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Defect Dominated Charge Transport and Fermi Level Pinning in MoS2/Metal Contacts
journal contribution
posted on 2017-05-16, 00:00 authored by Pantelis Bampoulis, Rik van Bremen, Qirong Yao, Bene Poelsema, Harold J. W. Zandvliet, Kai SotthewesUnderstanding 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.