MoS<sub>2</sub>–Titanium Contact Interface Reactions

McDonnell, Stephen; Smyth, Christopher M.; Hinkle, Christopher L.; Wallace, Robert M.

doi:10.1021/acsami.6b00275

Cited by 114 publications

(163 citation statements)

References 42 publications

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“…The results are also consistent with previously measured values of metal/MoS 2 interfaces [24,28]. We note that the three Au/Ti/MoS 2 samples had Ti thicknesses ranging from 2.9 to 5.2 nm and Ti metal thickness had no effect on h K for these samples, suggesting that the intrinsic [14], the presence of a partial pressure of oxygen during the deposition of Ti on MoS 2 inhibits the reaction between them as Ti reacts with oxygen impinging on the surface of the substrate during deposition. The Mo 3d and S 2p core levels exhibit a 0.64 eV shift to higher binding energy, corresponding to a change in the position of the Fermi level.…”

Section: Textsupporting

confidence: 92%

“…Following the deposition of Ti, the spectra exhibit new chemical states including Mo metal (Mo 0 ) at 227.5 eV in the Mo 3d spectrum and Ti-S states in the S 2pspectrum. This result is consistent with previous reports of the deposition of Ti in UHV[14].…”

supporting

confidence: 94%

“…Our previous work has shown that transport across contact interfaces is highly sensitive to the oxide composition of Ti for graphene as well as 3D substrates [12,13]. McDonnell et al [14] have demonstrated that Ti/MoS 2 and TiO 2 /MoS 2 interfaces exhibit vastly different chemical compositions and suggested potential detrimental effects on thermal transport due to the higher thermal resistance of TiO 2 compared to metallic Ti. They noted that work by Duda et al [15] concludes that the removal of native oxide along with the deposition of a Ti adhesion layer has been found to be critical to lowering thermal resistances at metal-semiconductor interfaces.…”

Section: Textmentioning

confidence: 99%

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Titanium contacts to MoS2 with interfacial oxide: Interface chemistry and thermal transport

Freedy

Olson

Hopkins

et al. 2019

Phys. Rev. Materials

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The deposition of a thin oxide layer at metal/semiconductor interfaces has been previously reported as a means of reducing contact resistance in 2D electronics. Using X-ray photoelectron spectroscopy with in-situ Ti deposition, we fabricate Au/Ti/TiO x /MoS 2 samples as well as Au/Ti/MoS 2 and Au/TiO x /MoS 2 for comparison. Elemental titanium reacts strongly with MoS 2 whereas no interface reactions are observed in the two types of samples containing TiO x /MoS 2 interfaces. Using time domain thermoreflectance for the measurement of thermal boundary conductance, we find that samples contacted with Ti and a thin TiO x layer at the interface (≤1.5 nm) exhibit the same behavior as samples contacted solely with pure Ti. The Au/TiO x /MoS 2 samples exhibit ~20% lower thermal boundary conductance, despite having the same MoS 2 interface chemistry as the samples with thin oxide at the Ti/MoS 2 interface. We identify the mechanism for this phenomenon, attributing it to the different interfaces with the top Au contact. Our work demonstrates that the use of thin interfacial oxide layers to reduce electrical contact resistance does not compromise heat flow in 2D electronic devices. We note that the thicknesses of the Ti and TiO x layers must be considered for optimal thermal transport.

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Section: Textsupporting

confidence: 92%

supporting

confidence: 94%

Section: Textmentioning

confidence: 99%

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Titanium contacts to MoS2 with interfacial oxide: Interface chemistry and thermal transport

Freedy

Olson

Hopkins

et al. 2019

Phys. Rev. Materials

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“…Large conductance variations induced by metal-like subsurface MoS 2 defects must be expected to play a prominent role in device characteristics and predictability, in addition to the known impact of surface reactions with the contact metal. 70,71 …”

