A photoelectron study of annealing induced changes to workfunction and majority carrier type in pulsed laser deposited few layer WS2 films

Rathod, Urmilaben P.; Jha, Jitendra Kumar; Voevodin, Andrey A.; Shepherd, Nigel D.

doi:10.1007/s10854-018-0135-5

Cited by 7 publications

(2 citation statements)

References 30 publications

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“…Using a base pressure of 10 −6 Torr and 1 cm 2 polished quartz substrates, few-layered WS 2 films were grown by PLD via ablation of a polycrystalline WS 2 target (Kurt J. Lesker) using the 248 nm KrF line of an excimer laser (Lambda Physik) with 25 ns pulses. 20 Low, moderate, and high laser fluencies of 0.35, 0.75, and 1.5 J/cm 2 , respectively, and laser frequencies of 1, 5, and 10 Hz were studied. We used a relatively low substrate temperature of 400 °C because of our interest in flexible substrates and expectation that the processing developed here can be transferred to such substrates.…”

Section: Methodsmentioning

confidence: 99%

Growth of pulsed laser deposited few-layer WS2 films

Rathod

Cai

Iheomamere

et al. 2019

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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X-ray photoelectron, Raman, and diffraction studies of few-layered pulsed laser deposited WS 2 films were performed as a function of laser fluence and frequency to understand the impact on structure and properties. Supersaturation of the growth surface created by high fluence was conducive to nucleation and growth, but the obtained films were sulfur deficient. Sulfur desorption at high fluence is due to large kinetic energy transfer and energetic peening of the growing film from the impinging flux. Loss of sulfur was also observed at low frequency where the off period of the supply flux was relatively large. With improvement of the S/W ratio from 1.1 to 1.8, the mobility increased from 0.1 to 6.5 cm 2 V −1 s −1 , while the associated change in the electron sheet concentration followed the opposite trend. Annealing at high temperature under conditions that conserved stoichiometry dramatically improved the crystallinity and further improved the mobility from 6.5 to 19.5 cm 2 V −1 s −1 . The correlations between structure, Hall mobility, and Fermi level positions indicate that reducing chalcogen vacancies is critical for optimal mobility in all pulsed laser deposited transition metal dichalcogenide films.

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Section: Methodsmentioning

confidence: 99%

Growth of pulsed laser deposited few-layer WS2 films

Rathod

Cai

Iheomamere

et al. 2019

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

Self Cite

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“…The switch from n to p-type was accompanied by an increase in workfunction from 3.6 eV to 4.52 eV as determined by UPS. The details of these studies have been reported 6 .…”

Section: Intrinsic P-typementioning

confidence: 99%

Extrinsic and intrinsic p-type doping of pulsed laser deposited few-layer WS2 films

Shepherd,

Rathod,

Voevodin

2023

Low-Dimensional Materials and Devices 2023

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X-ray photoelectron spectroscopy confirmed (XPS) that Nb substitutes on W lattice sites yielding substitutional extrinsic p-type doping in pulsed laser deposited (PLD) few-layer WS2:Nb films. A Fermi level separation of 0.31 eV from the valence band edge with 0.5 atomic % of Nb doping was measured by ultraviolet photoelectron spectroscopy (UPS), which decreased to 0.18 eV when doping was increased to 1.1 atomic %. The corresponding hole sheet concentrations increased from 3.9 x 10 12 to 8.6 x 10 13 cm -2 respectively while the mobility exhibited the opposite trend, presumably due to increased ionized impurity scattering. Separately, undoped PLD few-layer WS2 films exhibited a conductivity switch from n to p-type when the composition changed from sulfur-deficient to sulfur-rich. UPS revealed a workfunction increase from 3.36 to 4.52 eV and a corresponding change in the Fermi level separation from the valence band edge. The intrinsic p-type conductivity is assigned to excess sulfur in the form of interstitials. Despite the relatively large change in workfunction in these films, Ohmic contacts were obtained to both the n and p-type materials with indium, albeit with different contact resistances. This suggests that in addition to the interfacial energy barrier, tunneling from gap states associated with point defects and surface contamination are likely contributors to charge injection. The approach demonstrates the potential of PLD for controlled doping and the creation of p-n junctions from transition metal dichalcogenides.

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NO2-sensing proprieties of WS2/WO3 heterostructures obtained by hydrothermal treatment of tungsten oxide seed materials

Barbosa

Silva

et al. 2023

Chemical Physics Letters

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A photoelectron study of annealing induced changes to workfunction and majority carrier type in pulsed laser deposited few layer WS2 films

Cited by 7 publications

References 30 publications

Growth of pulsed laser deposited few-layer WS2 films

Growth of pulsed laser deposited few-layer WS2 films

Extrinsic and intrinsic p-type doping of pulsed laser deposited few-layer WS2 films

NO2-sensing proprieties of WS2/WO3 heterostructures obtained by hydrothermal treatment of tungsten oxide seed materials

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