen-peaks is ~ 8 cm -1 for both F-WSe2 and O-WSe2, suggesting BL configuration for F-WSe2. [33] The wavenumber difference of WSe2 shows evident dependence on thickness and no peak of tungsten oxide (or seledium oxides) was observed (see the magenta…”

Section: Resultsmentioning

confidence: 94%

Ambipolar and Robust WSe₂ Field‐Effect Transistors Utilizing Self‐Assembled Edge Oxides

Han

Liu

et al. 2019

Adv Materials Inter

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Transition metal oxides (TMOs) with high work function (WF) show promising properties as unipolar p-type contacts for transition metal dichalcogenides. Here, ambipolar field-effect transistors (FETs) enabled by bilayer WSe2 with self-assembled TMOs (WO2.57) as contacts are reported. Systematic material characterizations demonstrated the formation of WO2.57/WSe2 heterojunctions around nanoflake edges with Se atoms substituted by O atoms after air-exposure, while pristine properties of WSe2 almost sustained in inner domains. As-fabricated FETs exhibited both polarities, implying WO2.57 with lowered WF at edges can serve as both the p-type and n-type contact for inner WSe2. Noteworthy, greatly reduced contact resistance and enhanced channel current were achieved, compared to the devices without WO2.57 contacts. Linear drain-source current relationship from 77 K to 300 K indicated the ohmic contact between edge WO2.57 and inner WSe2. Density functional theory calculations further revealed the WO2.57/WSe2 heterojunction formed a barrier-less charge distribution. These nm-scale FETs possessed remarkable electrical conductivity up to ~ 2600 S/m, ultra-low leakage current down to ~ 10-12 A, robustness for high voltage operation and air stability, which even outperformed pristine WSe2 FETs. Theoretical calculations revealed the high conductivity was exclusively attributed to the air-induced WO2.57 and its further carrier injection to WSe2.

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Covalent nitrogen doping in molecular beam epitaxy-grown and bulk WSe2

Cited by 24 publications

References 29 publications

Atomically Controlled Tunable Doping in High‐Performance WSe₂ Devices

Atomically Controlled Tunable Doping in High‐Performance WSe₂ Devices

High-κ Dielectric on ReS2: In-Situ Thermal Versus Plasma-Enhanced Atomic Layer Deposition of Al2O3

Ambipolar and Robust WSe₂ Field‐Effect Transistors Utilizing Self‐Assembled Edge Oxides

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Covalent nitrogen doping in molecular beam epitaxy-grown and bulk WSe2

Cited by 24 publications

References 29 publications

Atomically Controlled Tunable Doping in High‐Performance WSe2 Devices

Atomically Controlled Tunable Doping in High‐Performance WSe2 Devices

High-κ Dielectric on ReS2: In-Situ Thermal Versus Plasma-Enhanced Atomic Layer Deposition of Al2O3

Ambipolar and Robust WSe2 Field‐Effect Transistors Utilizing Self‐Assembled Edge Oxides

Contact Info

Product

Resources

About

Atomically Controlled Tunable Doping in High‐Performance WSe₂ Devices

Atomically Controlled Tunable Doping in High‐Performance WSe₂ Devices

Ambipolar and Robust WSe₂ Field‐Effect Transistors Utilizing Self‐Assembled Edge Oxides