Section: Results and Discussionmentioning

confidence: 99%

Defect Dominated Charge Transport and Fermi Level Pinning in MoS₂/Metal Contacts

Bampoulis

Bremen

Yao

et al. 2017

ACS Appl. Mater. Interfaces

203

220

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Understanding the electronic contact between molybdenum disulfide (MoS2) and metal electrodes is vital for the realization of future MoS2-based electronic devices. Natural MoS2 has the drawback of a high density of both metal and sulfur defects and impurities. We present evidence that subsurface metal-like defects with a density of ∼1011 cm–2 induce negative ionization of the outermost S atom complex. We investigate with high-spatial-resolution surface characterization techniques the effect of these defects on the local conductance of MoS2. Using metal nanocontacts (contact area < 6 nm2), we find that subsurface metal-like defects (and not S-vacancies) drastically decrease the metal/MoS2 Schottky barrier height as compared to that in the pristine regions. The magnitude of this decrease depends on the contact metal. The decrease of the Schottky barrier height is attributed to strong Fermi level pinning at the defects. Indeed, this is demonstrated in the measured pinning factor, which is equal to ∼0.1 at defect locations and ∼0.3 at pristine regions. Our findings are in good agreement with the theoretically predicted values. These defects provide low-resistance conduction paths in MoS2-based nanodevices and will play a prominent role as the device junction contact area decreases in size.

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“…Even for the samples that have be held in high vacuum overnight before electron beam evaporation, the TiO x buffer layer between Ti/Au contact and WSe 2 may also be formed 39,40 , which will induce the formation of dipoles and further tune the Schottky barrier height. Thus, the transport property cannot be predicted by simple band offset, and, therefore, it is worth estimating the Schottky barrier to further reveal the thickness-dependent band profile.…”

Section: Resultsmentioning

confidence: 99%

The ambipolar transport behavior of WSe2 transistors and its analogue circuits

et al. 2018

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Tungsten diselenide (WSe 2 ) has many excellent properties and provides superb potential in applications of valleybased electronics, spin-electronics, and optoelectronics. To facilitate the digital and analog application of WSe 2 in CMOS, it is essential to understand the underlying ambipolar hole and electron transport behavior. Herein, the electric field screening of WSe 2 with a thickness range of 1-40 layers is systemically studied by electrostatic force microscopy in combination with non-linear Thomas-Fermi theory to interpret the experimental results. The ambipolar transport behavior of 1-40 layers of WSe 2 transistors is systematically investigated with varied temperature from 300 to 5 K. The thickness-dependent transport properties (carrier mobility and Schottky barrier) are discussed. Furthermore, the surface potential of WSe 2 as a function of gate voltage is performed under Kelvin probe force microscopy to directly investigate its ambipolar behavior. The results show that the Fermi level will upshift by 100 meV when WSe 2 transmits from an insulator to an n-type semiconductor and downshift by 340 meV when WSe 2 transmits from an insulator to a p-type semiconductor. Finally, the ambipolar WSe 2 transistor-based analog circuit exhibits phase-control by gate voltage in an analog inverter, which demonstrates practical application in 2D communication electronics.

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MoS₂–Titanium Contact Interface Reactions

Cited by 114 publications

References 42 publications

Titanium contacts to MoS2 with interfacial oxide: Interface chemistry and thermal transport

Titanium contacts to MoS2 with interfacial oxide: Interface chemistry and thermal transport

Defect Dominated Charge Transport and Fermi Level Pinning in MoS₂/Metal Contacts

The ambipolar transport behavior of WSe2 transistors and its analogue circuits

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MoS2–Titanium Contact Interface Reactions

Cited by 114 publications

References 42 publications

Titanium contacts to MoS2 with interfacial oxide: Interface chemistry and thermal transport

Titanium contacts to MoS2 with interfacial oxide: Interface chemistry and thermal transport

Defect Dominated Charge Transport and Fermi Level Pinning in MoS2/Metal Contacts

The ambipolar transport behavior of WSe2 transistors and its analogue circuits

Contact Info

Product

Resources

About

MoS₂–Titanium Contact Interface Reactions

Defect Dominated Charge Transport and Fermi Level Pinning in MoS₂/Metal Contacts